LTC3443 データシートの表示（PDF） - Linear Technology

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LTC3443

High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter

Linear Technology 

LTC3443

U

OPERATIO

SOFT-START

The soft-start function is combined with shutdown. When

the SHDN/SS pin is brought above typically 1V, the IC is

enabled but the EA duty cycle is clamped from the VC pin.

A detailed diagram of this function is shown in Figure 5.

The components RSS and CSS provide a slow ramping

voltage on the SHDN/SS pin to provide a soft-start

function.

PVIN

9

VOUT

8

A

dI

dt

≈

VIN

L

D

+

–

4

5

L

SW1

SW2

B

C

800mA

0mA

T1

6

GND

3443 F03

PVIN

9

VOUT

8

A

dI

dt

≈

–

VOUT

L

D

–

+

4

5

SW1

L

SW2

B

C

800mA

0mA

6

GND

T2

3443 F04

Figure 3. Inductor Charge Cycle During Burst Mode Operation Figure 4. Inductor Discharge Cycle During Burst Mode Operation

VIN

SOFT-START

CLAMP

TO PWM

VCI

COMPARATORS

14μA

ERROR AMP

1.22V

FB

12

VC CP1

11

VOUT

R1

R2

CHIP

ENABLE

SHDN/SS

1

RSS

CSS

ENABLE SIGNAL

3443 F05

1V

Figure 5. Soft-Start Circuitry

3443fa

10

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