AS3647 Datasheet, PDF (13/38 Pages) ams AG – 1600mA High Current LED Flash Driver

AS3647/47B
Datasheet, Confidential - Detailed Description
8 Detailed Description
The AS3647/47B 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 I²C
mode.
The actual operating mode like standby, assist light, indicator or flash mode, can then be chosen by the interface. If not
in standby mode, the device automatically enters shutdown mode by keeping SCL low for more than tTIMEOUT¹.
The AS3647/47B 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.
lid Internal Circuit Diagram
Figure 17. Internal circuit Diagram
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AS3647/47B

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ic _{Softstart / Soft ramp down}
During startup and ramp down the LED current is smoothly ramped up and ramped down. If the DCDC converter goes
n _{out of regulation (measured by monitoring the voltage across the current sinks), the ramp up is temporarily stopped in}
Tech ^{order for the DCDC to return to regulation2.}
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
28) to allow the camera processor to adopt to the actual operating conditions.
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1.5-4
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