Linear Technology LT3437IFE Manuale utente

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1232

HIGH VOLTAGE 500mA 200kHz BUCK CONVERTER WITH BURST MODE

LT3437IFE

DESCRIPTION

Demonstration Circuit 1232 is a high voltage 500mA

200kHz buck converter with burst mode featuring the

LT®3437IFE. The board is optimized for 3.3V output

at up to 400mA load current for a steady state input

voltage range of 3.7V to 60V* with input transients

up to 80V. *

Minimum on-time restrictions and 3.3V

output may limit the steady state maximum input

voltage to 42V before pulse skipping occurs. Up to

60V DC input is allowable for the LT3437, but with

higher output voltages than 3.3V. 80V input is allow-

able for a short transient regardless of output voltage

With its wide input voltage range, 500mA internal

power switch, 100uA supply current (at input volt-

ages above 14V), 200kHz switching frequency and

thermally enhanced package, the LT3437IFE is a very

versatile and powerful IC for DC/DC converters that

require compact space, high efficiency at both heavy

and light loads and high input voltage.

The LT3437 200kHz switching frequency allows all of

the components to be small, surface mount devices.

Synchronization with an external clock of up to

700kHz is possible. The current-mode control topol-

ogy creates fast transient response and good loop

stability with a minimum number of external compo-

nents. The low resistance internal power switch

(0.8Ω) achieves high efficiencies of up to 81%. The

shutdown pin can be used to program undervoltage

lockout or place the part in micropower shutdown,

reducing supply current to less than 1µA. Burst

Mode™ reduces zero load current to under 100µA at

most input voltages while maintaining a regulated

output. Burst Mode can be defeated or enabled by

setting the Burst Mode jumper position. When Burst

Mode is defeated, the IC runs at constant frequency

without skipping pulses at light load. This provides

low output ripple at light load, but the quiescent cur-

rent (1-2mA) is higher than in burst mode. The soft

start function reduces inrush current and output volt-

age overshoot during startup.

The LT3437 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 1232. The

LT3437IFE is assembled in a small 16-pin thermally

enhanced package with exposed pad where proper

board layout is essential for maximum thermal per-

formance. See the datasheet section ‘Layout Consid-

erations’.

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 1232 is easy to set up to evalu-

ate the performance of the LT3437. Refer to Figure 5

for proper measurement equipment setup and follow

the procedure below:

NOTE:

The synchronization and shutdown functions

are optional and their terminals can be left floating

(disconnected) if they are not being used.

NOTE:

Do not hot-plug the input voltage terminal VIN.

The absolute maximum voltage on VIN is 80V 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. This is due to high currents in-

stantaneously generated in the inductive supply leads

from an input voltage step on the low-ESR ceramic

input capacitor. A bulky higher-ESR capacitor and an

additional inductive filter can be added to the circuit

to dampen hot-plug transient ringing.

See Application

Note 88 for more details.

In order to protect the IC, a

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1232

HIGH VOLTAGE 500mA 200kHz BUCK CONVERTER WITH BURST MODE

transient voltage suppressor diode can be added be-

tween VIN and GND terminals to absorb any high

voltage transient ringing that may occur due to hot-

plugging.

After all connections are made with power off, turn

on input power and verify that the output voltage is

3.3V.

NOTE:

If the output voltage is low, disconnect the

load to make sure that it is not too high.

Once the output voltage is established, adjust the

load within the operating range and observe the

output voltage regulation, ripple voltage, efficiency

and other parameters.

Figure 1.

DC1232A Typical Efficiency

Figure 2.

DC1232 Typical Supply Current in Burst Mode

Figure 3.

Output Ripple with Burst Mode Defeat. With Burst Mode

Enabled, zero load ripple may be as high as 30mV under the

same conditions.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1232

HIGH VOLTAGE 500mA 200kHz BUCK CONVERTER WITH BURST MODE

Figure 5. Proper Measurement Equipment Setup

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1232

HIGH VOLTAGE 500mA 200kHz BUCK CONVERTER WITH BURST MODE

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