AN2653 datasheet(19/22 Pages) STMICROELECTRONICS

19 / 22 page

AN2653

Snubber network compensation method

19/22

The results are almost the same whether RL = 1 kΩ, 10 kΩ or 100 kΩ because in all cases, at

the frequency range that has a significant impact on stability, the resistive load on the

amplifier is RSN // RL

≅ R

SN.

From Table 7, you can see that, in the case of a voltage follower configuration, this

compensation method doesn’t work for capacitive loads higher than 1 nF because CSN is

limited to 100 nF. Figure 27 and Figure 28 show that lower RSN values would give better

results. However, in this case, these abacus are not valid because the CSN impedance is not

negligible compared with RSN at the frequency range where RSN plays its role of stabilizer.

For RL = 10 kΩ and CL = 1 nF, the snubber network compensation method gives the loop

gain and closed loop gain shown in Figure 31 and Figure 32 respectively.

This compensation has the main advantage of neither reducing the output swing nor the

gain accuracy, unlike the two other compensation methods. Nevertheless, for the TS507,

this method is limited to capacitive loads lower than 1 nF in a voltage follower configuration,

and the stability improvement provided by the compensation is not as good as with the two

other methods.

Table 10.

Results of snubber network compensation for different load conditions in the case of

a gain configuration of either -30 or +31 (Rg = 100 Ω and Rf = 3 kΩ) for TS507

RL =1kΩ

RL =10kΩ

RL =100 kΩ

RSN

(

Ω)

CSN

(nF)

Mg(1)

(dB)

ϕ(1)

(degree)

RSN

(

Ω)

CSN

(nF)

Mg(1)

(dB)

ϕ(1)

(degree)

RSN

(

Ω)

CSN

(nF)

Mg(1)

(dB)

ϕ(1)

(degree)

1nF

88.2 °

25.2

88.4 °

25.1

88.4 °

198

100

29.8

87.3 °

168.5

100

29.8

87.3 °

166

100

29.8

87.3 °

10 nF

7.9

87.9 °

7.2

88 °

7.1

88.1 °

30.7

100

19.6

82.7 °

100

19.2

82.7 °

100

19.1

82.8 °

100 nF

-4.2

-44.7 °

-4.5

-45.8 °

-4.5

-45.9 °

16.6

100

3.4

63.8 °

16.5

100

3.3

64 °

16.5

100

3.3

64.1 °

Negative values indicate instability.

Figure 31.

Loop gain

Figure 32.

Measured closed loop gain

Voltage Follower Configuration - Loop Gain

Compensation with the Snubber Network Technique

-30

-10

110

130

150

Frequency (Hz)

-270

-240

-210

-180

-150

-120

-90

-60

-30

Gain without Compensation

Gain with RSN = 30 Ω and CSN = 100 nF

Phase without Compensation

Phase with RSN = 30 Ω and CSN = 100 nF

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C

RL = 10 kΩ

CL = 1 nF

Voltage Follower Configuration - Closed Loop Gain

Compensation with the Snubber Network Technique

-40

-30

-20

-10

Frequency (Hz)

Gain without Compensation

Gain with RSN = 30 Ω and CSN = 100 nF

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C

RL = 10 kΩ

CL = 1 nF

Without Compensation

With Snubber Network Compensation Technique

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