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MAX1574ETB+-MAX1574ETB+T
180mA, 1x/2x, White LED Charge Pump in 3mm x 3mm TDFN
General DescriptionThe MAX1574 charge pump drives up to three white
LEDs with regulated constant current for uniform intensity.
By utilizing adaptive 1x/2x charge-pump modes and
very-low-dropout current regulators, it achieves 180mA
output drive capability and high efficiency over the 1-cell
lithium-battery input voltage range. Fixed-frequency
(1MHz) switching allows for tiny external components,
and the regulation scheme is optimized to ensure low EMI
and low input ripple.
The MAX1574 uses an external resistor to set the full-
scale 100% LED current. An enable input (EN) is used for
simple on/off control or can be pulsed repeatedly to set
lower LED current in multiple steps down to 5%. Once the
desired brightness is set, the MAX1574 maintains con-
stant LED current as long as EN is kept high. If EN is kept
low for more than 2ms, the MAX1574 enters shutdown.
The MAX1574 is available in a 10-pin 3mm x 3mm TDFN
package (0.8mm max height).
ApplicationsLCD Backlighting
Camera Strobes/Flashes and Movie Lights
Cell Phones/Smart Phones
PDAs, Digital Cameras, and Camcorders
FeaturesUp to 180mA (60mA/LED) Drive Capability83% Average Efficiency (PLED / PBATT) Over Li+
Battery Discharge0.5% (typ) LED Current MatchingAdaptive 1x/2x Mode SwitchoverLow Input Ripple and EMI5% to 100% Dimming Through Single-Wire Serial
Pulse InterfaceLow 0.1μA Shutdown Current2.7V to 5.5V Supply Voltage RangeSoft-Start Limits Inrush CurrentOutput Overvoltage ProtectionThermal-Shutdown Protection10-Pin 3mm x 3mm TDFN Package
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFNTOP VIEW
MAX1574
TDFN
3mm × 3mm987
OUTGNDLED1LED2
LED334CP5
SET
Pin Configuration
Ordering Information1µF1µF
MAX1574
LED3
LED2
LED1
OUT
SET
GND
0.22µFCN2.7V TO 5.5V
ON/OFF AND
DIMMING
UP TO 180mA
Typical Operating Circuit19-3117; Rev 0; 12/03
EVALUATION KIT
AVAILABLE
PARTTEMP RANGEPIN-
PACKAGE
TOP
MARKMAX1574ETB-40°C to +85°C10 TDFN
3mm x 3mm
ABB
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= 3.6V, VGND= 0V, EN = IN, RSET= 13.7kΩ, TA= -40°C to +85°C,unless otherwise noted. Typical values are at TA= +25°C.)
(Note 1)
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, OUT, EN to GND..............................................-0.3V to +6.0V
SET, LED1, LED2, LED3, CN to GND.........-0.3V to (VIN + 0.3V)
CP to GND ......................................................................-0.3V to
the greater of (VOUT+ 1V) or (VIN + 1V)
OUT Short Circuit to GND..........................................Continuous
Continuous Power Dissipation (TA = +70°C)
10-Pin TDFN (derate 18.2mW/°C above +70°C).......1454mW
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
PARAMETERCONDITIONSMINTYPMAXUNITS
IN Operating Voltage2.75.5V
Undervoltage-Lockout ThresholdVIN falling2.252.452.60V
Undervoltage-Lockout Hysteresis40mV
Output Overvoltage-Protection ThresholdVOUT rising5V
2x mode2No-Load Supply Current10% setting, 1x mode0.35mA
EN = GND, TA = +25°C0.011Shutdown Supply CurrentEN = GND, TA = +85°C0.1µA
Soft-Start Time2ms
SET Bias Voltage0.6V
EN = GND, TA = +25°C0.011SET Leakage in ShutdownEN = GND, TA = +85°C0.1µA
SET Current Range4153µA
SET-to-LED_ Current Ratio (ILED/ISET)100% setting393A/A
LED Current AccuracyTA = +25°C±0.7%
LED-to-LED Current Matching(Note 2)-4±0.5+4%
Maximum LED_ Sink CurrentRSET = 4.12kΩ5260mA
LED_ Dropout VoltageRSET = 4.12kΩ (Note 3)80120mV
1x to 2x Mode Transition ThresholdVLED_ falling120130140mV
Input-Voltage-Mode Transition Hysteresis150mV
EN = GND, TA = +25°C0.012LED Leakage in ShutdownEN = GND, TA = +85°C0.1µA
Maximum OUT CurrentVIN ≥ 3.12V, VOUT = 3.9V180mA
1x mode, (VIN - VOUT) / IOUT1.52.5Open-Loop OUT Resistance2x mode, (2 x VIN - VOUT) / IOUT915Ω
Switching Frequency1MHz
OUT Pulldown Resistance in ShutdownEN = GND5kΩ
EN High VoltageVIN = 2.7V to 5.5V1.6V
EN Low VoltageVIN = 2.7V to 5.5V0.4V
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
Note 1:Limits are 100% production tested at TA= +25°C. Limits over the operating temperature range are guaranteed by design.
