Linear LTC4440, LTC3722, LT1431, LTC3901 User Manual

Description

DEMO MANUAL DC607A

LTC3722, LTC4440, LTC3901,

and LT1431

Isolated Full Bridge Converter

Demonstration circuit 607A is an isolated full bridge
converter featuring the LTC3722, LTC4440, LTC3901,
and LT1431. This circuit was designed to demonstrate the
phase-shifted full bridge power supply to generate 12V
at 35A from a typical telecom input voltage range of 36V
to 72V. Isolation voltage is 1500VDC. Fixed zero-voltage

bridge leg transition times with a 48V input. The DC607A
PCB layout includes options to implement adaptive timing.

Design files for this circuit board are available at

http://www.linear.com/demo/DC607A

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog
Devices, Inc. All other trademarks are the property of their respective owners.

transition timing was chosen because of the relatively fast

performance summary

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IN

V

OUT

I

OUT

f

SW

V

OUT(P-P)

I

REG

P

OUT/PIN

P

OUT/PIN

Input Supply Range 36 72 V

Output Voltage 12.0 V

Output Current Range VIN = 48V, 200LFM 0 35 A

Switching (Clock) Frequency 200 kHz

Output Ripple VIN = 48V, I

Output Regulation Line and Load (36V to 72V, 0A to 35A) ±0.08 %

Efficiency VIN = 48V, I

Efficiency VIN = 48V, I

Isolation Basic 1500 VDC

Approximate Size Component Area × Top Component Height 4.3 × 2.9 × 0.4 Inches

Specifications are at TA = 25°C

= 35A (20MHz BW) 140 mV

OUT

= 35A >93.9 %

OUT

= 25A >94.6 %

OUT

P-P

operating principles

The LTC3722 synchronous dual mode phase modulated
full bridge controller is used on the primary and works
together with the LTC3901 secondary side synchronous
driver to provide a synchronous rectified output. When an
input voltage is applied, the LTC3722 begins a controlled
soft-start of the output voltage. As this voltage begins
to rise, the LT1431 programmable reference is quickly
powered up via the output voltage. The LT1431 provides
feedback via opto-coupler ISO1 to set the output voltage
at 12V. The LTC4440 high voltage gate driver is used to
level shift the high side primary MOSFETs gate signals.

The LTC3722 provides precise control of gate signals to
primary MOSFETs and secondary MOSFETs via T3 and
U1 (LTC3901). The

LTC3901 includes a timer and current

sense to limit reverse inductor current.

For large values of input inductance, a 100V, 47µF electro

­lytic capacitor can be added across the input terminals to
damp the input filter and provide adequate stability. See
Linear Technology Application Note 19 for a discussion
on input filter stability analysis. A recommended part is
the SUNCON 100ME47AX.

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DEMO MANUAL DC607A

Quick start proceDure

Demonstration circuit 607A is easy to set up to evaluate
the performance of the LTC3722, LTC4440, LTC3901,
and LT1431. 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 output (or input) voltage
ripple by touching the probe tip and probe ground directly
across the +Vout and –Vout (or +Vin and –Vin) terminals
or input/output capacitors. See Figure 2 for proper scope
probe technique.

1. Set an input power supply that is capable of 36V to 72V
to a voltage of 36V. Then turn off the supply.

2. With power off, connect the supply to the input terminals
+Vin and –Vin.

a. Input voltages lower than 36V can keep the converter

from turning on due to the undervoltage lockout
feature of the LTC3722.

b. If efficiency measurements are desired, an ammeter

capable of measuring 15Adc or a resistor shunt can
be put in series with the input supply in order to
measure the DC607A’s input current.

c. A voltmeter with a capability of measuring at least

can be placed across the input terminals in order

72V
to get an accurate input voltage measurement.

3. Turn on the power at the input.

NOTE. Make sure that the input voltage never exceeds

72V.

4. Check for the proper output voltage of 12V ±1%. Turn
off the power at the input.

5. Once the proper output voltage is established, connect
a variable load capable of sinking 35A at 12V to the
output terminals +Vout and –Vout. Set the current
for 0A.

a. If efficiency measurements are desired, an ammeter

or a resistor shunt that is capable of handling 35Adc
can be put in series with the output load in order to
measure the DC607A’s output current.

b. A voltmeter with a capability of measuring at least 12V

can be placed across the output terminals in order
to get an accurate output voltage measurement.

6. Turn on the power at the input.

NOTE. If there is no output, temporarily disconnect the

load to make sure that the load is not set too high.

7. Once the proper output voltage is again established,
adjust the load within the operating range and observe
the output voltage regulation, ripple voltage, efficiency

other desired parameters.

and

2

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Quick start proceDure

GND

DEMO MANUAL DC607A

Figure 1. Proper Measurement Equipment Setup

VIN

Figure 2. Measuring Input or Output Ripple

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DEMO MANUAL DC607A

Quick start proceDure

Figure 3. Transient Response, 0A to 35A, 48VIN (200mV and 0.5ms/Div)

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