Datasheet
Output On/Off Inhibit
Vo (2V/Div)
Iin (2A/Div)
Q1Vds (5V/Div)
10 ms/div
PTH05020W
V
IN
1
10
4
5
62
3
C
IN
1,000 µF
+
C
OUT
330 µF
+
1 =Inhibit
GND
V
OUT
9
V
o
Sense
8
Q
1
BSS138
R
SET
7
L
O
A
D
GND
Auto-Track™ Function
PTH05050W
www.ti.com
............................................................................................................................................................ SLTS213E – MAY 2003 – REVISED MARCH 2009
For applications requiring output voltage on/off control, each series of the PTH family incorporates an output
Inhibit control pin. The inhibit feature can be used wherever there is a requirement for the output voltage from the
regulator to be turned off. The power modules function normally when the Inhibit pin is left open-circuit, providing
a regulated output whenever a valid source voltage is connected to V
I
with respect to GND.
Figure 8 shows the typical application of the inhibit function. Note the discrete transistor (Q
1
). The Inhibit control
has its own internal pull-up to V
in
potential. The input is not compatible with TTL logic devices. An open-collector
(or open-drain) discrete transistor is recommended for control.
Figure 8. Figure 9.
Turning Q
1
on applies a low voltage to the Inhibit control and disables the output of the module. If Q
1
is then
turned off, the module will execute a soft-start power-up. A regulated output voltage is produced within 20 msec.
Figure 9 shows the typical rise in both the output voltage and input current, following the turn-off of Q
1
. The turn
off of Q1 corresponds to the rise in the waveform, Q
1
V
ds
. The waveforms were measured with a 5-A load.
The Auto-Track function is unique to the PTH/PTV family, and is available with all POLA products. Auto-Track
was designed to simplify the amount of circuitry required to make the output voltage from each module power up
and power down in sequence. The sequencing of two or more supply voltages during power up is a common
requirement for complex mixed-signal applications that use dual-voltage VLSI ICs such as the TMS320™ DSP
family, microprocessors, and ASICs.
How Auto-Track™ Works
Auto-Track works by forcing the module output voltage to follow a voltage presented at the Track control pin
(1)
.
This control range is limited to between 0 V and the module set-point voltage. Once the track-pin voltage is
raised above the set-point voltage, the module output remains at its set-point
(2)
. As an example, if the Track pin
of a 2.5-V regulator is at 1 V, the regulated output is 1 V. If the voltage at the Track pin rises to 3 V, the regulated
output does not go higher than 2.5 V.
Under Auto-Track control, the regulated output from the module follows the voltage at its Track pin on a
volt-for-volt basis. By connecting the Track pin of a number of these modules together, the output voltages follow
a common signal during power up and power down. The control signal can be an externally generated master
ramp waveform, or the output voltage from another power supply circuit
(3)
. For convenience, the Track input
incorporates an internal RC-charge circuit. This operates off the module input voltage to produce a suitable rising
waveform at power up.
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