Datasheet

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LM5101

PUSH

PULL

35V - 80V

OUT

LM5041

Buck Stage Push-Pull Stage

Powering and Loading Considerations

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Figure 1. Simplified Cascaded Push-Pull Converter

3 Powering and Loading Considerations

When applying power to the LM5041 evaluation board certain precautions need to be followed. 125W is a

considerable amount of continuous power. A failure or mistake can present itself in a very alarming

manner. A few simple rules can easily prevent any startling surprises.

4 Proper Connections

When operated at low input voltages the UUT can draw over 4A of current at full load. The maximum

rated output current for the evaluation board is 50A. Be sure to choose the correct connector and wire size

when attaching the source supply and the load. Monitor the current into and out of the UUT (evaluation

board or unit under test). Monitor the voltage directly at the output terminals of the UUT. The voltage drop

across the load connecting wires will give inaccurate measurements. For accurate efficiency

measurements, the same precautions should be taken, attaching a meter directly at the UUT input

terminals.

5 Source Power

The evaluation board can be viewed as a constant power load. At low input line voltage (35V) the input

current can exceed 4A, while at high input line voltage the input current will be approximately 1.8A.

Therefore to fully test the LM5041 evaluation board a DC power supply capable of at least 80V and 5A is

required. The power supply must have adjustments for both voltage and current. An accurate readout of

output current is desirable since the current is not subject to loss in the cables as in the voltage.

The power supply and cabling must present a low impedance to the UUT. Insufficient cabling or a high

impedance power supply will droop during power supply application with the UUT inrush current. If large

enough, this droop will cause a chattering condition upon power up. This chattering condition is an

interaction with the UUT undervoltage lockout, the cabling impedance and the inrush current.

AN-1299 LM5041 Evaluation Board SNVA074A–May 2004–Revised May 2013

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