Datasheet

Scope Volt-meter Volt-meter Current-meter
80 Volt, 5 Amp
Power Supply
with Current
Meter
200 Watt, 60
Amp Electronic
Load
-
+
+
-
+
Evaluation Board
ON/OFF
(SHUTDOWN)
IN
OUT
Jumper
www.ti.com Powering and Loading Considerations
supply and cabling must present a 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 undervoltage lockout, the cabling impedance and the
inrush current.
4.3 Loading
An appropriate electronic load, with specified operation down to 3.0V minimum, is desirable. The
resistance of a maximum load is 0.11Ω. You need thick cables! Consult a wire chart if needed. 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.
4.4 Air Flow
An appropriate electronic load, with specified operation down to 3.0V minimum, is desirable. The
resistance of a maximum load is 0.11Ω. You need thick cables! Consult a wire chart if needed. 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.
4.5 Powering Up
Using the shutdown pin provided will allow powering up the source supply with the current level set low. It
is suggested that the load be kept quite nominal 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
shutdown 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 undervoltage shutdown
will start an oscillation, or chatter, that may have highly 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.
4.6 Over Current Protection
The evaluation board is configured with hiccup over-current protection. In the event of an output overload
(approximately 33A) the unit will discharge the softstart capacitor, which disables the power stage. After a
delay the soft-start is released. The shutdown, delay and slow recharge time of the softstart capacitor
protects the unit, especially during short circuit event where the stress is highest.
Figure 2. Typical Evaluation Setup
3
SNVA400B–August 2009–Revised May 2013 AN-1976 LM5027 Evaluation Board
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