LTC1479CG - Linear Technology

LTC1479

PowerPath Controller

for Dual Battery Systems

FEATURES

DESCRIPTION

■

Complete Power Path Management for Two

Batteries, DC Power Source, Charger and Backup

■

Compatible with Li-Ion, NiCd, NiMH and Lead-Acid

Battery Chemistries

■

“3-Diode” Mode Ensures Powers is Available

under “Cold Start” Conditions

■

All N-Channel Switching Reduces Power Losses

■

Capacitor and Battery Inrush Current Limited

■

“Seamless” Switching Between Power Sources

■

Independent Charging and Monitoring of Two

Battery Packs

■

New, Small Footprint, 36-Lead SSOP Package

The LTC

1479 is the “heart” of a total power management

solution for single and dual battery notebook computers

and other portable equipment. The LTC1479 directs power

from up to two battery packs and a DC power source to the

input of the main system switching regulator. It works in

concert with related LTC power management products

(e.g. LTC1435, LT

1511, etc.) to create a total system

solution; starting from the batteries and the DC power

source, and ending at the input of each of the computer’s

complex loads. A system-provided power management

µP monitors and actively directs the LTC1479.

The LTC1479 uses low loss N-channel MOSFET switches

to direct power from three main sources. An adaptive

current limiting scheme reduces capacitor and battery

inrush current by controlling the gates of the MOSFET

switches during transitions. The LTC1479 interfaces di-

rectly to the LT1510, LT1511 and LT1620/LTC1435 bat-

tery charging circuits.

TYPICAL APPLICATION

Dual Battery PowerPath

Controller System Block Diagram

PowerPath is a trademark of Linear Technology Corporation.

, LTC and LT are registered trademarks of Linear Technology Corporation.

■

Notebook Computer Power Management

■

Portable Instruments

■

Handheld Terminals

■

Portable Medical Equipment

■

Portable Industrial Control Equipment

APPLICATIONS

BAT1

BAT2

BATTERY CHARGER

(LT1510/LT1511/

LT1620/LTC1435)

SW A/B

SENSE

SW C/D

SW E/F

SW G SW H

DCIN

1479 TA01

AC

ADAPTER

POWER

MANAGEMENT

µP

BACKUP

REGULATOR

(LT1304)

HIGH EFFICIENCY 

DC/DC SWITCHING 

REGULATOR

(LTC1435/LTC1438

ETC.)

LTC1479

PowerPath CONTROLLER STATUS &

CONTROL

LTC1479

ABSOLUTE MAXIMUM RATINGS

PACKAGE/ORDER INFORMATION

ORDER PART

NUMBER

JMAX

= 100°C, θ

= 95°C/W

Consult factory for Military grade parts.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

TOP VIEW

G PACKAGE (209 mils)

36-LEAD PLASTIC SSOP

36

35

34

33

32

31

30

29

28

27

26

25

24

23

22

21

20

19



DCIN

DCDIV

LOBAT

GA

SAB

GB

GC

SCD

GD

GE

SEF

GF

SENSE



SENSE

–



BKUP



BAT1

BAT2

BDIV

BAT



CHGMON

BATSEL

GG

SG

GH

SH

DCINGOOD

DCIN/BAT

BATDIS

3DM

CHGSEL

CCP



GND

DCIN, BAT1, BAT2 Supply Voltages.......... –0.3V to 32V

SENSE

, SENSE

–

, V

BAT

, V

..................... –0.3V to 32V

GA, GB, GC, GD, GE, GF, GG, GH .............. –0.3V to 42V

SAB, SCD, SEF, SG, SH ............................ –0.3V to 32V

SW, V

................................................... –0.3V to 42V

DCDIV, BDIV............................................ –0.3V to 5.5V

All Logic Inputs (Note 1).......................... –0.3V to 7.5V

All Logic Outputs (Note 1) ....................... –0.3V to 7.5V

Regulator Output Current................................ 1mA

CCP

Regulator Output Current .............................. 1mA

Output Current.................................................. 1mA

Regulator Output Current ............................ 100µA

Operating Temperature

LTC1479CG ............................................. 0°C to 70°C

LTC1479IG ........................................ –40°C to 85°C

Junction Temperature........................................... 125°C

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Power Supplies

DCIN

DCIN Operating Range (Mode 1) DCIN Selected 6 28 V

BAT1

Battery 1 Operating Range (Mode 5) Battery 1 Selected 6 28 V

BAT2

Battery 2 Operating Range (Mode 6) Battery 2 Selected 6 28 V

BKUP

Backup Operating Range (Mode 8) Backup Operation 6 28 V

DCIN

DCIN Operating Current (Mode 1) DCIN Selected 175 500 µA

VBAT1

Battery 1 Operating Current (Mode 5) Battery 1 Selected 150 500 µA

VBAT2

Battery 2 Operating Current (Mode 6) Battery 2 Selected 150 500 µA

VBKUP

Backup Operating Current (Mode 8) Backup Operation (V

BKUP

= 6V) 40 100 µA

CCP

Regulator Output Voltage (Modes 1, 5, 6) DCIN, Battery 1 or Battery 2 Selected ●4.0 4.8 6.0 V

Regulator Output Voltage (Modes 1, 5, 6) DCIN, Battery 1 or Battery 2 Selected ●3.3 3.6 3.9 V

Gate Supply Voltage (Modes 1, 5, 6) DCIN, Battery 1 or Battery 2 Selected ●34.0 36.3 40.0 V

UVLO

UV Lockout Threshold (Mode 9) No Power, V

BATX

Falling from 12V 4.0 4.5 5.0 V

UVLOHYS

UV Lockout Hysteresis (Mode 9) No Power, V

BATX

Rising from 1V 0.2 0.5 1.0 V

VDCIN = 25V, VBAT1 = 16V, VBAT2 = 12V, TA = 25°C unless otherwise noted. (Note 2)

DC ELECTRICAL CHARACTERISTICS

LTC1479CG

LTC1479IG

LTC1479

VDCIN = 25V, VBAT1 = 16V, VBAT2 = 12V, TA = 25°C unless otherwise noted. (Note 2)

DC ELECTRICAL CHARACTERISTICS

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

DCIN Good Monitor

THDCDIV

DCDIV Threshold Voltage (Mode 1) V

DCDIV

Rising from 1V to 1.5V ●1.190 1.215 1.240 V

HYSDCDIV

DCDIV Hysteresis Voltage (Mode 1) V

DCDIV

Falling from 1.5V to 1V 10 35 50 mV

BIASDCDIV

DCDIV Input Bias Current (Mode 1) V

DCDIV

= 1.5V 20 nA

LODCGD

DCINGOOD Output Low Voltage (Mode 1) V

DCDIV

= 1V, I

DCINGOOD

= 100µA 0 0.1 0.4 V

PUDCGD

DCINGOOD Pull-Up Current (Mode 1) V

DCDIV

= 1.5V, V

DCINGOOD

= 0V 1 2 6 µA

LKGDCGD

DCINGOOD Leakage Current (Mode 1) V

DCDIV

= 1.5V, V

DCINGOOD

= 7V ±1µA

Battery Monitor

THLOBAT

Low-Battery Threshold Voltage (Modes 5, 6) V

BDIV

Falling from 1.5V to 1V ●1.190 1.215 1.240 V

HYSLOBAT

Low-Battery Hysteresis Voltage (Modes 5, 6) V

BDIV

Rising from 1V to 1.5V 10 35 50 mV

BIASBDIV

BDIV Input Bias Current (Modes 5, 6) V

BDIV

= 1.5V 20 nA

LOLOBAT

LOBAT Output Low Voltage (Modes 5, 6) V

BDIV

= 1V, I

LOBAT

= 100µA 0 0.1 0.4 V

LKGLOBAT

LOBAT Output Leakage Current (Modes 5, 6) V

BDIV

= 1.5V, V

LOBAT

= 7V ±1µA

ONBATSW

Battery Switch ON Resistance (Modes 5, 6) Each Switch Tested Independently 200 400 800 Ω

LKGBATSW

Battery Switch OFF Leakage (Modes 5, 6) Each Switch Tested Independently ±1µA

Gate Drivers

GS(ON)

