LM2759
C2
VIN
C2+
C2-
GND
CIN 2.2 µF
2.2 µF
COUT
VOUT
4.7 µF
TX
C1
C1+
C1-
2.2 µF
VIN = 3.0V - 5.5V ILED = Up to 1A
SDA
SCL
ISINK
D1
Strobe
TDK: 2.2 µF ± C1608X5R1C225
4.7 µF ± C2012X5R1C475
LM2759
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LM2759 1A Switched Capacitor Flash LED Driver with I
2
C Compatible Interface
Check for Samples: LM2759
1FEATURES APPLICATIONS
2• Up to 1A Output Current • Camera Flash in Cellular Phones
• Solution Area < 22 mm2DESCRIPTION
• No Inductor Required LM2759 is an integrated low-noise, high-current
• 90% Peak Efficiency switched capacitor DC/DC converter with a regulated
• Adaptive 1x, 1.5x and 2x Gains for Maximum current source. The device requires only four small
Efficiency ceramic capacitors making the total solution area less
than 22 mm2and the height less than 1 mm. The
• Load Disconnect in Shutdown LM2759 is capable of driving loads up to 1A from a
• Accurate Input Current Control During Gain single-cell Li-Ion battery. Maximum efficiency is
Transitions achieved over the input voltage range by actively
• Flash Time-Out selecting the proper gain based on the LED forward
voltage and current requirements.
• TX Input Pin Ensures Synchronization with RF
Power Amplifier Pulse The LED current can be programmed up to 1A via an
I2C-compatible interface, along with eight selectable
• Torch, Flash, and Indicator Modes Flash Time-Out durations. One high-current Flash
• External Flash Enable via Strobe Input Pin LED can be driven either in a high-power Flash mode
• Strobe Input Disable via I2Cor a low-power Torch mode. The Strobe pin allows
the flash to be toggled via a Flash enable signal from
• Programmable Flash Pulse Duration, and a camera module. The TX input pin limits the Flash
Torch and Flash Currents via I2C-Compatible LED current to the Torch current level during a RF
Interface PA pulse, to reduce high loads on the battery.
• 1MHz Constant Frequency Operation Internal soft-start circuitry limits the amount of inrush
• Low Profile 12–Pin WSON (3mm x 3mm x current during start-up.
0.8mm) LM2759 is offered in a small 12-pin thermally
enhanced WSON package.
Typical Application Circuit
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 2008–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
1
3
4
5
6
12
10
9
8
7
Die-Attach Pad: GND
1
3
4
5
6
12
10
9
8
7
Die-Attach Pad: GND
Top View Bottom View
211 11 2
LM2759
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Connection Diagram
Figure 1. 12-Pin WSON Package
3mm x 3mm x 0.8mm
Package Number DQB0012A
PIN DESCRIPTIONS
Pin Name Description
10 VIN Input voltage connection.
3 VOUT Charge pump regulated output.
12 C1−
11 C1+ Flying capacitor connections.
2 C2+
1 C2−
4 GND Ground connection.
6 ISINK Regulated current sink input.
8 SDA Serial data I/O pin.
7 Strobe Manual flash enable pin. Flash will remain on for the duration that the Strobe pin is held high or
when the Flash Timeout occurs, whichever comes first.
5 TX Transmission pulse Flash interrupt pin. High = RF PA pulse active, LED current reduced to Torch
level, Low = RF PA pulse off, LED at full programmed current level.
9 SCL Serial clock pin.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
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Absolute Maximum Ratings(1)(2)(3)
VIN pin: Voltage to GND -0.3V to 6.0V
Strobe, TX, SDA, SCL, ISINK pins: Voltage to GND -0.3V to (VIN + 0.3V)
w/ 6.0V max
Continuous Power Dissipation(4) Internally Limited
Junction Temperature (TJ-MAX) 150°C
Storage Temperature Range -65°C to 150°C
Maximum Lead Temp. (Soldering) (5)
ESD Rating Human Body Model(6) 2.5KV
(1) Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits
and associated test conditions, see the Electrical Characteristics tables.
(2) All voltages are with respect to the potential to the GND pin.
(3) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(4) Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150°C (typ.) and
disengages at TJ= 120°C (typ.).
