Datasheet

Application information A7986A
22/42 DocID022801 Rev 5
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), anyway 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
= 3 A, L = 18 μH, C
OUT
= 22 μF, and ESR<1
mΩ, the Type III compensation network is:
Equation 28
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
200Ω= R
4
2kΩ= C
3
3.3nF= C
4
22nF= C
5
220pF=,,,, ,,