TPS40090_15 Datasheet, PDF (14/31 Pages) Texas Instruments – HIGH-FREQUENCY, MULTIPHASE CONTROLLER

TPS40090
TPS40091
SLUS578B – OCTOBER 2003 – REVISED MAY 2006
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FEEDBACK LOOP COMPENSATION
The TPS4009x operates in a peak current mode and the converter exhibits a single pole response with ESR zero
for which Type II compensation network is usually adequate, as shown in Figure 7.
The following equations show where the load pole and ESR zero calculations are situated.
f_OP + _2p
1
R_OUT
C_OUT
f_ESRZ + _2p
1
R_ESR
C_OUT
(10)
To achieve desired bandwidth the error amplifier must compensate for modulator gain loss on the crossover
frequency and this is facilitated by placing the zero over the load pole. The ESR zero alters the modulator's -1
slope at higher frequencies. To compensate for that alteration, the pole in-error amplifier transfer function should
be added at frequency of the ESR zero as shown in Figure 6.
Figure 6.
The following equations help in choosing components of the error amplifier compensation network. Fixing the
value of the resistor R1 first is recommended as it simplifies further adjustments of the output voltage without
altering the compensation network.
R2 + R1
ǒ Ǔ ^*GOMAG
10 ²⁰ ;
C1 + _ǒ2p
1
F_OP
R2^{Ǔ ;}
C2 + _ǒ2p
1
F _ESRZ
R2^Ǔ
where:
• G_OMAG is the control to output gain at desired system crossover frequency.
(11)
Introduction of output voltage droop as a measure to reduce amount of filter capacitors changes the transfer
function of the modulator as it is shown in the Figure 8.
14
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