General Description
The MAX8556/MAX8557 low-dropout linear regulators
operate from input voltages as low as 1.425V and are
able to deliver up to 4A of continuous output current
with a typical dropout voltage of only 100mV. The out-
put voltage is adjustable from 0.5V to VIN - 0.2V.
Designed with an internal p-channel MOSFET pass tran-
sistor, the MAX8556/MAX8557 maintain a low 800µA typi-
cal supply current, independent of the load current and
dropout voltage. Using a p-channel MOSFET eliminates
the need for an additional external supply or a noisy inter-
nal charge pump. Other features include a logic-con-
trolled shutdown mode, built-in soft-start, short-circuit
protection with foldback current limit, and thermal-over-
load protection. The MAX8556 features a POK output that
transitions high when the regulator output is within ±10%
of its nominal output voltage. The MAX8557 offers a
power-on reset output that transitions high 140ms after the
output has achieved 90% of its nominal output voltage.
The MAX8556/MAX8557 are available in a 16-pin thin
QFN 5mm x 5mm package with exposed paddle.
Applications
Servers and Storage Devices
Networking
Base Stations
Optical Modules
Point-of-Load Supplies
ATE
Features
o1.425V to 3.6V Input Voltage Range
oGuaranteed 4A Output Current
o±1% Output Accuracy Over Load/Line/
Temperature
o100mV Dropout at 4A Load (typ)
oBuilt-In Soft-Start
o800µA (typ) Operating Supply Current
o150µA (max) Shutdown Supply Current
oShort-Circuit Current Foldback Protection
oThermal-Overload Protection
o±10% Power-OK (MAX8556)
o140ms Power-On Reset Output (MAX8557)
oFast Transient Response
o16-Pin Thin QFN (5mm x 5mm) Package
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
________________________________________________________________
Maxim Integrated Products
1
12 11 10 9
5
6
7
EP
8
IN
IN
OUT
OUT
TOP VIEW
16
15
14
13
EN
+
N.C.
GND
FB
1234
IN
IN
IN
IN
MAX8556
(MAX8557)
POK (POR)
OUT
OUT
OUT
THIN QFN
5mm x 5mm
Pin Configuration
Ordering Information
IN
EN
GND
OUT
FB
N.C.
POK
(POR)
VIN
1.425V TO 3.6V
VOUT
0.5V TO VIN - 0.2V
MAX8556
(MAX8557)
Typical Operating Circuit
19-3257; Rev 2; 8/09
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP
RANGE
PIN-
PACKAGE FEATURE
MAX8556ETE+ - 40°C to + 85°C 16 Thin QFN-EP* POK
M AX 8556E TE /V + - 40°C to + 85°C 16 Thin QFN-EP* POK
MAX8557ETE+ - 40°C to + 85°C 16 Thin QFN-EP* POR
+
Denotes a lead(Pb)-free/RoHS-compliant package.
/V Denotes an automotive qualified part.
*EP = Exposed pad.
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VEN = VIN = 1.8V, VOUT = 1.5V, IOUT = 2mA, TA = -40°C to +85°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
IN, EN, POK, POR to GND .......................................-0.3V to +4V
FB, OUT to GND ..........................................-0.3V to (VIN + 0.3V)
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (TA = +70°C)
16-Pin Thin QFN (derate 33.3mW/°C
above +70°C) (Note 1)............................................2666.7mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER CONDITIONS MIN TYP MAX UNITS
IN
Input Voltage Range 1.425 3.600 V
VIN rising, 70mV hysteresis 1.30 1.35 1.40
Input Undervoltage Lockout VIN falling 1.23 1.28 1.33 V
OUT
Output Voltage Range 0.5 3.4 V
Load Regulation IOUT = 2mA to 4A 0.1 %/A
Line Regulation VIN = 1.425V to 3.6V, VOUT = 1.225V -0.15 0 +0.15 %/V
Dropout Voltage VIN = 1.425V, IOUT = 4A, VFB = 480mV 100 200 mV
Regulated Output-Voltage Current
Limit VIN = 3.6V, VOUT = 3V, VFB = 460mV 5 7 9 A
Load Capacitance ESR < 50mA 16 120 µF
FB
FB Threshold Accuracy
(Note 3)
VOUT = 1.225V to 3V, VIN = VOUT + 0.2V to 3.6V,
IOUT = 2mA to 4A 495 500 505 mV
FB Input Bias Current VFB = 0.5V, VIN = 3.6V 0.001 1 µA
GND
VIN = 1.425V to 3.6V, VOUT = 1.225V 800 1600
GND Supply Current Dropout, VIN = 3.6V, VFB = 480mV 1000 2000 µA
GND Shutdown Current VIN = 3.6V, EN = GND 150 µA
POK
FB high 540 550 560
FB Power-OK Fault Threshold FB moving out of regulation,
VIN = 1.425V to 3.6V, 10mV hysteresis FB low 440 450 460 mV
POK Output Voltage, Low VFB = 0.4V or 0.6V, IPOK = 2mA 25 200 mV
Note 1: Maximum power dissipation is obtained using JEDEC JESD51-5 and JESD51-7 standards.
