LTC1530CS8 Linear Technology, LTC1530CS8 Datasheet - Page 15

• Manufacturer Part Number: LTC1530CS8
• Description: IC SW REG CNTRLR SYNC ADJ 8-SOIC
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1530CS8

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.3 ~ 3.5 V
• Current - Output: 20A
• Frequency - Switching: 300kHz
• Voltage - Input: 3.3V, 5V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIO S I FOR ATIO
The ESR of the output capacitor and the output capacitor
value form a zero at the frequency:
The compensation network used with the error amplifier
must provide enough phase margin at the 0dB crossover
frequency for the overall open-loop transfer function. The
zero and pole from the compensation network are:
respectively. Figure 8b shows the Bode plot of the overall
transfer function.
The compensation values used in this design are based on
the following criteria, f
closed-loop frequency f
filter and the input resistor divider is compensated by the
gain of the PWM modulator and the gain of the error
amplifier (g
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
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.
f
f
f
LC
ESR
Z
2
2
2
mERR
R
L C
1
C
O OUT
ESR C
1
)(R
C
1
C
U
C
).
SW
OUT
and f
CO
= 12f
U
, the attenuation due to the LC
P
CO
, f
2
Z
W
= f
R
LC
1
C
, f
P
C
= 5f
1
U
CO
. At the
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.
L
O
2.7
2.7
2.7
5.6
5.6
5.6
Figure 8b. Bode Plot of the LTC1530 Overall
Transfer Function
( H)
1
1
1
f
Figure 8a. Compensation Pin Hook-Up
Z
R
C
f
LC
C
C
1980
4950
1980
4950
1980
4950
O
f
f
990
990
990
SW
CO
C
( F)
= CLOSED-LOOP CROSSOVER FREQUENCY
f
= LTC1530 SWITCHING FREQUENCY
ESR
COMP
C1
4
f
CO
R
–20dB/DECADE
C
LTC1530
1.3
2.7
6.8
3.6
7.5
7.5
18
15
36
(k )
ERR
–
+
f
BG
P
FREQUENCY
V
C
0.0047
0.022
0.022
0.022
OUT
3
1530 F08a
C
0.01
0.01
0.01
0.01
0.01
1530 F08b
( F)
LTC1530
C1 (pF)
1000
470
220
330
220
220
100
15
68
47
1530fa