LTC1530CS8 datasheet(15/24 Pages) LINER

15 / 24 page

LTC1530

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

µF 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.

Table 2. Suggested Compensation Network for a 5V Input

Application Using Multiple Paralleled 330

µF AVX TPS Output

Capacitors for 2.5V Output

LO (µH)

CO (µF)

RC (kΩ)CC (µF)

C1 (pF)

990

1.3

0.022

1000

1980

2.7

0.022

470

4950

6.8

0.01

220

2.7

990

3.6

0.022

330

2.7

1980

7.5

0.01

220

2.7

4950

0.01

5.6

990

7.5

0.01

220

5.6

1980

0.01

100

5.6

4950

0.0047

An alternate output capacitor is the Sanyo MV-GX series.

Using multiple paralleled 1500

µF 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

µF SANYO MV-GX

Output Capacitors for 2.5V Output

LO (µH)

CO (µF)

RC (kΩ)CC (µF)

C1 (pF)

4500

0.022

470

6000

0.022

330

9000

0.022

220

2.7

4500

8.2

0.022

150

2.7

6000

0.01

100

2.7

9000

0.01

100

5.6

4500

0.01

100

5.6

6000

0.01

5.6

9000

0.01

Note: For different values of VOUT, multiply the RC value by VOUT/2.5 and

multiply the CC and C1 values by 2.5/VOUT. This maintains the same

crossover frequency for the closed-loop transfer function.

LTC1530

VOUT

COMP

1530 F08a

–

ERR

Figure 8a. Compensation Pin Hook-Up

FREQUENCY

1530 F08b

–20dB/DECADE

fSW = LTC1530 SWITCHING FREQUENCY

fCO = CLOSED-LOOP CROSSOVER FREQUENCY

fLC fESR

fCO

Figure 8b. Bode Plot of the LTC1530 Overall

Transfer Function

APPLICATIO S I FOR ATIO

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