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
_______________________________________________________________________________________ 3
Note 2: Specifications to TA= -40°C are guaranteed by design and not production tested.
Note 3: Minimum supply voltage for output accuracy must be at least 1.425V.
ELECTRICAL CHARACTERISTICS (continued)
(VEN = VIN = 1.8V, VOUT = 1.5V, IOUT = 2mA, TA = -40°C to +85°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
POK Output Current, High VPOK = 3.6V VFB = 0.5 0.001 1 µA
POK Delay Time From FB rising to POK high 25 50 100 µs
EN
EN rising 1.25
Enable Input Threshold VIN = 1.425V to 3.6V EN falling 0.4 V
Enable Input Bias Current VEN = 0V or 3.6V -1 +1 µA
THERMAL SHUTDOWN
TJ rising +160
Thermal-Shutdown Threshold Output on and off TJ falling +115 °C
POR
FB Power-On Reset Fault Threshold FB falling, VIN = 1.425V to 3.6V, 10mV hysteresis 440 450 460 mV
POR Output Voltage, Low VFB = 0.4V, IPOR = 2mA 25 200 mV
POR Output Current, High VPOR = 3.6V, VFB = 0.5V 0.001 1 µA
POR Rising Delay Time FB rising to POR high impedance 100 140 200 ms
SOFT-START
Soft-Start Time 100 µs
Typical Operating Characteristics
(VEN = VIN = +1.8V, VOUT = +1.5V, IOUT = 4A, COUT = 20µF, CIN = 20µF, and TA= +25°C, unless otherwise noted.)
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX8556 toc01
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3.02.41.8
1.35
1.40
1.45
1.50
1.55
1.30
1.2 3.6
TA = -25°C
TA = -40°C
TA = -85°C
ILOAD = 2A
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX8556 toc02
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)
321
1.4980
1.4985
1.4990
1.4995
1.5000
1.5005
1.5010
1.5015
1.5020
1.5025
1.4975
04
TA = -40°C
TA = +85°C
TA = +25°C
GND CURRENT vs. INPUT VOLTAGE
MAX8556 toc03
INPUT VOLTAGE (V)
GND CURRENT (µA)
2.41.2
100
200
300
400
500
600
700
800
900
1000
0
0 3.6
ILOAD = 4A
ILOAD = 2A
ILOAD = 0A
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VEN = VIN = +1.8V, VOUT = +1.5V, IOUT = 4A, COUT = 20µF, CIN = 20µF, and TA= +25°C, unless otherwise noted.)