(5) For detailed soldering specifications and information, please refer to Texas Instruments Application Note AN-1187 (SNOA401).
(6) The Human body model is a 100 pF capacitor discharged through a 1.5 kΩresistor into each pin. (MIL-STD-883 3015.7)
Operating Ratings(1)(2)
Input Voltage Range 2.7V to 5.5V
LED Voltage Range 2.0V to 4.0V
Junction Temperature Range (TJ) -30°C to +125°C
Ambient Temperature Range (TA)(3) -30°C to +85°C
(1) Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits
and associated test conditions, see the Electrical Characteristics tables.
(2) All voltages are with respect to the potential to the GND pin.
(3) In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operation junction temperature (TJ-MAX-OP =
125ºC), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the
part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP - (θJA × PD-MAX).
Thermal Information
Junction-to-Ambient Thermal Resistance, (θJA), (1) 36.7°C/W
(1) Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. The test board is a 4–layer FR-4 board measuring 102 mm x 76 mm x 1.6 mm with a 2x1 array
of thermal vias. The ground plane on the board is 50 mm x 50 mm. Thickness of copper layers are 53µm/35µm/35µm/53µm
(1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22°C, still air. Power dissipation is 1W.The value of θJA of this product in the
WSON package could fall in a range as wide as 30ºC/W to 150ºC/W (if not wider), depending on PWB material, layout, and
environmental conditions. In applications where high maximum power dissipation exists (high VIN, high IOUT), special care must be paid
to thermal dissipation issues. For more information on these topics, please refer to Application Note AN-1187 (SNOA401): and the
Power Efficiency and Power Dissipation section of this datasheet.
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Electrical Characteristics(1)(2)
Limits in standard typeface are for TJ= 25°C. Limits in boldface type apply over the full operating junction temperature range
(-30°C ≤TJ≤+125 °C). Unless otherwise noted, specifications apply to the LM2759 Typical Application Circuit (pg.1) with VIN
= 3.6V, VTX = 0V, VSTROBE = 0V, CIN = C1= C2= 2.2 µF, COUT = 4.7 µF.(3)
Symbol Parameter Conditions Min Typ Max Units
ILED LED Current Sink Accuracy Flash Mode 198 220 242 mA
ADDR xB0 = 0x02 −10% +10%
IFLASH Max Flash Output Current Flash Mode 1 A
ADDR xB0 = 0x0F
VGDX Gain Transition Voltage ILED = 500mA 350 mV
Threshold on ISINK (VISINK falling)
VOUT Output Voltage 1x Mode, IOUT = 0 mA (VIN >VOUT)(4) 4.7 4.9
1.5x Mode, IOUT = 0 mA 4.7 4.9 V
2x Mode, IOUT = 0 mA 5.1 5.4
ROUT x1 Mode Output Impedance IOUT = 200mA, VIN = 3.3V 0.33
Ω
1.5x Mode Output IOUT = 500mA, VIN = 3.3V 1.9
Impedance
x2 Mode Output Impedance 2.25
FSW Switching Frequency 2.7V ≤VIN ≤5.5V 0.7 11.3 MHz
VIH Input Logic High Pins: TX, Strobe 1.26 V
VIL Input Logic Low Pins: TX, Strobe 0.7 V
IOUT = 0 mA, 1x Mode 0.6 0.9
IQQuiescent Current IOUT = 0 mA, 1.5x Mode 3.4 4.0 mA
IOUT = 0 mA, 2x Mode 5.9 7.0
ISD Shutdown Current Device Disabled 5.8 9.7 µA
2.7V ≤VIN ≤5.5V
I2C Compatible Interface Voltage Specifications (SCL, SDA)
VIL Input Logic Low “0” 2.7V ≤VIN ≤5.5V 0.72 V
VIH Input Logic High “1' 2.7V ≤VIN ≤5.5V 1.25 V
VOL Output Logic Low “0” ILOAD = 3 mA 300 mV
I2C Compatible Interface Timing Voltage Specifications (SCL, SDA)(5)
t1SCL (Clock Period) 2.5 µs
t2Data in Setup Time to SCL 100 ns
High
t3Data Out Stable After SCL 0ns
Low
t4SDA Low Setup Time to 100 ns
SCL Low (Start)
t5SDA High Hold Time After 100 ns
SCL High (Stop)
(1) All voltages are with respect to the potential to the GND pin.
