FA5640 Datasheet, PDF (21/35 Pages) Fuji Electric – Fuji Switching Power Supply Control IC

FA5640/41/42
• Burst operation
When the FB pin voltage decreases to lower than the pulse shutdown threshold voltage, switching is stopped. On the
contrary, if the FB voltage increases to higher than the pulse shutdown threshold voltage, switching is resumed. Overshoot
and undershoot of the FB pin voltage occur over and under the pulse shutdown threshold voltage for mode switching.
Continuous pulses are issued during this overshoot period, and long-cycle burst frequency is obtained during the
undershoot period. The pulse shutdown threshold voltage is switched to 0.45 V when input voltage is low, whereas it is
switched to 0.35 V when input voltage is high, as input voltage compensation.
FB pin
voltage
Pulse stop
voltage
VthFB01=0.45V
VthFB02=0.35V
OUT pin
switching
pulse
Heavy load
Light load
(burst switching)
Fig.7 Burst operation at light load
Fuji Electric Co., Ltd.
AN-064E Rev.1.1
April 2011
21
http://www.fujielectric.co.jp/products/semiconductor/