LTC1530CS8-2.5(RevA) 查看數據表（PDF） - Linear Technology

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LTC1530CS8-2.5
(Rev.:RevA)

High Power Synchronous Switching Regulator Controller

Linear Technology 

LTC1530

APPLICATIO S I FOR ATIO

( ) fLC =

1

2π LO COUT

The ESR of the output capacitor and the output capacitor

value form a zero at the frequency:

( )( )( ) fESR =

2π

1

ESR

COUT

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:

fZ

=

1

(2π)(RC)(CC)

and

fP

=

1

(2π)(RC)(C1)

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, fSW = 12fCO, fZ = fLC, fP = 5fCO. At the

closed-loop frequency fCO, the attenuation due to the LC

filter and the input resistor divider is compensated by the

gain of the PWM modulator and the gain of the error

amplifier (gmERR)(RC).

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 330µF 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.

VOUT

3

LTC1530

COMP

4

ERR

RC

C1

BG

CC

1530 F08a

Figure 8a. Compensation Pin Hook-Up

fSW = LTC1530 SWITCHING FREQUENCY

fCO = CLOSED-LOOP CROSSOVER FREQUENCY

fZ

–20dB/DECADE

fLC fESR

fCO

fP

FREQUENCY

1530 F08b

Figure 8b. Bode Plot of the LTC1530 Overall

Transfer Function

Table 2. Suggested Compensation Network for a 5V Input

Application Using Multiple Paralleled 330µF AVX TPS Output

Capacitors for 2.5V Output

LO (µH)

1

CO (µF)

990

RC (kΩ)

1.3

CC (µF)

0.022

C1 (pF)

1000

1

1980

2.7

0.022

470

1

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

18

0.01

68

5.6

990

7.5

0.01

220

5.6

1980

15

0.01

100

5.6

4950

36

0.0047

47

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

Using multiple paralleled 1500µF 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.

1530fa

15

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