l5953 STMicroelectronics, l5953 Datasheet - Page 28

• Manufacturer Part Number: l5953
• Description: Multiple Switching Voltage Regulator
• Manufacturer: STMicroelectronics

Application note
28/31
1. Fix the cross-over frequency f
where f
2. Calculate the high frequency error amplifier gain
3. Chose R3 and calculate
The value for R3 has not to be very high (for example 10KΩ) so to limit the error due to an
error amplifier input offset current.
4. Calculate
5. Finally calculate
and
sw,min
is the minimum switching frequency
C
G
R
c
of the overall loop gain. Usually:
R1
p
R2
=
C8
C9
f
c
=
R4
0.25 f
=
=
=
-------------------------------------------- -
⎛
⎝
=
=
------------ -
ESR
R
0.1 f
----------------------------------
1
=
2
2
2
p
⋅
–
⋅
⋅
⋅
G
c
---------------------- -
V
------------------------ -
---------------------- -
⋅
--------------------------
V
C
⋅
⋅
R3
L1 C7
R
ref,PWM
L1 C7
ref PWM
sw,min
2 π
⋅
R3
R4
p
V
V
------- -
C7
⋅
L1
R1
,
⋅
O
⋅
O
⎞
⎠
⋅
------------ -
ESR
–
L1
1
L5953