FA5546 Datasheet, PDF (18/27 Pages) Fuji Electric – Switching Power Supply Control IC

FA5546/47
Fig. 12 Overload protection timing chart (auto reset type)
Since the OLP timer for overload protection delay time uses
an up/down counter, a period for counting down is required
to clear the count. Note that switching frequency (Fosc) is
counted to detect the overload protection delay time
(TdOLP).
Consequently, if overload is reset within the overload
protection delay time (less than 200ms), and the switching
frequency decreases (down to less than 60kHz or 100kHz)
immediately after that, the time for resetting the count is
prolonged. In the case of a pulse load with which another
overload occurs before the counter is reset, the next
overload delay time should be made shorter (200ms or
shorter).
Example: In the case of a load with which overload current
period of 50ms and no-load period of 1s are repeated,
overload protection occurs within the overload delay time
(200ms or shorter) as shown in Fig.13. Pay attention to the
above in the case of a load with which overload and light
load are repeated.
Fig. 13 Typical overload/light load repetition timing chart
Fuji Electric Co., Ltd.
AN-027E Rev.0.4
April -2011
18
http://www.fujielectric.co.jp/products/semiconductor/