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1.5-4

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AS3648

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

Before a flash is started the voltage on VIN is measured. If the voltage is below the setting of vin_low_v the fault_uvlo

(see page 27) is set and the flash is disabled (driver stays in shutdown) if vin_low_v_shutdown=1. The flash current is

reduced to flash_txmask_current if vin_low_v_shutdown=0.

During flash, if the voltage on VIN drops below the threshold defined by vin_low_v_run, the flash current is reduced (or

ramping of the current is stopped during flash current startup) and fault_uvlo is set. The timing for the reduction of the

current is 8µs/LSB current change.

During the flash pulse the actual used current can be readout by the register led_current_actual.

After the flash pulse the minimum current can be readout by the register led_current_min - this allows to adjust the

camera sensitivity (gain or iso-settings) for the subsequent flash pulse (e.g. when using a pre-flash and a main flash

pulse).

The internal circuit for low voltage current reductions are shown in Figure 20:

Figure 20. Low Voltage current Reduction Internal Circuit

A mobile phone camera flash system can trigger a diagnostic flash and a main-flash:

The diagnostic flash is initiated by the processor. After this diagnostic flash, the determined maximum flash current can

be read back through the I

main flash. Therefore the current in the main-flash is constant and additionally the camera system can use this current

for picture quality adjustments - the waveforms for this concept are shown in Figure 21:



















  

 



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AS3648