Linear Technology LTC3805/-5 User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1311

TELECOM DC/DC CONVERTER

LTC3805/-5

DESCRIPTION

Demonstration circuit 1311 is a Telecom isolated

DC/DC converter featuring the LTC3805/-5 constant

frequency current mode flyback controller. The

DC1311 converts 18V to 72V input voltage to an

isolated 3A of output current at 3.3V. The 300kHz

constant frequency operation is maintained down to

very light load to reduce low frequency noise

generated over a wide range of load current. The

converter provides high output voltage accuracy

(typically ±2%) over wide load range with no

minimum load requirement.

The DC1311 also provides non-isolated design by

removing opto coupler and LTC4430 circuit. The

demonstration circuit can be easily modified to

generate different output voltages up to 15V. As

output voltage is increased, the maximum

output current must be reduced to limit the

output power to no more than 10W. Higher

output voltages and currents can be achieved by

changing the MOSFET, transformer and output

capacitors. Please consult LTC factory for details.

The DC1311 has a small circuit footprint. It is a high

performance and cost effective solution for Telecom,

Automotive and Power over Ethernet applications.

Design files for this circuit board are available. Call

the LTC factory.

LTC and LT are registered trademarks of Linear Technology Corporation.

QUICK START PROCEDURE

Demonstration circuit 1311 is easy to set up to

evaluate the performance of the LTC3805/-5. For

proper measurement equipment setup refer to

Figure 1 and follow the procedure below.

When measuring the input or output voltage ripple,

care must be taken to minimize the length of the

oscilloscope probe ground lead. Measure the input or

output voltage ripple by connecting the probe tip

directly across the V

or V

OUT

and GND terminals,

see Figure 2.

With power off, connect the input power supply to

+Vin and -Vin.

Move the J1 (RUN) switch to ON position.

Turn the input power source on and slowly

increase the input voltage. Be careful not to exceed

72V. Make sure that the input voltage V

does not

exceed 72V. If higher operating voltage is required,

power components with higher voltage ratings

should be used.

Check for proper output voltage. Vout=3.3V.

If there is no output, temporarily disconnect the

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

To shut the converter down, move the RUN switch

into OFF position

To synchronize converter to external clock, set

jumper JP2 (SYNC) to ‘EXT’ position, apply signal

to FSET pin. See LTC3805/-5 datasheet for

synchronization signal parameters.

Once the proper output voltage is established,

adjust the load within 3.0A range and observe the

output voltage regulation, ripple voltage, efficiency

and other parameters.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1311

TELECOM DC/DC CONVERTER

Figure 1. Proper Measurement Equipment Setup

Figure 2. Measuring Input or Output Ripple

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1311

TELECOM DC/DC CONVERTER

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