Note 2:LED current matching is defined as: (ILED- IAVG) / IAVG
Note 3:Dropout voltage is defined as the LED_-to-GND voltage at which current into LED_ drops 10% from the value at VLED_= 0.2V.
ELECTRICAL CHARACTERISTICS (continued)
(VIN= 3.6V, VGND= 0V, EN = IN, RSET= 13.7kΩ, TA= -40°C to +85°C,unless otherwise noted. Typical values are at TA= +25°C.)
(Note 1)
PARAMETERCONDITIONSMINTYPMAXUNITS
EN = GND or 5.5V, TA = +25°C0.011EN Input CurrentEN = GND or 5.5V, TA = +85°C0.1µA
EN Low Shutdown Delay1.023.3ms
EN tLO (Figure 1)0.5500µs
EN tHI (Figure 1)0.5µs
Initial EN tHI (Figure 1)Only required for first EN_ pulse50µs
Thermal-Shutdown Threshold+160°C
Thermal-Shutdown Hysteresis20°C
Typical Operating Characteristics
(Circuit of Figure 2, VIN= 3.6V, EN = IN, driving three white LEDs, TA= +25°C, unless otherwise noted.)
EFFICIENCY vs. INPUT VOLTAGE
MAX1574 toc01
INPUT VOLTAGE (V)
EFFICIENCY (%)
ILED = 2mA
ILED = 8mA
ILED = 20mA
ILED = 40mA
VIN FALLING
INPUT CURRENT vs. INPUT VOLTAGE
MAX1574 toc02
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
VIN FALLING
ILED = 40mA
ILED = 20mA
ILED = 8mA
ILED = 2mA
INPUT RIPPLE vs. SUPPLY VOLTAGE
MAX1574 toc03
SUPPLY VOLTAGE (V)
INPUT RIPPLE (mV
P-P
60mA/LED
20mA/LED8mA/LED
2mA/LED
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN= 3.6V, EN = IN, driving three white LEDs, TA= +25°C, unless otherwise noted.)
LED CURRENT MATCHING
vs. INPUT SUPPLY VOLTAGE
MAX1574 toc04
INPUT SUPPLY VOLTAGE (V)
LED CURRENT MATCHING (%)
ILED = 8mA
LED CURRENT vs. TEMPERATURE
MAX1574 toc05
TEMPERATURE (°C)
LED CURRENT (mA)35-1510
LED CURRENT vs. RSETMAX1574 toc06
RSET (kΩ)
LED CURRENT (mA)
100% BRIGHTNESS
SETTING
OPERATING WAVEFORMS (1x)MAX1574 toc07
VIN
VOUT
IIN
20mV/div
AC-COUPLED
50mV/div
AC-COUPLED
0mA
50mA/div
400ns/div
OPERATING WAVEFORMS (2x)MAX1574 toc08
VIN
VOUT
IIN
20mV/div
AC-COUPLED
50mV/div
AC-COUPLED
0mA
400ns/div
50mA/div
STARTUP AND SHUTDOWNMAX1574 toc09
IIN
VEN
VOUT
100mA/div
0mA
5V/div
2V/div
1ms/div
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
Typical Operating Characteristics (continued)(Circuit of Figure 2, VIN= 3.6V, EN = IN, driving three white LEDs, TA= +25°C, unless otherwise noted.)
DIMMING RESPONSEMAX1574 toc10
IOUT
VEN
VOUT
50mA/div
2V/div
2V/div
10ms/div
LINE TRANSIENT 3.8V TO 3.3V TO 3.8VMAX1574 toc11
VOUT
VIN
IOUT
1V/div
1V/div
60mA,
20mA/div
100µs/div
Pin Description
PINNAMEFUNCTION1INSupply Voltage Input. Connect a 0.47µF to 1µF ceramic capacitor from IN to GND. The input voltage
range is 2.7V to 5.5V. IN is high impedance during shutdown.
2EN
Enable and Dimming Control. Pulsing EN low dims the LEDs in multiple steps. Drive low for longer than
2ms (typ) to shut down the IC. From shutdown, drive EN high (50µs min) to set ILED to the maximum
current (see the SETfunction). Pulse EN low for 0.5µs to 500µs to dim the LEDs (Figure 1).
