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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1092

36V 500KHZ H-GRADE DFN STEP-DOWN REGULATOR

LT1933H

DESCRIPTION

Demonstration circuit 1092 is a monolithic step-down

DC/DC switching converter featuring the LT®1933H.

The board is optimized for 3.3V output at up to

500mA load current for a steady state input voltage

range of 4.5V to 36V. With its H-grade temperature

rating, wide input voltage range, high current internal

power switch, low dropout operation, 500kHz switch-

ing frequency and tiny DFN package, the LT1933H is

a very versatile and powerful IC for DC/DC converters

that require extremely compact space, high efficiency

and high input voltage with a high temperature range.

The LT1933H 500kHz switching frequency allows all

of the components to be small, surface mount de-

vices. The board is designed to run at maximum

power up to 85ºC ambient. The IC is rated for up to

150ºC junction temperature. The current-mode con-

trol topology creates fast transient response and

good loop stability with a minimum number of exter-

nal components. The low resistance internal power

switch (0.37V V

sat) achieves high efficiencies of up

to 84%. The shutdown pin can be used to program

undervoltage lockout or place the part in micropower

shutdown, reducing supply current to less than 2µA

by driving the pin low (

without R1 installed

). The in-

ternal soft start function reduces input current surge

during start-up.

The LT1933H datasheet gives a complete description

of the part, operation and applications information.

The datasheet must be read in conjunction with this

Quick Start Guide for demonstration circuit 1092. In

particular, the datasheet section on ‘Thermal Calcula-

tions’ is important for estimating whether a given ap-

plication’s combination of input voltage, load current,

ambient temperature and frequency will cause the

LT1933H to exceed it’s absolute maximum rated junc-

tion temperature. The LT1933H is assembled in a

small DFN package. Proper board layout is essential

for maximum thermal performance. See the data-

sheet section ‘Layout Considerations’.

Design files for this circuit board are available. Call

the LTC factory.

LT is a trademark of Linear Technology Corporation

QUICK START PROCEDURE

Demonstration circuit 1092 is easy to set up to evalu-

ate the performance of the LT1933H. Refer to Figure

1 for proper measurement equipment setup and fol-

low the procedure below:

NOTE:

Make sure that the input voltage does not ex-

ceed 36V.

NOTE:

The shutdown function is optional and its ter-

minal can be left floating (disconnected) if shutdown

is not being used.

NOTE:

Do not hot-plug the input voltage terminal VIN.

The absolute maximum voltage on VIN is 36V and

hot-plugging a power supply through wire leads to

the demonstration circuit can cause the voltage on

the extremely low-ESR ceramic input capacitor to ring

to twice its DC value. In order to protect the IC, a

higher ESR Aluminum Electrolytic capacitor, C4, is

placed at the input terminals. This may protect

against some, but not all, input transients due to hot-

plugging with a power supply.

See Application Note

88 for more details.

NOTE:

Connect the power supply (with power off),

load, and meters as shown in Figure 1.

After all connections are made, turn on input power

and verify that the output voltage is 3.3V.

NOTE:

If the output voltage is too low, temporarily

disconnect the load to make sure that the load is

not set too high.