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ADJUSTING THE UNDERVOLTAGE LOCKOUT (UVLO) OF THE PTV08040W POWER MODULES

UVLO Adjustment

Adjustment Method

PTV08040W

6,7

13,14

20,21

4

5

11

16 Inhibit/

UVLOProg

GND

GND

PTV08040W

SLTS257A – SEPTEMBER 2005 – REVISED JANUARY 2007

The PTV08040W 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.

threshold, the Inhibit control is overridden, and the module does not produce an output. The hysterisis voltage is

the difference between the ON and OFF threshold voltages. It ensures a clean power-up, even when the input

voltage is rising slowly. 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 PTV08040W module allows for limited adjustment of both the on threshold and

hysterisis voltages. The adjustment is made via the UVLO Prog control pin. When the UVLO Prog pin is left

open circuit, the ON threshold and hysterisis voltages are internally set to their default values. The ON threshold

has a nominal voltage of 7.5 V, and the hysterisis 1 V. This ensures that the module produces a regulated

output when the minimum input voltage is applied (see specifications). The combination correlates to an OFF

threshold of approximately 6.5 V. The adjustments are limited. The ON threshold can only be adjusted higher,

and the hysterisis voltage can only be reduced in magnitude.

The ON threshold might need to be raised if the module is powered from a tightly regulated 12-V bus. This

prevents it from operating if the input bus fails to completely rise to its specified regulation voltage. The hysterisis

should not be changed unless absolutely necessary. The hysterisis ensures that the module exhibits a clean

startup. Therefore, adjustment of the hysterisis should only be considered if there is a system requirement to

specifically set the off threshold voltage (in addition to the on threshold). Depending on the load regulation of the

input source, the hysterisis should not be adjusted below 0.5 V without careful consideration.

The recommended adjustment method requires that any change to the hysterisis be determined first. If the

Figure 10. UVLO Program Resistor Placement

12

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