PM6681A STMicroelectronics, PM6681A Datasheet - Page 37

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

PM6681A
where ∆I
voltage. It should be chosen higher than approximately 30 mV.
The new closed loop gain depends on C
that:
Equation 30
Where:
Equation 31
where R
given by the virtual ESR network R
Moreover C
Equation 32
Where k is a free design parameter greater than 3 and determines the minimum integrator
capacitor value C
Equation 33
C must be selected as shown:
Equation 34
R must be chosen in order to have enough ripple voltage on integrator input:
Equation 35
R1 can be selected as follows:
TOT
L
is the inductor current ripple and VRIPPLE is the overall ripple of the T node
INT
is the sum of the ESR of the output capacitor Rout and the equivalent ESR
must meet the following condition:
INT
:
f
C
sw
INT
>
ESR
C
f
Z
k
>
INT
=
×
2
.
R
f
π
C
2
Z
>
INT
π
=
×
=
>
2
×
. In order to ensure stability it must be verified
⎛
⎜
⎝
R
π
5
g
g
2
f
C
sw
ESR
k
×
m
m
π
×
out
f
L
×
C
Z
1
−
C
INT
×
×
×
f
Z
out
C
R
V
k
⎞
⎟
⎠
TOT
Vr
OUT
×
×
R
V
Vr
OUT
TOT
Design guidelines
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