AN2653

Stability basics

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Figure 6.

Impact of closed loop gain on stability

this parameter in the model of the amplifier leads to the model shown in Figure 7.

impedance varies with the frequency in the case of the TS507. These variations complicate

the stability study.

Finally, to study the stability of an op-amp based system, two parameters need to be taken

into account in order to better fit reality: the amplifier open-loop gain and the amplifier output

impedance. Then, a calculation of the loop gain indicates how stable the system is.

f

G

0

Case 1

Case 2

Closed Loop Gain (Case1) < Closed Loop Gain (Case 2)

Figure 7.

Follower configuration model with

capacitive load for loop gain

calculation

Figure 8.

TS507 Output Impedance (Zo)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

Frequency (Hz)

-135

-90

-45

0

45

90

Impedance

Phase

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C