AS3685A/AS3685B

Datasheet

www.austriamicrosystems.com/

AS3685

(ptr)

Revision 2.2

9 - 24

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.

Pulsed Indicator Mode (only AS3685A): The control device sends a short sequence to the AS3685A and the

AS3685A enables the flash LED for a defined fixed duration (torch current setting). This duration is

controlled by the AS3685A and the control device does not need to start an internal timer function.

The current through the LED and the operating mode is controlled by the two digital pins EN1 and EN2. There

are two versions of the AS3685 available: AS3685A and AS3685B. The only difference between these versions

is the digital interface as shown below:

7.2.1 AS3685A Current Setting

For the AS3685A, the operating mode and the current through the LED is defined by the following table:

Table

7 – AS3685A Current Settings

EN1

EN2

Mode

14.2kΩ

10kΩ

Percent of

Full Scale

0

0

Off

0mA

0mA

0%

0

(Off)

1

0

Indicator

4.7mA average

(=150mA with

1/32 duty cycle

6.7mA average

(=214mA with

1/32 duty cycle

0.67%

(=21.4% /

32)

52.2

0

1

Torch

150mA

214mA

21.4%

1639

1

1

Flash

700mA

1000mA

100%

7650

Notes:

1) The on-time for indicator mode is 1μs, off time 31μs (32μs = 32.25kHz)

I

ISET

V

ISET

R

ISET

1.3 V

R

ISET