鈭?/div>
Hz
f
CO1
100 k
1M
Figure 18. Overall System Bode Plot
Using these values and the equations above the resistors and capacitors around the compensation network can
be calculated.
1. Set R
Z1
= 10 k鈩?
2. Calculate R
SET
using
Equation 49;
R
SET
= 8750
鈩?
Two resistors in parallel, R
SET1
and R
SET2
, are used to
make up R
SET
. R
SET1
= 9.53 k鈩? R
SET2
= 105 k鈩?
3. Using
Equation 54
and f
Z1
= 3559 Hz, C
PZ1
can be calculated to be 4.47 nF; C
PZ1
= 4.7 nF.
4. F
P1
and
Equation 52
yields R
P1
to be 677
鈩?
R
P1
= 680
鈩?
5. The required gain of 17.6 dB (7.586) and
Equation 52
sets the value for R
PZ1
. Note actual gain used for this
calculation was 20 dB (10), this ensures that the gain of the transfer function is high enough, R
PZ1
= 6.2 k鈩?
6. C
Z2
is calculated using
Equation 55
and the desired frequency for the second zero, C
Z2
= 6.8 nF.
7. C
P2
is calculated using the second pole frequency and
Equation 53,
C
P2
= 150 pF.
Using MathCAD the above values were used to draw the actual Bode plot for gain and phase. From these plots
the crossover frequency, phase margin and gain margin can be recorded.
Table 3. Equivalent Series Resistance
ESR
(鈩?
0
0.0095
CROSSOVER FREQUENCY
(kHz)
23.1
98.6
PHASE MARGIN
(擄)
72
78.8
GAIN MARGIN
(dB)
> 46
> 33
30