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Demonstration Circuit

Vo (1 V/Div)

1

Vo (1 V/Div)

2

Io (5 A/Div)

2

HORIZ SCALE: 10 ms/Div

Vin (5 V/Div)

Vo (1 V/Div)

HORIZ SCALE 5 ms/Div

Startup

Period

PTH12020W/L

SLTS208E–MAY 2003–REVISED OCTOBER 2005

the pre-bias voltage, which is passed from the VCCIO to the VCORE voltage rail through the ASIC. Note that the

pre-bias.

Figure 20. PTH12020W Startup

Figure 21. Pre-Bias Startup Waveforms

NOTES:

1. Output pre-bias holdoff is an inherent feature to all PTH120x0L and PTV120x0W/L modules. It has now been

incorporated into all modules (including W-suffix modules with part numbers of the form PTH120x0W), with a

production lot date code of 0423 or later.

2. The pre-bias start-up feature is not compatible with Auto-Track. If the rise in the output is limited by the

voltage applied to the Track control pin, the output will sink current during the period that the track control

voltage is below that of the back-feeding source. For this reason, it is recommended that Auto-Track be

disabled when not being used. This is accomplished by connecting the Track pin to the input voltage, Vin.

This raises the Track pin voltage well above the set-point voltage prior to the module’s start up, thereby

defeating the Auto-Track feature.

3. To further ensure that the regulator's output does not sink current when power is first applied (even with a

ground signal applied to the Inhibit control pin), the input voltage must always be greater than the applied

pre-bias source. This condition must exist throughout the power-up sequence of the power system.

21