LM5001ISOEVAL National Semiconductor, LM5001ISOEVAL Datasheet - Page 2

• Manufacturer Part Number: LM5001ISOEVAL
• Description: BOARD EVALUATION LM5001ISO
• Manufacturer: National Semiconductor

Specifications of LM5001ISOEVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Isolated
• Voltage - Output: 5V
• Current - Output: 1A
• Voltage - Input: 16 ~ 42V
• Regulator Topology: Flyback
• Frequency - Switching: 250kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5001
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

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Powering and Loading
Considerations
Read this entire page prior to attempting to power the evalu-
ation board.
QUICK SETUP PROCEDURE
Step 1: Set the input source current limit to 1A. Turn off the
input source. Connect the positive output of the input source
to J1 and the negative output to J2.
Step 2: Connect the load, with 1A capability, to J3 for the
positive connection and J4 for the negative connection.
Step 3: The ENABLE pin, J7, should be left open for normal
operation.
Step 4: Set the input source voltage to 28V and the load to
0.1A. The load voltage should be in regulation with a nominal
5V output.
Step 5: Slowly increase the load while monitoring the load
voltage at J3 and J4. It should remain in regulation with a
nominal 5V output as the load is increased up to 1 Amp.
Step 6: Slowly sweep the input source voltage from 16V to
42V. The load voltage should remain in regulation with a
nominal 5V output.
Step 7: Temporally short the ENABLE pin (J7) to GND (J5)
to check the shutdown function.
Step 8: Increase the load beyond the normal range to check
current limiting while the input source is set to 28V. The output
current should limit at approximately 1.9A. The input source
current limit should be increased for this step. Fan cooling is
critical during this step.
AIR FLOW
Prolonged operation at full power and high ambient temper-
ature will cause the thermal shutdown circuit within the regu-
lator IC to activate. A fan with a minimum of 200 LFM should
always be provided.
2
POWERING UP
Using the ENABLE pin (J7) provided will allow powering up
the input source with the current level set low. It is suggested
that the load power be kept low during the first power up. Set
the current limit of the input source to provide about 1.5 times
the anticipated wattage of the load. As you remove the con-
nection from the ENABLE pin to GND (J5), immediately check
for 5 volts at the output.
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.
OVER CURRENT PROTECTION
The evaluation board is configured with cycle-by-cycle over-
current protection. This function is completely contained in the
LM5001. The Primary current is limited to approximately 1A.
This equates to about 1.4A load current when the input volt-
age is 16V, and about 2.1A load current when the input is 42V.
The thermal stress on various circuit components is quite se-
vere while in an overloaded condition, therefore limit the
duration of the overload and provide sufficient cooling (air-
flow).
SYNCHRONIZATION
A SYNC pin (J6) has been provided on the evaluation board.
This pin can be used to synchronize the regulator to an ex-
ternal clock or multiple evaluation boards can be synchro-
nized together by connecting their SYNC pins together. Refer
to the LM5001 datasheet for complete information.
FLYBACK TOPOLOGY
An excellent introduction to the isolated flyback converter is
available on the National Semiconductor website. The Appli-
cation Note AN-1095 discusses both loop compensation with
a secondary side error amplifier and the phase-shift caused
by opto-couplers.