rt9245b Richtek Technology Corporation, rt9245b Datasheet - Page 19

• Manufacturer Part Number: rt9245b
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

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