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Soft-Start Power Up

UDG−06044

Track

GND

PTH04T220W/221W

1

9

2,3

+

GND

T − Time − 4 ms/div

PTH04T220W, PTH04T221W

SLTS275A – DECEMBER 2006 – REVISED FEBRUARY 2007

The Auto-Track feature allows the power-up of multiple PTH/PTV modules to be directly controlled from the

Track pin. However in a stand-alone configuration, or when the Auto-Track feature is not being used, the Track

Figure 21. Defeating the Auto-Track Function

When the Track pin is connected to the input voltage the Auto-Track function is permanently disengaged. This

allows the module to power up entirely under the control of its internal soft-start circuitry. When power up is

under soft-start control, the output voltage rises to the set-point at a quicker and more linear rate.

From the moment a valid input voltage is applied, the soft-start control introduces a short time delay (typically

2 ms–7 ms) before allowing the output voltage to rise.

Figure 22. Power-Up Waveform

The output then progressively rises to the module’s setpoint voltage. Figure 22 shows the soft-start power-up

characteristic of the PTH04T220/221W operating from a 5-V input bus and configured for a 1.8-V output. The

waveforms were measured with a 10-A constant current load and the Auto-Track feature disabled. The initial

rise in input current when the input voltage first starts to rise is the charge current drawn by the input capacitors.

Power-up is complete within 40 ms.

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