Gate-to-Source ON Voltage (GA to GF) (Modes 1, 2, 4, 5, 6) I

= –1µA 5.0 5.5 7.0 V

Gate-to-Source ON Voltage (GG, GH) (Modes 2, 4) I

= –1µA 4.5 5.2 7.0 V

GS(OFF)

Gate-to-Source OFF Voltage (Modes 1, 2, 4, 5, 6) I

= 100µA 0 0.4 V

BSENSE

+ SENSE

Input Bias Current (Modes 1, 5, 6) 5 15 30 µA

BSENSE

– SENSE

–

Input Bias Current (Modes 1, 5, 6) 5 15 30 µA

SENSE

Inrush Current Limit Sense Voltage (Modes 1, 5, 6) ●0.15 0.20 0.25 V

PDSAB

SAB Pull-Down Current (Modes 5, 6) V

SAB

= 10V 30 100 300 µA

PDSCD

SCD Pull-Down Current (Mode 1) V

SCD

= 10V 30 100 300 µA

PDSEF

SEF Pull-Down Current (Mode 1) V

SEF

= 10V 30 100 300 µA

PDSG

SG Pull-Down Current (Mode 1) V

= 10V 3 mA

PDSH

SH Pull-Down Current (Mode 1) V

= 10V 3 mA

Charge Monitor

ONCMON

CHGMON Switch ON Resistance (Modes 5, 6) Each Switch Tested Independently 50 150 250 Ω

LKGCMON

CHGMON Switch OFF Leakage (Modes 5, 6) Each Switch Tested Independently ±1µA

Digital Inputs

HIDIGIN

Input High Voltage (Mode 1) All Digital Inputs ●2V

LODIGIN

Input Low Voltage (Mode 1) All Digital Inputs ●0.8 V

HIDIGIN

Input Leakage Current (Mode 1) All Digital Inputs, V

DIGINX

= 7V ±1µA

LODIGIN

Input Leakage Current (Mode 1) V

DIGINX

= 0V (Note 3) ±1µA

PUDIGIN

Input Pull-Up Current (Mode 1) V

DIGINX

= 0V (Note 4) 1 2 6 µA

LTC1479

AC ELECTRICAL CHARACTERISTICS

VDCIN = 25V, VBAT1 = 16V, VBAT2 = 12V, TA = 25°C unless otherwise noted. (Note 2)

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

ONGA/GB

Gate A/B Turn-On Time V

> 3V (Note 5) 30 µs

ONGC/GD

Gate C/D Turn-On Time V

> 3V (Note 5) 30 µs

ONGE/GF

Gate E/F Turn-On Time V

> 3V (Note 5) 30 µs

OFFGA/GB

Gate A/B Turn-Off Time V

< 1V (Note 5) 3 µs

OFFGC/GD

Gate C/D Turn-Off Time V

< 1V (Note 5) 3 µs

OFFGE/GF

Gate E/F Turn-Off Time V

< 1V (Note 5) 3 µs

ONGG/GH

Gate G/H Turn-On Time V

> 3V (Note 5) 300 µs

OFFGG/GH

Gate G/H Turn-Off Time V

< 1V (Note 5) 5 µs

OVGG

Reg Operating Frequency 30 kHz

dLOBAT

LOBAT Delay Times ∆V

BDIV

= ±100mV, R

PULLUP

= 51k 5 µs

dDCINGOOD

DCINGOOD Delay Times ∆V

DCDIV

= ±100mV, R

PULLUP

= 51k 5 µs

The ● denotes specifications which apply over the full operating

temperature range.

Note 1: The logic inputs are high impedance CMOS gates with ESD

protection diodes to ground and therefore should not be forced below

ground. These inputs can however be driven above the V

CCP

or V

supply

rails as there are no clamping diodes connected between the input pins

and the supply rails. This facilitates operation in mixed 5V/3V systems.

Note 2: The Selected Operating Mode Truth Table, which defines the

operating conditions and logical states associated with each “normal”

operating mode, should be used in conjunction with the Electrical

Characteristics table to establish test conditions. Actual production test

conditions may be more stringent.

Note 3: The following inputs are high impedance CMOS inputs:

3DM and DCIN/BAT and have no internal pull-up current.

Note 4: The following inputs have built-in 2µA pull-up current sources

(passed through series diodes): BATSEL, BATDIS and CHGSEL.

Note 5: Gate turn-on and turn-off times are measured with no inrush

current limiting, i. e., V

SENSE

= 0V, using Si4936DY MOSFETs in the typical

application circuit.

TRUTH TABLE

SELECTED MODES LOGIC INPUTS SWITCH STATUS OUTPUTS

SW SW SW SW SW

NO. MODE 3DM DCIN/BAT BATSEL BATDIS CHGSEL A/B C/D E/F G H CHGMON V

BAT

LOBAT DCINGOOD

1 DC Operation H H H L H On Off Off Off Off Hi-Z BAT1 H H

2 DC Operation and H H H H H On Off Off On Off BAT1 BAT1 H H

BAT1 Charging

3 DC Operation and H H L L L On Off Off Off Off Hi-Z BAT2 H H

BAT2 Disconnected

4 DC Operation and H H L H L On Off Off Off On BAT2 BAT2 H H

BAT2 Charging

5 BAT1 Operation H L H H H Off On Off Off Off Hi-Z BAT1 H L

6 BAT2 Operation H L L H H Off Off On Off Off Hi-Z BAT2 H L

7 BAT1 Low and H L H L H Off Off Off Off Off Hi-Z BAT1 L L

Disconnected

8 Backup Operation H L H L H Off Off Off Off Off Hi-Z BAT1 L L

9 No Power L L L L L Off Off Off Off Off Hi-Z BAT2 L L

(No Backup)

10 DC Reconnected L L H L H 3DM* 3DM* 3DM* Off Off Hi-Z BAT1 L H

11 DC Connected H H H L H On Off Off Off Off Hi-Z BAT1 L H

and Reset

(Selected Operating Modes)

*3DM = Three Diode Mode. When this mode is invoked, only the first

MOSFET switch in each back-to-back switch pair, i. e., SW A, SW C and

SW E is turned on. Current may still pass through the inherent body

diode of the idled switches, i.e., SW B, SW D and SW F to help restart

the system after abnormal operating conditions have been encountered.

See the Timing Diagram and Applications Information sections for

further details.

LTC1479

TYPICAL PERFORMANCE CHARACTERISTICS

DCIN Supply Current BAT1 Supply Current BAT2 Supply Current

VGG Supply Voltage

JUNCTION TEMPERATURE (°C)

–50



25 75

1479 G05

–25 0 50 100 125

SUPPLY VOLTAGE (V)

MODE 1

DCIN

= 24V

VBKUP Supply Current

BKUP

SUPPLY VOLTAGE (V)



15 25

1479 G04

510 20 30 35

BKUP

SUPPLY CURRENT (µA)

MODE 8

NO OTHER POWER

= 25°C

VCC Supply Voltage

JUNCTION TEMPERATURE (°C)

–50



3.7

3.8

4.0

25 75

1479 G06

3.6

3.5

–25 0 50 100 125

3.4

3.3

3.9

SUPPLY VOLTAGE (V)

MODE 1

DCIN

= 24V

VCCP Supply Voltage

JUNCTION TEMPERATURE (°C)

–50



5.0

5.5

6.5

25 75

1479 G07

4.5

4.0

–25 0 50 100 125

3.5

3.0

6.0

CCP

SUPPLY VOLTAGE (V)

MODE 1

DCIN

= 24V

DCIN SUPPLY VOLTAGE (V)



200

250

350

15 25

1479 G01

150

100

510 20 30 35

300

DCIN SUPPLY CURRENT (µA)

MODE 1, DCDIV = 1.5V

NO OTHER POWER

= 25°C

BAT1 SUPPLY VOLTAGE (V)



200

250

350

15 25

1479 G02

150

100

510 20 30 35

300

BAT1 SUPPLY CURRENT (µA)

MODE 5

NO OTHER POWER

= 25°C

BAT2 SUPPLY VOLTAGE (V)



200

250

350

15 25

1479 G03

150

100

510 20 30 35

300

BAT2 SUPPLY CURRENT (µA)

MODE 6

NO OTHER POWER

= 25°C

LTC1479

PIN FUNCTIONS

UUU

External Power Supply Pins

DCIN (Pin 1): Supply Input. A 330Ω resistor should be

put in series with this pin and the external DC power

source. A 0.1µF bypass capacitor should be connected to

this pin as close as possible.