(2) Min and Max limits are specified by design, test, or statistical analysis. Typical (Typ) numbers are not ensured, but do represent the
most likely norm. Unless otherwise specified, conditions for Typ specifications are: VIN = 3.6V and TA= 25°C.
(3) CIN, COUT, C1, C2: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.
(4) For input voltage below the regulation target during the gain of 1x, the output voltage will typically be equal to the input voltage.
(5) SCL and SDA should be glitch-free in order for proper brightness control to be realized.
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D
4.7 µF
SDA
Gain
Control
Current
Control
Power
on Reset
FLASH
Timeout
STROBE
TX
C2+
C2-
C1+
C1-
VOUT
VIN
CIN 2.2 µF Thermal
Shutdown
I2C Control
Logic
GND
SCL
FLASH
LED
MODULE
LM2759
2.2 µF
2.2 µF
COUT
VOUT
REG
1x,1.5x,
2x
Charge
Pump
VREF
LM2759
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Block Diagram
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Typical Performance Characteristics
Unless otherwise specified: TA= 25°C, VIN = 3.6V, CIN = C1= C2= 2.2µF, COUT = 4.7µF. Capacitors are low-ESR multi-layer
ceramic capacitors (MLCC's). Luxeon PWF3 Flash LED.
Efficiency Input Current
vs vs
VIN VIN
Figure 2. Figure 3.
Quiescent Current Quiescent Current
vs vs
VIN, Gain = 1X VIN, Gain = 2X
Figure 4. Figure 5.
ILED Shutdown Current
vs vs
VISINK VIN
Figure 6. Figure 7.
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Typical Performance Characteristics (continued)
Unless otherwise specified: TA= 25°C, VIN = 3.6V, CIN = C1= C2= 2.2µF, COUT = 4.7µF. Capacitors are low-ESR multi-layer
ceramic capacitors (MLCC's). Luxeon PWF3 Flash LED.
Oscillator Frequency
vs
VIN Torch Code Levels
Figure 8. Figure 9.
Flash Code Levels Shutdown to Torch Mode, 100mA
CH1: SDA; Scale: 2V/Div, DC Coupled
CH2: VOUT; Scale: 2V/Div, DC Coupled
CH3: IIN; Scale: 100mA/Div, DC Coupled
CH4: ILED; Scale: 100mA/Div, DC Coupled
Time scale: 400µs/Div
Figure 10. Figure 11.
Shutdown to Flash Mode, 1A Torch to Flash Mode, 100mA to 1A
CH1: SDA; Scale: 2V/Div, DC Coupled CH1: SDA; Scale: 2V/Div, DC Coupled
CH2: VOUT; Scale: 2V/Div, DC Coupled CH2: VOUT; Scale: 2V/Div, DC Coupled
CH3: IIN; Scale: 1A/Div, DC Coupled CH3: IIN; Scale: 1A/Div, DC Coupled
CH4: ILED; Scale: 1A/Div, DC Coupled CH4: ILED; Scale: 1A/Div, DC Coupled
Time scale: 1ms/Div Time scale: 1ms/Div
Figure 12. Figure 13.
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Typical Performance Characteristics (continued)
Unless otherwise specified: TA= 25°C, VIN = 3.6V, CIN = C1= C2= 2.2µF, COUT = 4.7µF. Capacitors are low-ESR multi-layer
ceramic capacitors (MLCC's). Luxeon PWF3 Flash LED.
Flash Timeout, Timeout Code (x03) = 325ms
Torch Level (x0F) = 180mA, Flash Level (x05) = 410mA
CH1(bottom): IIN; Scale: 200mA/Div, DC Coupled
CH2(middle): SDA; Scale: 2V/Div, DC Coupled
CH3(top): VOUT; Scale: 2V/Div, DC Coupled
Time scale: 100ms/Div Figure 14.
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APPLICATION INFORMATION
CIRCUIT DESCRIPTION
The LM2759 is an adaptive CMOS charge pump with gains of 1x, 1.5x, and 2x, optimized for driving Flash LEDs
in camera phones and other portable applications. It provides a constant current of up to 1A (typ.) for Flash mode
and 180 mA (typ.) for Torch mode.
