Datasheet

UNDERVOLTAGE LOCKOUT (UVLO)
R
UVLO
+
68.54 * V
THD
V
THD
* 2.07
kW
(5)
Inhibit/
UVLO Prog
GND
PTH04T240W/241W
3
2
11
4
+
GND
V
I
C
I
R
UVLO
V
I
UDG−06052
PTH04T240W , PTH04T241W
www.ti.com ...................................................................................................................................................... SLTS276D – OCTOBER 2006 – REVISED JULY 2009
The PTH04T240/241W 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 hysteresis voltage, which is the difference
between the ON and OFF threshold voltages, is set at 500 mV. The hysteresis 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 PTH04T240/241W module allows for limited adjustment of the ON threshold voltage.
The adjustment is made via the Inhbit/UVLO Prog control pin (pin 11) using a single resistor (see Figure 18 ).
When pin 11 is left open circuit, the ON threshold voltage is internally set to its default value, which is 1.95 volts.
The ON threshold might need to be raised if the module is powered from a tightly regulated 5-V bus. Adjusting
the threshold 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
UVLO
required to adjust V
THD
to a new value. The default value is 1.95 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 R
UVLO
values for Various V
THD
values
V
THD
(V) 2.5 3.0 3.5 4.0 4.5
R
UVLO
(k Ω ) 154 71.5 53.6 33.2 26.7
Figure 18. Undervoltage Lockout Adjustment Resistor Placement
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