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RT9245BPC Datasheet(PDF) 19 Page - Richtek Technology Corporation

Part # RT9245BPC
Description  Multi-Phase PWM Controller for K8 CPU Core Power Supply
PDF  23 Pages
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Manufacturer  RICHTEK [Richtek Technology Corporation]
Direct Link  http://www.richtek.com
Logo RICHTEK - Richtek Technology Corporation

RT9245BPC Datasheet(HTML) 19 Page - Richtek Technology Corporation

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RT9245B
19
DS9245B-02
March 2007
www.richtek.com
Figure 29. The Frequency Response with No Load
1. Compensation Setting
a. Modulator Gain, Pole and Zero:
From the following formula:
Modulator Gain = VIN/VRAMP = 12/1.9 = 6.3 (i.e 16dB)
where VRAMP : Ramp amplitude of saw-tooth wave
LC Filter Pole = 3.88kHz and
ESR Zero = 28kHz
b. EA Compensation Network:
Select RB1 = 1.5k, RB2 = 15k, C1 = 2.7nF, C2 = 5.6pF,
C3 = 680pF and use the Type 3 compensation scheme
shown in Figure 28. By calculation.
20dB)
(i.e.
10
Gain
Band
Middle
5.8kHz
(C2//C1)
x
RB2
x
2
1
F
3.9kHz
C1
x
RB2
x
2
1
F
156kHz
C3
x
RB1
x
2
1
F
P
Z2
Z1
=
=
=
=
=
=
=
π
π
π
Figure 28. Type 3 compensation network of EA
The over all loop gain with load is shown in Figure 29 to
Figure 31.
3. Over-Current Protection Setting
Consider the tem perature coeff icient of copper
3900ppm/
°C,
Let RIMAX = 14k
Ω
4. Soft-Start Capacitor Selection
For most application cases, 0.1
µF is a good engineering
value.
Ω
Ω
×
×
⇔
×
×
×
⇔
×
330
1.39m
40A
3
1
R
1.690V
2
1
R
DCR
I
3
1
R
V
2
1
IMAX
COMMON
L
IMAX
IMAX
EA
RB2
RB1
+
-
15k
C1
2.7nF
C2 5.6pF
1.5k
C3 680pF



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