RT9245C 데이터 시트보기 (PDF) - Richtek Technology
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RT9245C Datasheet PDF : 25 Pages
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RT9245C
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.
FZ1 =
2π
1
x RB1 x C3
= 156kHz
FZ2
=
2π
x
1
RB2
x
C1
=
3.9kHz
FP
=
2π
1
x RB2 x
(C2//C1)
=
5.8kHz
Middle Band Gain = 10 (i.e. 20dB)
C3 680pF
RB1
1.5k
C2 5.6pF
RB2 C1
15k 2.7nF
-
+EA
Figure 28. Type 3 compensation network of EA
The over all loop gain with load is shown in Figure 29 to
Figure 31.
2. Over-Current Protection Setting
Consider the temperature coefficient of copper
3900ppm/°C,
1
2
×
VIMAX
RIMAX
⇔
1
3
×
IL × DCR
RCSN
1
2
×
1V
RIMAX
⇔
1
3
×
40A
× 1.39m
330Ω
Ω
⇒ RIMAX = 8.9kΩ
3. Soft-Start Capacitor Selection
For most application cases, 0.1µF is a good engineering
value.
DS9245C-02 March 2007
Figure 29. The Frequency Response with No Load
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