FA5590 FUJI [Fuji Electric], FA5590 Datasheet - Page 13

• Manufacturer Part Number: FA5590
• Description: FUJI Power Supply Control IC
• Manufacturer: FUJI [Fuji Electric]

feedback control. For this IC, a transconductance type is used for the
error amplifier.
The non-inverting input terminal is connected to internal reference
voltage of 2.5V (typ.).
power-factor correction converter, and normally use divided voltage
with resistors. To the inverting input, internal constant current source
of 1.8μA is connected for FB open detection function.
comparator and controls the on time of the OUT output.
The output voltage of PFC contains much of ripple of frequency 2
times AC power line (50 or 60Hz). When this ripple component
becomes largely appears in the output of the error amplifier, the
power-factor correction converter does not stably operate. In order to
obtain the stable operation, connect capacitors and a resistor at Pin
No. 2 (COMP) as shown in Fig.5.
startup and overshoot of output voltage when starting.
and before the soft start cancellation voltage is exceeded. In the
meantime, the soft start function restricts the startup speed of the
output voltage by limiting the maximum on time to about 80% when
the FB terminal voltage is lower than the reference voltage. (Fig. 6)
The on time limited by the soft start is cancelled when the FB terminal
voltage becomes higher than the soft start cancellation voltage.
power-factor correction converter exceeds the set value.
of the converter may exceed the set value. In such a case, this
protect circuit works to control the output voltage.
the FB terminal voltage becomes above 2.5V, and static OVP function
to stop the output when it becomes higher than 1.09 times the
reference voltage.
Normally the voltage of the FB terminal is 2.5V, approximately same
as the reference voltage of the error amplifier. When the output
voltage rises due to starting up or sharp load changes and the voltage
of the FB terminal becomes higher than 2.5V, the on time narrows by
the dynamic OVP function. When the voltage further rises and
exceeds the comparator reference voltage, output voltage of the
comparator(OVP) inverts to stop the OUT pulse.(Fig. 7)
voltage, the OUT pulse resumes.
10. Description of each circuit block
AN-016E Rev.1.2
April-2011
The output of the error amplifier (COMP) is connected to the PWM
When this IC starts up or load changes sharply, the output voltage
The error amplifier is to make the output voltage constant with
The inverting input terminal is fed with output voltage of the
FA5590/91 is equipped with soft start function to suppress rushing
The soft start circuit works after UVLO and standby is released
This circuit is to limit the voltage when the output voltage of the
FA5590/91 has dynamic OVP function to narrow the on tme when
When the output voltage turns below 1.05 times the reference
(1) Error amplifier
(2) Soft start circuit
(3) Overvoltage protection circuit (OVP)
Fuji Electric Co., Ltd.
FA5590N,FA5591N
13
最大オン幅
100%
80%
Maximum
on time
R1
R2
C5
R3
100%
On time
70%
オン幅
Vout
http://www.fujielectric.co.jp/products/semiconductor/
COMP
Fig.6 maximum on time at soft start
Fig.7 on time at overvoltage
FB
C4
C3
(2.5V)
Vfb
Fig.5 Error amplifier circuit
1
2
1.8uA
Vfb*1.05
VREF(2.5V)
RAMP
ERRAMP
OSC
Vfb*0.95
Vfb*1.09
Comp
PWM
(2.5V)
Vfb
VF voltage
VF voltage
OUT
F/F
FB電圧
FB電圧