Datasheet

TLC271, TLC271A, TLC271B
LinCMOS PROGRAMMABLE LOW-POWER
OPERATIONAL AMPLIFIERS
SLOS090D – NOVEMBER 1987 – REVISED MARCH 2001
58
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
input offset voltage nulling
The TLC271 offers external input offset null control. Nulling of the input off set voltage may be achieved by
adjusting a 25-kΩ potentiometer connected between the offset null terminals with the wiper Connected as
shown in Figure 105. The amount of nulling range varies with the bias selection. In the high-bias mode, the
nulling range allows the maximum offset voltage specified to be trimmed to zero. In low-bias and medium-bias
modes, total nulling may not be possible.
25 kΩ
N2
V
DD
N2
N1
25 kΩ
GND
(a) SINGLE SUPPLY (b) SPLIT SUPPLY
–
+
–
+
N1
OUTOUT
IN–
IN+
IN–
IN+
Figure 105. Input Offset Voltage Null Circuit
bias selection
Bias selection is achieved by connecting the bias select pin to one of the three voltage levels (see Figure 106).
For medium-bias applications, R is recommended that the bias select pin be connected to the mid-point
between the supply rails. This is a simple procedure in split-supply applications, since this point is ground. In
single-supply applications, the medium-bias mode necessitates using a voltage divider as indicated. The use
of large-value resistors in the voltage divider reduces the current drain of the divider from the supply line.
However, large-value resistors used in conjunction with a large-value capacitor requires significant time to
charge up to the supply midpoint after the supply is switched on. A voltage other than the midpoint may be used
if it is within the voltages specified in the table of Figure 106.
0.01 µF
1 MΩ
V
DD
Low
Medium
High
1 MΩ
To BIAS SELECT
BIAS MODE
BIAS-SELECT VOLTAGE
(single supply)
Low
Medium
High
V
DD
1 V to V
DD
– 1 V
GND
Figure 106. Bias Selection for Single-Supply Applications