AS1343 datasheet(10/17 Pages) AMSCO

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AS1343

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

9 Application Information

Shutdown and Output Discharge

A logic low on the EN pin shuts down the AS1343 and a logic high on the EN pin powers on the device. In shutdown

mode the supply current drops to below 3µA and the POK pin is set to high impedance to maximize battery life.

When the battery disconnect switch is used, the battery is disconnected from the output and the output is discharged

down to 0V. The time for fully discharging the output depends on the COUT and on the load.

Note:

Pin EN should not be left floating. If the shutdown feature is not used, connect EN to VCC. The output will be

discharged during shutdown but the output also must be fully discharged before the device is enabled again.

Battery Disconnect

The AS1343 has an integrated PMOS switch that can be used to disconnect the battery during shutdown. The opera-

tion voltage of this switch is limited to 3.6V. When EN is high, the switch is closed and supplies the inductor. Due to the

RON resistance the efficiency is slightly lower if the battery disconnect switch is used.

PLOSS = IIN² x

RON

(EQ 1)

Setting Output Voltage

Output voltage can be adjusted by connecting a voltage divider between pins

VOUT and FB (see Figure 28).

Figure 28. Typical Application

The output voltage can adjusted by selecting different values for R1 and R2. For R2, select a value between 10k and

200k

Ω.

Calculate R1 by:

Where:

VOUT = 5.5V to 42V, VFB = 1.25V; VOUT > VIN

The input bias current of FB has a maximum value of 100nA which allows for large-value resistors. For less than 1%

error, the current through R2 should be 100 times the feedback input bias current (IFB). That’s why the feeback current

can be neglected in the calculation of VOUT.

Note:

For the optimal operation condition the following ratio between VOUT and VIN should be used:

3, 8

GND

VCC

Off

2.2M

VOUT = 18V

AS1343

6.8µH

10µF

VCC = 0.9V

to 3.6V

COUT

4.7µF

165k

SWOUT

PGND

VOUT

POK

100k

(EQ 2)

VOUT

VFB

--------------

–

⎝⎠

⎛⎞

⋅

(EQ 3)

VOUT

VIN

≤

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