FA5590 FUJI [Fuji Electric], FA5590 Datasheet - Page 14

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

(standby circuit)
provided to the FB terminal due to short-circuit or open-circuit around R1,
R2, the error amplifier cannot control the constant voltage and the output
voltage abnormally rises. In such a case, the overvoltage protection
circuit also cannot operate because the detection of the output voltage is
abnormal.
detection circuit.
comparator (SP), and when the input voltage of the FB terminal
becomes 0.3V or lower due to such trouble as short-circuit of R2 or
opening of R1, the output of the comparator (SP) inverts to stop the
output of the IC and the IC stops operation resulting in standby state.
output of the IC stops, and then when the voltage of the FB terminal
returns to 0.3V or higher, the IC resumes from the standby state and the
OUT pulse restarts.
voltage dividing resistors is broken, the FB terminal voltage is forcefully
raised by the internal constant current source of 1.8μA connected to the
FB terminal. Since the error amplifier output (COMP) voltage decreases
as the FB terminal voltage rises, the output voltage decreases or OUT
output is stopped.
detection circuit or restart circuit, and outputs the set signal of F/F for
OUT output and saw tooth wave signal for deciding the duty of the PWM
comparator.
(5-1) Maximum frequency limiting
characteristic to rise at light load.
the efficiency at light load and limits the switching frequency to Fmax
(Hz). (Fig. 10)
between the RT terminal and GND.
the inductor current is detected and MOSFET is turned on after the zero
current detection delay Tzcd to adjust turning on take place at the
bottom of Vds wave, as shown in Fig. 11.
the zero level of the inductor current is detected and no turn-on occurs
after the zero current detection delay, but turn-on occurs at the cycle of
1/Fmax, as shown in Fig. 12.
and overcurrent detection. (Fig. 9)
(6-1) Zero current detection circuit
mode instead of the oscillator with the fixed frequency. The zero current
detection circuit ZCD. Comp detects that the inductor current becomes
zero to perform the critical mode operation.
detection resistor Rs connected to the GND line is fed to the IS terminal,
and it is compared by the zero current detection comparator, and when it
becomes -4mV or more, the inductor current is regarded as zero level.
zero cross delay detection circuit, and then set the F/F for OUT to make
AN-016E Rev.1.2
April-2011
When the connection between the FB terminal and the node of
When the switching frequency is lower than Fmax, the zero level of
In case of light load where the switching frequency is limited to Fmax,
With the zero current detection, the voltage across the current
In the PFC circuit of booster type, if feedback voltage is not properly
To avoid such situation, this IC is equipped with FB short-circuit
This circuit is composed of the reference voltage of 0.3V (typ.) and
Once the voltage of the FB terminal decreases to almost zero and the
The ramp oscillating circuit receives signal from the zero current
The switching frequency of PFC in the critical mode has
FA55901/91 has the maximum frequency limiting function to improve
The maximum frequency Fmax depends on the resistance connected
The current detection circuit is composed of zero current detection
This IC performs the switching operation by self-oscillation in critical
When the zero level is detected, the delay Tzcd is generated by the
(4) FB short-circuit/open detection circuit
(5) Ramp oscillating circuit
(6) Current detection circuit
Fuji Electric Co., Ltd.
FA5590N,FA5591N
14
21.9kΩ
46.7kΩ
1.4kΩ
1.5V
Switching frequency
SW周波数
Fmax
R1
R2
IS
http://www.fujielectric.co.jp/products/semiconductor/
Vout
5
Fig.10 maximum frequency limiting
100mV
20mV
C6
R4
C1
ZCD.comp
OCP.comp
FB
C3
Fig.9 Current detection circuit
L1
Rs
1
1.8uA
C8
Fig.8 FB pin circuit
Q1
RTZC
OCP
R6 C7
Delay
Ｄｙｎａｍｉｃ ＯＶＰ
ERRAMP
ＯＶＰ Ｃｏｍｐ
D1
4
Short Ｃｏｍｐ
C2
VREF(2.5V)
Vdovp(1.05*VREF)
Vthfb(0.3V)
Vsovp(1.09*VREF)
RAMP
RT
OSC
R5
負荷
Load
COMP
RAMP OSC
OVP
3
SP
OUT用
F/F
PWM
Comp