Datasheet

SLUU182 − March 2004
10
High-Performance Dual Synchronous Buck Conversion Using the TPS5124
4.5 Compensation Design
The following compensation loop design uses Channel 1 as example, but a design for Channel 2
follows the same rules.
TPS5124 uses voltage-mode control method. A Type III compensation network, formed by R1,
R2, R4, C14, C12, and C23, is used to guarantee the stability. The L-C frequency of the power
stage is around 5.4 kHz and the ESR zero is at 790 KHz due to the low ESR of the ceramic
capacitors. An overall crossover frequency (f
0db
) of 30 kHz is chosen for reasonable transient
response and stability. Both zeros (f
Z1
and f
Z2
) from the compensator are set at 2.68 kHz. The
two poles (f
P1
and f
P2
) and are set at 150 kHz and 2 MHz. The frequency of poles and zeros are
defined by the following equations.
f
Z1
+
1
2p R4 C14
f
Z2
+
1
2p R1 C12
, assuming R1 ơ R2
f
P1
+
1
2p R4 C23
f
P2
+
1
2p R2 C12
, assuming C14 ơ C23
The transfer function for the compensator is calculated as:
A(s) +
(
1 ) s C14 R2
) [
1 ) s C12
(
R1 ) R2
)]
s R1 C14
ƪ
ǒ
1 )
C23
C14
Ǔ
) s R4 C23
ƫ
(
1 ) s R2 C12
)
100
−10
−30
−20
20
0
10
50
30
40
120
180
140
160
40
100
60
80
0
20
100 k
1 k 10 k
GAIN AND PHASE
vs
OSCILLATOR FREQUENCY
(CHANNEL 1)
Figure 4.
f
OSC
− Frequency − Hz
Phase − °
Gain − dB
Gain
Phase
V
IN
= 12 V
V
OUT
= 3.3 V
I
OUT
= 15 A
−10
−30
−20
20
0
10
30
40
120
140
160
40
100
60
80
0
20
180
100 100 k1 k 10 k
f
OSC
− Frequency − Hz
Gain − dB
GAIN AND PHASE
vs
OSCILLATOR FREQUENCY
(CHANNEL 2)
Figure 5. Channel 2
L = 0.6 µH
Phase − °
V
IN
= 12 V
V
OUT
= 1.5 V
I
OUT
= 10 A
Gain
Phase
−20
(11)
(12)
(13)
(14)
(15)