AN2653 datasheet(17/22 Pages) STMICROELECTRONICS

17 / 22 page

AN2653

Snubber network compensation method

17/22

In fact, this compensation introduces a zero and an additional pole into the loop gain:

Because Zo is not a pure resistance over frequency, choosing the minimum RSN is not

always the best case.

5.2

Application on the TS507

For the TS507, according to the abacus in Figure 27 and Figure 28, this compensation

method in the case of a voltage follower configuration, works only if the capacitive load is

less than 1 nF, in order to obtain (at least) a phase margin of 20°.

Figure 29 and Figure 30 are the same abacus in case of a gain of either -10 or +11.

You can use the abacus in Figure 27 to Figure 30 to determine the best RSN value.

------

–

()

1jR

SNCSNω

()

⋅

-------

o CL

()ω j1

-------

⎝⎠

⎛⎞ R

SNCSNω

oRSNCLCSNω

–

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Figure 27.

Gain margin abacus in a voltage

follower configuration

Figure 28.

Phase margin abacus in a voltage

follower configuration

Voltage Follower Configuration - Load Abacus

Gain Margin

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

RL (Ω)

0 dB

10 dB

20 dB

30 dB

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C

STABLE

UNSTABLE

Voltage Follower Configuration - Load Abacus

Phase Margin

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

RL (Ω)

0 °

C1 (10 °)

20 °

C1 (30 °)

40 °

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C

STABLE

UNSTABLE

Figure 29.

Gain margin abacus in a gain

configuration of either -10 or +11

Figure 30.

Phase margin abacus in a gain

configuration of either -10 or +11

Gain Configuration of either -10 or +11 - Load Abacus

Gain Margin

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

RL (Ω)

0 dB

10 dB

20 dB

30 dB

40 dB

50 dB

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C

STABLE

UNSTABLE

Gain Configuration of either -10 or +11 - Load Abacus

Phase Margin

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

RL (Ω)

0 °

20 °

40 °

60 °

80 °

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C

STABLE

UNSTABLE

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