mb3775pfv Fujitsu Microelectronics, Inc., mb3775pfv Datasheet - Page 16

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

16
MB3775
1.
Note: As shown above, the frequency characteristic of the error amplifier is set by the external phase compensating
APPLICATION
Figure 22 shows the equivalent circuit of the error amplifier.
The frequency characteristic of the error amplifier is set by R
ratio of resistors R
When C
external phase compensating capacitor C
When high frequency gain is needed or the phase must be advanced at a low frequency, connect a resistor R
between the FB terminal and C
How to set the error amplifier frequency characteristic
capacitor CP .
When a ceramic chip capacitor must be used to meet the requirements of a small system, be careful of its
temperature characteristic. ( 30 C 1/5 and 80 C 1/3 for the frequency characteristic, so a sufficient
phase margin must be allowed for at room temperature.) Ceramic chip capacitors with a low temperature
characteristic (B characteristic) or film capacitors are recommended (see Fig. 26 to 28).
P
= 0.1 F, the gain at 20 kHz
[ IN]
[+ IN]
1
and R
[ IN]
[+ IN]
2
in the IC (set value
P
as shown in Figure 23 (see Fig. 25).
+
Fig. 23 - Error Amp. Equivalent Circuit (Insert R
+
x 120
= . .
f
Fig. 22 - Error Amp. Equivalent Circuit
x 120
P
5 MHz is about 0 dB. The roll-off frequency is adjusted by changing
(see Fig. 24).
Error Amp.
Error Amp.
0 dB).
R
1
R
= . .
1
38 k
38 k
[FB]
1
[FB]
, R
2
, and C
R
C
2
P
R
R
C
2
P
P
470
470
P
. The high-frequency gain is set by the
PWM COMP
PWM COMP
P
)
P