DCDIV (Pin 2): Supply Divider Input. This is a high

impedance comparator input with a 1.215V threshold

(rising edge) and approximately –35mV hysteresis.

BAT1, BAT2 (Pins 35, 34): Supply Input. These two pins

are the inputs from the two batteries. A 1µF bypass

capacitor should be connected to each pin as close as

possible if there is no larger battery supply capacitor

within 2".

BAT

(Pin 32): Battery Voltage Sense. This pin connects

the top of the battery resistor ladder to either BAT1 or

BAT2.

BDIV (Pin 33): Battery Divider Input. A high impedance

comparator input with a 1.215V threshold (falling edge)

and approximately 35mV hysteresis.

BKUP

(Pin 36): Supply Input. This input supplies power to

the LTC1479 when in the backup mode of operation. A 1µF

bypass capacitor should be connected to the V

BKUP

pin as

close as possible if there is no larger backup supply

capacitor within 2".

Internal Power Supply Pins

CCP

(Pin 20): Power Supply Output. Bypass this output

with at least a 0.1µF capacitor. The V

CCP

power supply is

used primarily to power internal logic circuitry.

(Pin 15): Power Supply Output. This is a nominal

3.60V output. Bypass this regulator output with a 2.2µF

tantalum capacitor.

This capacitor is required for stability.

(Pin 17): Supply. The V

pin is connected via three

internal diodes to the DCIN, BAT1 and BAT2 pins and

powers the top of the V

switching regulator inductor.

Bypass this pin with a 1µF/35V capacitor.

(Pin 16): Gate Supply. This high voltage (36.5V)

switching regulator is intended only for driving the internal

micropower gate drive circuitry.

Do not load this pin with

any external circuitry.

Bypass this pin with a 1µF/50V

capacitor.

SW (Pin 18): Output. This pin drives the “bottom” of the

switching regulator inductor which is connected

between this pin and the V

pin.

GND (Pin 19): Ground. The V

and V

bypass capacitors

should be returned to this ground which is connected

directly to the source of the N-channel switch in the V

regulator.

Input Power Switches

GA, GB (Pins 4, 6): DCIN Switch Gate Drive. These two

pins drive the gates of the back-to-back N-channel switches

in series with the DCIN input.

SAB (Pin 5): Source Return. The SAB pin is connected to

the sources of SW A and SW B. A small pull-down current

source returns this node to 0V when the switches are

turned off.

GC, GD (Pins 7, 9): BAT1 Switch Gate Drive.

These two

pins drive the gates of the back-to-back N-channel

switches in series with the BAT1 input.

SCD (Pin 8): Source Return. The SCD pin is connected to

the sources of SW C and SW D. A small pull-down current

source returns this node to 0V when the switches are

turned off.

GE, GF (Pins 10, 12): BAT2 Switch Gate Drive.

These two

pins drive the gates of the back-to-back N-channel

switches in series with the BAT2 input.

SEF (Pin 11): Source Return. The SEF pin is connected to

the sources of SW E and SW F. A small pull-down current

source returns this node to 0V potential when the switches

are turned off.

SENSE

(Pin 13):

Inrush Current Input. This pin should

be connected directly to the “top” (switch side) of the low

valued resistor in series with the three input power

selector switch pairs, SW A/B, SW C/D and SW E/F, for

detecting and controlling the inrush current into and out

of the power supply sources and the output capacitor.

LTC1479

PIN FUNCTIONS

UUU

SENSE

–

(Pin 14):

Inrush Current Input. This pin should

be connected directly to the “bottom” (output side) of the

low valued resistor in series with the three input power

selector switch pairs, SW A/B, SW C/D and SW E/F, for

detecting and controlling the inrush current into and out

of the power supply sources and the output capacitor.

Battery Charging Switches

GG, GH (Pins 29, 27): Charger Switch Gate Drive. These

two pins drive the gates of the back-to-back N-channel

switch pairs, SW G and SW H, between the charger output

and the two batteries.

SG, SH (Pin 28, 26): Source Returns. These two pins are

connected to the sources of SW G and SW H respectively.

A small pull-down current source returns these nodes to

0V when the switches are turned off.

CHGMON (Pin 31):

Battery Selector Output. This pin is

the output of an internal switch which is connected to

BAT1 and BAT2 and connects the positive terminal of the

selected battery to the voltage feedback resistors in the

charger circuit.

Microprocessor Interface

DCINGOOD (Pin 25): Comparator Output. This open-drain

output has an internal 2µA pull-up current source con-

nected through a diode to the V

CCP

power supply. An

external pull-up resistor can be added if more pull-up

current is required. This output is active high when the DC

supply rises above the programmed voltage.

LOBAT (Pin 3): Comparator Output. This open-drain out-

put does not have an internal pull-up current source and

is active low when the selected battery voltage drops

below the programmed voltage.

DCIN/BAT (Pin 24): Selector Input. This high impedance

logic input allows the µP to make the ultimate decision on

the connection of the DC power source, based upon the

DCINGOOD pin information. In some minimized systems,

the DCIN/BAT pin may be connected directly to the

DCINGOOD pin.

BATDIS (Pin 23): Battery Disconnect Input. This high-

impedance logic input has a built-in 2µA pull-up current

source and allows the µP to disconnect the battery from

the system.

3DM (Pin 22): Three Diode Mode Input. This high imped-

ance logic input has no built-in pull-up current source.

Connect a 100k resistor from this pin to ground to ensure

three diode mode operation from a “cold start.”

CHGSEL (Pin 21): Battery Charger Selector Input. This

high impedance logic input has a built-in 2µA pull-up

current source and allows the µP to determine which

battery is being charged by connecting the selected

battery to the charger output via one of the switch pairs,

SW G or SW H. (The charger voltage feedback ladder is

simultaneously switched to the selected battery.)

BATSEL (Pin 30): Battery Selector Input. This high imped-

ance logic input has a built-in 2µA pull-up current source

and allows the µP to select which battery is connected to

the system and the battery monitor comparator input.

Battery 1 is selected with a logic high on this input and

battery 2 is selected with a logic low.

LTC1479

BLOCK DIAGRAM

DCDIV

GA GBSAB V

SENSE+

SENSE–

BAT2

INRUSH

SENSE

BAT1

INRUSH

SENSE

DCIN

INRUSH

SENSE

GC GDSCD GE GFSEF

BAT1 BAT2 DCIN

BDIV

BAT2

BAT1

BAT

CHGMONBATSEL CHGSEL

SW G

GATE

DRIVER

SG GG

SW H

GATE

DRIVER

SH GH

CCP

DCINGOOD

LOBAT

GND

DCIN

3DM

DCIN/BAT

2µA

CCP

BATDIS

2µA

CCP

2µA

CCP

2µA

CCP

1479 BD

DCIN

MONITOR SW A/B

GATE

DRIVERS

SW C/D

GATE

DRIVERS

SW E/F

GATE

DRIVERS



REGULATOR

& BIAS

GENERATOR



SWITCHING

REGULATOR

BATTERY

MONITOR

SWITCH

CONTROL

LOGIC

BKUP

LTC1479

TI I G DIAGRA S

DC and Battery Operation Timing

DCIN

DCINGOOD

DCIN/BAT

BATSEL

MODE 1

DC OPERATION

BAT1 DISCONNECTED

MODE 2

DC OPERATION 

BAT1 CHARGING

CHGSEL

MODE 3

DC OPERATION 

BAT2 DISCONNECTED

MODE 4

DC OPERATION 

BAT2 CHARGING

BATDIS

MODE 5

BAT1 OPERATION MODE 6

BAT2 OPERATION

NOTE: FOR MODES 1 TO 6, 3DM = H, BAT1 = 16V, BAT2 = 12V

25V

25V (16V) (12V)

1479 TD01

OUTPUT

Backup and DC Restoration Timing

DCIN

MODE 7

BAT1 LOW &

DISCONNECTED

MODE 8

BACKUP

OPERATION

MODE 9

NO POWER

(NO BACKUP)

MODE 10

DC RESTORED

(THREE DIODE MODE)

BATDIS

MODE 11

DC RECONNECTED

(SW A/B ON)

MODE 12

THREE DIODE MODE

NOTE: FOR MODES 7 TO 12, BATSEL = H, BAT1 = 16V AND DISCHARGING, BAT2 = 0V

25V

OUTPUT

DCIN/BAT

3DM

LOBAT

BAT1

DISCHARGING (V

BKUP

= 6V)

(0V)

(24.3V) (24.3V)

1479 TD02

(25V)

LTC1479

OPERATION

The LTC1479 is responsible for low-loss switching at the

“front end” of the power management system, where up

to two battery packs and a DC power source can be

indiscriminately connected and disconnected. Smooth

switching between input power sources is accomplished

with the help of low-loss N-channel switches driven by

special gate drive circuitry which limits the inrush current

in and out of the battery packs and the system power

supply capacitors.

