MAX797H
High-Voltage, Step-Down Controller with
Synchronous Rectifier for CPU Power
_______________________________________________________________________________________ 7
Figure 1. Powering V+ and VL from a Regulated +5V supply
Similarly, at 150kHz, the minimum duty factor is
0.425µs / 6.67µs = 0.064. This means that duty factor is
not an issue except at the maximum input voltage and
minimum output voltage. For example, if V
IN
is 40V,
the lowest V
OUT
that does not require less than the
minimum duty factor is 40V x 0.064 = 2.56V. If V
OUT
/
V
IN
is less than this value, the IC will properly regulate
the output voltage, but may extend the period and
switch at 75kHz instead of 150kHz. It may also alter -
nate between these two frequencies.