GND CURRENT vs. TEMPERATURE
MAX8556 toc04
TEMPERATURE (°C)
GND CURRENT (µA)
603510-15
100
200
300
400
500
600
700
800
900
0
-40 85
ILOAD = 2A
ILOAD = 0A
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX8556 toc05
LOAD CURRENT (A)
DROPOUT VOLTAGE (mV)
3.53.02.0 2.51.0 1.50.5
10
20
30
40
50
60
70
80
90
0
0 4.0
VIN = 1.5V
LINE-TRANSIENT RESPONSE
MAX8556 toc06
100µs/div
1.8V
10mV/div
2.5V
VIN
VOUT
(AC-COUPLED)
4A LOAD-TRANSIENT RESPONSE
MAX8556 toc07
40µs/div
2A/div
50mV/div
VOUT
(AC-COUPLED)
IOUT
2A LOAD-TRANSIENT RESPONSE
MAX8556 toc08
40µs/div
1A/div
50mV/div
VOUT
(AC-COUPLED)
IOUT
ENABLE WAVEFORMS
MAX8556 toc09
100µs/div
1V/div
2V/div
VEN
VOUT
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
_______________________________________________________________________________________
5
EXPOSED PADDLE TEMPERATURE
vs. AMBIENT TEMPERATURE
MAX8556 toc13
AMBIENT TEMPERATURE (°C)
EXPOSED PADDLE TEMPERATURE (°C)
68513417
10
20
30
40
50
60
70
80
90
100
0
085
DATA TAKEN USING
MAX8556 EVALUATION KIT
FB REGULATION vs. TEMPERATURE
MAX8556 toc14
TEMPERATURE (°C)
FB (V)
603510-15
0.495
0.500
0.505
0.510
0.490
-40 85
ILOAD = 50mA
FOLDBACK CURRENT-LIMIT WAVEFORMS
MAX8556 toc15
100µs/div
500mV/div
5A/div
VOUT
IOUT
CURRENT-LIMIT THRESHOLD
vs. TEMPERATURE
MAX8556 toc16
TEMPERATURE (°C)
CURRENT-LIMIT THRESHOLD (A)
603510-15
6.2
6.4
6.6
6.8
7.0
7.2
7.4
7.6
7.8
8.0
6.0
-40 85
PSRR vs. FREQUENCY
MAX8556 toc11
FREQUENCY (kHz)
PSRR (dB)
10010
10
20
30
40
50
60
70
80
90
0
1 1000
VIN = 2.5V
ILOAD = 1A
STARTUP WAVEFORMS
MAX8556 toc12
100µs/div
1V/div
2V/div
2A/div
VIN
IIN
VOUT
Typical Operating Characteristics (continued)
(VEN = VIN = +1.8V, VOUT = +1.5V, IOUT = 4A, COUT = 20µF, CIN = 20µF, and TA= +25°C, unless otherwise noted.)
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
6 _______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1–6 IN
LDO Input. Connect to a 1.425V to 3.6V input voltage. Bypass with a 22µF ceramic capacitor to GND.
7–11 OUT LDO Output. Bypass with 2 x 10µF ceramic capacitors to GND. A smaller capacitance can be used if
the maximum load current is less than 4A.
POK
(MAX8556)
Power-OK Output. Open-drain output that pulls low when VOUT is outside ±10% of the expected
regulation voltage or when EN is low. POK is high impedance when VOUT is within ±10% of the
nominal output voltage. Connect a resistor from POK to a logic supply of less than 3.6V.
12
POR
(MAX8557)
Power-On Reset. Open-drain output goes high impedance 140ms after the output is above 90% of its
nominal regulation voltage. POR pulls low immediately after an output fault or when EN is low.
Connect a resistor from POR to a logic supply of less than 3.6V.
13 FB Feedback Input. VFB is regulated to 0.5V. Connect to the center tap of a resistor-divider from output
to GND to set the desired output voltage.
14 GND Ground
15 N.C. Connect to GND or Leave Unconnected
16 EN Enable Input. Connect to GND or a logic low to shut down the device. Connect to IN or a logic high
for normal operation.
— EP Exposed Paddle. Connect to GND and to a ground plane for heatsinking.
P
MAX8556
(MAX8557)
THERMAL-
OVERLOAD
PROTECTION
REF
SHUTDOWN
LOGIC
ERROR
AMP
CURRENT-
LIMIT
COMPARATOR
THRESHOLD
EN
GND
IN
0.50V
OUT
FB
POK
(POR)
0.45V
0.55V
UNDERVOLTAGE
LOCKOUT
POK (POR)
CIRCUITRY N
Block Diagram
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
_______________________________________________________________________________________ 7
Detailed Description
The MAX8556/MAX8557 low-dropout linear regulators
are capable of delivering up to 4A from low-input volt-
age supplies ranging from 1.425V to 3.6V with only
200mV of dropout (max). The pMOS output stage can
be driven from input voltages down to 1.425V without
sacrificing stability or transient performance. Supply
current is not a significant function of load or input head-
room because this regulator has a pMOS output device.
The MAX8556/MAX8557 are fully protected from an out-
put short circuit by current-limiting and thermal-overload
circuitry. The low-power shutdown mode reduces sup-
ply current to 0.2µA (typ) to maximize battery life in
portable applications. The MAX8556 includes an open-
drain power-OK signal (POK) that goes high when the
regulator output is within ±10% of its nominal output
voltage. The MAX8557 includes an open-drain power-
on-reset output (POR) that goes high 140ms after the
output has risen above 90% of its nominal value.
