Powering and Loading Considerations
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2.1
Quick Setup Procedure
1. Set the power supply current limit to 10A. Turn off the power supply. Connect the power supply to the
VIN terminals.
2. Connect the load, with a 7A capability, to the VOUT terminals.
3. Slowly increase the load while monitoring the output, VOUT should be in regulation with a nominal 5V
output.
4. Slowly sweep the input voltage from 5.5V to 36V, VOUT should remain in regulation with a nominal 5V
output
5. Temporarily short the EN pin to check the shutdown function, Also, EN pin can be set between 0.4V
and 1.2V, for example, by shorting EN pin to ground with a diode, to check the standby function.
6. Increase the load beyond the rated current to check the current limiting. The output current should limit
at approximately 10A. The LM25088-1 board will enter cycle-by-cycle current limiting, while LM25088-2
is configured for a hiccup mode restart. Cooling is critical in this step.
2.2
Air Flow
Prolonged operation with high input voltage (>24V) at full load will cause the LM25088 and MOSFETs to
overheat and could potentially result in thermal shutdown. A fan with a minimum of 100LFM should always
be used to cool the LM25088 evaluation board.
2.3
Powering Up
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. A quick efficiency check is the best
way to confirm that everything is operating properly. If something is amiss one can be reasonably sure
that it will affect the efficiency adversely. Few parameters can be correct in a switching power supply
without creating losses and potentially damaging heat.
2.4
Over Current Protection
The LM25088-1 and LM25088-2 evaluation boards are both configured with over-current protection
schemes. The LM25088-1 employs a cycle-by-cycle current limiting, while the LM25088-2 is configured for
a hiccup mode restart. Please refer the LM25088/LM25088Q Wide Input Range Non-Synchronous Buck
Controller (
SNVS609
) data sheet for more information on RES pin.
2.5
Synchronization
A Sync pin has been provided on the evaluation board. This pin can be used to synchronize the LM25088
to an external clock. It is recommended not to exceed 500 kHz while synchronizing. Refer the LM25088
datasheet for complete information.
2.6
Active Loads
When using electronic load, it is strongly recommended to power up the evaluation board at light load and
then slowly increase the load. This is necessary as most of the electronic loads do not draw any current till
the output reaches an internally set point; this can result in soft-start function to not work as desired and
can trip the current sense comparator. Electronic loads, in general, are best suited for monitoring steady
state waveforms. If it is desired to power up the evaluation board at maximum load, resistor banks can be
used. This will ensure a soft-start and evaluation board will perform as desired. Ensure that there is
sufficient cooling for both the resistor banks and the LM25088 evaluation board, while running at full load.
2
AN-1931 LM25088 Evaluation Board
SNVA383D – November 2008 – Revised April 2013
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