ISL6741_14 Datasheet, PDF (24/28 Pages) Intersil Corporation – Flexible Double Ended Voltage and Current Mode PWM Controllers

ISL6740, ISL6741
The following compensation components were selected
R₂₃ = 9.53kΩ
R₂₄ = 2.49kΩ
R₄ = 499Ω
R₂₁ = 4.22kΩ
C₂₂ = 1nF
C₂₀ = 82pF
C₁₉ = 0.22μF
From (Equations 27, 28, 29 and 30), the poles and zeroes are:
f_z1 = 171Hz
f_z2 = 16.7kHz
f_p2 = 460kHz
f_p3 = 319kHz
The calculated gain and phase plots of the error amplifier appear
below using an ideal op amp.
20
10
0
-10
10
100
1•10³
1•10⁴
1•10⁵
1•10⁶
FREQUENCY (Hz)
FIGURE 23A. IDEAL ERROR AMPLIFIER GAIN
90
45
0
-45
-90
10
100
1•10³
1•10⁴
1•10⁵
1•10⁶
FREQUENCY (Hz)
FIGURE 23B. IDEAL ERROR AMPLIFIER PHASE
The gain and phase plots combined with the opto coupler’s
transfer characteristics appear in Figures 24A and 24B:
30
20
10
0
-10
10
100
1•10³
1•10⁴
1•10⁵
1•10⁶
FREQUENCY (Hz)
FIGURE 24A. EA PLUS OPTO COUPLER GAIN
90
45
0
-45
-90
-135
-180
10
100
1•10³
1•10⁴
1•10⁵
1•10⁶
FREQUENCY (Hz)
FIGURE 24B. EA PLUS OPTO COUPLER GAIN
Using the control-to-output transfer function combined with the
EA transfer function, the loop gain and phase may be predicted.
The predicted loop gain and phase margin of the converter
appear in Figures 25A and 25B:
50
40
30
20
10
0
-10
-20
-30
-40
-50
100
1•10³
1•10⁴
FREQUENCY (Hz)
FIGURE 25A. PREDICTED LOOP GAIN
1•10⁵
24
FN9111.6
December 2, 2011