AS3543 datasheet(38/92 Pages) AMSCO

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AS3543 3v2

Data Sheet - D e t a i l e d D e s c r i p t i o n - P o w e r M a n a g e m e n t F u n c t i o n s

9.3

15V Step-Up DCDC Converter

9.3.1

General

The integrated Step-Up DC/DC Converter is a high efficiency current-mode PWM regulator, providing an output volt-

age up to 15V. A constant switching-frequency results in a low noise on supply and output voltages.

It has two programable high voltage current sinks (1.2 to 37.2mA) for driving e.g. white LEDs as back-light. It can drive

also unbalanced strings due to the internal automatic feedback selection.

A voltage feedback mode allows generating constant supply voltages for e.g. OLEDs by using an external Zener diode.

To bias the diode ISINK1 is sinking about 50uA in this voltage feedback mode.

An internal protection circuit will shut down the regulator if the voltage on SW15 exceeds 15V. No more external pro-

tection has to be used to avoid an exceeding of the operation conditions in a no load situation.

9.3.2

Dimming

The DCDC booster together with the current sinks has an adjustable automatic logarithmic dimming for a smooth ON/

OFF transition. It is also possible to control the dimming with an external signal via a GPIO pin. PWGD, Q24M or Q32K

pin can be selected as input for the external dimming signal.

9.3.3

Current Sink Only Mode

The current sinks are normally only working when the DCDC booster is switched on, but can also be activated sepa-

rately. To do so reg. 1Bh-1 has to be set to 08h (select external dimming), and reg. 1Ah-4 has to be set to xxxx xx00b

(no ext. dimming source selected).

Figure 25. DCDC15 Block Diagram

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