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Typical Auto-Track™ Application

Notes on Use of Auto-Track™

PTH08T260W, PTH08T261W

SLTS272A – DECEMBER 2006 – REVISED MAY 2007

The basic implementation of Auto-Track allows for simultaneous voltage sequencing of a number of Auto-Track

compliant modules. Connecting the Track inputs of two or more modules forces their track input to follow the

same collective RC-ramp waveform, and allows their power-up sequence to be coordinated from a common

Track control signal. This can be an open-collector (or open-drain) device, such as a power-up reset voltage

supervisor IC. See U3 in Figure 24.

To coordinate a power-up sequence, the Track control must first be pulled to ground potential. This should be

done at or before input power is applied to the modules. The ground signal should be maintained for at least

20 ms after input power has been applied. This brief period gives the modules time to complete their internal

that includes a built-in time delay, is an ideal component for automatically controlling the Track inputs at power

up.

Figure 24 shows how the TL7712A supply voltage supervisor IC (U3) can be used to coordinate the sequenced

power up of PTH08T260/261W modules. The output of the TL7712A supervisor becomes active above an input

voltage of 3.6 V, enabling it to assert a ground signal to the common track control well before the input voltage

has reached the module's undervoltage lockout threshold. The ground signal is maintained until approximately

28 ms after the input voltage has risen above U3's voltage threshold, which is 10.95 V. The 28-ms time period is

controlled by the capacitor C3. The value of 2.2 µF provides sufficient time delay for the modules to complete

their internal soft-start initialization. The output voltage of each module remains at zero until the track control

voltage is allowed to rise. When U3 removes the ground signal, the track control voltage automatically rises.

This causes the output voltage of each module to rise simultaneously with the other modules, until each reaches

its respective set-point voltage.

The same circuit also provides a power-down sequence. When the input voltage falls below U3's voltage

threshold, the ground signal is re-applied to the common track control. This pulls the track inputs to zero volts,

forcing the output of each module to follow, as shown in Figure 26. Power down is normally complete before the

input voltage has fallen below the modules' undervoltage lockout. This is an important constraint. Once the

modules recognize that an input voltage is no longer present, their outputs can no longer follow the voltage

applied at their track input. During a power-down sequence, the fall in the output voltage from the modules is

limited by the Auto-Track slew rate capability.

1. The Track pin voltage must be allowed to rise above the module set-point voltage before the module

regulates at its adjusted set-point voltage.

2. The Auto-Track function tracks almost any voltage ramp during power up, and is compatible with ramp

speeds of up to 1 V/ms.

4. The module cannot follow a voltage at its track control input until it has completed its soft-start

initialization. This takes about 20 ms from the time that a valid voltage has been applied to its input.

During this period, it is recommended that the Track pin be held at ground potential.

Auto-Track is disabled, the output voltage rises at a quicker and more linear rate after input power has

been applied.

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