PM6681A STMicroelectronics, PM6681A Datasheet - Page 35

• Manufacturer Part Number: PM6681A
• Description: Dual synchronous step down controller with adjustable LDO
• Manufacturer: STMicroelectronics

PM6681A
Figure 39. Circuitry for output ripple compensation
The stability of the system depends firstly on the output capacitor zero frequency. The
following condition should be satisfied:
Equation 24
where k is a design parameter greater than 3 and R
determinates the minimum integrator capacitor value C
Equation 25
where gm = 50 µs is the integrator trans conductance.
In order to ensure stability it must be also verified that:
Equation 26
In order to reduce ground noise due to load transient on the other section, it is
recommended to add a resistor R
low pass filter (see
times) than the switching frequency of the section:
Figure 39
). The cutoff frequency f
C
f
sw
INT
INT
C
>
>
INT
k
and a capacitor C
2
×
π
f
>
Zout
×
2
⎛
⎜
⎝
π
f
=
sw
g
k
g
×
m
m
f
2
Zout
−
π
f
×
Zout
×
C
out
out
V
k
⎞
⎟
⎠
CUT
Vr
OUT
×
×
is the ESR of the output capacitor. It
INT
filt
V
R
must be much greater (10 or more
Vr
OUT
that, together with C
:
out
Design guidelines
INT
, realize a
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