All N-Channel Switching

The LTC1479 drives external back-to-back N-channel

MOSFET switches to direct power from the three main

power sources: the external DC power source, the pri-

mary battery and the secondary battery connected to the

main supply pins—DCIN, BAT1 and BAT2 respectively.

(N-channel MOSFET switches are more cost effective

and provide lower voltage drops than their P-channel

counterparts.)

Gate Drive (V

) Power Supply

The gate drive for the low-loss N-channel switches is

supplied by a micropower boost regulator which is regu-

lated at approximately 36.5V. The V

supply provides

sufficient headroom above the maximum 28V operating

voltage of the three main power sources to ensure that the

MOSFET switches are fully enhanced.

The power for this inductor based regulator is taken from

three internal diodes as shown in Figure 1. The three

Figure 1. VGG Switching Regulator

BAT1 BAT2

DCIN

GND

1479 F01

L1

1mH

C1

1µF

35V

C2

1µF

50V

TO GATE

DRIVERS

(36.5V)

LTC1479



SWITCHING

REGULATOR

diodes are connected to each of the three main power

sources, DCIN, BAT1 and BAT2. The highest voltage

potential is directed to the top of the boost regulator

inductor to maximize regulator efficiency. C1 provides

filtering at the top of the 1mH switched inductor, L1, which

is housed in a small surface mount package.

A fourth internal diode directs the current from the 1mH

inductor to the V

output capacitor, C2, further reducing

the external parts count. In fact, as demonstrated in Figure

1, only three external components are required by the V

regulator, L1, C1 and C2.

Inrush Current Limiting

The LTC1479 uses an adaptive inrush current limiting

scheme to reduce current flowing in and out of the three

main power sources and the DC/DC converter input ca-

pacitor during switch-over transitions. The voltage across

a single small-valued resistor, R

SENSE

, is measured to

ascertain the instantaneous current flowing through the

three main switch pairs, SW A/B, SW C/D, and SW E/F

during the transitions.

Figure 2 is a block diagram showing only the DCIN switch

pair, SW A/B. (The gate drive circuits for switch pairs SW

C/D and SW E/F are identical). A bidirectional current

sensing and limiting circuit determines when the voltage

drop across R

SENSE

reaches plus or minus 200mV. The

gate-to-source voltage, V

, of the appropriate switch is

limited during the transition period until the inrush current

subsides, generally within a few milliseconds, depending

upon the value of the DC/DC converter input capacitor.

SENSE+

SENSE–

GA GBSAB

SW A SW B R

SENSE

LTC1479

1479 F02

DCIN

OUTPUT

TO DC/DC

CONVERTER

OUT

6V 6V ±200mV

THRESHOLD

SW A/B

GATE

DRIVERS

BIDIRECTIONAL

INRUSH CURRENT

SENSING AND

LIMITING

Figure 2. SW A/B Inrush Current Limiting

LTC1479

OPERATION

This scheme allows capacitors and MOSFET switches of

differing sizes and current ratings to be used in the same

system without circuit modifications.

After the transition period has passed, the V

of both

MOSFETs in the selected switch pair rises to approxi-

mately 6V. The gate drive is set at 6V to provide ample

overdrive for logic level MOSFET switches without ex-

ceeding their maximum V

rating.

Internal Power Supplies

Two internal supplies provide power for the control logic

and power source monitoring functions. The V

CCP

logic

supply is approximately 5V and provides power for the

majority of the internal logic circuitry. The V

supply is

approximately 3.60V and provides power for the V

switching regulator control circuitry and the gate drivers.

The V

supply has an undervoltage lockout circuit which

minimizes power consumption in the event of a total loss

of system power; i.e., when all available power sources fall

below approximately 4.5V.

DCIN Voltage Monitoring

The DCIN input is continuously monitored via a two

resistor ladder connected between the DCIN pin and the

DCDIV input. The input threshold is 1.215V (rising edge)

with approximately –35mV hysteresis. The use of a defini-

tive voltage threshold ensures that the DC supply is not

only connected but “healthy” before being attached to the

DC/DC converter input.

Battery Voltage Monitoring

The LTC1479 has the ability to independently monitor both

battery packs. (Because of this, one battery pack may be

discharged as the other is being charged.)

A low-battery detector signals when the selected battery

pack has dropped to the level where a shutdown sequence

should be initiated or the other battery pack engaged.

Battery Charging Management Functions

The LTC1479 directly interfaces with LT1510/LT1511

battery charger circuits. Two gate drive circuits control

the two back-to-back N-channel switch pairs, SW G and

SW H, under logic (CHGSEL) control to connect the

output of the charger to the selected battery pack. Break-

before-make action ensures that current does not pass

from one battery pack to the other during switch-over of

the charger output. The CHGSEL input also simulta-

neously switches the positive terminal of the selected

battery pack to the top of the voltage feedback resistor

ladder in the charger system through the CHGMON pin.

Backup Supply Interface

Power for the LTC1479 is obtained from the backup

supply when power is unavailable from the three main

sources of power.

Interface to Companion Microprocessor

A companion µP must be used in conjunction with the

LTC1479 to provide overall control of the power manage-

ment system. The LTC1479 communicates with the µP by

means of five logic inputs and two logic outputs as

described in Table 1.

Table 1. LTC1479 µP Interface Inputs and Outputs

INPUT ACTION

DCIN/BAT Logic High Required to Connect a Good DC Supply

BATDIS Logic Low Disconnects the Battery from the System

BATSEL Selects Which Battery is Connected to the System

(Logic High Selects BAT1; Logic Low Selects BAT2)

CHGSEL Selects Which Battery is Charged and Monitored

(Logic High Selects BAT1; Logic Low Selects BAT2)

3DM Forces the Main Three Power Path Switches Into

“3-Diode Mode.” See Applications Information Section

OUTPUT ACTION

DCINGOOD Logic High When a Good DC Supply is Present

LOBAT Logic Low When Selected Battery Voltage is Low

LTC1479

APPLICATIONS INFORMATION

WUU U

POWER PATH SWITCHING CONCEPTS

Power Source Selection

The LTC1479 drives low-loss switches to direct power in

the main power path of a dual rechargeable battery system

— the type found in most notebook computers and other

portable equipment.

Figure 3 is a conceptual block diagram which illustrates

the main features of an LTC1479 dual battery power

management system, starting with the three main power

sources and ending at the system DC/DC regulator.

Switches SW A/B, SW C/D and SW E/F direct power from

either the AC adapter (DCIN) or one of the two battery

packs (BAT1 and BAT2) to the input of the DC/DC switch-

ing regulator. Switches SW G and SW H connect the

desired battery pack to the battery charger.

Each of the five switches is intelligently controlled by the

LTC1479 which interfaces directly with a power manage-

ment system µP.

Using Tantalum Capacitors

The inrush and “outrush” current of the system DC/DC

regulator input capacitor is limited by the LTC1479. i.e.,

the current flowing both in and out of the capacitor during

transitions from one input power source to another is

limited. In many applications, this inrush current limiting

makes it feasible to use lower cost/size tantalum surface

mount capacitors in place of more expensive/larger alumi-

num electrolytics at the input of the DC/DC converter.

