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UNDERVOLTAGE LOCKOUT (UVLO)

Threshold Adjust

R

UVLO

=

70.74-V

THD

V

-4.26

THD

k W

(5)

Calculated Values

Inhibit/

UVLO Prog

GND

PTH08T230W

3

2

10

+

GND

PTH08T230W, PTH08T231W

SLTS265F – NOVEMBER 2005 – REVISED MAY 2007

The PTH08T230/231W 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.

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 PTH08T230/231W module allows for limited adjustment of the ON threshold voltage.

The adjustment is made via the Inhibit/UVLO control pin (pin 10) using a single resistor (see Figure 19). When

pin 10 is left open circuit, the ON threshold voltage is internally set to its default value, which is 4.3 V. The ON

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

threshold prevents the module from operating if the input bus fails to completely rise to its specified regulation

voltage.

it may be adjusted, but only to a higher value.

voltage.

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

10.5

11.0

88.7

52.3

37.4

28.7

23.2

19.6

16.9

14.7

13.0

11.8

10.5

9.76

8.87

Figure 19. UVLO Implementation

22

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