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PM6685 数据表(PDF) 39 Page - STMicroelectronics

部件名 PM6685
功能描述  Dual step-down main supply controller with auxilary voltages for notebook system power
PDF  52 Pages
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制造商  STMICROELECTRONICS [STMicroelectronics]
网页  http://www.st.com
标志 STMICROELECTRONICS - STMicroelectronics

PM6685 数据表(HTML) 39 Page - STMicroelectronics

Back Button PM6685 Datasheet HTML 35Page - STMicroelectronics PM6685 Datasheet HTML 36Page - STMicroelectronics PM6685 Datasheet HTML 37Page - STMicroelectronics PM6685 Datasheet HTML 38Page - STMicroelectronics PM6685 Datasheet HTML 39Page - STMicroelectronics PM6685 Datasheet HTML 40Page - STMicroelectronics PM6685 Datasheet HTML 41Page - STMicroelectronics PM6685 Datasheet HTML 42Page - STMicroelectronics PM6685 Datasheet HTML 43Page - STMicroelectronics Next Button
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PM6685
Monitoring and protections
39/52
The stability of the system depends firstly on the output capacitor zero frequency. The
following condition should be satisfied:
Equation 21
where k is a design parameter greater than 3 and Rout is the ESR of the output capacitor. It
determinates the minimum integrator capacitor value CINT:
Equation 22
where gm=50us is the integrator transconductance.
In order to ensure stability it must be also verified that:
Equation 23
In order to reduce ground noise due to load transient on the other section, it is
recommended to add a resistor RINT and a capacitor Cfilt that, together with CINT, realize a
low pass filter (see Figure 36). The cutoff frequency fCUT must be much greater (10 or more
times) than the switching frequency of the section:
Equation 24
Due to the capacitive divider (CINT, Cfilt), the ripple voltage at the COMP pin is given by:
Equation 25
out
out
Zout
sw
R
C
2
k
f
k
f
×
×
π
=
×
>
OUT
Zout
sw
m
INT
V
Vr
f
k
f
2
g
C
×
⎟
⎠
⎞
⎜
⎝
⎛
−
×
π
>
OUT
Zout
m
INT
V
Vr
f
2
g
C
×
×
π
>
filt
INT
filt
INT
CUT
INT
C
C
C
C
f
2
1
R
+
×
×
×
π
=
q
V
C
C
C
V
V
RIPPLEout
filt
INT
INT
RIPPLEout
RIPPLEINT
×
=
+
×
=



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