AS3685A/AS3685B

Datasheet

www.austriamicrosystems.com/

AS3685

(ptr)

Revision 2.2

15 - 24

7.2.3 AS3685A and AS3685B TXMask Function

If the battery has to supply two high currents at the same time (e.g. the AS3685 flash and a RF-power amplifier) it

is possible, that the total current causes a high voltage drop on the battery resulting in a shutdown of the

complete system. In order to avoid this shutdown, the AS3685 (AS3685A or AS3685B) can reduce its current

with the signal ‘TXMask’ using the following circuit:

Figure 22 – TXMask function of the AS3685

The TXMask signal is connected to e.g. the (RF-) power amplifier enable pin (active high if the PA is enabled).

This reduces the flash current if the power amplifier is enabled and avoids the unexpected shutdown of the

system.

Note

TXMask function (see also section ‘Flash Timeout’).

V(TXMask) is the actual voltage for the high level (‘1’) for the signal TXMask

ISET

VBAT

EN1

EN2

EN1

EN2

AS3685A

AS3685B

TXMask

I

ISET , TXMask 0

V

ISET

R

ISET

V

ISET

R

TXMASK

1.3 V

R

ISET

1.3 V

R

TXMASK

I

ISET , TXMask 1

V

ISET

R

ISET

V

ISET

V TXMask

R

TXMASK

1.3 V

R

ISET

1.3 V V TXMask

R

TXMASK

I

LEDMAX

I

7650 I

ISET