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UVLO ADJUSTMENT
The UVLO feature of the PTH04040W gives the user the option of adjusting the on-threshold voltage higher than
the default value. This might be desirable if the module is powered from a 5-V input bus. This prevents the
module from operating until the input bus has risen closer to its regulation voltage.
ADJUSTMENT METHOD
Figure 10
shows the placement of the resistor, R
THD
, for adjusting the UVLO on-threshold voltage. It connects
from the
UVLO Prog
control pin to
GND
.
Equation 2
determines the value of R
THD
required to adjust V
THD
to a
new value. The default value is 2.63 V, and it can only be adjusted higher. Once the value of R
THD
has been set,
Equation 3
is used to determine the new hystersis voltage.
THD
R
=
12.9
V 2.63
k
(2)
= 2.191
1
R
+
0.283
V
V
HYS
THD
(3)
P
T
H
0
4
0
4
0
W
2
4
6
1
3
5
V
I
V
I
7
8
UVLOProg
Inhibit
GND
GND
R
THD
C
1,000 F
I
m
FEATURES OF THE PTH FAMILY OF NONISOLATED WIDE OUTPUT ADJUST POWER
MODULES
POLA COMPATIBILITY
Soft-Start Power Up
PTH04040W
SLTS238A–SEPTEMBER 2005–REVISED FEBRUARY 2006
The adjustment method uses the
UVLO Prog
control (pin 8). If the
UVLO Prog
pin is left open circuit, the
onthreshold voltage remains at its nominal value of 2.63 V (see electrical specification table). This ensures that
the unadjusted module produces a regulated output when the minimum input voltage is applied. The hysterisis
voltage is approximately 0.62 V, which correlates to an off-threshold voltage of about 2 V. The magnitude of the
hysterisis is automatically set to about 22% of the onthreshold. So if the on-threshold voltage is increased, then
the hystersis also increases.
Figure 10. UVLO Program Resistor Placement
The PTH/PTV family of nonisolated, wide-output adjustable power modules are optimized for applications that
require a flexible, high performance module that is small in size. Each of these products are POLA compatible.
POLA-compatible products are produced by a number of manufacturers, and offer customers advanced,
nonisolated modules with the same footprint and form factor. POLA parts are also assured to be interoperable,
thereby providing customers with second-source availability.
Many of the POLA-compatible parts include a feature called Auto-Track. Auto-Track was specifically designed
to simplify the task of sequencing the supply voltages in a power system. This and other features are described
the following sections.
The Auto-Track feature allows the power-up of multiple PTH modules to be directly controlled from the
Track
pin.
However in a stand-alone configuration, or when the Auto-Track feature is not being used, the
Track
pin should
be directly connected to the input voltage, V
in
(see
Figure 11
).
13
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