Internal p-Channel Pass Transistor
The MAX8556/MAX8557 feature a 25mΩp-channel
MOSFET pass transistor. Unlike similar designs using
pnp pass transistors, p-channel MOSFETs require no
base drive, which reduces quiescent current; pnp-
based regulators also waste considerable current in
dropout when the pass transistor saturates, and use
high base-drive currents under large loads. The
MAX8556/MAX8557 do not suffer from these problems
and consume only 800µA (typ) of quiescent current
under heavy loads, as well as in dropout.
Short-Circuit/Thermal Fault Protection
The MAX8556/MAX8557 are fully protected from output
short circuits through current-limiting and thermal-over-
load circuitry. When the output is shorted to ground, the
output current is foldback limited to 3A (max). Under
these conditions, the device quickly heats up. When
the junction temperature reaches +160°C, the thermal-
overload circuitry turns off the output, allowing the
device to cool. When the junction cools to +115°C, the
output turns back on and attempts to establish regula-
tion. Current limiting and thermal protection continue
until the fault is removed.
Shutdown Mode
The MAX8556/MAX8557 feature a low-power shutdown
mode that reduces quiescent current to 0.2µA (typ).
Drive EN low to disable the voltage reference, error
amplifier, gate-drive circuitry, and pass transistor, and
pull the output low with 5kΩimpedance. Drive EN high
or connect to IN for normal operation.
Power-OK Output (POK, MAX8556 Only)
The MAX8556 features a power-OK (POK) output to
indicate the status of the output. POK is high impedance
when the regulator output is within ±10% of its nominal
output voltage. If the output voltage falls/rises outside
this range or the IC experiences thermal fault, POK is
internally pulled low. This open-drain output requires an
external pullup resistor to VIN or another logic supply
below 3.6V. For glitch immunity, an internal delay circuit
prevents the output from switching for 50µs (typ) after
the trip threshold is initially reached. POK is low when
the IC is in shutdown mode.
Power-On Reset (POR, MAX8557 Only)
The MAX8557 features a power-on reset output that
goes high impedance 140ms (typ) after the output
reaches 90% of its nominal value. This open-drain out-
put requires an external pullup resistor to VIN or another
logic supply less than 3.6V. When the output falls below
90% of the nominal output voltage or the IC experi-
ences a thermal fault, POR immediately transitions low.
POR is low when the IC is in shutdown mode.
Operating Region and Power Dissipation
The maximum power dissipation depends on the ther-
mal resistance of the IC package and the circuit board,
the temperature difference between the die junction and
ambient air, and the rate of ambient airflow. The power
dissipated by the IC is P = IOUT x (VIN - VOUT). Proper
PCB layout can increase the allowed power dissipation
by dissipating heat in the board instead of the package.
See the
Thermal Considerations in PCB Layout
section
for more details.
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
8 _______________________________________________________________________________________
Applications Information
Output Voltage Selection
The MAX8556/MAX8557 feature an adjustable output
voltage from 0.5V to 3.4V. Set the output voltage using
an external resistor-divider from the output to GND with
FB connected to the center tap as shown in Figures 1
and 2. Choose R3 ≤1kΩfor light-load stability.
Determine R2 using the following equation:
where VOUT is the desired output voltage and VFB is 0.5V.
Capacitor Selection and
Regulator Stability
Capacitors are required at the MAX8556/MAX8557
inputs and outputs for stable operation over the full
temperature range and with load currents up to 4A.
Connect 2 x 10µF capacitors between IN and GND and
2 x 10µF low equivalent-series-resistance (ESR) capac-
itors between OUT and GND. The input capacitor (CIN)
lowers the source impedance of the input supply. If the
MAX8556/MAX8557s’ input is close to the output of the
source supply, a smaller input capacitance can be
used. Otherwise, 2 x 10µF ceramic input capacitors are
recommended. The output capacitor’s (COUT) ESR
affects output noise and may affect output stability. Use
output capacitors with an ESR of 0.05Ωor less to
ensure stability and optimum transient dropout. For
good output transient performance, use the following
formula to select a minimum output capacitance:
COUT = IOUT(MAX) x 1µF/200mA
Noise, PSRR, and Transient Response
The MAX8556/MAX8557 are designed to operate with
low-dropout voltages and low quiescent currents while
still maintaining low noise, good transient response,
and high AC rejection (see the
Typical Operating
Characteristics
for a plot of Power-Supply Rejection
Ratio (PSRR) vs. Frequency). When operating from
noisy sources, improved supply-noise rejection and
transient response can be achieved by increasing the
values of the input and output bypass capacitors and
through passive filtering techniques. The MAX8556/
MAX8557 load-transient response graphs (see the
Typical Operating Characteristics
) show two compo-
nents of the output response: a DC shift from the output
impedance due to the load current change, and the
transient response. A typical transient overshoot for a
step change in the load current from 40mA to 4A is
40mV. Use an output capacitance from 20µF to 120µF
to attenuate the overshoot.
