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AS3685A Datasheet(PDF) 16 Page - TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS

Part No. AS3685A
Description  Ultra Small High Efficiency 1000mA Charge Pump
Download  25 Pages
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Maker  TAOS [TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS]
Homepage  http://www.taosinc.com
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AS3685A Datasheet(HTML) 16 Page - TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS

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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
: The internal flash timeout timer (tFLASHTIMEOUT) to limit the total flash duration, is not affected by the
TXMask function (see also section ‘Flash Timeout’).
The IISET current (current into the pin ISET) for TXMask = 0 can be calculated with:
For TXMask = 1 the current IISET is reduced to:
V(TXMask) is the actual voltage for the high level (‘1’) for the signal TXMask
The maximum flash current ILEDMAX for TXMask=0 or 1 can be calculated according to the following formula
using the above obtained IISET values:
Choose the values for RISET and RTXMASK according to your application requirements.
ISET
VBAT
EN1
EN2
VBAT
EN1
EN2
RISET
RTXMASK
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
FLASH2BIAS IISET
7650 I
ISET


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