The LM2759 has selectable modes including Flash, Torch, Indicator and Shutdown. Flash mode for the LM2759
can also be enabled via the Strobe input pin. The LED is driven from VOUT and connected to the current sink.
The LED drive current and operating modes are programmed via an I2C compatible interface. The LM2759
adaptively selects the next highest gain mode when needed to maintain the programmed LED current level.
To prevent a high battery load condition during a simultaneous RF PA transmission and Flash event, LM2759
has a Flash interrupt pin (TX) to reduce the LED current to the programmed Torch current level for the duration
of the RF PA transmission pulse.
CHARGE PUMP AND GAIN TRANSITIONS
The input to the 1x, 1.5x, 2x charge pump is connected to the VIN pin, and the loosely regulated output of the
charge pump is connected to the VOUT pin. In 1x mode, as long as the input voltage is less than 4.7V (typ.), the
output voltage is approximately equal to the input voltage. When the input voltage is over 4.7V (typ.) the output
voltage is regulated to 4.7V (typ.). In 1.5x mode, the output voltage is regulated to 4.7V (typ.) over entire input
voltage range. For the gain of 2x, the output voltage is regulated to 5.1V (typ.). When under load, the voltage at
VOUT can be less than the target regulation voltage while the charge pump is still in closed loop operation. This is
due to the load regulation topology of the LM2759.
The charge pump’s gain is selected according to the headroom voltage across the current sink of LM2759. When
the headroom voltage VGDX (at the LED cathode) drops below 350 mV (typ.) the charge pump gain transitions to
the next available higher gain mode. Once the charge pump transitions to a higher gain, it will remain at that gain
for as long as the device remains enabled. Shutting down and then re-enabling the device resets the gain mode
to the minimum gain required to maintain the load.
SOFT START
The LM2759 contains internal soft-start circuitry to limit inrush currents when the part is enabled. Soft start is
implemented internally with a controlled turn-on of the internal voltage reference.
CURRENT LIMIT PROTECTION
The LM2759 charge pump contains current limit protection circuitry that protects the device during VOUT fault
conditions where excessive current is drawn. Output current is limited to 1.4A typically.
LOGIC CONTROL PINS
LM2759 has two asynchronous logic pins, Strobe and TX. These logic inputs function according to the table
below:
TX STROBE FUNCTION
0 0 Current I2C programmed state (Off, Torch,
Flash, Indicator)
1 0 Current I2C programmed state (Off, Torch,
Flash, Indicator). If Flash is enabled via I2C
and TX is logic High, the LED current will be
at the programmed Torch level.
0 1 Flash Mode (Total LED "ON" Duration limited
by Flash Timeout)
1 1 Torch Mode (Total LED "ON" Duration limited
by Flash Timeout)
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SCL
SDA
data
change
allowed
data
valid data
change
allowed
data
valid data
change
allowed
SDA
SCL S P
P
STO condition
START condition
LM2759
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I2C COMPATIBLE INTERFACE
START AND STOP CONDITIONS
START and STOP conditions classify the beginning and the end of the I2C session. A START condition is
defined as SDA signal transitioning from HIGH to LOW while SCL line is HIGH. A STOP condition is defined as
the SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates START and
STOP conditions. The I2C bus is considered to be busy after a START condition and free after a STOP condition.
During data transmission, the I2C master can generate repeated START conditions. First START and repeated
START conditions are equivalent, function-wise.
Figure 15. Start and Stop Conditions
DATA VALIDITY
The data on SDA line must be stable during the HIGH period of the clock signal (SCL). In other words, state of
the data line can only be changed when SCL is LOW.
Figure 16. Data Validity Diagram
A pull-up resistor between the controller's VIO line and SDA must be greater than [(VIO-VOL) / 3.5mA] to meet
the VOL requirement on SDA. Using a larger pull-up resistor results in lower switching current with slower edges,
while using a smaller pull-up results in higher switching currents with faster edges.