Note: The capacitor manufacturer should be consulted for

specific inrush current specifications and limitations and

some experimentation may be required to ensure compli-

ance with these limitations under all possible operating

conditions.

Back-to-Back Switch Topology

The simple SPST switches shown in Figure 3 actually

consist of two back-to-back N-channel switches. These

low-loss, N-channel switch pairs are housed in 8-pin SO

and SSOP packaging and are available from a number of

manufacturers. The back-to-back topology eliminates the

problems associated with the inherent body diodes in

power MOSFET switches and allows each switch pair to

block current flow in either direction when the two switches

are turned off.

The back-to-back topology also allows for independent

control of each half of the switch pair which facilitates

bidirectional inrush current limiting and the so called “3-

diode” mode described in the following section.

The “3-Diode” Mode

Under normal operating conditions, both halves of each

switch pair are turned on and off simultaneously. For

example, when the input power source is switched from a

good DC input (AC adapter) to a good battery pack, BAT1,

both gates of switch pair SW A/B are turned off and both

gates of switch pair SW C/D are turned on. The back-to-

back body diodes in switch pair, SW A/B, block current

flow in or out of the DC input connector.

Figure 3. LTC1479 PowerPath Conceptual Diagram

BAT1

BAT2

SW A/B

SW C/D

SW E/F

SW G SW H

HIGH

EFFICIENCY

DC/DC

SWITCHING

REGULATOR

3.3V

12V

SENSE

DCIN

1479 F03

POWER

MANAGEMENT

µP

LTC1479

PowerPath CONTROLLER

BATTERY

CHARGER

LTC1479

APPLICATIONS INFORMATION

WUU U

the Power Management µP Interface section for additional

information on when to invoke “3-diode” mode.)

COMPONENT SELECTION

N-Channel Switches

The LTC1479 adaptive inrush limiting circuitry permits the

use of a wide range of logic-level N-channel MOSFET

switches. A number of dual low R

DS(ON)

N-channel switches

in 8-lead surface mount packages are available that are

well suited for LTC1479 applications.

The maximum allowable drain source voltage, V

DS(MAX)

of the three main switch pairs, SW A/B, SW C/D and SW

E/F, must be high enough to withstand the maximum DC

supply voltage. If the DC supply is in the 20V to 28V range,

use 30V MOSFET switches. If the DC supply is in the 10V

to 18V range, and is well regulated, then use 20V MOSFET

switches.

As a general rule, select the switch with the lowest R

DS(ON)

at the maximum allowable V

. This will minimize the heat

dissipated in the switches while increasing the overall

system efficiency. Higher switch resistances can be toler-

ated in some systems with lower current requirements,

but care should be taken to ensure that the power dissi-

pated in the switches is never allowed to rise above the

manufacturer’s recommended levels.

The maximum allowable drain-source voltage, V

DS(MAX)

of the two charger switch pairs, SW G and SW H, need only

Figure 4. LTC1479 PowerPath Switches in “3-Diode” Mode

BAT1

BAT2

SW A

SW C

SW E

HIGH

EFFICIENCY

DC/DC

SWITCHING

REGULATOR

3.3V

12V

DCIN

1479 F04

SW B

SW F

SW D

SENSE

POWER

MANAGEMENT

µP

LTC1479

PowerPath CONTROLLER

ON OFF

In the “3-diode” mode, only the first half of each power

path switch pair, i.e., SW A, SW C and SW E, is turned on;

and the second half, i.e., SW B, SW D and SW F, is turned

off. These three switch pairs now act simply as three

diodes connected to the three main input power sources

as illustrated in Figure 4. The power ‘diode’ with the

highest input voltage passes current through to the input

of the DC/DC converter to ensure that the power manage-

ment µP is powered at start-up or under abnormal oper-

ating conditions. (An undervoltage lockout circuit defeats

this mode when the V

pin drops below approximately

4.5V).

“Cold Start” Initial Condition

The LTC1479 is designed to start in the “3- diode” mode

when all five logic inputs are low—when no power is

available (including the backup system). A 100k resistor

from the 3DM input to ground ensures that this input is low

during a “cold start.” This will cause the main PowerPath

switches to pass the highest voltage available to the input

of the DC/DC converter. Normal operation will then

resume after a good power source is identified.

Recovery from Uncertain Power Conditions

The “3-diode” mode can also be asserted (by applying an

active low to the 3DM input) when abnormal conditions

exist in the system, i.e., when all power sources are

deemed not “good” or are depleted, or the management

system µP is being reset or not functioning properly. (See

LTC1479

be high enough to withstand the maximum battery or

charger output voltage. In most cases, this will allow the

use of 20V MOSFET switches in the charger path, while

30V switches are used in the main power path.

Inrush Current Sense Resistor, R

SENSE

A small valued sense resistor (current shunt) is used by

the three main switch pair drivers to measure and limit the

inrush current flowing through the conducting switch

pair.

It should be noted that the inrush limiting circuit is not

intended to provide short-circuit protection

; but rather, is

designed to limit the large peak currents which flow into or

out of the large power supply capacitors and the battery

packs during power supply switch-over transitions. The

inrush current limit should be set at approximately 2× or

3× the maximum required DC/DC input current.

For example, if the maximum current required by the

DC/DC converter is 2A, an inrush current limit of 6A is set

by selecting a 0.033Ω sense resistor, R

SENSE

, using the

following formula:

SENSE

= (200mV)/I

INRUSH

Note that the voltage drop across the resistor in this

example is only 66mV under normal operating conditions.

Therefore, the power dissipated in the resistor is extremely

small (132mW), and a small 1/4W surface mount resistor

can be used in this application. A number of small valued,

surface mount resistors are available that have been

specifically designed for high efficiency current sensing

applications.

DC Input Monitor Resistor Divider

The DCDIV input continuously monitors the DC power

supply voltage via a two resistor divider network, R

DC1

and

DC2

, as shown in Figure 5. The threshold voltage of the

DC good comparator is 1.215V when the power supply

input voltage is rising. Approximately –35mV of hyster-

esis is provided to ensure clean switching of the compara-

tor when the DC supply voltage is falling.

To minimize errors due to the input bias current of the DC

good comparator, set R

DC1

= 12.1k so that approximately

100µA flows through the resistor divider when the desired

APPLICATIONS INFORMATION

WUU U

Figure 5. DC Monitor Resistor Divider

LTC1479

DCIN

DCDIV

DC

SUPPLY TO SW A/B

DC1



12.1k

DC2



1.215V

DCINGOOD

1479 F05

–

BATSEL

BAT1

BAT2

LOBAT

LTC1479

1479 F06

1.215V

BAT

BDIV



121k



–

SWITCH

CONTROL

LOGIC

threshold is reached. R

DC2

is then selected according to

the following formula:

DC2

= 12.1k – 1

GOOD

1.215V

)

Battery Monitor Resistor Divider

A switch controlled by the BATSEL input connects one of

the two batteries to the V

BAT

pin and therefore to the top

of the battery resistor divider as shown in Figure 6. The

threshold voltage of the low-battery comparator is 1.215V

when the battery voltage is falling. Approximately +35mV

of hysteresis is provided to ensure clean switching of the

comparator when the battery voltage rises again.

To minimize errors due to the input bias current of the low

battery comparator, assume R

= 121k so that approxi-

mately 10µA flows through the resistor divider when the

threshold is reached. R

is selected according to the

following formula:

Figure 6. Battery Monitor Resistor Divider

LTC1479

APPLICATIONS INFORMATION

WUU U

= 121k – 1

LOBAT

1.215V

)

Regulator Inductor and Capacitors

The V

regulator provides a power supply voltage signifi-

cantly higher than any of the three main power source

voltages to allow the control of N-channel MOSFET

switches. This 36.5V micropower, step-up voltage regula-

tor is powered by the highest potential available from the

three main power sources for maximum regulator effi-

ciency.

Because the three input supply diodes and regulator

output diode are built into the LTC1479, only three external

components are required by the V

regulator: L1, C1 and

C2 as shown in Figure 7.

L1 is a small, low current 1mH surface mount inductor. C1

provides filtering at the top of the 1mH switched inductor

and should be 1µF to filter switching transients. The V

output capacitor, C2, provides storage and filtering for the

output and should be 1µF and rated for 50V operation.