3CPTransfer-Capacitor Positive Connection. Connect a 0.22µF capacitor from CP to CN.
4CNTransfer-Capacitor Negative Connection. Connect a 0.22µF capacitor from CP to CN.SETCurrent-Set Input. Connect a resistor (RSET) from SET to GND to set the maximum LED current.
ILED(MAX) = 393 × 0.6V / RSET. SET is internally biased to 0.6V. SET is high impedance during shutdown.LED3LED2LED1
LED_ Cathode Connection. Current flowing into LED_ is based on SET description above. In 2x mode,
the charge pump regulates the lowest LED_ voltage to 0.18V. Connect LED_ to IN for unpopulated LEDs.
LED_ is high impedance during shutdown.GNDGround. Connect GND to system ground and as close as possible to the input-bypass capacitor ground.OUTOutput. Connect a 0.47µF to 1µF ceramic capacitor from OUT to GND, and connect OUT to the anodes
of all the LEDs. OUT is pulled to ground through an internal 5kΩ resistor in shutdown.
—EPExposed Paddle. Connect the exposed paddle directly to GND underneath the IC.
MAX1574
Detailed DescriptionThe MAX1574 charge pump drives up to three white
LEDs with regulated constant current for uniform inten-
sity. By utilizing adaptive 1x/2x charge-pump modes
and very-low-dropout current regulators, it achieves
180mA output drive capability and high efficiency over
the 1-cell lithium-battery input voltage range. Fixed-fre-
quency switching of 1MHz allows for tiny external com-
ponents, and the regulation scheme is optimized to
ensure low EMI and low input ripple.
1x to 2x SwitchoverWhen VINis higher than VOUT, the MAX1574 operates in
1x mode and VOUTis pulled up to VIN. The internal cur-
rent regulators regulate the LED current. As VINdrops,
VLED_eventually falls below the switchover threshold of
130mV, and the MAX1574 starts switching in 2x mode.
When the input voltage rises above VOUTby approxi-
mately 50mV, the MAX1574 switches back to 1x mode.
Soft-StartThe MAX1574 includes soft-start circuitry to limit inrush
current at turn-on. When starting up, the output capacitor
is charged directly from the input with a ramped current
source (with no charge-pump action) until the output volt-
age approaches the input voltage. Once this occurs, the
charge pump determines if 1x or 2x mode is required. In
the case of 1x mode, the soft-start is terminated and nor-
mal operation begins. During the soft-start time, the out-
put current is set to 5% of the maximum set by RSET. In
the case of 2x mode, soft-start operates until the lowest of
LED1 to LED3 reaches regulation. If an overload condi-
tion occurs, soft-start repeats every 2.1ms. If the output is
shorted to ground, the output current is limited by the
MAX1574 switching technique.
Setting the Output CurrentThe LED current at full brightness is set by a resistor,
RSET, as follows:
EN Dimming ControlWhen the LEDs are enabled by driving EN high, the
MAX1574 goes through soft-start, bringing the LED cur-
rent up to ILED_. Dimming is then done by pulsing EN
low (500ns to 500µs pulse width). Each pulse reduces
the LED current by 10%, so after one pulse the LED cur-
rent is 0.9 x ILED. The tenth pulse reduces the current by
5%, so the ILED_current reduces from 0.1 x ILED_to 0.05
x ILED. The eleventh pulse sets the LED current back to
ILED_. Figure 1 shows a timing diagram for EN.
If dimming control is not required, EN works as a simple
on/off control. Drive EN high to enable the LEDs, or
drive EN low for shutdown.
Shutdown ModeWhen EN is held low for 2ms or longer, the MAX1574
is shut down and put in a low-current mode. OUT is
internally pulled to GND with 5kΩduring shutdown.
Overvoltage ProtectionIf any LED fails as an open circuit, the output voltage is
limited to about 5V by gating on/off the charge pump.
If any LED_ is floating or grounded, the MAX1574 oper-
ates in the same overvoltage-protection mode. To avoid
overvoltage-protection mode when using fewer than
three LEDs, connect any unused LED_ to IN (Figure 3).
Thermal ShutdownThe MAX1574 includes a thermal-limit circuit that shuts
down the IC at approximately+160°C. The part turns on
after the IC cools by approximately 20°C.VSET
LED. ×06393
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFNILED_
SHDN
100%90%80%70%60%50%40%30%20%10%5%
100%90%
SHDN
2ms (typ)111098765432
tLOtHItSHDN
≥ 500ns500ns TO 500µs
tSOFT-START
INITIAL tHI≥ 50µs
Figure 1. EN Timing Diagram
