pth12050 Astec Powe, pth12050 Datasheet - Page 8

• Manufacturer Part Number: pth12050
• Description: Pth05020 5vin Single
• Manufacturer: Astec Powe

7.3 Pre-Bias Startup Capability
Only selected products in the PTH family incorporate this capability.
Consult Table 1 to identify which product series are compliant.
In complex digital systems an external voltage can sometimes be
present at the output of the module during power up. This voltage
may be backfed through a dual supply logic component, such as an
FPGA or ASIC. Another path might be via a clamp diode (to a lower
supply voltage) as part of a power-up sequencing implementation.
Although the PTH family of modules can sink current under steady-
state operating conditions, those that incorporate this capability will
not do so during the soft-start cycle
held low. However, to ensure the satisfactory operation of this feature
certain conditions must be maintained during the application of input
power
Note
The pre-bias start-up feature is not compatible with Auto-Track
This is because when the module is under Auto-Track
fully active and will sink current if the output voltage is below that of
a back-feeding source. Therefore to ensure a pre-bias hold-off, one
of the following two techniques must be followed when input power
is first applied to the module. The Auto-Track
be disabled
The latter allows Auto-Track’s internal RC charge ramp to rise above
the setpoint voltage.
C
1000µF
1 = Inhibit
in
Figure 10 - Typical Rise in Output Voltage and Input Current
V
8 8
GND
in
2 .
Figure 9 - Typical Application of the Inhibit Function
+
Q1
BSS138
3
, or the module’s output held off using the Inhibit pin.
2
10
3
9
1
PTH05020W
7
File Name: an_pth05020.pdf Rev (05): 21 Dec 2005
8
1
, or whenever the Inhibit pin is
R
set
4
5
™
6
V
o
function must either
Sense
+
™
C
330µF
control, it is
out
GND
V
out
™
L
O
A
D
.
Notes:
1 The soft-start cycle is a relatively short period (up to 20ms) that
2 To ensure that the regulator does not sink current when power is
3 The Auto-Track
7.4 Margin Up/Down Controls
The PTHxx060W, PTHxx010W, PTHxx020W, and PTHxx030W
module series incorporate Margin Up and Margin Down control
inputs. These controls allow the output voltage set point to be
momentarily adjusted
provides a convenient method for dynamically testing the operation
of the load circuit over its power supply margin or range. The ±5%
change is applied to the adjusted output voltage as set by the
external resistor, R set at the V o Adjust pin.
The 5% adjustment is made by driving the appropriate margin
control input directly to the GND terminal
device, such as a MOSFET or p-channel JFET is recommended for
this purpose. Adjustments of less than 5% can also be
accommodated by adding series resistors to the control inputs (See
Figure 11). The value of the resistor can be selected from Table 6 or
calculated using the following formula.
7.4.1 Up/Down Adjust Resistance Calculation
To reduce the margin adjustment to something less than 5%, series
resistors are required (See R
amount of adjustment, the resistor value calculated for R
will be the same. The formulas is as follows.
Where ∆% = The desired amount of margin adjust in percent.
Notes
1 The Margin Up and Margin Down controls were not intended to
2 The ground reference should be a direct connection to the
immediately follows either the application of a valid input source
voltage, or the release of a ground signal at the Inhibit pin
first applied (even with a ground signal applied to the Inhibit
control pin), the input voltage must always be greater than the
output voltage through-out the power-up and power-down
sequence.
immediately applying a voltage to the module’s Track pin that is
greater than its set-point voltage. This can be easily
accomplished by pulling the Track pin up to V
resistor.
be activated simultaneously. If they are their affects on the output
voltage may not completely cancel, resulting in the possibility of a
slightly higher error in the output voltage set point.
module GND at pin 7 (pin 1 for the PTHxx050). This will produce
a more accurate adjustment at the load circuit terminals. The
transistors Q1 and Q2 should be located close to the regulator.
Table 6 - Margin Up/Down Resistor Values
PTH05020 Single Series | Application Note 156
™
% ADJUST
function can be disabled at power up by
1
, either up or down, by a nominal 5%. This
5
4
3
2
1
D
and R
U
150.0kΩ
397.0kΩ
24.9kΩ
66.5kΩ
in Figure 11). For the same
R
0.0kΩ
U
/R
2
. A low-leakage open-drain
D
in
through a 1kΩ
D
and R
U