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AS3642

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

8 Detailed Description

The AS3642 is a high performance DCDC step up converter with internal PMOS and NMOS switches. The switching

frequency of 4MHz allows the use of tiny coils. Its output is connected to a flash LED by an internal current source.

The AS3642 is controlled by an I

support following operating modes:

1. Flash mode (enabled by mode=11):

The LED current is defined by register flash_current. A timer defines the output flash duration (30ms...480ms

in 30ms steps defined by register flash_timer). The flash is started immediately after the end of the I

mand.

2. Assist light mode (=video or torch light mode) (enabled by mode=10):

The LED current is defined by register assist_current. The current is enabled until another mode is chosen by

the interface.

3. Indicator light mode (enabled by mode=01):

The LED current is PWM modulated

effective current of 1.35mA / 2.9mA / 4.4mA or 6.0mA. The current is enabled until another mode is chosen by

the interface.

4. Shutdown mode (mode=00), SCL=0V, SDA=0V:

The DCDC and the current source is disabled and the AS3642 is configured to draw minimum current.

Internal Circuit

The AS3642 includes a fixed frequency DCDC step-up with accurate startup control. Together with the output current

source (on LED_OUT) it includes protection and safety functions as shown in the following internal blockdiagram:

Figure 16. AS3642 internal circuit

1. The PWM modulation frequency is 31.25kHz to avoid audible noise on the external capacitors.





 



 



 

 

 

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AS3642