Datasheet

Application information L7986TA
24/43 Doc ID 022098 Rev 3
6.4.2 Type II compensation network
If the equivalent series resistance (ESR) of the output capacitor introduces a zero with a
frequency lower than the desired bandwidth (that is: 2π∗ESR∗COUT>1/BW), this zero helps
stabilize the loop. Electrolytic capacitors show non-negligible ESR (>30 mΩ), so with this
kind of output capacitor the type II network combined with the zero of the ESR allows to
stabilize the loop.
In Figure 12 the type II network is shown.
Figure 12. Type II compensation network
The singularities of the network are:
Equation 29
In Figure 13 the Bode diagram of the PWM and LC filter transfer function (G
PW0
· G
LC
(f))
and the open-loop gain (G
LOOP
(f) = G
PW0
· G
LC
(f) · G
TYPEII
(f)) are drawn.
f
Z1
1
2π R
4
C
4
⋅⋅
------------------------------------= f
P0
0= f
P1
1
2π R
4
C
4
C
5
⋅
C
4
C
5
+
----------------------
⋅⋅
---------------------------------------------------=,,