Texas Instruments Evaluation Board for the LM5039 LM5039EVAL/NOPB LM5039EVAL/NOPB 데이터 시트

The secondary side employs synchronous rectification
scheme, which is controlled by the LM5039, during the soft-
start, the sync FET body diodes act as the secondary recti-
fiers. Once, the soft-start is finished, the synchronous
rectifiers are engaged with a non-overlap time programmed
by the DLY resistor. Feedback from the output is processed
by an amplifier and reference, generating an error voltage,
which is coupled back to the primary side control through an
opto-coupler. The LM5039 controller pulse width modulates
the error signal with a ramp signal derived from the line volt-
age (feed-forward) to reduce the response time. A standard
“type III” network is used for the compensator.

When applying power to the LM5039 evaluation board, cer-
tain precautions need to be followed. A misconnection can
damage the assembly.

When operated at low input voltages the evaluation board can
draw up to 3.5A of current at full load. The maximum rated
output current is 30A. 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 evaluation board. Mon-
itor the voltage directly at the output terminals of the evalua-
tion board. The voltage drop across the load connecting wires
will give inaccurate measurements. This is especially true for
accurate efficiency measurements.

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
LM5039 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 ap-

plication 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.

An appropriate electronic load, with specified operation down
to 3.0V minimum, is desirable. The resistance of a maximum
load is 0.11

Ω. 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.

Full power loading should never be attempted without pro-
viding the specified 200 CFM of air flow over the evaluation
board. A stand-alone fan should be provided.

Using the ON/OFF 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 wattage of the load. As you remove the connection from
the ON/OFF pin to ground, immediately 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 un-
dervoltage shutdown will start an oscillation, or chatter, that
may have undesirable consequences.
A quick efficiency check is the best way to confirm that ev-
erything 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.

30112702

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