LM5035EVAL National Semiconductor, LM5035EVAL Datasheet - Page 2

• Manufacturer Part Number: LM5035EVAL
• Description: BOARD EVALUATION LM5035
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5035EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Isolated
• Voltage - Output: 3.3V
• Current - Output: 30A
• Voltage - Input: 36 ~ 75V
• Regulator Topology: Buck
• Frequency - Switching: 400kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5035
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -

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Theory of Operation
Powering and Loading
Considerations
When applying power to the LM5035 evaluation board cer-
tain precautions need to be followed. A misconnection can
damage the assembly.
Proper Connections
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 evalu-
ation board. Monitor the voltage directly at the output termi-
nals of the evaluation board. The voltage drop across the
load connecting wires will cause inaccurate measurements.
This is especially true for accurate efficiency measurements.
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 (75V) the input
current will be approximately 1.5A. Therefore, to fully test the
LM5035 evaluation board a DC power supply capable of at
least 85V and 5A 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 cause voltage droop dur-
ing turn-on due to the evaluation board inrush current. If
large enough, this droop will cause a chattering condition
(Continued)
Simplified Half Bridge Converter
2
upon power up. This chattering condition is an interaction
with the evaluation board undervoltage lockout, the cabling
impedance and the inrush current.
Loading
An appropriate electronic load, with specified operation
down to 1.0V minimum, is desirable. The resistance of a
maximum load is 0.11Ω. 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 there is sufficient
cooling provided for the load.
Air Flow
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.
Powering Up
Using the ON/OFF pin (J2) provided will allow powering up
the source supply with the current level set low. It is sug-
gested 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 (J1), 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
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