TRANSFERING DATA
Every byte put on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each
byte of data has to be followed by an acknowledge bit. The acknowledge related clock pulse is generated by the
master. The master releases the SDA line (HIGH) during the acknowledge clock pulse. The LM2759 pulls down
the SDA line during the 9th clock pulse, signifying an acknowledge. The LM2759 generates an acknowledge
after each byte is received.
After the START condition, the I2C master sends a chip address. This address is seven bits long followed by an
eighth bit which is a data direction bit (R/W). The LM2759 address is 53h. For the eighth bit, a “0” indicates a
WRITE and a “1” indicates a READ. The second byte selects the register to which the data will be written. The
third byte contains data to write to the selected register.
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1
bit7 1
bit6 1
bit5 1
bit4 1
bit3 C2
bit2 C1
bit1 C0
bit0
MSB LSB
Flash Timeout Duration
Register Address: 0xC0
1
bit7 1
bit6 1
bit5 1
bit4 B3
bit3 B2
bit2 B1
bit1 B0
bit0
MSB LSB
Flash Current
Register Address: 0xB0
1
bit7 1
bit6 1
bit5 1
bit4 A3
bit3 A2
bit2 A1
bit1 A0
bit0
MSB LSB
Torch Current
Register Address: 0xA0
1
bit7 1
bit6 1
bit5 1
bit4 G4
bit3 G2
bit2 G1
bit1 G0
bit0
MSB LSB
General Purpose
Register Address: 0x10
ADR6
bit7 ADR5
bit6 ADR4
bit5 ADR3
bit4 ADR2
bit3 ADR1
bit2 ADR0
bit1 R/W
bit0
MSB LSB
0 1 1 0 1 1 0
I2C SLAVE address (chip address)
10
1
011
0
start msb Chip Address lsb w ack msb Register Add lsb ack msb DATA lsb ack stop
ack from slave ack from slave ack from slave
SCL
SDA
start Id = 53h w ack addr = 10h ack ackGDWDK¶03 (Flash) stop
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w = write (SDA = "0")
r = read (SDA = "1")
ack = acknowledge (SDA pulled down by either master or slave)
id = chip address, 53h for LM2759
Figure 17. Write Cycle
I2C COMPATIBLE CHIP ADDRESS
The chip address for LM2759 is 1010011, or 53h.
INTERNAL REGISTERS
Power On Value
Register Internal Hex Address (lowest 4 bits)
General Purpose Register 10h 0000
Flash Current Register B0h 1010
Torch Current Register A0h 0111
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Power On Value
Register Internal Hex Address (lowest 4 bits)
Flash Timeout Duration Register C0h 1011
GENERAL PURPOSE REGISTER AND STROBE INHIBIT FUNCTION
The general purpose register (x10) is used set the mode of operation for the LM2759. The selectable operating
modes using the lower 4 bits in the general purpose register are listed in the table below.
The Strobe Input Pin can be disabled via I2C to ignore external signals into this pin when desired. This function is
implemented through bit 3 of the General Purpose Register (See table below). In the default state, input signals
on the Strobe Input are enabled. (Bit3 = “0”, inputs into the Strobe Pin are not inhibited).
Table 1. General Purpose Register (Reg x10)
Bit3 Bit2 Bit1 Bit0 Mode
X X X 0 Shutdown
X 0 0 1 Torch
X X 1 1 Flash
X 1 0 1 Indicator (Lowest Torch Level)
1 X X X Inhibit Inputs into the Strobe Pin
SETTING LED CURRENT
The current through the LED is set by programming the appropriate register with the desired current level code
for Flash and Torch. The time that Flash mode is active is dependent on the lesser of the duration that it is set to
"ON" (via I2C or the Strobe pin), or the duration of the Flash Timeout. Use the tables below to select the desired
current level.
Using the part in conditions where the junction temperature might rise above the rated maximum requires that
the operating ranges and/or conditions be de-rated. The printed circuit board also must be carefully laid out to
account for high thermal dissipation in the part.
