pth12050 Astec Powe, pth12050 Datasheet - Page 11

• Manufacturer Part Number: pth12050
• Description: Pth05020 5vin 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.
As the regulated output from the module simply follows the voltage
at the Track pin, it is able to ‘track’ virtually any voltage source
during the power-up sequence
externally generated master ramp waveform, or the output voltage
from another power supply circuit
is also provided with an internal RC charge circuit that can produce a
compatible voltage ramp from the input source voltage.
10.3 Typical Application
The simplest implementation of Auto-Track™ is to connect the Track
control pins of two or more compliant PTH modules together. This
forces the Track pins of the modules to follow the same collective
internal RC ramp waveform, and also allows them to be controlled
through a single transistor or switch.
To initiate a power-up sequence, it is recommended that the Track
control be first pulled to ground potential. This should be done at or
before input power is applied to the modules, and then held for at
least 20ms
complete their internal soft-start initialization. Applying a logic level
high signal to the circuit’s ON/0FF Control turns Q1 on and applies a
ground signal to the Track pins. After completing their internal soft-
start intialization, the output of all modules will remain at zero volts
while Q1 is on.
20ms after a valid input voltage has been applied to the modules, Q1
may 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 15 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, V
from the two power modules, U1 (3.3V) and U2 (2.0V) respectively.
V
simultaneous power-up characteristic.
o
1 and V
o
4
2 are shown rising together to produce the desired
thereafter. This brief period gives the modules time to
o
1 and V
1
2
. As an example, if the Track pin of a
File Name: an_pth05020.pdf Rev (05): 21 Dec 2005
. This can be the rising voltage of an
3
. For convenience, each Track pin
o
2 represent the output voltages
Application Note 156
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 5V/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 0.047µF correlate to
a decay rate of about 0.6V/ms.
The power-down sequence is initiated with a low-to-high transition at
the On/Off Control input to the circuit. Figure 15 shows the power-up
and 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 of the Use Auto-Track™
1.
2.
3.
4.
5.
On/Off Control
1 = Power Down
0 = Power Up
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+5V
0V
The Track pin voltage must be allowed to rise above the
module’s set-point voltage before the module can regulate at
its adjusted set-point voltage.
The Auto-Track™ function will track almost any voltage ramp
during power up, and is compatible with ramp speeds of up to
5V/ms.
The absolute maximum voltage that may be applied to the
Track pin is V
The module output will not follow the voltage at the Track pin
until the module has completed its soft-start cycle. The soft-
start-cycle takes up to about 20 ms to complete. During this
time it is recommended that the Track pin be held at ground
potential.
After the soft-start sequence is complete, the module is
capable of both sinking and sourcing current when following
the voltage at the Track pin.
Figure 15 - Sequenced Power Up and Power Down
R1
100k
0.047µF
Q
BSS138
1
C
1
in
.
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
4k12
698
R2
R
3
V
V
5
4
5
4
o
o
6
C
6
C
out
out
+
+
V
o1
V
o2
= 3.3V
= 2V
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