FA5695 Datasheet, PDF (16/21 Pages) Fuji Electric – Fuji Switching Power Supply Control IC

FA5695
10. Description of use for each pin
(1) Terminal No. 1 (FB terminal)
Functions
(i) Input of feedback signal of output voltage setting
(ii) Detect short-circuit of FB terminal
(iii) Detect output overvoltage
Application
(i) Feedback signal input
- Wiring
Connect the node between voltage dividing resistors for setting output
voltage.
- Operation
The output voltage Vout of PFC is controlled so that FB voltage matches
the internal reference voltage (2.5V).
VREF
Vout 
 R1  VREF
R2
VREF : Reference voltage = 2.5V (typ.)
To prevent malfunction due to noise, capacitor C3 of 100pF~3300pF
should be connected between the FB terminal and GND.
(ii) FB terminal short-circuit detection
- Wiring
Same as for the (i) Feedback signal input
- Operation
When the input voltage of the FB terminal becomes 0.3V or lower due to
short-circuit of R2, the output of the comparator (SP) inverts to stop the
output of the IC.
(iii) Output overvoltage detection
- Wiring
Same as for the (i) Feedback signal input
- Operation
Normally the voltage of the FB terminal is 2.5V almost same as the
reference voltage of the error amplifier. When the output voltage rises for
some reason and the voltage of the FB terminal reaches the comparator
reference voltage (1.08*VREF), the output of the comparator (OVP)
inverts to stop the OUT pulse. If the output voltage returns to the normal
value, the OUT pulse resumes.
(2) Terminal No. 2 (COMP terminal)
Function
(i) Phase compensation of internal ERRAMP output
Application
(i) Phase compensation of internal ERRAMP output
- Wiring
Connect C, R between COMP terminal and GND as shown in Fig. 16.
- Operation
Connecting C, R to the COMP terminal suppress ripple component at 2
times the frequency of the AC line that appears in the FB output.
(Reference)
Example of application circuit：C4=0.15uF
C5=0.15uF
R3=68kΩ
The above is a reference example, and it should be decided by
sufficiently verifying with actual application circuit.
Vout
R1
FB
1
R2
C3
VREF(2.5V)
COMP
ERRAMP
Short Ｃｏｍｐ
SP
Vthfb(0.3V)
Vsovp(1.08*VREF)
OVP
ＯＶＰ Ｃｏｍｐ
Vdovp(1.05*VREF)
RAMP OSC
Ｄｙｎａｍｉｃ ＯＶＰ
Fig.15 FB pin circuit
PWM.comp _COMP
2
ERRAMP
R3
C4
C5
Fig.16 COMP pin circuit
Fuji Electric Co., Ltd.
AN-073E Rev.1.1
April-2011
http://www.fujielectric.co.jp/products/semiconductor/
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