Datasheet

TLC271, TLC271A, TLC271B
LinCMOS PROGRAMMABLE LOW-POWER
OPERATIONAL AMPLIFIERS
SLOS090D – NOVEMBER 1987 – REVISED MARCH 2001
62
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
output characteristics (continued)
Although the TLC271 possesses excellent high-level output voltage and current capability, methods are
available for boosting this capability, if needed. The simplest method involves the use of a pullup resistor (R
P
)
connected from the output to the positive supply rail (see Figure 113). There are two disadvantages to the use
of this circuit. First, the NMOS pulldown transistor, N4 (see equivalent schematic) must sink a comparatively
large amount of current. In this circuit, N4 behaves like a linear resistor with an on-resistance between
approximately 60 Ω and 180 Ω, depending on how hard the operational amplifier input is driven. With very low
values of R
P
, a voltage offset from 0 V at the output occurs. Secondly, pullup resistor RP acts as a drain load
to N4 and the gain of the operational amplifier is reduced at output voltage levels where N5 is not supplying the
output current.
R
P
V
DD
–V
O
I
F
I
L
I
P
V
I
V
DD
R
P
V
O
R2
R1 R
L
I
P
I
F
I
L
I
P
= Pullup current required
by the operational amplifier
(typically 500 µA)
–
+
Figure 113. Resistive Pullup to Increase V
OH
5 V
BIAS SELECT
0.016 µF
Low Pass
High Pass
Band Pass
R = 5 kΩ(3/d-1)
(see Note A)
0.016 µF
BIAS SELECT
5 V
10 kΩ
10 kΩ
10 kΩ
5 V
BIAS SELECT
V
I
5 kΩ
10 kΩ
10 kΩ
–
+
TLC271
–
+
TLC271
–
+
TLC271
NOTE B: d = damping factor, I/O
Figure 114. State-Variable Filter