Micrel, Inc.
MIC4720
Max. Amount of Phase Boost
Obtainable using CFF vs. Output
Voltage
50
45
40
35
30
25
20
15
10
5
VREF = 1V
0
1
2
3
4
5
OUTPUT VOLTAGE (V)
As you can see the typical phase margin, using the
same resistor values as before without a feedforward
capacitor results in 33.6 degrees of phase margin. Our
prior measurement with a feedforward capacitor yielded
a phase margin of 47 degrees. The feedforward
capacitor has given us a phase boost of 13.4 degrees
(47 degrees- 33.6 Degrees = 13.4 Degrees).
By looking at the graph, phase margin can be affected to
a greater degree with higher output voltages.
The next bode plot shows the phase margin of a 1.8V
output at 2A without a feedforward capacitor.
M9999-051707
May 2007
16
MICREL [ MICREL SEMICONDUCTOR ]
