Datasheet

UNDERVOLTAGE LOCKOUT (UVLO)
UVLO Adjustment
R
UVLO
+
101 * V
THD
V
THD
* 1
kW
(5)
2
3 4
1
Inhibit/
UVLO Prog
GND
GND
V
I
V
I
R
UVLO
C
I
PTH05T210W
PTH05T210W
www.ti.com ...................................................................................................................................................... SLTS263I – AUGUST 2007 – REVISED MARCH 2009
The PTH05T210W power modules incorporate an input undervoltage lockout (UVLO). The UVLO feature
prevents the operation of the module until there is sufficient input voltage to produce a valid output voltage. This
enables the module to provide a clean, monotonic powerup for the load circuit, and also limits the magnitude of
current drawn from the regulator ’ s input source during the power-up sequence.
The UVLO characteristic is defined by the ON threshold (V
THD
) voltage. Below the ON threshold, the Inhibit
control is overridden, and the module does not produce an output. The hysterisis voltage, which is the difference
between the ON and OFF threshold voltages, is nominally set at 150mV. The hysterisis prevents start-up
oscillations, which can occur if the input voltage droops slightly when the module begins drawing current from the
input source.
The UVLO feature of the PTH05T210W module allows for limited adjustment of the ON threshold voltage. The
adjustment is made via the Inhbit/UVLO Prog control pin (pin 1) using a single resistor (see figure below). When
pin 1 is left open circuit, the ON threshold voltage is internally set to its default value. The ON threshold has a
nominal voltage of 4.25 V, and a hysterisis of 150 mV. Adjusting the threshold voltage prevents the module from
operating if the input bus fails to completely rise to its specified regulation voltage.
Equation 5 determines the value of R
THD
required to adjust V
THD
to a new value. The default value is 4.25 V, and
it may only be adjusted to a higher value.
Table 7 lists the standard resistor values for R
UVLO
for different values of the ON-threshold (V
THD
) voltage.
Table 7. Standard Values of R
UVLO
for Various Values of V
THD
V
THD
5.00 V 4.75 V 4.50 V 4.25 V
R
UVLO
24.3 k Ω 25.5 k Ω 27.57 k Ω OPEN
Figure 11. UVLO Program Resistor Placement
Copyright © 2007 – 2009, Texas Instruments Incorporated Submit Documentation Feedback 19
Product Folder Link(s): PTH05T210W