UNDERVOLTAGE LOCKOUT (UVLO)

R

V

kW

(4)

V

I

Inhibit/

UVLO Prog

GND

PTH04T240F

3

2

R

UVLO

C

I

11

4

+

GND

UDG-08161

V

I

PTH04T240F

The PTH04T240F 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 input source during the power-up sequence.

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 PTH04T240F 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 16). When

pin 11 is left open circuit, the ON threshold voltage is internally set to the 1.95-V default value. 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.

and it may be adjusted to a higher value only.

2.5

3.0

3.5

4.0

4.5

154

71.5

53.6

33.2

26.7

Figure 16. Undervoltage Lockout Adjustment Resistor Placement

Copyright © 2008–2009, Texas Instruments Incorporated

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Product Folder Link(s): PTH04T240F