Datasheet

Performance Characteristics

www.ti.com

15 Performance Characteristics

Turn-on Waveforms

When applying power to the LM5027 evaluation board a certain sequence of events occurs. Soft-start

capacitor values and other components allow for a minimal output voltage for a short time until the

feedback loop can stabilize without overshoot. Figure 18 shows the output voltage during a typical start-up

with a 48V input and a load of 5A. There is no overshoot during startup.

Output Ripple Waveforms

Figure 19 shows the transient response for a load of change from 2A to 25A. The lower trace shows

minimal output voltage droop and overshoot during the sudden change in output current shown by the

upper trace.

Figure 20 shows typical output ripple seen directly across the output capacitor, for an input voltage of 48V

and a load of 30A. This waveform is typical of most loads and input voltages.

Figure 21 and Figure 22 show the drain voltage of Q1 with a 25A load. Figure 21 represents an input

voltage of 38V and Figure 22 represents an input voltage of 78V.

Figure 23 shows the gate voltages of the synchronous rectifiers. The drive from the main power

transformer is delayed slightly at turn-on by a resistor interacting with the gate capacitance. This provides

improved switching transitions for optimum efficiency. The difference in drive voltage is inherent in the

topology and varies with line voltage

Conditions: Input Voltage = 48VDC Output Current = 2A to

Conditions: Input Voltage = 48VDC Output Current = 5A

25A Trace1: Output Voltage Volts/div = 0.2V Trace 2: Output

Trace 1: Output Voltage Volts/div = 1.0V Horizontal

Current Amps/Div = 5.0 A Horizontal Resolution = 1 ms/div

Resolution =1 ms/div

Figure 18. Turn-On Waveforms Figure 19. Output Ripple Waveforms

AN-1976 LM5027 Evaluation Board SNVA400B–August 2009–Revised May 2013

Submit Documentation Feedback