Datasheet

Soft-Start Power Up
10
Track
GND
GND
3,4
V
I
V
I
C
I
2
PTH08T240W/241W
t − Time − 4ms/div
V
O
(2V/div)
V (5V/div)
I
I
I
(2 A/div)
PTH08T240W , PTH08T241W
www.ti.com ................................................................................................................................................... SLTS264J – NOVEMBER 2005 – REVISED JUNE 2009
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
pin should be directly connected to the input voltage, V
I
(see Figure 21 ).
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 – 10 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 PTH08T240/241W operating from a 12-V input bus and configured for a 3.3-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 15 ms.
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