RRx
V
V
OUT
FB
23 1 =−
⎛
⎝
⎜⎞
⎠
⎟
IN 7–11
13
14
15
POR
POR
GND
SHUTDOWN
OUT
FB
1–6
12
R1
100kΩ
R2
2kΩ
R3
1kΩ
C1
2 x 10µF
C2
2 x 10µF
18
N.C.
U2
EN
ENABLED
VIN
1.7V TO 3.6V
VOUT
1.5V AT 4A
MAX8557
Figure 2. MAX8557 Typical Application Circuit
IN 7–11
13
14
15
POK
POK
GND
SHUTDOWN
OUT
FB
1–6
12
R1
100kΩ
R2
1.4kΩ
R3
1kΩ
C1
2 x 10µF
C2
2 x 10µF
18
N.C.
U1
EN
ENABLED
VIN
1.425V TO 3.6V
VOUT
1.2V AT 4A
MAX8556
Figure 1. MAX8556 Typical Application Circuit
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
_______________________________________________________________________________________ 9
Thermal Considerations
in PCB Layout
How much power the package can dissipate strongly
depends on the mounting method of the IC to the PCB
and the copper area for cooling. Using the JEDEC test
standard, the maximum power dissipation allowed in
the package is 2667mW. This data is obtained with
+70°C ambient temperature and +150°C maximum
junction temperature. The test board has dimensions of
3in x 3in with four layers of 2oz copper and FR-4 mater-
ial with 62mil finished thickness. Nine thermal vias are
used under the thermal paddle with a diameter of 12mil
and 1mil plated copper thickness. Top and bottom lay-
ers are used to route the traces. Two middle layers are
solid copper and isolated from the nine thermal vias.
More power dissipation can be handled by the pack-
age if great attention is given during PCB layout. For
example, using the top and bottom copper as a
heatsink and connecting the thermal vias to one of the
middle layers (GND) transfers the heat from the pack-
age into the board more efficiently, resulting in lower
junction temperature at high power dissipation in some
MAX8556/MAX8557 applications. Furthermore, the sol-
der mask around the IC area on both top and bottom
layers can be removed to radiate the heat directly into
the air. The maximum allowable power dissipation in
the IC is as follows:
where TJ(MAX) is the maximum junction temperature
(+150°C), TAis the ambient air temperature, θJC
(1.7°C/W for the 16-pin TQFN) is the thermal resistance
from the junction to the case, and θCA is the thermal
resistance from the case to the surrounding air through
the PCB, copper traces, and the package materials.
θCA is directly related to system level variables and can
be modified to increase the maximum power dissipa-
tion. The TQFN package has an exposed thermal pad
on its underside. This pad provides a low thermal resis-
tance path for heat transfer into the PCB. This low ther-
mally resistive path carries a majority of the heat away
from the IC. The PCB is effectively a heatsink for the IC.
The exposed paddle should be connected to a large
ground plane for proper thermal and electrical perfor-
mance. The minimum size of the ground plane is
dependent upon many system variables. To create an
efficient path, the exposed paddle should be soldered
to a thermal landing, which is connected to the ground
plane by thermal vias. The thermal landing should be at
least as large as the exposed paddle and can be made
larger depending on the amount of free space from the
exposed paddle to the other pin landings.
A sample layout is available on the MAX8556 evalua-
tion kit to speed designs.
PTT
MAX J MAX A
JC CA
(
() )
=−
+θθ
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
16 TQFN-EP T1655+2 21-0140
Chip Information
TRANSISTOR COUNT: 3137
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in
the package code indicates RoHS status only. Package draw-
ings may show a different suffix character, but the drawing per-
tains to the package regardless of RoHS status.
MAX8556/MAX8557
4A Ultra-Low-Input-Voltage
LDO Regulators
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
10
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 4/04 Initial release —
1 8/08 Revised Pin Configuration.1
2 8/09 Added automotive version of the MAX8556. 1