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Powering and Loading Considerations
3
Powering and Loading Considerations
Read this entire page prior to attempting to power the evaluation board.
3.1
Quick Setup Procedure
1. Set the power supply current limit to 3.5A. Turn off the power supply. Connect the power supply to the
V
terminals.
IN
2. Connect the load, with a 3A capability, to the V
connection to J3.
3. Leave the SD pin open for normal operation.
4. Set V
to 24 V with no load applied. V
IN
5. Slowly increase the load while monitoring the output voltage, V
nominal 5 V output as the load is increased up to 2.5 Amps.
6. Slowly sweep the input voltage from 7 V to 75 V, V
output.
7. Temporally short the SD pin to GND to check the shutdown function.
8. Increase the load beyond the normal range to check current limiting. The output current should limit at
approximately 3.8A. The power supply (Vin source) current limit may need to be increased for this
step. Cooling is critical during this step.
3.2
Air Flow
Prolonged operation with high input voltage at full power causes the thermal shutdown circuit within the
regulator IC to activate. A stand-alone fan with at lease 200 LFM should always be provided.
3.3
Powering Up
Using the provided shutdown pin allows powering up the source supply with the current level set low. It is
suggested that the load be kept low during the first power up. Set the current limit of the source supply to
provide about 1.5 times the anticipated wattage of the load. As you remove the connection from the
shutdown pin to ground, immediately check for 5 V at the output.
A quick efficiency check is the best way to confirm that everything is operating properly. If something is
amiss, you can be reasonably sure that it will affect the efficiency adversely. Few parameters can be
incorrect in a switching power supply without creating losses and potentially damaging heat.
3.4
Over Current Protection
The evaluation board is configured with over-current protection. The output current is limited to
approximately 3.8A. The thermal stress is quite severe while in an overloaded condition, limit the duration
of the overload and provide sufficient cooling (airflow).
3.5
Synchronization
A SYNC pin has been provided on the evaluation board. This pin can be used to synchronize the regulator
to an external clock or multiple evaluation boards can be synchronized together by connecting their SYNC
pins together. For complete information, see the LM5005 High Voltage 2.5 Amp Buck Regulator Data
Sheet (SNVS397).
2
AN-1748 LM5005 Evaluation Board
terminals. Positive connection to J2 and negative
OUT
should be in regulation with a nominal 5 V output.
OUT
OUT
Copyright © 2007–2013, Texas Instruments Incorporated
should remain in regulation with a
OUT
should remain in regulation with a nominal 5 V
SNVA298A – November 2007 – Revised April 2013
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