Diodes AL3157 - Manual (Page 6)

AL3157
HIGH EFFICIENCY 1x/2x CHARGE PUMP LED DRIVER
FOR SMALL SCREEN BACKLIGHTING AND FLASHLIGHT
AL3157
Document number: DS35116 Rev. 1 - 2
6 of 9
www.diodes.com
March 2011
© Diodes Incorporated
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PRODUC
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Functional Description
The AL3157 is a dual-mode high efficiency charge pump (1x and 2x) device, driving 3-channel standard backlight LEDs
and one high-current Flash/Torch LED, intended for white LED backlight applications. An internal comparator circuit
compares the voltage at each constant current sink input against a reference voltage. To ensure maximum power
efficiency, the most appropriate switching mode (1x and 2x) is automatically selected.
The APL3157 requires only three external components: one 1µF ceramic flying capacitor (C
1
) for the charge pump, one
2.2µF ceramic input capacitor (C
IN
), and one 2.2µF ceramic charge pump output capacitor (C
OUT
).
The each output channel of the AL3157 can drive three individual LEDs with a maximum current of 30mA per channel and
a Flash/Torch LED with a maximum current of 210mA. These can be paralleled to give a total output current of 300mA.
LED Control Table
Disabled Current Sinks
Unused current channels must be disabled by connecting the sinks to VOUT with only a small sense current flowing
through the disabled channel.
Soft-Start
Soft-start is incorporated to prevent excessive in-rush current during power-up, mode switching, and transitioning out of
stand-by mode.
Short-Circuit Protection
Short-circuit protection function is incorporated to prevent excessive load current when either flying cap terminals or output
pin electrically tied to a very lower voltage or ground.
Over-Voltage Protection
Over-Voltage Protection function is incorporated to limit the output voltage under a safe value to avoid on-chip device
breakdown.
Under-Voltage Lockout
Under-Voltage lockout feature disables the device when the input voltage drops below UVLO threshold.
Thermal Auto Shutdown
When the die temperature exceeds the thermal limit, the device will be disabled and enter stand-by mode. The operation
resumes whenever the die cools off sufficiently.
PWM Dimming Control
The AL3157 provides simple PWM dimming control through ENx pins, and the current is adjusted by the duty cycle of the
signal applied on ENx pin. The recommended PWM frequency is from 200Hz to 50kHz depending on applications.
.
EN1 EN2 D1 D2, D3, D4
0 0 OFF OFF
0 1 OFF ON
1 0 ON OFF
1 1 ON ON