Table 2. Flash Current Table (Reg xB0)
CODE (Hex) FLASH CURRENT (mA)
00 80
01 150
02 220
03 280
04 350
05 410
06 470
07 530
08 590
09 650
0A 710
0B 770
0C 830
0D 890
0E 950
0F 1010
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Table 3. Torch Current Table (Reg xA0)
CODE (Hex) TORCH CURRENT (mA)
00 15
01 30
02 40
03 50
04 65
05 80
06 90
07 100
08 110
09 120
0A 130
0B 140
0C 150
0D 160
0E 170
0F 180
FLASH TIME-OUT FEATURE
Time-out Protection Circuitry disables the current sink when either the Strobe pin is held at logic high or the
Flash mode is enabled via the I2C compatible interface longer than the programmed timeout duration. This
prevents the device from self-heating due to the high power dissipation during Flash conditions. During the time-
out condition, voltage will still be present on VOUT but the current sink will be shut off, resulting in no current
through the Flash LED. When the device goes into a time-out condition, disabling and then re-enabling the
device will reset the time-out. Use the table below to set the desired Flash timeout duration.
Table 4. Flash Timeout Duration (Reg xC0)
CODE (Hex) TIME (ms)
00 60
01 125
02 250
03 375
04 500
05 625
06 750
07 1100
CAPACITOR SELECTION
The LM2759 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors
are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance (ESR
<20 mΩtyp.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are not
recommended for use with the LM2759 due to their high ESR, as compared to ceramic capacitors. For most
applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with the
LM2759. These capacitors have tight capacitance tolerance (as good as ±10%) and hold their value over
temperature (X7R: ±15% over -55°C to 125°C; X5R: ±15% over -55°C to 85°C). Capacitors with Y5V or Z5U
temperature characteristic are generally not recommended for use with the LM2759. Capacitors with these
temperature characteristics typically have wide capacitance tolerance (+80%, -20%) and vary significantly over
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temperature (Y5V: +22%, -82% over -30°C to +85°C range; Z5U: +22%, -56% over +10°C to +85°C range).
Under some conditions, a nominal 1 μF Y5V or Z5U capacitor could have a capacitance of only 0.1 μF. Such
detrimental deviation is likely to cause Y5V and Z5U capacitors to fail to meet the minimum capacitance
requirements of the LM2759. The voltage rating of the output capacitor should be 6.3V or more. For example, a
6.3V 0603 4.7 μF output capacitor (TDK C1608X5R0J475) is acceptable for use with the LM2759, as long as the
capacitance on the output does not fall below a minimum of 3μF in the intended application. All other capacitors
should have a voltage rating at or above the maximum input voltage of the application and should have a
minimum capacitance of 1 μF.
Table 5. Suggested Capacitors and Suppliers
MFG Part No. Type MFG Voltage Rating Case Size Inch (mm)
4.7 µF for COUT
C1608X5R0J475 Ceramic X5R TDK 6.3V 0603 (1608)
JMK107BJ475 Ceramic X5R Taiyo-Yuden 6.3V 0603 (1608)
2.2 µF for C1, C2, CIN
C1608X5R0J225 Ceramic X5R TDK 6.3V 0603 (1608)
JMK107BJ225 Ceramic X5R Taiyo-Yuden 6.3V 0603 (1608)
POWER EFFICIENCY
Efficiency of LED drivers is commonly taken to be the ratio of power consumed by the LED (PLED) to the power
drawn at the input of the part (PIN). With a 1x, 1.5x, 2x charge pump, the input current is equal to the charge
pump gain times the output current (total LED current). The efficiency of the LM2759 can be predicted as follows:
PLED = VLED × ILED (1)
PIN = VIN × IIN (2)
PIN = VIN × (Gain × ILED + IQ) (3)
E = (PLED ÷ PIN) (4)
For a simple approximation, the current consumed by internal circuitry (IQ) can be neglected, and the resulting
efficiency will become:
E = VLED ÷ (VIN × Gain) (5)
Neglecting IQwill result in a slightly higher efficiency prediction, but this impact will be negligible due to the value
of IQbeing very low compared to the typical Torch and Flash current levels (100mA - 1A). It is also worth noting
that efficiency as defined here is in part dependent on LED voltage. Variation in LED voltage does not affect
power consumed by the circuit and typically does not relate to the brightness of the LED. For an advanced
analysis, it is recommended that power consumed by the circuit (VIN x IIN) be evaluated rather than power
efficiency.
