LT1935 Ver la hoja de datos (PDF) - Linear Technology

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componentes Descripción

Fabricante

LT1935

1.2MHz Boost DC/DC Converter in ThinSOT with 2A Switch

Linear Technology 

LT1935

APPLICATIONS INFORMATION

VOUT

100mV/DIV

ILOAD

200mA/DIV

50µs/DIV

OUT

84.5k

68pF

1935 F05

FB

10k

20µF

Soft Start

The SHDN pin can be used to soft start the LT1935,

reducing the maximum input current during start up. The

SHDN pin is driven through an external RC filter to create

a ramp at this pin. Figure 6 shows the start-up waveforms

with and without the soft start circuit. Without soft start,

the input current peaks at ~3A. With soft start, the peak

current is reduced to 1A. By choosing a large RC time

constant, the peak start-up current can be reduced to the

current that is required to regulate the output, with no

overshoot. Choose the value of the resistor so that it can

supply 100µA when the SHDN pin reaches 1.8V.

Figure 5. Transient Response with a 68pF Phase-Lead Capacitor

RUN

5V/DIV

VOUT

2V/DIV

IIN

1A/DIV

20µs/DIV

RUN SHDN

GND

1935 F06a

RUN

5V/DIV

VOUT

2V/DIV

IIN

1A/DIV

10k

RUN

0.22µF

200µs/DIV

SHDN

GND

1935 F06b

Figure 6. Adding a Resistor and Capacitor to the SHDN Pin

Reduces the Peak Input Current During Start-Up. VIN = 3.3V,

VOUT = 5V, C2 = 20µF, Output Load = 10Ω.

Layout Hints

L1

D1

C1

The high speed operation of the LT1935 demands careful

attention to board layout. You will not get advertised

VOUT

VIN

performance with careless layout. Figure 7 shows the

+

recommended component placement. Make the ground

C2

SHDN

pin copper area large. This helps to lower the die

R2

temperature.

GND

R1

C3

1935 F03

Figure 7. Suggested Layout

1935f

6

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