Datasheet

F
SW
= 200 kHz
D1
D2
5 Ps
2.5 Ps
5 Ps
F
SW
= 150 kHz
D1
D2
6.67 Ps
6.67 Ps
2.5 Ps
F
SW
= 250 kHz
D1
D2
4 Ps
4 Ps
2.5 Ps
(a)
(b)
(c)
LM5642, LM5642X
SNVS219K –JUNE 2003–REVISED APRIL 2013 www.ti.com
Figure 30. Period Fixed Delay Example
Component Selection
OUTPUT VOLTAGE SETTING
The output voltage for each channel is set by the ratio of a voltage divider as shown in Figure 31. The resistor
values can be determined by the following equation:
where
• Vfb = 1.238V (6)
Although increasing the value of R1 and R2 will increase efficiency, this will also decrease accuracy. Therefore, a
maximum value is recommended for R2 in order to keep the output within .3% of Vnom. This maximum R2 value
should be calculated first with the following equation:
where
• 200nA is the maximum current drawn by FBx pin (7)
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