Datasheet

TLV2731, TLV2731Y
Advanced LinCMOS RAIL-TO-RAIL
LOW-POWER SINGLE OPERATIONAL AMPLIFIERS
SLOS198A – AUGUST 1997 – REVISED MARCH 2001
25
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
driving large capacitive loads
The TLV2731 is designed to drive larger capacitive loads than most CMOS operational amplifiers. Figure 49
through Figure 54 illustrate its ability to drive loads greater than 100 pF while maintaining good gain and phase
margins (R
null
= 0).
A small series resistor (R
null
) at the output of the device (see Figure 55) improves the gain and phase margins
when driving large capacitive loads. Figure 49 through Figure 52 show the effects of adding series resistances
of 50 Ω, 100 Ω, 500 Ω, and 1000 Ω. The addition of this series resistor has two effects: the first effect is that
it adds a zero to the transfer function and the second effect is that it reduces the frequency of the pole associated
with the output load in the transfer function.
The zero introduced to the transfer function is equal to the series resistance times the load capacitance. To
calculate the approximate improvement in phase margin, equation 1 can be used.
∆φ
m1
tan
–1
2 ×π×UGBW × R
null
× C
L
∆φ
m1
Improvement in phase margin
UGBW Unity-gain bandwidth frequency
R
null
Output series resistance
C
L
Load capacitance
(1)
Where :
The unity-gain bandwidth (UGBW) frequency decreases as the capacitive load increases (see Figure 53 and
Figure 54). To use equation 1, UGBW must be approximated from Figure 53 and Figure 54.
V
DD–
/GND
V
DD+
R
null
C
L
V
I
+
–
R
L
Figure 55. Series-Resistance Circuit