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Soft-Start Power Up
3.3V
C1
100 Fm
+
C3
100 Fm
+
GND
GND
1.8V
R
SET
5.49k
1%,0.05W
W
C 2
10 Fm
PTV03010W
Track
V
I
V
O
GND
Adjust
GND
L
O
A
D
t-Time=5ms/div
I (5 A/div)
I
V (1V/div)
O
V (2V/div)
I
PTV03010W
SLTS241A – FEBRUARY 2005 – REVISED JULY 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
pin is directly connected to the input voltage, V
I
(see Figure 7 ).
Figure 7. Power-Up Application Circuit
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.
Figure 8. Power-Up Waveform
From the moment a valid input voltage is applied, the soft-start control introduces a short time delay (typically
8 ms to 15 ms) before allowing the output voltage to rise. The output then progressively rises to the module
set-point voltage. Figure 8 shows the soft-start power-up characteristic of the PTV03010W, operating from a
3.3-V input bus and configured for a 1.8-V output. The waveforms were measured with a 5-A resistive 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 25 ms.
10
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