Datasheet

Application information L5987
22/41 Doc ID 14972 Rev 3
Equation 21
Figure 11. Type III compensation network
In Figure 12 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
TYPEIII
(f)) are drawn.
Figure 12. Open loop gain: module Bode diagram
The guidelines for positioning the poles and the zeroes and for calculating the component
values can be summarized as follow:
1. Choose a value for R
1
, usually between 1 kΩ and 5 kΩ.
2. Choose a gain (R
4
/R
1
) in order to have the required bandwidth (BW), that means:
f
P0
0= f
P1
1
2π R
3
C
3
⋅⋅
------------------------------= f
P2
1
2π R
4
C
4
C
5
⋅
C
4
C
5
+
--------------------
⋅⋅
------------------------------------------- -=,,