C1 and C2 can be either tantalum or ceramic capacitors.

and V

CCP

Regulator Capacitors

The V

CCP

logic supply is approximately 5V and provides

power for the majority of the internal logic circuitry.

Bypass this output with a 0.1µF capacitor.

The V

supply is approximately 3.60V and provides

power for the V

switching regulator control circuitry and

the gate drivers. Bypass this output with a 2.2µF tantalum

capacitor.

This capacitor is required for stability of the V

regulator output

SYSTEM LEVEL CONSIDERATIONS

The Complete Power Management System

The LTC1479 is the “heart” of a complete power manage-

ment system and is responsible for the main power path

and charger switching. A companion power management

µP provides overall control of the power management

system in concert with the LTC1479 and the auxiliary

power management systems.

A typical dual Li-Ion battery power management system is

illustrated in Figure 8. If “good” power is available at the

DCIN input (from the AC adapter), switch pair SW A/B are

turned on—providing a low-loss path for current flow to

the input of the LTC1538-AUX DC/DC converter. Switch

pairs, SW C/D and SW E/F are turned off to block current

from flowing back into the two battery packs from the DC

input.

In this case, an LT1510 constant-voltage/constant-cur-

rent (CC/CV) battery charger circuit is used to alternately

charge the two Li-Ion battery packs. The µP “decides”

which battery is in need of recharging by either querying

the “smart” battery directly or by more indirect means.

After the determination is made, either switch pair, SW G

or SW H, is turned on to pass charger output current to one

of the batteries. Simultaneously, the selected battery volt-

age is returned to the voltage feedback input of the LT1510

CV/CC battery charger via the CHGMON output of the

LTC1479. After the first battery has been charged, it is

disconnected from the charger circuit and the second

battery is connected through the other switch pair and the

second battery charged.

Backup power is provided by the LT1304 circuit which

ensures that the DC/DC input voltage does not drop

below 6V.

Backup System Interface

The LTC1479 is designed to work in concert with related

power management products including the LT1304 mi-

Figure 7. VGG Step-Up Switch Regulator

BAT1 BAT2

DCIN

GND

*COILCRAFT 1812LS-105 XKBC (708) 639-6400

OR EQUIVALENT

1479 F07

L1*

1mH

C1

1µF

35V

C2

1µF

50V

TO GATE

DRIVERS

(36.5V)

LTC1479



SWITCHING

REGULATOR

LTC1479

APPLICATIONS INFORMATION

WUU U

DCIN

BAT1

BAT2

SW V

1µF

50V 1µF

50V

1mH*

SENSE

0.033Ω

SW A SW B

SW C SW D

SW E SW F

330Ω

GB GC GD GE GFSAB SCD SEF SENSE

SENSE

–

CCP

2.2µF

16V 0.1µF

BAT

POWER

MANAGEMENT

µP

BDIV

BKUP

BACKUP

REGULATOR

LTC1538-AUX 

TRIPLE, HIGH EFFICIENCY,

SWITCHING REGULATOR

DCDIV

0.1µF

LTC1479

LT1510

Li-ION BATTERY

CHARGER

GG SG GH SH

CHGMON

3.3V

SW G

SW H

DCIN

Li-ION

BATTERY

PACK #1

Li-ION

BATTERY

PACK #2

1479 F08

BACKUP

NiCD

*COILCRAFT 1812LS-105 XKBC (708) 639-1469

12V AUX

DC2

DC1

cropower DC/DC converter. As shown in Figure 9, the

LT1304 monitors the input supply voltage and activates

when it drops below 6V.

Power for the DCIN and battery monitors and the logic

supply in the LTC1479 is then obtained from the output of

the LT1304 step-up regulator.

Charger System Interface

The LTC1479 is designed to work directly with constant-

voltage (CV), constant-current (CC) battery chargers such

as the LT1510 and LT1511.

LT1510 Battery Charger Interface

As illustrated in Figure 10, the LT1510 CV/CC battery

charger, takes power from the DC adapter input through

Schottky diode D1. The output of the charger is directed to

FROM 

PowerPath

CONTROLLER

BACKUP

NiCD

CELL

TO INPUT 

OF DC/DC 

CONVERTER

L1*

10µH

(BOLD LINES INDICATE HIGH CURRENT PATHS)



FROM 

DC/DC

D1 

MBR0530

R4

390k

R5

100k

SHDN

GND

LT1304

C1

0.1µF

C3

0.1µF

LIM

R3

22k

LBI

R2

470k

1479 F09

C2

0.1µF

2LBO

CC

FROM

DC/DC

D2

BAS16LT1

Q1

2N7002

ROHM

DTA144E R1

10k

Figure 9. LT1304 Micropower Backup Converter Circuit

Figure 8. Simplified Dual Li-Ion Battery Power Management System

LTC1479

APPLICATIONS INFORMATION

WUU U

the charging battery through one of the N-channel switch

pairs, SW G or SW H. The charging battery voltage is

simultaneously connected through the CHGMON switch

in the LTC1479 to the top of the charger voltage resistor

divider, R4 and R5, for constant voltage charging. (See the

LT1510 data sheet for further detail.)

LT1511 Battery Charger Interface

The LT1511, 3A CC/CV battery charger with input current

limiting, is connected in a slightly different manner than

the LT1510 as illustrated in Figure 11.

Figure 11. Interfacing to the LT1511 Constant-Voltage/Constant-Current Battery Charger with Input Current Limiting

1479 F11

SW H

Si9926DY

SW G

Si9926DY

BAT1

4 Li-ION

BATTERY

PACK

BAT2

4 Li-ION

BATTERY

PACK

BAT1

47µF

BAT2

47µF

DC INPUT

(FROM AC

ADAPTOR)

D1

MBRS340T

R1

500Ω

C2

0.33µF

C1

1µF

PROG



4.93k



0.05Ω

C3

200pF

BOOSTCOMP1

SPIN

BAT SENSE

GND

C6

0.47µF

C7

50pF

C12

1µF

C5

10µF

D3

MBR0540T

L1

20µH

D2

MBRS340T

LT1511

C4

10µF

CERAMIC

0.1µF

330Ω

CHG



22µF

TANT

(CHARGER OUTPUT)

Q1

2N7002

R2

CURRENT CONTROL

FROM POWER

MANAGEMENT µP

–

R6

649k

0.25%

R5

6.8k

R4

R3

500Ω

R7

115k

0.25%



200Ω



200Ω

1% R



0.033Ω

OVP

CLPCLN

TO SW C/D

TO SW E/F TO

SW A/B

–

POWER

MANAGEMENT

µPBAT1 BAT2 GG SG GH SH

CHGMON

DCIN

LTC1479

1479 F10

SW H

Si9926DY

SW G

Si9926DY

BAT1

4 Li-ION

BATTERY

PACK

BAT2

4 Li-ION

BATTERY

PACK

CBAT1

47µF

CBAT2

47µF

DC INPUT

(FROM AC

ADAPTOR)

VCC

D1

MBRS140T

R2

300Ω

C1

1µF

PROG

RPROG

11k

R3

C2

0.1µF

BOOST

SENSE

BAT

GND

C3

0.22µF

0.1µF

D3

1N4148

L1*

33µH

D2

MBRS140T

LT1510

C6

10µF

CERAMIC

+CCHG

22µF

TANT

(CHARGER OUTPUT)

Q1

2N7002

R1

100k

CURRENT CONTROL

FROM POWER

MANAGEMENT µP

–

R4

649k

0.25%

R5

115k

0.25%

OVP

*COILTRONICS CTX33-2

TO SW C/D

TO SW E/F

TO

SW A/B

330Ω

–

POWER

MANAGEMENT

µPBAT1 BAT2 GG SG GH SH

CHGMON

DCIN

LTC1479

Figure 10. Interfacing to the LT1510 Constant-Voltage/Constant-Current Battery Charger

LTC1479

APPLICATIONS INFORMATION

WUU U

The LT1511 has a third control loop that regulates the

current drawn from the AC adapter. Therefore, the DC

input to the LTC1479 and the input to the host system

through SW A/B, is obtained from the “output” of the

LT1511 adapter sense resistor, R

, and not directly from

the DC input connector as with the LT1510. This allows

simultaneous operation of the host system while charging

a battery without overloading the AC adapter. Charging

current is reduced to keep the adapter current within

specified levels.

