FSQ0565R Fairchild Semiconductor, FSQ0565R Datasheet - Page 16

• Manufacturer Part Number: FSQ0565R
• Description: Green-mode Fairchild Power Switch Fps? For Quasi-resonant Operation - Low Emi And High Efficiency
• Manufacturer: Fairchild Semiconductor

FSQ0565R, FSQ0765R Rev. 1.0.0
© 2007 Fairchild Semiconductor Corporation
If no valley is found during t
forced to turn on at the end of t
the devices have a minimum switching frequency of
48kHz and a maximum switching frequency of 67kHz.
Figure 34. QRC Operation with Limited Frequency
W
, the internal SenseFET is
W
Figure 36. Alternating Valley Switching (AVS)
(Case D). Therefore,
16
8. AVS (Alternating Valley Switching): Due to the
quasi-resonant operation with limited frequency, the
switching frequency varies depending on input voltage,
load transition, and so on. At high input voltage, the
switching on time is relatively small compared to low
input voltage. The input voltage variance is small and the
switching frequency modulation width becomes small. To
improve the EMI performance, AVS is enabled when
input voltage is high and the switching on time is small.
Internally, quasi-resonant operation is divided into two
categories; one is first valley switching and the other is
second-valley switching after blanking time. In AVS, two
successive occurrences of first-valley switching and the
other two successive occurrences of second-valley
switching is alternatively selected to maximize frequency
modulation. As depicted in Figure 35, the switching
frequency hops when the input voltage is high. The
internal timing diagram of AVS is described in Figure 36.
Figure 35. Switching Frequency Range
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