LT1613CS5 데이터 시트보기 (PDF) - Linear Technology

부품명

상세내역

일치하는 목록

LT1613CS5

1.4MHz, Single Cell DC/DC Converter in 5-Lead SOT-23

Linear Technology 

U

OPERATIO

START-UP/SOFT-START

When the LT1613 SHDN pin voltage goes high, the device

rapidly increases the switch current until internal current

limit is reached. Input current stays at this level until the

output capacitor is charged to final output voltage. Switch

current can exceed 1A. Figure 16’s oscillograph details

start-up waveforms of Figure 17’s SEPIC into a 50Ω load

without any soft-start. The output voltage reaches final

value in approximately 200µs, while input current reaches

400mA. Switch current in a SEPIC is 2x the input current,

so the switch is conducting approximately 800mA peak.

Soft-start reduces the inrush current by taking more time

to reach final output voltage. A soft-start circuit consisting

of Q1, RS1, RS2 and CS1 as shown in Figure 17 can be used

to limit inrush current to a lower value. Figure 18 pictures

VOUT and input current with RS2 of 33kΩ and CS of 10nF.

Input current is limited to a peak value of 200mA as the

LT1613

time required to reach final value increases to 1.7ms. In

Figure 19, CS is increased to 33nF. Input current does not

exceed the steady-state current the device uses to supply

power to the 50Ω load. Start-up time increases to 4.3ms.

CS can be increased further for an even slower ramp, if

desired.

VOUT

2V/DIV

IIN

200mA/DIV

VS

5V/DIV

500µs/DIV

1613 F18

Figure 18. Soft-Start Components in Figure 17’s SEPIC

Reduces Inrush Current. CSS = 10nF, RLOAD = 50Ω

VOUT

2V/DIV

VOUT

2V/DIV

IIN

200mA/DIV

VSHDN

5V/DIV

200µs/DIV

1613 F16

Figure 16. Start-Up Waveforms of

Figure 17’s SEPIC Into 50Ω Load

IIN

200mA/DIV

VS

5V/DIV

1ms/DIV

1613 F18

Figure 19. Increasing CS to 33nF Further

Reduces Inrush Current. RLOAD = 50Ω

VIN

4V

SOFT-START COMPONENTS

C1 +

22µF

RS1

33k

VS

CS

10nF/

33nF

RS2

33k

Q1

2N3904

L1

22µH

C3

1µF

L2

VIN

SW 22µH

LT1613

R3

10k

SHDN

FB

GND

R2

12.1k

CPL

330pF

R1

37.4k

D1

C2

10µF

RLOAD

VOUT

5V

1613 F17

C1: AVX TAJB226M006

C2: TAIYO YUDEN LMK325BJ106MN

C3: TAIYO YUDEN LMK212BJ105MG

D1: MOTOROLA MBR0520

L1, L2: MURATA LQH3C220

Figure 17. 5V SEPIC with Soft-Start Components

9

Share Link: