AS1321
Datasheet - D e t a i l e d D e s c r i p t i o n
Low-Battery Cutoff
The AS1321 SHDNN trip threshold (1.228V) can be used as an input voltage detector that disables the device when
the battery input voltage falls to a pre-set level. An external resistor-divider network can be used to set the battery-
detection voltage
Figure 18. Low-Battery Cutoff Application Diagram
+1.5 to +5.0V
Battery
C
IN
22µF
2
BATT
5
OUT
R
3
100kΩ
C
OUT
22µF
+5.0V
Output
4
R
1
220kΩ
L1
10µH
LX
AS1321
6
RESETN
Power-On
Reset
1
R
2
1MΩ
10nF
SHDNN
3
GND
For the resistor-divider network shown in
calculate the value for R
1
by:
R
1
= R
2
x ((V
OFF
/V
SHDNN
) - 1)
Where:
V
OFF
is the battery voltage at which the AS1321 shuts down.
V
SHDNN
= 1.228V
The value of R
2
should be between 100kΩ and 1MΩ to minimize battery drain.
Note:
Input ripple can cause false shutdowns, therefore to minimize the effect of ripple, a low-value capacitor from
SHDNN to GND should be used to filter out input noise. The value of the capacitor should be such that the R/C
time constant is > 2ms.
(EQ 1)
Power-On Reset
The AS1321 provides a power-on reset output (RESETN) that goes high-impedance when the output reaches 90% of
its regulation point. RESETN goes low when the output is below 90% of the regulation point. A 100kΩ to 1MΩ pullup
resistor between pin RESETN and pin OUT can provide a microprocessor logic control signal.
Note:
Connect pin RESETN to GND when the power-on reset feature is not used.
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