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Soft-Start Power Up

t − Time − 10ms/div

V (5V/div)

I

14

Track

GND

GND

2, 6

3,4

7,8

PTH08T210W

Remote Sense

PTH08T210W

SLTS262D – OCTOBER 2005 – REVISED OCTOBER 2006

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

Figure 20. Power-Up Application Circuit

Figure 21. 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 8 ms–15

ms) before allowing the output voltage to rise. The output then progressively rises to the module’s setpoint

voltage.

Figure 21 shows the soft-start power-up characteristic of the PTH08T210W operating from a 12-V input bus and

configured for a 3.3-V output. The waveforms were measured with a 20-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 25 ms.

Products with this feature incorporate one or two remote sense pins. Remote sensing improves the load

regulation performance of the module by allowing it to compensate for any IR voltage drop between its output

and the load. An IR drop is caused by the high output current flowing through the small amount of pin and trace

resistance.

To use this feature simply connect the Sense pins to the corresponding output voltage node, close to the load

circuit. If a sense pin is left open-circuit, an internal low-value resistor (15-

Ω or less) connected between the pin

and the output node, ensures the output remains in regulation.

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.

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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