TLC271_01 Datasheet, PDF (62/82 Pages) Texas Instruments – LinCMOSE PROGRAMMABLE LOW-POWER OPERATIONAL AMPLIFIERS

TLC271, TLC271A, TLC271B
LinCMOS PROGRAMMABLE LOW-POWER
OPERATIONAL AMPLIFIERS
SLOS090D – NOVEMBER 1987 – REVISED MARCH 2001
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.
VI ^{ÏÏÏÏÏ}–₊^{ÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏ}
R2
R1
VDD
IP
RP
VO
+ _{) )} RP
VDD–VO
IF IL IP
IP = Pullup current required
IF
by the operational amplifier
(typically 500 µA)
IL _RL
Figure 113. Resistive Pullup to Increase V_OH
10 kΩ
10 kΩ
0.016 µF
0.016 µF
VI
ÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏ _{ÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏ} ^10kΩ
5V
–
TLC271
10 kΩ
+
BIAS SELECT
5V
–
TLC271
+
BIAS SELECT
10 kΩ
5V
ÏÏÏÏ _–
ÏÏÏÏ _TLC271
Low Pass
ÏÏÏÏÏÏÏÏ ₊
BIAS SELECT
5 kΩ
NOTE B: d = damping factor, I/O
R = 5 kΩ(3/d-1)
(see Note A)
Figure 114. State-Variable Filter
High Pass
Band Pass
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