pth12040 Astec Powe, pth12040 Datasheet - Page 13

• Manufacturer Part Number: pth12040
• Description: Pth12040 12vin Single
• Manufacturer: Astec Powe

10. Auto-Track™
10.1 Auto-Track™ Function
The Auto-Track™ function is unique to the PTH family, and is
available with the all “Point-of-Load Alliance” (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 DSPs, micro-
processors, and ASICs.
10.2 How Auto-Track™ Works
Auto-Track™ works by forcing the module’s output voltage to follow
a voltage presented at the Track control pin. This control range is
limited to between 0V and the module’s set-point voltage. Once the
track-pin voltage is raised above the set-point voltage, the module’s
output remains at its set-point
2.5V regulator is at 1V, the regulated output will be 1V. But if the
voltage at the Track pin rises to 3V, the regulated output will not go
higher than 2.5V.
When under 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 will 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
internal RC charge circuit. This operates off the module’s input
voltage to provide a suitable rising voltage ramp waveform.
10.3 Typical Applications
The basic implementation of Auto-Track allows for simultaneous
voltage sequencing of a number of Auto- Track compliant modules.
Connecting the Track control pins of two or more modules forces the
Track control of all modules to follow the same collective RC ramp
waveform, and allows them to be controlled through a single
transistor or switch; Q1 in Figure 15.
To initiate a power-up sequence the Track control pin must first be
pulled to ground potential. This should be done at or before input
power is applied to the modules, and then held for at least 10ms
thereafter. This brief period gives the modules time to complete their
internal soft-start initialization, which enables them to produce an
output voltage.
Applying a logic-level high signal to the circuit’s On/Off Control turns
Q1 on and applies a ground signal to the Track control. After
completing their internal soft-start initialization, the output of all
modules will remain at zero volts while Q1 is on. 10ms after a valid
input voltage has been applied to all modules, Q1 can be turned off.
This allows the track control voltage to automatically rise toward to
the modules' input voltage. During this period the output voltage of
each module will rise in unison with other modules, to its respective
set-point voltage.
Figure 16 shows the output voltage waveforms from the circuit of
Figure 15 after the On/Off Control is set from a high to a low-level
voltage. The waveforms, Vo1 and Vo2 represent the output voltages
from the two power modules, U1 (3.3V) and U2 (2V) respectively. Vo1
and Vo2 are shown rising together to produce the desired
simultaneous power-up characteristic.
(3)
. For convenience the Track control incorporates an
(1)
File Name: an_pth12040.pdf Rev (02): 21 Dec 2005
. As an example, if the Track pin of a
The same circuit also provides a power-down sequence. Power-
down is the reverse of power-up, and is accomplished by lowering
the track control voltage back to zero volts. The important constraint
is that a valid input voltage must be maintained until the power-down
is complete. It also requires that Q1 be turned off relatively slowly.
This is so that the Track control voltage does not fall faster than
Auto-Track's slew rate capability, which is 1V/ms. The components
R1 and C1 in Figure 15 limit the rate at which Q1 can pull down the
Track control voltage. The values of 100kΩ and 0.1µF correlate to a
decay rate of about 0.17V/ms.
The power-down sequence is initiated with a low-to-high transition at
the On/Off Control input to the circuit. Figure 17 shows the power-
down waveforms. As the Track control voltage falls below the
nominal set-point voltage of each power module, then its output
voltage decays with all the other modules under Auto-Track™
control.
Notes on the Use of Auto-Track™
1 The Track pin voltage must be allowed to rise above the module’s
2 The Auto-Track™ function will track almost any voltage ramp
3 The absolute maximum voltage that may be applied to the Track
4 The module will not follow a voltage at its Track control input until
5 The module is capable of both sinking and sourcing current when
6 The Auto-Track function can be disabled by connecting the Track
Application Note 193
set-point voltage before the module can regulate at its adjusted
set-point voltage.
during power-up, and is compatible with ramp speeds of up to
1V/ms.
pin is V
it has completed its soft-start initialization. This takes about 10
ms from the time that the module has sensed that a valid voltage
has been applied its input. During this period, it is recommended
that the Track pin be held at ground potential.
following a voltage at its Track pin. Therefore startup into an
output prebias is not supported during Auto-Track control.
Note: A pre-bias holdoff is not necessary when all supply voltages
rise simultaneously under the control of Auto-Track.
pin to the input voltage (Vin). With Auto-Track disabled,the output
voltage will rise at a quicker and more linear rate after input
power is applied.
On/Off Control
1 = Power Down
0 = Power Up
+12V
www.artesyn.com
0V
Figure 15 - Sequenced Power-up and Power-down
R1
100k
in
.
0.1µF
Q
BSS138
1
C
1
Using Auto-Track™
C
C
in
in
+
+
U1
U2
2
2
V
Inhibit
V
Inhibit
in
in
10
10
3
3
9
1
9
1
GND
GND
PTH05020W
PTH05010W
Track
Track
8
8
7
7
8k06
2kΩ
R2
R
3
V
V
5
4
5
4
o
o
6
6
C
C
o
o
+
+
V
o1
V
o2
= 3.3V
= 2V
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