ams Datasheet Page 25
[v2-23] 2016-Mar-30 Document Feedback
AS3685A/AS3685B − Detailed Description
The maximum flash current I
LEDMAX
for TXMask=0 or 1 can be
calculated according to the following formula using the above
obtained I
ISET
values:
Choose the values for R
ISET
and R
TXMASK
according to your
application requirements.
Protection Functions
Overtemperature Protection
If the AS3685 junction temperature exceeds T
OVTEMP
, the
current sink will be disabled and the charge pump forced into
1:1 mode. If the junction temperature drops below T
OVTEMP
–
T
OVTEMPHYST
, the device enables the current sink again and the
charge pump resumes normal operation.
LED Shortcircuit Protection
If the LED is shorted (VCP to ILED), then depending on the set
current and the resulting high power dissipation inside the
AS3685, the overtemperature protection will trigger. This
protects the AS3685 and the system against damage. If the
AS3685 is in off-mode, then shorting of the diode will have no
influence on the system.
Note(s): Do not short VCP to VSS if the supply is not current
limited (e.g. by an internal protection inside the battery), as
there is an internal diode between VBAT (anode) and VCP
(cathode).
Flash Timeout
The flash duration of a single flash is limited automatically to
t
FLASHTIMEOUT
(applies only for ‘Flash’ mode(s)). This protects
the flash LED against thermal damage.
I
LEDMAX
I
FLASH2BIAS
I
ISET
7650 I
ISET
⋅==
