Datasheet

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
ADJ to R
ADJ
–5V
ADJ to R
ADJ
, R0 to GND –4.5V
ADJ to R
ADJ
, R1 to R0 –4V
ADJ to R
ADJ
, R1 to GND –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-
APPLICATIONS INFORMATION
WUU
U
TYPICAL APPLICATIONS N
U
3.3V Input, –4.5V Output GaAs FET Bias Generator
2
3
4
5
8
13
12
11
10
9
SHDN
REG
OUT
ADJ
R
ADJ
C1
+

C1
–

C2
+

C2
–
R1
0.1µF
100pF
1µF
NC
LTC1261 • TA03
3.3µF
–4.5V BIAS
10k
76
14
0.1µF
SHUTDOWN
3.3V
V
BAT
LTC1261
V
CC
R0 GND
GaAs
TRANSMITTER
P-CHANNEL
POWER SWITCH
+