The AS3642 is controlled by an I C interface. All timings and currents can be accurately adjusted by this interface. It
in 30ms steps defined by register flash_timer ). The flash is started immediately after the end of the I C com-
The LED current is PWM modulated by 1/32, 2/32, 3/32 or 4/32 (defined by register ind_current resulting in a
AS3642
Datasheet - D e t a 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.
2
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
2
mand.
If SCL and SDA are L for more than t TIMEOUT , shutdown mode is automatically entered.
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.
If SCL and SDA are L for more than t TIMEOUT , shutdown mode is automatically entered.
3. Indicator light mode (enabled by mode =01):
1
effective current of 1.35mA / 2.9mA / 4.4mA or 6.0mA. The current is enabled until another mode is chosen by
the interface.
If SCL and SDA are L for more than t TIMEOUT , shutdown mode is automatically entered
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
  
 
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AS3642
1. The PWM modulation frequency is 31.25kHz to avoid audible noise on the external capacitors.
www.austriamicrosystems.com/AS3642
1.2-2
9 - 26
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