Datasheet

85V, 4A
Power Supply
With
Current Meter
100W, 30A
Electronic
Load
+
-
+
-
Volt-Meter Volt-Meter Current-Meter
IN
OUT
Evaluation
Board
Scope
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Source Power
Figure 2.
5 Source Power
The evaluation board can be viewed as a constant power load. At low input line voltage (36V) the input
current can reach 3.5A, while at high input line voltage (72V) the input current will be approximately 1.5A.
Therefore, to fully test the LM5045 evaluation board a DC power supply capable of at least 85V and 4A is
required. The power supply must have adjustments for both voltage and current.
The power supply and cabling must present low impedance to the evaluation board. Insufficient cabling or
a high impedance power supply will droop during power supply application with the evaluation board
inrush current. If large enough, this droop will cause a chattering condition upon power up. This chattering
condition is an interaction with the evaluation board under voltage lockout, the cabling impedance and the
inrush current.
6 Loading
An appropriate electronic load, with specified operation down to 3.0V minimum, is desirable. The
resistance of a maximum load is 0.11. The high output current requires thick cables! If resistor banks are
used there are certain precautions to be taken. The wattage and current ratings must be adequate for a
30A, 100W supply. Monitor both current and voltage at all times. Ensure that there is sufficient cooling
provided for the load.
7 Air Flow
Full power loading should never be attempted without providing the specified 200 LFM of air flow over the
evaluation board. A stand-alone fan should be provided.
8 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 wattage of the load. As soon as the appropriate input voltage is
supplied to the board, check for 3.3 volts at the output.
A most common occurrence, that will prove unnerving, is when the current limit set on the source supply is
insufficient for the load. The result is similar to having the high source impedance referred to earlier. The
interaction of the source supply folding back and the evaluation board going into undervoltage shutdown
will start an oscillation, or chatter, that may have undesirable consequences.
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
SNVA468CFebruary 2011Revised May 2013 AN-2111 LM5045 Evaluation Board
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