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PM6680 Datasheet(PDF) 38 Page - STMicroelectronics

Part # PM6680
Description  No Rsense dual step-down controller with adjustable voltages for notebook system power
PDF  49 Pages
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Manufacturer  STMICROELECTRONICS [STMicroelectronics]
Direct Link  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

PM6680 Datasheet(HTML) 38 Page - STMicroelectronics

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Device description
PM6680
38/49
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 26
Due to the capacitive divider (CINT, Cfilt), the ripple voltage at the COMP pin is given by:
Equation 27
Where VRIPPLEout is the output ripple and q is the attenuation factor of the output ripple.
If the ripple is very small (lower than approximately 30mV), a further compensation network,
named virtual ESR network, is needed. This additional part generates a triangular ripple
that is added to the ESR output voltage ripple at the input of the integrator network. The
complete control schematic is represented in Figure 37.
Figure 37.
Virtual ESR network
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
×
=
+
×
=
COMP
COMP
OUT
OUT
C
CINT
INT
R
RINT
INT
C
CFILT
FILT
t
Vr
C
COUT
OUT
COMP PIN
VOLTAGE
L
L
D
D
OUTPUT
VOLTAGE
C
C
R
R
R1
R1
t
t
T
T NODE
VOLTAGE
?V
?V1
R
ROUT
OUT
?V1
+
-
Vr
Vr
gm
gm
Vr
Vr
+
PWM
PWM
Comparator
Comparator
V1
V1
FB
FB
R
R11
R
R22
COMP
COMP
OUT
OUT
C
CINT
INT
R
RINT
INT
C
CFILT
FILT
t
Vr
C
COUT
OUT
COMP PIN
VOLTAGE
L
L
D
D
OUTPUT
VOLTAGE
C
C
R
R
R1
R1
t
t
T
T NODE
VOLTAGE
?V
?V1
R
ROUT
OUT
?V1
+
-
Vr
Vr
gm
gm
Vr
Vr
+
PWM
PWM
Comparator
Comparator
V1
V1
FB
FB
R
R11
R
R22
R
R11
R
R22



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