Datasheet

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PTV03010W
SLTS241A – FEBRUARY 2005 – REVISED JULY 2007
The same circuit also provides a power-down sequence. When the input voltage falls below U3's voltage
threshold, the ground signal is reapplied 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 13 . In order for a simultaneous power-down to
occur, the track inputs must be pulled low before the input voltage has fallen below the modules' undervoltage
lockout. This is an important constraint. Once the modules recognize that a valid 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 maximum output capacitance and the
Auto-Track slew rate. If the Track pin is pulled low at a slew rate greater than 1 V/ms, the discharge of the
output capacitors will induce large currents which could exceed the peak current rating of the module. This will
result in a reduction in the maximum allowable output capacitance as listed in the Electrical Characteristics
table. When controlling the Track pin of the PTV03010W using a voltage supervisor IC, the slew rate is
increased, therefore C
O
max is reduced to 2200 μ F.
Notes on Use of Auto-Track™
1. The Auto-Track function tracks almost any voltage ramp during power up, and is compatible with ramp
speeds of up to 1 V/ms.
2. 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.
3. The absolute maximum voltage that may be applied to the Track pin is the input voltage V
I
.
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.
5. The Auto-Track function is disabled by connecting the Track pin to the input voltage (V
I
). When
Auto-Track is disabled, the output voltage rises at a quicker and more linear rate after input power has
been applied.
13
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