MIC2169 Micrel Semiconductor, MIC2169 Datasheet - Page 12

• Manufacturer Part Number: MIC2169
• Description: 500 KHZ PWM SYNCHRONOUS BUCK CONTROL IC
• Manufacturer: Micrel Semiconductor

MIC2169
Figures 7 and 8 show the gain and phase curves for the above
transfer function with R1 = 9.3k, C1 = 1000pF, C2 = 100pF,
and g
amplifier exhibits approximately 45 of phase margin.
Total Open-Loop Response
The open-loop response for the MIC2169 controller is easily
obtained by adding the power path and the error amplifier
gains together, since they already are in Log scale. It is
desirable to have the gain curve intersect zero dB at tens of
kilohertz, this is commonly called crossover frequency; the
phase margin at crossover frequency should be at least 45 .
Phase margins of 30 or less cause the power supply to have
substantial ringing when subjected to transients, and have
little tolerance for component or environmental variations.
Figures 9 and 10 show the open-loop gain and phase margin.
It can be seen from Figure 9 that the gain curve intersects the
0dB at approximately 50kHz, and from Figure 10 that at
50kHz, the phase shows approximately 50 of margin.
M9999-111803
m
= .005
Figure 8. Error Amplifier Phase Curve
Figure 7. Error Amplifier Gain Curve
–1
. It can be seen that at 50kHz, the error
12
269.097
42.933
71.607
360
250
300
350
100
50
50
0
Figure 10. Open-Loop Phase Margin
100
10
10
100
Figure 9. Open-Loop Gain Margin
100
1 . 10
3
1 . 10
3
1 . 10
f
f
4
1 . 10
4
1 . 10
1 . 10
November 2003
5
5
1000000
1000000
1 . 10
1 . 10
Micrel
6
6