AS1340
Datasheet - Application Information
9 Application Information
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 bat-
tery 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.
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.
Battery Disconnect
The AS1340 has an integrated switch that can be used to disconnect the battery during shutdown. The operation volt-
age 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)
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.)
Supply
2.7V to VOUT
L1
4.7µH
CIN
10µF
3
6
SWVIN
SWOUT
2
VIN = 2.7V
to 5.5V
D1
5
VOUT = 18V
VCC
C1
0.1µF
LX
COUT
1µF
R1
2.2MΩ
4
8
AS1340
POK
FB
1
On
Off
R2
165kΩ
EN
7,9
GND
The output voltage can be adjusted by selecting different values for R1 and R2. For R2, select a value between 10k and
200kΩ.
Calculate R1 by:
VOUT
VFB
⎛
⎝
⎞
– 1
--------------
R1 = R2 ⋅
(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).
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