Rainbow Electronics MAX1574 User Manual
General Description
The 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 fullscale 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 constant 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).
Applications
LCD Backlighting
Camera Strobes/Flashes and Movie Lights
Cell Phones/Smart Phones
PDAs, Digital Cameras, and Camcorders
Features
♦ Up to 180mA (60mA/LED) Drive Capability
♦ 83% Average Efficiency (P
LED
/ P
BATT
) Over Li+
Battery Discharge
♦ 0.5% (typ) LED Current Matching
♦ Adaptive 1x/2x Mode Switchover
♦ Low Input Ripple and EMI
♦ 5% to 100% Dimming Through Single-Wire Serial
Pulse Interface
♦ Low 0.1µA Shutdown Current
♦ 2.7V to 5.5V Supply Voltage Range
♦ Soft-Start Limits Inrush Current
♦ Output Overvoltage Protection
♦ Thermal-Shutdown Protection
♦ 10-Pin 3mm x 3mm TDFN Package
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
________________________________________________________________ Maxim Integrated Products 1
Pin Configuration
Ordering Information
1µF
1µF
MAX1574
LED3
LED2
LED1
OUT
SET
EN
GND
IN
0.22µF
CP CN
2.7V TO 5.5V
ON/OFF AND
DIMMING
UP TO 180mA
Typical Operating Circuit
19-3117; Rev 0; 12/03
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE
MAX1574ETB -40°C to +85°C
PINPACKAGE
10 TDFN
3mm x 3mm
TOP
MARK
ABB
GND
LED1
LED26LED3
MAX1574
4
5
EN
CP
CN
SET
TDFN
3mm × 3mm
TOP VIEW
OUT
10 9 8 7
1234
IN
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN= 3.6V, V
GND
= 0V, EN = IN, R
SET
= 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 (V
IN
+ 0.3V)
CP to GND ......................................................................-0.3V to
the greater of (V
OUT
+ 1V) or (V
IN
+ 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
IN Operating Voltage 2.7 5.5 V
Undervoltage-Lockout Threshold VIN falling 2.25 2.45 2.60 V
Undervoltage-Lockout Hysteresis 40 mV
Output Overvoltage-Protection Threshold V
No-Load Supply Current
Shutdown Supply Current
Soft-Start Time 2ms
SET Bias Voltage 0.6 V
SET Leakage in Shutdown
SET Current Range 4 153 µA
SET-to-LED_ Current Ratio (I
LED Current Accuracy TA = +25°C ±0.7 %
LED-to-LED Current Matching (Note 2) -4 ±0.5 +4 %
Maximum LED_ Sink Current R
LED_ Dropout Voltage R
1x to 2x Mode Transition Threshold V
Input-Voltage-Mode Transition Hysteresis 150 mV
LED Leakage in Shutdown
Maximum OUT Current V
Open-Loop OUT Resistance
Switching Frequency 1 MHz
OUT Pulldown Resistance in Shutdown EN = GND 5 kΩ
EN High Voltage V
EN Low Voltage V
PARAMETER CONDITIONS MIN TYP MAX UNITS
LED/ISET
rising 5 V
OUT
2x mode 2
10% setting, 1x mode 0.35
EN = GND, TA = +25°C 0.01 1
EN = GND, T
EN = GND, TA = +25°C 0.01 1
EN = GND, T
) 100% setting 393 A/A
= 4.12kΩ 52 60 mA
SET
= 4.12kΩ (Note 3) 80 120 mV
SET
falling 120 130 140 mV
LED_
EN = GND, TA = +25°C 0.01 2
EN = GND, T
≥ 3.12V, V
IN
1x mode, (V
2x mode, (2 x V
= 2.7V to 5.5V 1.6 V
IN
= 2.7V to 5.5V 0.4 V
IN
IN
= +85°C 0.1
A
= +85°C 0.1
A
= +85°C 0.1
A
= 3.9V 180 mA
OUT
- V
IN
OUT
- V
) / I
OUT
OUT
) / I
OUT
1.5 2.5
915
mA
µA
µA
µA
Ω
MAX1574
180mA, 1x/2x, White LED Charge Pump
in 3mm x 3mm TDFN
_______________________________________________________________________________________ 3
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: (I
LED
- I
AVG
) / I
AVG
Note 3: Dropout voltage is defined as the LED_-to-GND voltage at which current into LED_ drops 10% from the value at V
LED_
= 0.2V.
ELECTRICAL CHARACTERISTICS (continued)
(VIN= 3.6V, V
GND
= 0V, EN = IN, R
SET
= 13.7kΩ, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
(Note 1)
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 (%)
3.93.63.33.0
10
20
30
40
50
60
70
80
90
100
0
2.7 4.2
I
LED
= 2mA
I
LED
= 8mA
I
LED
= 20mA
I
LED
= 40mA
VIN FALLING
INPUT CURRENT vs. INPUT VOLTAGE
MAX1574 toc02
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
3.93.63.33.0
50
100
150
200
250
300
0
2.7 4.2
VIN FALLING
I
LED
= 40mA
I
LED
= 20mA
I
LED
= 8mA
I
LED
= 2mA
INPUT RIPPLE vs. SUPPLY VOLTAGE
MAX1574 toc03
SUPPLY VOLTAGE (V)
INPUT RIPPLE (mV
P-P
)
5.04.54.03.53.0
5
10
15
20
25
0
2.5 5.5
60mA/LED
20mA/LED
8mA/LED
2mA/LED
EN Input Current
EN Low Shutdown Delay 1.0 2 3.3 ms
EN tLO (Figure 1) 0.5 500 µs
EN tHI (Figure 1) 0.5 µs
Initial EN tHI (Figure 1) Only required for first EN_ pulse 50 µs
Thermal-Shutdown Threshold +160 °C
Thermal-Shutdown Hysteresis 20 °C
PARAMETER CONDITIONS MIN TYP MAX UNITS
EN = GND or 5.5V, TA = +25°C 0.01 1
EN = GND or 5.5V, T
= +85°C 0.1
A
µA
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