MB3775 Datasheet, PDF (22/25 Pages) Fujitsu Component Limited. – SWITCHING REGULATOR CONTROLLER

MB3775
(3) As shown in Fig. 39, the phase is advanced by using both example 1 and 2 (Fig. 35 and 37).
Fig. 39 - External circuit example 3 to advance the phase
C1
+ IN
- IN
R1
R2
+
-
VREF
V0+
FB
RP
CP
4. Error amplifier input ripple voltage
The boost circuit for charging the phase compensating capacitor CP is connected to the error amplifier as shown 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 am-
plifier exceeds 15 mV. Be careful with the differential input voltage of the error amplifier.
Fig. 40 - Error Amp. /Boost Equivalent circuit
V0 ⁺
VCC
Advanced phase
compensation
R4
capacitor
R3
[+ IN]
[- IN]
VREF
+
Boost circuit
-
15mV
+
x 120
-
R1 38 kΩ
R2 470 Ω
Error Amp.
[FB]
CP
22