LOW DROPOUT

LOW DROPOUT

LOW DROPOUT

LOW DROPOUT

LOW DROPOUT

REGULA

REGULA

REGULA

REGULA

REGULAT

TT

T

TOR

OR

OR

OR

OR

AS1185

AustinSemiconductor,Inc.reservestherighttochangeproductsorspecificationswithoutnotice.

4

AS1185

Rev. 1.1 6/05

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

R2 =

V

REF

for R1 = 2.37k and V

REF

= 2.37V, this reduces to:

R2 = V

OUT

- 2.37k

suggested values of 1% resistors are shown.

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.

R2 WHEN R1 = 2.37k

5V

2.67k

5.2V

2.87k

6V

3.65k

12V

9.76k

15V

12.7k