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200
−40
−20
0
20
40
60
80
−100
−50
0
50
100
150
10 100 1 k 10 k 100 k 1 M
G − Gain − dB
Phase − °
f − Frequency − Hz
ESR Zero
Load Pole
Droop Zero
Modulator
Converter Overall
EA
Modulator
Converter Overall
EA
200
10
−40
100 1 k 10 k 100 k 1 M
−20
0
20
40
60
80
−100
−50
0
50
100
150
f − Frequency − Hz
G − Gain − dB
Phase − °
Modulator
Phase
Converter Overall
EA
Type II
ESR Zero
Load Pole
Modulator
Converter Overall
EA
f
DROOPZ
+
1
2p
ǒ
V
DROOP
I
OUT(max)
Ǔ
C
OUT
(20)
TPS40130
SLUS602B – JUNE 2004 – REVISED SEPTEMBER 2005
GAIN AND PHASE GAIN AND PHASE
vs vs
FREQUENCY WITHOUT DROOP FREQUENCY WITH DROOP
Figure 6. Figure 7.
The droop function, as well as the the output capacitor ESR, introduce a zero on some frequency left from the
crossover point. See Equation 20
To compensate for this zero, pole on the same frequency should be added to the error amplifier transfer
function. With Type II compensation network a new value for the capacitor C2 is required compared to the case
without droop.
17
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