Out-of-the-loop compensation method

AN2653

10/22

Figure 15 and Figure 16 show the loop gain and closed loop gain respectively. These curves

Both figures further demonstrates the stability improvement.

presence of peaking in the loop gain curve, depending on the load capacitor. This is

because the denominator is equal to

It leads to a resonance frequency of approximately

For the peaking frequency

the damping is given by the term:

When there is no compensation, it is only:

With the compensation, at the resonance frequency,

therefore the peaking is attenuated.

To help implement the compensation, the abacus given in Figure 17 to Figure 20 provide the

the case of a voltage follower configuration and a gain configuration of -10 or +11, with a

load resistor of 10 k

Ω..

Figure 15.

Loop gain

Figure 16.

Measured closed loop gain

Voltage Follower Configuration - Loop Gain

Compensation with the Out-of-the-Loop Technique

-30

-10

10

30

50

70

90

110

130

150

Frequency (Hz)

-270

-240

-210

-180

-150

-120

-90

-60

-30

0

Gain without Compensation

Gain with ROL = 100 Ω

Phase without Compensation

Phase with ROL = 100 Ω

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 Out-of-the-Loop Technique

-40

-30

-20

-10

0

10

20

Frequency (Hz)

Gain without Compensation

Gain with ROL = 100 Ω

TS507 :

Vcc = 5 V

Vicm = 2,5 V

T = 25 °C

RL = 10 kΩ

CL = 1 nF

Without Compensation

With Out-of-the-Loop Compensation Technique

1

R

OL

R

L

-----------

j

L

ω

()

R

L

-----------

R

+

⎝⎠

⎛⎞ L ω

()C

2

–

++

1

2

π

L

ω

()C

L

⋅

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

f

1

2

π

L

ω

()C

L

⋅

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

=

L

ω

()

R

L

-----------

R

+

L

ω

()

R

L

-----------

L

ω

()

R

L

-----------

R

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