Datasheet

Application information L7985
22/43 Doc ID 022446 Rev 3
Equation 25
4. Calculate C
5
by placing the second pole at four times the system bandwidth (BW):
Equation 26
5. Set also the first pole at four times the system bandwidth and also the second zero at
the output filter double pole:
Equation 27
The suggested maximum system bandwidth is equal to the switching frequency divided by
3.5 (F
SW
/3.5), anyhow, lower than 100 kHz if the F
SW
is set higher than 500 kHz.
For example, with V
OUT
=5 V, V
IN
=24 V, I
O
=2 A, L=22 μH, C
OUT
=22 μF, and ESR < 1 mΩ, the
type III compensation network is:
In Figure 12 the module and phase of the open-loop gain is shown. The bandwidth is about
32 kHz and the phase margin is 51 °.
C
4
1
π R
4
f
LC
⋅⋅
----------------------------------=
C
5
C
4
2π R
4
C
4
4BW⋅ 1–⋅⋅⋅
-------------------------------------------------------------------------=
R
3
R
1
4BW⋅
f
LC
-------------------- 1–
------------------------------= C
3
1
2π R
3
4BW⋅⋅⋅
-------------------------------------------------=,
R
1
4.99kΩ= R
2
680Ω= R
3
270Ω= R
4
1.1k Ω= C
3
4.7nF= C
4
47nF= C
5
1nF=,,,, ,,