BD7690FJ-E2 Ver la hoja de datos (PDF) - ROHM Semiconductor
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BD7690FJ-E2 Datasheet PDF : 26 Pages
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BD7690FJ
(5) ZCD pin zero current detection
The zero current detection circuit is a function to detect a zero cross of the inductor current (IL) (cf. Figure 10). In addition, it
recommends that it adds CR filter for switching noise reduction. It inserts R1 for limit the current between auxiliary winding and
ZCD pin to use ZCD pin in rating. In addition, Vds of Q1 performs free resonance when inductor current disappears. It can
suppress a switching loss and the surge of Q1 by coordinating R1,C1 so that Q1 is turned on in the valley of the resonance
wave pattern.
D1
C0
R1
C1
OUT Q1
RCS
ZCD
Control
0.67/1.8V Logic
OUT
FMAX
Figure 10. ZCD circuit
Vds
Time
Figure 11. Drain wave patterns
(6) RT pin
This pin sets a slope wave pattern formed in the IC inside by external resistance. It shows RT resistor value and relations of the
maximum frequency in Figure 12. The maximum ON width on the application is calculated in the following formula. It shows
relations of RT resistor value and maximum ON width in Figure 13.
VAC: Input voltage,
TON
_
MAX
[s]
2 L PO
V2
ACMin
L: Inductance, Po: Max output power,
:Efficiency
Necessary TON_MAX on application can be check as upper formula. Please set ON width in RT pin more than TONMAX.
In addition, the high-speed frequency in the light load is limited in RT pin. The external resistance range of the RT pin is 51kΩ -
390kΩ.
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TSZ02201-0F2F0A200280-1-2
27. Mar. 2017 Rev.002
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