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Powering and Loading Considerations

2.3

Powering Up

Using the enable pin provided will allow 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

enable pin to ground, immediately check for 12 volts 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.

2.4

Over Current Protection

The evaluation board is configured with hiccup mode over-current protection. This helps to limit the

thermal stress while in an overloaded condition. If a sustained overload is expected before the onset of

hiccup mode, ensure that sufficient cooling (airflow) is maintained. The peak short circuit current is limited

to approximately 11A.

For sustained short circuit protection, a counter trips the internal fault timer when a current limit condition

exists for more than 256 clock cycles. C7 sets the off-time of the current limit fault timer, which may be

lengthened by increasing the value of C7. D2 is used to discharge C7 in the event of a fast decay of the

input voltage. Though not recommended, the hiccup fault timer may be disabled by removing C7.

Figure 5. Short Circuit at 48V

IN

Figure 6. Short Circuit at 80V

IN

Figure 7. Short Circuit Recovery into Resistive Load

3

SNVA285A – October 2007 – Revised April 2013

AN-1713 LM5116-12 Evaluation Board

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