Diodes AL3158 - Manual (Page 6)

AL3158
HIGH EFFICIENCY 1x/2x CHARGE PUMP
FOR WHITE LED APPLICATIONS
AL3158
Document number: DS35047 Rev. 2 - 2
6 of 10
www.diodes.com
January 2011
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Functional Description
The AL3158 is a dual-mode high efficiency charge pump
(1x and 2x) device, driving three groups of three LED
channels at 30mA maximum each, 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 AL3158 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 AL3158 can drive three
groups of three individual LED channels with a maximum
current of fixed manufacture setting (20mA or 30mA) per
channel. These can be paralleled to give a total output
current of 270mA.
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 inrush
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 AL3158 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.
EN<3:1> LED ON/OFF CONTROL
XX0 LED1~LED3 OFF
XX1 LED1~LED3 ON
X0X LED4~LED6 OFF
X1x LED4~LED6 ON
0XX LED7~LED9 OFF
1xX LED7~LED9 ON