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AS3643

Datasheet, Confidential - D e ta i l e d D e s c r i p t i o n

8 Detailed Description

The AS3643 is a high performance DCDC step up converter with internal PMOS and NMOS switches. Its output is

connected to one flash LED with an internal current sink. The device is controlled by the pins SDA and SCL in I

mode.

The actual operating mode like standby, assist light, indicator or flash mode, can then be chosen by the interface. If not

The AS3643 includes a fixed frequency DCDC step-up with accurate startup control. Together with the current sink (on

LED_OUT1/2) it includes several protection and safety functions.

Internal Circuit Diagram

Figure 16. Internal circuit Diagram

Softstart / Soft ramp down

During startup and ramp down the LED current is smoothly ramped up and ramped down. If the DCDC converter goes

out of regulation (measured by monitoring the voltage across the current sinks), the ramp up is temporarily stopped in

order for the DCDC to return to regulation

1. Following registers are reset to their default value if the timeout expires: out_on=0, ext_torch_on=00,

mode_setting=00, const_v_mode=0.

2. The actual value of the LED current setting can be readout by the register led_current_actual (see page

26) to allow the camera processor to adopt to the actual operating conditions.





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AS3643