Page 16 ams Datasheet
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AS3685A/AS3685B − Detailed Description
Mode Switching
The AS3685 monitors the voltage at the current sink V(ILED) and
if this voltage falls below V
SWITCH
, for a time longer than the
debounce time, the charge pump automatically switches into
a higher mode. The debounce time is set to t
UP_DEB_LONG
at
enabling of the charge pump or immediately after a 1:1 to 1:1.5
mode change. Afterwards the debounce time is reduced to
t
UP_DEB
. (This allows the LED current to settle properly on
startup or after a mode change).
The charge pump enters always 1:1 mode in off mode or in case
of over temperature. I t is possible to avoid the 1:2 mod e (facto r y
programmable) to limit the battery current to 1.5 times the
output (=LED) current.
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.
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:
