www.ams.com/DC-DC_Step-Up/AS1340

Revision 1.20

10 - 17

AS1340

Datasheet - Application In form atio n

9 Application Information

9.1 Power Supply Concept

The AS1340 has an operating voltage range from 2.7 to 5.5V. If the inductor is supplied from the same source the battery disconnect switch can

be used as well (see Figure 1 on page 1). In case that a input voltage source is higher than 5.5V, the inductor can be supplied separately up to

50V (see Figure 28), but then the battery disconnect switch cannot be used, because its operating voltage range is limited to 5.5V.

9.2 Shutdown

A logic low on pin EN shuts down the AS1340 and a logic high on EN powers on the device.

In shutdown mode the supply current drops to below 1µA to maximize battery life. In case that the battery disconnect switch is used, the battery

is disconnected from the output during shutdown.

Note:

Pin EN should not be left floating. If the shutdown feature is not used, connect EN to VIN.

9.3 Battery Disconnect

The AS1340 has an integrated switch that can be used to disconnect the battery during shutdown. The operation voltage of this switch is limited

to 5.5V. 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)

9.4 Setting Output Voltage

Output voltage can be adjusted by connecting a voltage divider between pins LX and FB (see Figure 28).

Figure 28. Typical Application (SWVIN and SWOUT not in use)

The output voltage can be adjusted by selecting different values for R1 and R2. For R2, select a value between 10k and 200k

.

Calculate R1 by:

(EQ 2)

Where:

VOUT = VIN to 50V, VFB = 1.25V

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).

Supply

2.7V to VOUT

1

EN

7,9

GND

2

VCC

8

FB

5

LX

On

Off

R1

2.2M



VOUT = 18V

AS1340

L1

4.7µH

C1

0.1µF

CIN

10µF

D1

COUT

1µF

R2

165k



3

SWVIN

6

SWOUT

4

POK

VIN

= 2.7V

to 5.5V

R

1

R

2

V

OUT

V

FB

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

1

–







=