mb3775pfv Fujitsu Microelectronics, Inc., mb3775pfv Datasheet - Page 23

• Manufacturer Part Number: mb3775pfv
• Description: Switching Regulator Controller
• Manufacturer: Fujitsu Microelectronics, Inc.

4.
(3) As shown in Fig. 39, the phase is advanced by using both example 1 and 2 (Fig. 35 and 37).
The boost circuit for charging the phase compensating capacitor C
in Figure 40 to protect against output voltage overload at power-on.
A : =15 mV offset voltage is provided for the negative input side so that the boost circuit only operates at power-
on. When a capacitor is connected in parallel with the output feedback resistor, because the output ripple is too
large or for advanced phase compensation, the boost circuit starts operating, which may degrade regulation if
the differential input voltage of the error amplifier exceeds : =15 mV. Be careful with the differential input voltage
of the error amplifier.
Advanced phase
compensation
capacitor
Error amplifier input ripple voltage
R
R
4
3
V
0
+
Fig. 39 - External circuit example 3 to advance the phase
R
V
[+ IN]
[ IN]
1
REF
Fig. 40 - Error Amp. /Boost Equivalent circuit
V
+ IN
REF
IN
15 mV
+
+
+
x 120
C
R
1
2
R
1
P
38 k
FB
[FB]
is connected to the error amplifier as shown
R
C
V
P
CC
P
R
C
V
2
P
0
+
470
Boost circuit
Error Amp.
MB3775
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