Datasheet

Soft-Start Power Up
UDG−06044
V
I
V
I
Track
GND
PTH04T240W/241W
2
10
3,4
+
GND
C
I
V
O
(1 V/div)
V
I
(2 V/div)
T − Time − 4 ms/div
I
I
(2 A/div)
PTH04T240W , PTH04T241W
SLTS276D – OCTOBER 2006 – REVISED JULY 2009 ...................................................................................................................................................... www.ti.com
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 19 ).
Figure 19. 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 20. Power-Up Waveform
The output then progressively rises to the module ’ s setpoint voltage. Figure 20 shows the soft-start power-up
characteristic of the PTH04T240/241W 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 20 ms.
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