Texas Instruments TPS40003 - Manual (Page 8)

SLUU130A – September 2002 – Revised February 2003
8 TPS40003-Based 5-A Converter in Less Than One Square Inch
4.7 Compensation Design
The TPS40003 uses voltage mode control in conjunction with a high frequency error amplifier. For the fastest
transient response, the loop crossover frequency is set at 1/10 f
S
, or 60 kHz. The power circuit L-C double pole
corner frequency f
C
is situated at 24 kHz, and the output capacitor ESR zero is far higher at approximately 1MHz.
The feedback compensation network is implemented to provide two zeroes and three poles. The first pole is
placed at the origin to improve dc regulation.
The first zero is placed at approximately 2/3 f
C
, 18 kHz,
f
z1
+ 1
2
p
R
2
C
4
The second zero is selected at f
C
,
f
z2
+
1
2
p
ǒ
R
4
)
R
5
Ǔ
C
12
The two poles are placed at approximately 300 kHz, which is one-half the switching frequency,
f
p1
+ 1
2
p
R
2
ǒ
C
4
C
8
C
4
) C
8
Ǔ
and
f
p2
+
1
2
p
R
5
C
12
(6)
(7)
(8)
(9)