However, as with the LT1510 , the output of the LT1511 is

directed to the charging battery through either SW G or SW

H, and the charging battery voltage is connected to the top

of the voltage resistor divider, R6 and R7, for constant

voltage charging. (See the LT1511 data sheet for further

detail on battery charging techniques and applications

hints.)

LT1620/LTC1435 Battery Charger Interface

The LTC1479 also interfaces with the LT1620/LTC1435

synchronous high efficiency low dropout battery charger.

The circuit shown in Figure 12 is a constant-current/

constant-voltage battery charger specifically designed for

lithium-ion applications having thermal, output current, or

input voltage headroom constraints which preclude the

use of other high performance chargers such as the

LT1510 or LT1511.

This circuit can charge batteries at up to 4A. The precision

current sensing of the LT1620 combined with the high

efficiency and low dropout characteristics of the LTC1435

provide a battery charger with over 96% efficiency requir-

ing only 0.5V input-to-output differential at 3A charging

current.

Charge current programming is achieved by applying a

0µA to 100µA current from the LT1620 PROG pin to

ground, which can be derived from a resistor or DAC

output controlled by the power management µP. (See the

LT1620 data sheet for further details on this circuit.)

Capacitive Loading on the CHGMON Output

In most applications, there is virtually no capacitive load-

ing on the CHGMON output—just a simple resistor

divider. Care should be taken to restrict the amount of

capacitance to ground on the CHGMON output to less than

100pF. If more capacitance is required, it may become

necessary to “mask” the LOBAT output when the charge

monitor is switched between batteries. (Internal resis-

tance between the BAT1 and BAT2 inputs and the charge

monitor switch may create a transient voltage drop at the

BAT

output during transitions which could be falsely

interpreted by the µP as a low battery condition.)

THE POWER MANAGEMENT MICROPROCESSOR

Interfacing to the LTC1479

The LTC1479 can be thought as a “real world” interface to

the power management µP. It takes logic level commands

directly from the µP, and makes changes at high current

and high voltage levels in the power path. Further, it

provides information directly to the µP on the status of the

AC adapter, the batteries and the charging system.

The LTC1479 logic inputs are TTL level compatible and

therefore interface directly with standard power manage-

ment µPs. Further, because of the direct interface via the

five logic inputs and the two logic outputs, there is virtually

no latency (i.e. time delay) between the µP and the LTC1479.

In this way, time critical decisions can be made by the µP

without the inherent delays associated with bus protocols,

etc. These delays are acceptable in certain portions of the

power management system, but it is vital that the power

path switching control be made through a direct connec-

tion to the power management µP. The remainder of the

power management system can be easily interfaced to the

µP through a serial interface.

Selecting a Power Management Microprocessor

The power management µP provides intelligence for the

entire power system, is programmed to accommodate the

custom requirements of each individual system and allow

performance updates without resorting to costly hard-

ware changes.

The power management µP must meet the requirements

of the total power management system, including the

LTC1479 controller, the batteries (and interface), the

backup system, the charging system and the host proces-

sor. A number of inexpensive processors are available

which can easily fulfill these requirements.

LTC1479

APPLICATIONS INFORMATION

WUU U

OSC

RUN/SS

SFB

SGND

OSENSE

SENSE

–

BOOST

INTV

PGND

LTC1435

SENSE

OUT

GND

NIN PIN

PROG

AVG

LT1620

SHDN

PROG

DC INPUT

(FROM AC

ADAPTER)

TO

W A/B

330Ω

R1

1M

0.1%

R2

76.8k

0.1%

C1

100pF

0.1µF

C2

100pF

C3 

0.1µF

R5

1.5M

R5, 1k

C4

0.033µF

C6

0.1µF

C5

0.01µF

C8

0.1µF

C9, 100pF

C10

100pF

C7

0.33µF

R3

10k

C11

56pF

C12

0.1µF

D1*

CMDSH-3

C13

0.33µF

D2*

CMDSH-3

Q1

Si4412DY

Q2

Si4412DY

L1

27µH

C15

22µF

35V

×2

R4

0.025Ω

C14

4.7µF

C16

22µF

35V

1479 F12

SW H

Si9926DY

SW G

Si9926DY

BAT1

4 Li-ION

BATTERY

PACK

BAT2

4 Li-ION

BATTERY

PACK

BAT1

10µF

BAT2

10µF

–

TO SW C/D

TO SW E/F

–

POWER

MANAGEMENT

µPBAT1 BAT2 GG SG GH SH

CHGMON

DCIN

LTC1479

*CENTRAL SEMICONDUCTOR CO. (516) 435-1110

Figure 12. Interfacing to an LT1620/LTC1435 High Efficiency Constant-Voltage/Constant-Current Battery Charger

LTC1479

APPLICATIONS INFORMATION

WUU U

Interfacing to the Battery Pack

The LTC1479 is designed to work with virtually any

battery pack chemistry or cell count, as long as the

battery pack operating voltage range is somewhere

between 6V and 28V. This permits great flexibility in

system design. The low-battery threshold is adjustable

and can be set anywhere between 6V and 28V.

Conventional Battery Packs

Conventional battery packs do not include a “smart”

battery interface between the battery pack and the host

system. Thus, these battery packs generally have only

three terminals to connect the battery and a temperature

sensor (thermistor) to the host system. The NTC ther-

mistor typically has a nominal resistance of 10k at room

temperature and is used to monitor the battery pack

temperature.

LOBAT and DCINGOOD Blanking/Filtering

It is good practice to include some delay in accepting low

battery and DCIN good information during transitional

periods, e.g., when switching the charger from one battery

to another or when switching from batteries to DC power.

This technique will eliminate false triggering at the asso-

ciated µP I/O. (Remember that the “3-diode” mode may be

used during periods of uncertainty to eliminate the need

for “instantaneous” DCIN and battery status information.)

Smart Battery Packs

Smart battery packs, compliant with the Smart Battery

System specification, have a five-terminal connector. Two

of the terminals are the minus and plus connections to the

battery. A third terminal is connected to the top of a

thermistor in NiCd and NiMH battery packs and to a

resistor in Li-Ion battery packs. A fourth and fifth terminal

are connected to the Smart Management Bus (SMBus)

SMBDATA and SMBCLK lines from an integrated circuit

inside the battery pack.

Applications Assistance

Linear Technology applications engineers have developed

a smart battery charger around the LT1511 charger IC.

Contact the factory for applications assistance in develop-

ing a complete smart battery system with intelligent

PowerPath control using the LTC1479.

LTC1479

TYPICAL APPLICATIONS N

Dual NiMH Battery Power Management System (Using an LT1510, 1A Charger)

1479 TA02

DCIN

BAT1

BAT2

SW V

C3

1µF

50V

L1*

1mH

C4

1µF

50V

SENSE

0.033Ω

SW A SW B

SW C SW D

SW E SW F

GA GB GC GD GE GFSAB SCD SEF SENSE

SENSE

–

CCP

C2

2.2µF

16V

C1

0.1µF

BAT

POWER

MANAGEMENT

µP

BDIV

BKUP

DCDIV

LTC1479

GG SG GH SH

NiCD

CELL

1812LS-105 XKBC, COILCRAFT

CD43, SUMIDA

CTX33-2, COILTRONICS

*

**

***



909k

DC2



205k

330Ω

DC1



12.1k



121k

LOBAT

DCINGOOD

TO INPUT 

OF DC/DC 

CONVERTER

L2**

10µH

3DM



FROM 

DC/DC

D1 

MBR0530

BATSEL

GND BATDIS DCIN/BAT

CHGSEL

DC INPUT

(FROM AC

ADAPTOR)

D2

MBRS140T

R5

300Ω

C8

1µF

PROG



11k

R6

C9

0.1µF

BOOST

SENSE

BAT

GND

C7

0.22µF

D3

1N4148

L3***

33µH

D4

MBRS140T

LT1510

SW H

Si9926DY

C6

10µF

CERAMIC

CHG



22µF

TANT

(CHARGER OUTPUT)