THERMAL PROTECTION
Internal thermal protection circuitry disables the LM2759 when the junction temperature exceeds 150°C (typ.).
This feature protects the device from being damaged by high die temperatures that might otherwise result from
excessive power dissipation. The device will recover and operate normally when the junction temperature falls
below 120°C (typ.). It is important that the board layout provide good thermal conduction to keep the junction
temperature within the specified operating ratings.
POWER DISSIPATION
The power dissipation (PDISSIPATION) and junction temperature (TJ) can be approximated with the equations
below. PIN is the power generated by the 1x, 1.5x, 2x charge pump, PLED is the power consumed by the LED, TA
is the ambient temperature, and θJA is the junction-to-ambient thermal resistance for the 12 pin WSON package.
VIN is the input voltage to the LM2759, VLED is the nominal LED forward voltage, and ILED is the programmed
LED current.
PDISSIPATION = PIN - PLED (6)
= (Gain × VIN × ILED)−(VLED × ILED) (7)
TJ= TA+ (PDISSIPATION ×θJA) (8)
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SNVS577D –JUNE 2008–REVISED MAY 2013
The junction temperature rating takes precedence over the ambient temperature rating. The LM2759 may be
operated outside the ambient temperature rating, so long as the junction temperature of the device does not
exceed the maximum operating rating of 105°C. The maximum ambient temperature rating must be derated in
applications where high power dissipation and/or poor thermal resistance causes the junction temperature to
exceed 105°C.
MAXIMUM OUTPUT CURRENT
The maximum LED current that can be used for a particular application depends on the rated forward voltage of
the LED used, the input voltage range of the application, and the Gain mode of the LM2759’s charge pump. The
following equation can be used to approximate the relationship between the maximum LED current, the LED
forward voltage, the minimum input voltage, and the charge pump gain:
(VIN_MIN x Gain) > (VF+ VHR) + (ILED x ROUT_GAIN) (9)
VHR or the voltage required across the current sink to remain in regulation can be approximated by (ILED x KHR),
where KHR is 0.8 mV/mA (typ). ROUT_GAIN is the output impedance of the charge pump according to its gain
mode. When using the equation above, keep in mind that the (VF+ VHR) portion of the equation can not be
greater than the nominal output regulation voltage for a particular gain. In other words, when making calculations
for an application where the term (VF+ VHR) is higher than a particular gain’s regulation voltage, the next higher
gain level must be used for the calculation.
Example: VF= 4V @ 1A, Charge Pump in the Gain of 2x with a ROUT of 2.25Ω(typ.)
VIN_MIN > [(4V + 0.8V) + (1A x 2.25Ω) ] ÷ 2
VIN_MIN > 3.53V (typ.)
The maximum power dissipation in the LM2759 must also be taken into account when selecting the conditions
for an application, such that the junction temperature of the device never exceeds its rated maximum. The input
voltage range, operating temperature range, and/or current level of the application may have to be adjusted to
keep the LM2759 within normal operating ratings.
BOARD LAYOUT CONSIDERATIONS
PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance
of a DC-DC converter and surrounding circuitry by contributing to EMI, ground bounce, and resistive voltage loss
in the traces. These can send erroneous signals to the DC-DC converter IC, resulting in poor regulation or
instability. Poor layout can also result in re-flow problems leading to poor solder joints between the WSON
package and board pads. Poor solder joints can result in erratic or degraded performance.
Copyright © 2008–2013, Texas Instruments Incorporated Submit Documentation Feedback 15
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LM2759
SNVS577D –JUNE 2008–REVISED MAY 2013
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REVISION HISTORY
Changes from Revision C (May 2013) to Revision D Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 15
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TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LM2759SD/NOPB WSON DQB 12 1000 178.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1
LM2759SDX/NOPB WSON DQB 12 4500 330.0 12.4 3.3 3.3 1.0 8.0 12.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 20-Sep-2016
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LM2759SD/NOPB WSON DQB 12 1000 210.0 185.0 35.0
LM2759SDX/NOPB WSON DQB 12 4500 367.0 367.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 20-Sep-2016
Pack Materials-Page 2
MECHANICAL DATA
DQB0012A
www.ti.com
SDF12A (Rev B)
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