11

LTC1261

able. The output voltage can be trimmed, if desired, by

connecting external resistance from the COMP pin to OUT

or ground to alter the divider ratio. As in the adjustable

parts, the absolute value of the internal resistors may vary

significantly from unit to unit. As a result, the further the

trim shifts the output voltage the less accurate the output

voltage will be. If a precise output voltage other than one

of the available fixed voltages is required, it is better to use

an adjustable LTC1261 and use precision external resis-

tors. The internal reference is trimmed at the factory to

within 3.5% of 1.24V; with 1% external resistors the

output will be within 5.5% of the nominal value, even

under worst case conditions.

The LTC1261 can be internally configured with nonstand-

ard fixed output voltages. Contact the Linear Technology

Marketing Department for details.

Table 2. Output Voltages Using the Internal Resistor Divider

PIN CONNECTIONS

OUTPUT VOLTAGE

–5V

– 4.5V

– 4V

– 3.5V

ADJ to R1

– 1.77V

ADJ to R0

– 1.38V

ADJ to GND

– 1.24V

There are some oddball output voltages available by

connecting ADJ to R0 or R1 and shorting out some of the

internal resistors. If one of these combinations gives you

the output voltage you want, by all means use it!

The internal resistor values are the same for the fixed

output versions of the LTC1261 as they are for the adjust-

3.3V Input, – 4.5V Output GaAs FET Bias Generator

2

3

4

5

8

13

12

11

10

9

SHDN

REG

OUT

ADJ

R1

0.1

µF

100pF

1

µF

NC

LTC1261 • TA03

3.3

µF

–4.5V BIAS

10k

76

14

0.1

µF

SHUTDOWN

3.3V

LTC1261

R0

GND

GaAs

TRANSMITTER

P-CHANNEL

POWER SWITCH