IRS27951S IRS27952(4)S - International Rectifier
IRS27951S IRS27952(4)S - International Rectifier
IRS27951S IRS27952(4)S - International Rectifier
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<strong>IRS27951S</strong><br />
<strong>IRS27952</strong>(4)S<br />
Dead-Time vs. CT Value<br />
DT (ns)<br />
2000<br />
1800<br />
1600<br />
1400<br />
1200<br />
1000<br />
800<br />
600<br />
400<br />
200<br />
0<br />
0 500 1000 1500 2000<br />
CT (pF)<br />
Figure 3: Dead-time with CT capacitor chart<br />
The running frequency of the IRS2795(1,2)(4) is given by:<br />
f<br />
SW<br />
=<br />
2 ⋅[<br />
R<br />
Teq<br />
1<br />
(0.85C<br />
+ 40 pF)<br />
+ t<br />
T<br />
DT<br />
]<br />
R Teq is the total equivalent resistance at RT pin.<br />
Or just simply select the RT value form the frequency chart shown below:<br />
Frequency Chart<br />
Frequency (KHz)<br />
500<br />
450<br />
400<br />
350<br />
300<br />
250<br />
200<br />
150<br />
100<br />
50<br />
0<br />
CT=220pF<br />
CT=330pF<br />
CT=470pF<br />
CT=1nF<br />
0 10 20 30 40 50<br />
RT (KΩ)<br />
Figure 4: Switching frequency and RT selection<br />
The maximum duty cycle is given by:<br />
DC<br />
MAX<br />
= 0.5<br />
− ( t * f )<br />
DT<br />
16 www.irf.com © 2012 <strong>International</strong> <strong>Rectifier</strong> November 8 th , 2012
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