Datasheet

Soft-Start Power Up
UDG−06044
V
I
V
I
Track
GND
2
9
3
+
GND
C
I
PTH04T260/261W
V
I
(2 V/div)
V
O
(1 V/div)
I
I
(1 A/div)
T − Time − 4 ms/div
Remote Sense
PTH04T260W , PTH04T261W
www.ti.com .................................................................................................................................................. SLTS273E – SEPTEMBER 2006 – REVISED JULY 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 19 ).
Figure 19. Defeating the Auto-Track Function Figure 20. 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 2ms – 10ms)
before allowing the output voltage to rise. The output then progressively rises to the module ’ s setpoint voltage.
Figure 20 shows the soft-start power-up characteristic of the PTH04T260/261W operating from a 5-V input bus
and configured for a 1.8-V output. The waveforms were measured with a 3-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.
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. Connecting the +Sense (pin
5) and – Sense (pin 6) pins to the respective positive and ground reference of the load terminals improves the
load regulation of the output voltage at the connection points.
With the sense pins connected at the load, 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 300mV.
If the remote sense feature is not used at the load, connect the +Sense pin to V
O
(pin4) and connect the – Sense
pin to the module GND (pin 3).
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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Product Folder Link(s): PTH04T260W PTH04T261W