Si4936DY

(BOLD LINES INDICATE HIGH CURRENT PATHS)

Si4936DY

SW G

Si9926DY

Q1

2N7002

R2

390k

R3

100k

BAT1

10µF

BAT2

10µF

SMBUS

BAT2

12-CELL

NiMH

BATTERY

PACK

BAT1

12-CELL

NiMH

BATTERY

PACK

R4

100k

CHGMON

TH1

TH2

C5

0.1µF

C11

0.1µF

R1

22k

100k

R7

470k

C10

0.1µF

CC

FROM

DC/DC

D5

BAS16LT1

Q2

2N7002

ROHM

DTA144E

CM2

909k

CM1

100k

R8

10k

(BACKUP)

SW FB

SHDN

GNDI

LIM

LBI

LBO

LT1304

DCIN



10µF

35V

ALUM

0.1µF

LTC1479

Dual Li-Ion Battery Power Management System

1479 TA03

DCIN

330Ω

BAT1

BAT2

V+SW VGG

C3

1µF

50V

L1*

1mH

C4

1µF

50V

VCC

RSENSE

0.033Ω

SW A SW B

SW C SW D

SW E SW F

GA GB GC GD GE GFSAB SCD SEF SENSE+SENSE–

VCCP

C2

2.2µF

16V

C1

0.1µF

VBAT

POWER

MANAGEMENT

µP

BDIV

VBKUP

DCDIV

LTC1479

GG SG GH SH

NiCD

CELL

1812LS-105 XKBC, COILCRAFT

DT1608-223, COILCRAFT

CTX33-2, COILTRONICS

*

**

***

RB2

909k

RDC2

205k

RDC1

12.1k

RB1

121k

LOBAT

DCINGOOD

TO INPUT 

OF DC/DC 

CONVERTER

L2**

10µH

3DM

5VCC

FROM 

DC/DC

VCC

D1 

MBR0530

BATSEL

GND BATDIS DCIN/BAT

CHGSEL

DC INPUT

(FROM AC

ADAPTOR)

VCC

D2

MBRS140T

R5

300Ω

C8

1µF

PROG

RPROG

3.83k

R6

1k R7

649k

0.25%

R8

115k

0.25%

C9

0.1µF

BOOST

SENSE

OVP

BAT

GND

C7

0.22µF

D3

1N4148

L3***

33µH

D4

MBRS140T

LT1510

SW H

Si9926DY

C6

10µF

CERAMIC

CCHG

22µF

TANT

(CHARGER OUTPUT)

Si4936DY

SW G

Si9926DY

Q1

2N7002

R2

390k

R3

100k

CBAT1

10µF

CBAT2

10µF

SMBUS

BAT2

4 Li-ION

SMART

BATTERY

PACK

BAT1

4 Li-ION

SMART

BATTERY

PACK

CHGMON

RBAT1

RBAT2

+C5

0.1µF

C11

0.1µF

R1

22k

100k

R7

470k

C10

0.1µF

5VCC

FROM

DC/DC

D5

BAS16LT1

Q2

2N7002

ROHM

DTA144E R8

10k

(BACKUP)

1, 7-10, 16

14, 15

SW FB

SHDN

VIN

GNDILIM

LBI

LBO

LT1304

(BOLD LINES INDICATE HIGH CURRENT PATHS)

CDCIN

10µF

35V

ALUM

0.1µF

TYPICAL APPLICATIONS N

LTC1479

Dual Li-Ion Battery Power Management System (Using an LT1511, 3A Charger)

TYPICAL APPLICATIONS N

1479 TA04

DCIN

BAT1

BAT2

V+SW VGG

C3

1µF

50V

L1*

1mH

C4

1µF

50V

VCC

RSENSE

0.033Ω

SW A

330Ω

SW B

SW C SW D

SW E SW F

GA GB GC GD GE GFSAB SCD SEF SENSE+SENSE–

VCCP

C2

2.2µF

16V

C1

0.1µF

VBAT

POWER

MANAGEMENT

µP

BDIV

VBKUP

DCDIV

LTC1479

GG SG GH SH

NiCD

CELL

1812LS-105 XKBC, COILCRAFT

DT1608-223, COILCRAFT

CTX20-4, COILTRONICS

*

**

***

RB2

1.05M

RDC2

205k

RDC1

12.1k

RB1

121k

LOBAT

DCINGOOD

TO INPUT 

OF DC/DC 

CONVERTER

L2**

10µH

3DM

5VCC

FROM 

DC/DC

VCC

D1 

MBR0530

BATSEL

GND BATDIS DCIN/BAT

CHGSEL

DC INPUT

(FROM AC

ADAPTOR)

SW H

Si9926DY

Si4936DY

SW G

Si9926DY

R2

390k

R3

100k

CBAT1

10µF

CBAT2

10µF

SMBUS

BAT2

4 Li-ION

SMART

BATTERY

PACK

BAT1

4 Li-ION

SMART

BATTERY

PACK

CHGMON

RBAT1

RBAT2

C5

0.1µF

C15

0.1µF

R1

22k

R11

470k

100k

C14

0.1µF

5VCC

FROM

DC/DC

D5

BAS16LT1

Q2

2N7002

ROHM

DTA144E R12

10k

(BACKUP)

SW FB

SHDN

VIN

GNDILIM

LBI

LBO

LT1304

VCC

R5

500ΩC9

0.33µF

C8

1µF

PROG

14 12

1, 4, 5, 7,

16, 23, 24

20 TO 22

RPROG

4.93k

1% C10

200pF

VCSW

BOOSTCOMP1

SPIN

BAT SENSE

GND

C13

0.47µF

C11

50pF

C12

1µF

C7

10µF

D3

MBR0540T

L3***

20µH

D2

MBRS340T

LT1511

C6

10µF

CERAMIC

CCHG

22µF

TANT

CDCIN

10µF

35V

ALUM

(CHARGER OUTPUT)

Q1

2N7002

R6

R7

649k

0.25%

R9

6.8k

R10

R4

500Ω

RS4

0.05Ω

R8

115k

0.25%

RS3

200Ω

RS2

200Ω

1% RS1

0.033Ω

OVP

CLPCLN

D1

MBRS340T

(BOLD LINES INDICATE HIGH CURRENT PATHS)



0.1µF

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

LTC1479

1479f LT/TP 0697 7K • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 1996

Dimensions in inches (millimeters) unless otherwise noted.

PACKAGE DESCRIPTION

G Package

36-Lead Plastic SSOP (0.209)

(LTC DWG # 05-08-1640)

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1304 Micropower DC/DC Step-Up Converter 5V at 200mA from 2 Cells, I

= 10µA in Shutdown

LTC1435 High Efficiency Synchronous Step-Down Converter Fixed Frequency, Ultrahigh Efficiency

LTC1438 Dual High Efficiency Synchronous Step-Down Converter Fixed Frequency, PLL Lockable, Ultrahigh Efficiency

LTC1473 Dual PowerPath Switch Driver Protected Power Management Building Block

LT1510 Constant-Voltage/Constant-Current Battery Charger 1.5A Internal Switch, Precision 0.5% Reference

LT1511 Constant-Voltage/Constant-Current 3A Battery Charger Adapter Current Limit Loop

LTC1538-AUX Dual, Synchronous Controller with Aux Regulator 5V Standby in Shutdown

LT1620 Battery Charger Current Controller 96% Efficiency When Used with LTC1435

LT1621 Dual Battery Charger Current Controller For Dual Loop Applications

G36 SSOP 1196

0.005 – 0.009

(0.13 – 0.22)

0° – 8°

0.022 – 0.037

(0.55 – 0.95)

0.205 – 0.212**

(5.20 – 5.38)

0.301 – 0.311

(7.65 – 7.90)

12345678 9 10 11 12 14 15 16 17 1813

0.499 – 0.509*

(12.67 – 12.93)

2526 22 21 20 19232427282930313233343536

0.068 – 0.078

(1.73 – 1.99)

0.002 – 0.008

(0.05 – 0.21)

0.0256

(0.65)

BSC 0.010 – 0.015

(0.25 – 0.38)

DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH 

SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE

DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD 

FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE



*

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

●

(408) 432-1900

FAX: (408) 434-0507

●

TELEX: 499-3977

●