Linear Technology LT3971 User manual

DESCRIPTION

Demonstration circuit 1527 is a monolithic step-down

DC/DC switching regulator featuring the LT3971 The

switching frequency is adjustable up to 2MHz The

demo circuit is designed for 3 3V, 1 2A output from a

4 5V to 38V input The wide input range of the LT3971

allows a variety of input sources including automotive

batteries and 24V industrial supplies Low ripple Burst

Mode increases the efficiency at the light load while

keeping the output ripple below 15mV The part is in

shutdown when the EN pin is low and active when the

pin is high The threshold of the EN pin is accurate at

1V with 30mV of hysteresis When Vin is above 6V,

adding a resistor divider from Vin to EN can program

the LT3971 to regulate the output only when Vin is

above a desired voltage

The circuit consumes only 2 8

µA of quiescent current

The boost diode, control and logic circuit are inte-

grated to reduce the components count and solution

size The current mode control scheme creates fast

transient response and good loop stability

The LT3971 datasheet gives a complete description of

the part, operation and application information The

datasheet must be read in conjunction with this quick

start guide for demo circuit 1527

Design files for this circuit board are available. Call

the LTC factory.

, LTC and LT are registered trademarks of Linear Technology Corporation

Performance Summary (TA = 2 oC)

PARAMETER CONDITION VALUE

Minimum Input Voltage 4 5V

Maximum Input Voltage 38V

Output Voltage V

OUT

3 307±2 5%

Typical switching Frequency 800kHz

Maximum Output Current 1 2A

Typical efficiency V

=12V, I

out

=1 2A 82 43%

Typical output voltage Ripple V

=12V, I

out

=1 2A 10mV

QUICK START PROCEDURE

Demonstration circuit 1527 is easy to set up to

evaluate the performance of the LT3971 Refer to

Figure 1 for proper measurement equipment setup

and follow the procedure below:

NOTE.

When measuring the input or output voltage ripple, care must

be taken to avoid a long ground lead on the oscilloscope probe

Measure the input or output voltage ripple by touching the probe tip

directly across the Vin or Vout and GND terminals See Figure 2 for

proper scope probe technique

Place JP1 on the ON position

Place JP2 on the RT FREQ position

With power off, connect the input

power supply to Vin and GND

Turn on the power at the input

NOTE.

Make sure that the input voltage does not exceed 38V

Check for the proper output voltage

EMO

IRCUIT 1

QUICK START GUIDE

LT397

38V, 1.2A

Micropo er Buck Regulator

NOTE.

If there is no output, temporarily disconnect the load to

make sure that the load is not set too high

Once the proper output voltage is es-

tablished, adjust the load within the op-

erating range and observe the output

voltage regulation, ripple voltage, effi-

ciency and other parameters

Figure 1.

Proper Measurement Equipment Setup

VIN

GND

Figure 2.

Measuring Input or Output Ripple

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