Austin Semiconductor, Inc.
SETTING OUTPUT VOLTAGE
The AS1185 output voltage is set by two external resistors
(see Figure 2). Internal reference voltage is trimmed to 2.37V so
that a standard 1% 2.37k resistor (R1) can be used to set divider
current at 1mA. R2 is then selected from:
(V
OUT
- 2.37) R1
V
REF
LOW DROPOUT
REGULAT
REGULATOR
AS1185
R2 =
External Current Limit
The AS1185 requires a resistor to set current limit. The value
of this resistor is 15k divided by the desired current limit (in
amps). The resistor for 2A current limit would be 15k/2A = 7.5k.
Tolerance over temperature is ±10%, so current limit is normally
set 15% above maximum load current. Foldback limiting can be
employed if short-circuit current must be lower than full load
current (see Typical Applications).
The AS1185 has internal current limiting which will override
external current limit if power in the pass transistor is
excessive. The internal limit is
≈
3.6A with a foldback
characteristic which is dependent on input-output voltage, not
output voltage
per se
(see Typical Performace Characteristics).
Assembly considerations for this package requires that
the fixed internal current limit circuit be bypassed at all times.
An external current limit resistor set to a maximum of 2.7A
must be used. Failure to do so on this package can result in
damage to the device.
for R1 = 2.37k and V
REF
= 2.37V, this reduces to:
R2 = V
OUT
- 2.37k
suggested values of 1% resistors are shown.
V
OUT
5V
5.2V
6V
12V
15V
R2 WHEN R1 = 2.37k
2.67k
2.87k
3.65k
9.76k
12.7k
AS1185
Rev. 1.1 6/05
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
4
AUSTIN [ AUSTIN SEMICONDUCTOR ]
