MIC2124 Datasheet, PDF (16/24 Pages) Micrel Semiconductor – Constant Frequency, Synchronous Current Mode Buck Controller

Micrel, Inc.
D = 0.15
R_LOAD = 0.18Ω.
The output capacitor and the inductor parameters are:
C_OUT = 760μF
ESR_COUT = 0.002Ω
L = 2.2μH.
Also,
Ri = 0.007Ωx2.4
f_SW = 300kHz
Rfb1 = 10kΩ
Rfb2 = 8.06kΩ
The error amplifier gm and external compensation
component are:
g_m = 110μS
R1 = 150kΩ
C1 = 220pF
C2 = 47pF
The gain and phase of the control-to-output transfer
function predicted by the equation (29) are shown in
Figure 7. The gain and phase of the error amplifier
transfer function predicted by the equation (32) are
shown in Figure 8. The total open-loop bode plot
predicted by the equation (35) is shown in Figure 9.
30
20
10
0
-10
-20
-30
10
Gain of Control-to-Output
Phase of Control-to-Output
100
1000
f (Hz)
10000
0
-20
-40
-60
-80
-100
-120
100000
Figure 7. Control-to-Output Bode Plot
MIC2124
90
70
50
30
10
-10
-30
10
20
Gain of Error Amplifier
Phase of Error Amplifier
0
-20
-40
-60
-80
-100
100
1000
10000
100000
f (Hz)
Figure 8. Error Amplifier Bode Plot
120
90
60
30
0
-30
-60
10
0
Total Open Loop Gain
Total Open Loop Phase
-30
-60
-90
-120
-150
-180
100
1000
10000
100000
f (Hz)
Figure 9. Total Open Loop Bode Plot
The crossover frequency of this MIC2124 buck converter
is 40kHz and the phase margin is about 50°, as shown in
Figure 9.
June 2010
16
M9999-060810-D