AS3685C

Datasheet

www.austriamicrosystems.com/AS3685

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1.1

9 - 21

7.1.2 Soft Start

The soft start mechanism reduces the inrush current. Battery current is smoothed when switching the

charge pump on and also at each switching condition. This precaution reduces electromagnetic radiation

significantly.

7.2 Current Source (Sink)

The AS3685 operates in three different modes:

Indicator Mode: A small (average) current is used to obtain an indication function with the flash LED (e.g.

indication for camera operation)

Torch Mode: A moderate current of e.g. 150mA allows the use of the flash LED as a torch or video light

Flash Mode: A high current of e.g. 700mA (up to 1000mA) is set for a high brightness flash. Only in this

mode, the flash timeout timer limits the total flash time.

The current through the LED and the operating mode is controlled by the two digital interface connected to SCL

and SDA.

The current is controlled with a two wire bus interface commands similar to I2C communication (device address

82h, only commands writing to the AS3685 are possible, no readback) as shown in following figure:

Figure

10 – Two wire interface waveform

Data from the bus is always captured on the rising edge of the SCL signal; therefore the data on SDA has to be

stable slightly before this rising edge.

The strobe command is merged with the interface commands and all other devices connected to the bus will

ignore these commands. Only the AS3685 will also use these commands and switch on/off the flash led with the

strobe pin (The strobe function can be enabled/disabled by the interface and its polarity is selectable):