MAX1576
480mA White LED 1x/1.5x/2x Charge Pump for
Backlighting and Camera Flash
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Detailed Description
The MAX1576 charge pump drives up to four white
LEDs in the main display for backlighting and up to four
white LEDs for flash with regulated constant current for
uniform intensity. By utilizing adaptive 1x/1.5x/2x
charge-pump modes and very-low-dropout current reg-
ulators, it achieves high efficiency over the 1-cell lithi-
um-battery input voltage range. 1MHz fixed-frequency
switching allows for tiny external components and low
input ripple.
1x to 1.5x Switchover
When V
IN
is higher than V
OUT
, the MAX1576 operates
in 1x mode and V
OUT
is pulled up to V
IN
. The internal
current regulators regulate the LED current. As V
IN
drops, V
LED_
eventually falls below the switchover
threshold of 100mV and the MAX1576 starts switching
in 1.5x mode. When the input voltage rises above V
OUT
by approximately 50mV, the MAX1576 switches back to
1x mode.
1.5x to 2x Switchover
When V
IN
is less than V
OUT
but greater than two-thirds
V
OUT
, the MAX1576 operates in 1.5x mode. The inter-
nal current regulators regulate the LED current. As V
IN
drops, V
LED_
eventually falls below the switchover
threshold of 100mV, and the MAX1576 starts switching
in 2x mode. When the input voltage rises above two-
thirds V
OUT
by approximately 50mV, the MAX1576
switches back to 1.5x mode.
Soft-Start
The MAX1576 includes soft-start circuitry to limit inrush
current at turn-on. Once the input voltage is applied,
the output capacitor is charged directly from the input
with a ramped current source (with no charge-pump
action) until the output voltage approaches the input
voltage. Once this occurs, the charge pump deter-
mines if 1x, 1.5x, or 2x mode is required. In the case of
1x mode, the soft-start is terminated and normal opera-
tion begins. In the case of 1.5x or 2x mode, soft-start
operates until the lowest of LED1–LED4 reaches regu-
lation. If the output is shorted to ground or is pulled less
than 1.25V, the output current is limited by soft-start.
True Shutdown™ Mode
When ENM1, ENM2, ENF1, and ENF2 are simultaneously
held low, the MAX1576 is shut down after a 0.5ms shut-
down delay and the input is isolated from the output. OUT
is internally pulled to GND with 5kΩ during shutdown.
Thermal Shutdown
The MAX1576 includes a thermal-limit circuit that shuts
down the IC at approximately +160°C. Turn-on occurs
after the IC cools by approximately 20°C.
Applications Information
Setting the Main Output Current
SETM controls LED1–LED4 bias current. Current flow-
ing into LED1, LED2, LED3, and LED4 is a multiple of
the current flowing out of SETM.
I
LED1
= I
LED2
= I
LED3
= I
LED4
= K x (0.604V / R
SETM
)
True Shutdown is a trademark of Maxim Integrated Products, Inc.
Pin Description (continued)
PIN NAME FUNCTION
18 IN
Supply Voltage Input. Bypass to ground with a 1µF ceramic capacitor. The input voltage range is 2.7V to
5.5V. IN is high impedance during shutdown.
19 PGND Power Ground. Connect PGND to system ground. PGND is used for charge-pump switching currents.
20 C1N
Transfer Capacitor 1 Negative Connection. Connect to a 1µF ceramic capacitor between C1P and C1N.
C1N is internally shorted to IN during shutdown.
21 C2N
Transfer Capacitor 2 Negative Connection. Connect to a 1µF ceramic capacitor between C2P and C2N.
C2N is internally shorted to IN during shutdown.
22 INP
Supply Voltage Input. Bypass to PGND with a 4.7µF ceramic capacitor. The input voltage range is 2.7V to
5.5V. INP is high impedance during shutdown.
23 C2P
Transfer Capacitor 2 Positive Connection. Connect a 1µF ceramic capacitor from C2P to C2N. During
shutdown, if OUT > IN, C2P is shorted to OUT, and if OUT < IN, C2P is shorted to IN.
24 C1P
Transfer Capacitor 1 Positive Connection. Connect a 1µF ceramic capacitor from C1P to C1N. During
shutdown, if OUT > IN, C1P is shorted to OUT, and if OUT < IN, C1P is shorted to IN.
—EP
Exposed Paddle. Connect the exposed paddle to ground. Connect PGND, GND1, and GND2 to the
exposed paddle directly under the IC.
