Datasheet

t − Time − 10 ms/div
I
I
(5 A/div)
V
I
(2 V/div)
V
O
(500 mV/div)
Track
V
I
GND
PTH08T250W
6
20
7
8 9 12 13
GNDGNDGND
C
I
+
UDG-07102
14
15
V
I
V
I
V
I
GND
V
I
PTH08T250W
www.ti.com SLTS278G –NOVEMBER 2010–REVISED MARCH 2009
Soft-Start Power Up
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 17).
Figure 17. Defeating the Auto-Track Function Figure 18. Power-Up Waveform
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
10 ms–15 ms) before allowing the output voltage to rise.
The output then progressively rises to the module’s setpoint voltage. Figure 18 shows the soft-start power-up
characteristic of the PTH08T250W operating from a 5-V input bus and configured for a 1.2-V output. The
waveforms were measured with a 25-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 30 ms.
Differential Output Voltage Remote Sense
Differential remote sense improves the load regulation performance of the module by allowing it to compensate
for any IR voltage drop between its output and the load in either the positive or return path. An IR drop is caused
by the output current flowing through the small amount of pin and trace resistance. With the sense pins
connected, the difference between the voltage measured directly between the V
O
and GND pins, and that
measured at the Sense pins, is the amount of IR drop being compensated by the regulator. This should be
limited to a maximum of 0.3 V.
If the remote sense feature is not used at the load, connect +Sense (pin 17) to V
O
(pin 11) and connect –Sense
(pin 16) to the module GND (pin 13).
The remote sense feature is not designed to compensate for the forward drop of nonlinear or frequency
dependent components that may be placed in series with the converter output. Examples include OR-ing
diodes, filter inductors, ferrite beads, and fuses. When these components are enclosed by the remote sense
connection they are effectively placed inside the regulation control loop, which can adversely affect the
stability of the regulator.
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