FA5527 FUJI [Fuji Electric], FA5527 Datasheet - Page 26

• Manufacturer Part Number: FA5527
• Description: Fuji Switching Power Control IC
• Manufacturer: FUJI [Fuji Electric]

(2) Hold time of Vcc
OFF threshold voltage as shown in Fig.25 before the
auxiliary winding voltage increases sufficiently. In this case,
Vcc repeatedly goes up and down between the ON and
OFF threshold voltages, and the power supply can not
start up.
(1-3) At stopping
input voltage, output voltage remains low for certain period
of time before the IC stops operation.
pin clamp circuit is cancelled because output voltage
remains low. As a result, CS pin voltage increases as
shown in Fig.26.
the latch mode. As shown in Fig.27, if CS pin voltage
reaches the threshold voltage, the latch mode is held for a
period of time until Vcc capacitor voltage drops to OFF
threshold voltage. As a result, the power supply cannot be
re-started even if input voltage is turned on again.
・Reduce the time taken until the IC stops operation after
・Suppress CS pin voltage rise through increasing CS pin
to hold Vcc above the OFF threshold voltage at abrupt load
change after the power supply has started up.
start-up time gets longer.
be kept long because power is supplied via C4 after
start-up.
AN-087E Rev.1.0
April-2011
When Vcc capacitance is too small, Vcc drops to the
When the power supply is turned off by shutdown of
During this period, FB pin voltage increases and the CS
CS pin voltage shall not reach the threshold voltage of
In such a case, the following measures shall be taken:
the output voltage has dropped through reducing Vcc
capacitance.
capacitance.
In some cases, VCC pin capacitance shall be increased
However, when VCC pin capacitance becomes larger,
In such a case, the circuit shown in Fig.28 is effective.
Reducing C2 shortens start-up time, and hold time can
Fuji Electric Co., Ltd.
Fig.28 Vcc circuit
FA5526/5527/5528/5536/5537/5538
Secondary
Side DC
Output
Voltage
Secondary
Side DC
Output
Voltage
VCC pin
Voltage
FB pin
Voltage
CS pin
Voltage
VCC pin
Voltage
FB pin
Voltage
CS pin
Voltage
26
（when the power supply can not start up）
Fig.25 Vcc waveform at start-up (2)
Fig.26 Waveform at stopping (1)
Fig.27 Waveform at stopping (2)
http://www.fujielectric.co.jp/products/semiconductor/
( The period when
IC can not re-start )
Latch Mode
8.5V
8.5V
OFF
Threshold
Voltage
( 9V )
OFF
Threshold
Voltage
( 9V )