LTC1530 LINER [Linear Technology], LTC1530 Datasheet - Page 15

• Manufacturer Part Number: LTC1530
• Description: High Power Synchronous Switching Regulator Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Although a mathematical approach to frequency compen-
sation can be used, the added complication of input and/
or output filters, unknown capacitor ESR, and gross
operating point changes with input voltage, load current
variations and frequency of operation all suggest a more
practical empirical method. This can be done by injecting
a transient current at the load and using an RC network box
to iterate toward the final compensation values or by
obtaining the optimum loop response using a network
analyzer to find the actual loop poles and zeros.
Table 2 shows the suggested compensation components
for 5V input applications based on the inductor and output
capacitor values. The values were calculated using mul-
tiple paralleled 330 F AVX TPS series surface mount
Figure 8b. Bode Plot of the LTC1530 Overall
Transfer Function
Figure 8a. Compensation Pin Hook-Up
R
f
Z
C
C
C
f
LC
f
f
U
SW
CO
COMP
C1
= CLOSED-LOOP CROSSOVER FREQUENCY
= LTC1530 SWITCHING FREQUENCY
f
4
ESR
U
LTC1530
f
CO
ERR
–20dB/DECADE
–
+
BG
W
f
V
P
OUT
FREQUENCY
1530 F08a
3
1530 F08b
U
tantalum capacitors for the output capacitor. The opti-
mum component values might deviate from the suggested
values slightly because of board layout and operating
condition differences.
Table 2. Suggested Compensation Network for a 5V Input
Application Using Multiple Paralleled 330 F AVX TPS Output
Capacitors for 2.5V Output
An alternate output capacitor is the Sanyo MV-GX series.
Using multiple paralleled 1500 F Sanyo MV-GX capaci-
tors for the output capacitor, Table 3 shows the suggested
compensation components for 5V input applications based
on the inductor and output capacitor values.
Table 3. Suggested Compensation Network for a 5V Input
Application Using Multiple Paralleled 1500 F SANYO MV-GX
Output Capacitors for 2.5V Output
Note: For different values of V
multiply the C
crossover frequency for the closed-loop transfer function.
L
L
O
O
2.7
2.7
2.7
5.6
5.6
5.6
2.7
2.7
2.7
5.6
5.6
5.6
( H)
1
1
1
( H)
1
1
1
C
and C1 values by 2.5/V
C
C
1980
4950
1980
4950
1980
4950
4500
6000
9000
4500
6000
9000
4500
6000
9000
O
O
990
990
990
( F)
( F)
OUT
R
, multiply the R
R
C
C
8.2
11
16
16
22
33
1.3
2.7
6.8
3.6
7.5
7.5
(k )
3
4
6
18
15
36
(k )
OUT
. This maintains the same
C
C
0.0047
C
0.022
0.022
0.022
0.022
0.022
0.022
0.022
C
0.01
0.01
0.01
0.01
0.01
C
0.01
0.01
0.01
0.01
0.01
value by V
( F)
( F)
LTC1530
OUT
C1 (pF)
C1 (pF)
1000
/2.5 and
470
220
330
220
220
100
470
330
220
150
100
100
100
15
68
47
68
47