Datasheet

Scope Volt-meter Volt-meter Current-meter

75 Volt, 1 Amp

Power Supply

Electronic Load

Evaluation Board

ON/OFF

(SHUTDOWN)

OUT

Jumper or single-pole switch

Current

Meter

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Powering Up

7 Powering Up

Using the shutdown feature provided on the UUT will allow powering up the source supply initially with a

low current level. It is suggested that the load be kept reasonably low during the first power up. Set the

current limit of the source supply to provide about 1½ 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. If more than a

couple of seconds pass without seeing an output voltage, remove input power.

A quick efficiency check is the best way to confirm that the UUT 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 additional losses and potentially damaging heat. An

efficiency above 80% is expected.

After the unit is verified operationally, it can be powered up without use of the shutdown pin.

8 Typical Evaluation Setup

Figure 2. Typical Evaluation Setup

9 Performance Characteristics

9.1 Turn-on Waveforms

When applying power to the LM5020 evaluation board a certain sequence of events must occur. The soft-

start feature allows for a minimal output voltage for a short time until the feedback loop can stabilize

without overshoot. Figure 3, Figure 4, and Figure 5 show typical turn-on waveforms at no load, 5% load,

and at full load. Input voltage, output voltage and output current are shown.

Figure 6 shows the initial ramp-up of the Vcc pin to 7.7 volts through the internal regulator. The auxiliary

winding starts to supply a higher voltage as the output voltage rises. The resulting second ramp is shown

following the soft-start delay. This sequence is nearly identical for all loads and input voltages.

Trace 1: Input Voltage, at 30VDC. Volts/div = 20.0V Trace 2: Trace 1: Input Voltage, at 30VDC. Volts/div = 20.0V Trace 2:

Output Voltage, no load. Volts/div = 2.0V Trace 3: Output Output Voltage, at 5% load. Volts/div = 2.0V Trace 3: Output

Current, no load. Amps/div = 100mA Horizontal Resolution = Current, at 5% load. Amps/div = 100mA Horizontal

1.0ms/div Resolution = 1.0ms/div

Figure 3. Typical Turn-on Waveforms at No Load Figure 4. Typical Turn-on Waveforms at 5% Load

SNVA082B–March 2004–Revised May 2013 AN-1314 LM5020 Evaluation Board

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