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PM6641 数据表(PDF) 39 Page - STMicroelectronics

部件名 PM6641
功能描述  Monolithic VR for chipset and DDR2/3 supply for ultra-mobile PC (UMPC) applications
PDF  47 Pages
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制造商  STMICROELECTRONICS [STMicroelectronics]
网页  http://www.st.com
标志 STMICROELECTRONICS - STMicroelectronics

PM6641 数据表(HTML) 39 Page - STMicroelectronics

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From the definition of cross-over frequency, the value of the compensation resistor is
derived:
Equation 25
A good choice for the cross-over frequency is to assign fCO equal to
.
The fixed parameters gm = 300 µs and KL = 4.4 s are design parameters, whereas the
feedback divider factor (
α) is application dependant (see Chapter 7.3: SW regulators control
loop on page 24
section for details).
After computing RC, the compensation capacitor can be designed in order to place the
compensation zero near the power stage pole:
Equation 26
The roll-off capacitance, as said previously, must compensate for the power stage high
frequency zero, when necessary:
Equation 27
As final step, it’s important to verify that the compensation zero is quite far from the cross-
over frequency. An empirical rule is satisfied if the following holds:
Equation 28
All these considerations are true if the cross-over frequency is quite lower than the switching
frequency, and the compensation zero and the power stage pole are far enough from fCO.
O
L
m
O
ES
O
CO
C
CO
LOOP
R
K
g
)
R
R
(
C
f
2
R
1
)
f
2
j
(
G
α
+
π
=
⇒
=
π
10
f
SW
(
)
C
ES
O
O
C
R
R
R
C
C
+
=
C
ES
O
RO
R
R
C
C
=
5
f
R
C
2
1
f
CO
C
C
ZC
≤
π
=



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