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AS1325

Data Sheet - D e t a i l e d D e s c r i p t i o n

Shutdown

When pin SHDNN is low the AS1325 is switched off and no current is drawn from battery; when pin SHDNN is high the

device is switched on. If SHDNN is driven from a logic-level output, the logic high-level (on) should be referenced to

Note: If pin SHDNN is not used, it should be connected directly to pin OUT.

In shutdown the battery input is connected to the output through the inductor and the internal synchronous rectifier P-

FET. This allows the input battery to provide backup power for devices such as an idle microcontroller, memory, or real-

time-clock, without the usual diode forward drop. In this way a separate backup battery is not needed.

In cases where there is residual voltage during shutdown, some small amount of energy will be transferred from pin

OUT to pin BATT immediately after shutdown, resulting in a momentary spike of the voltage at pin BATT. The ratio of

Low-Battery Cutoff

The AS1325 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 (see Figure 28).

Figure 28. Low-Battery Cutoff Application Diagram

(EQ 1)

Where:

Ω 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.

+1.5 to +3.3V or

+1.5 to +5.0V

Battery

+3.3V or +5.0V

Output

22µF

22µF

L1

10µH

Power-On

Reset

100k

Ω

10nF

220k

Ω

1M

Ω

AS1325

4

LX

3

GND

2

BATT

6

RESETN

1

SHDNN

5

OUT

+5.0V Output only