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Output On/Off Inhibit

1 Inhibit/

UVLO

GND

2, 6

GND

3,4

7,8

1 = Inhibit

Q1

BSS 138

PTH05T210W

t − Time − 200

µs/div

Overcurrent Protection

PTH05T210W

SLTS263D – NOVEMBER 2005 – REVISED OCTOBER 2006

For applications requiring output voltage on/off control, the PTH05T210W incorporates an output Inhibit control

pin. The inhibit feature can be used wherever there is a requirement for the output voltage from the regulator to

be turned off.

The power modules function normally when the Inhibit pin is left open-circuit, providing a regulated output

Figure 14 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit input

has its own internal pull-up to a potential of 5 V. The input is not compatible with TTL logic devices and should

Figure 14. On/Off Inhibit Control Circuit

Figure 15. Power-Up Response from Inhibit Control

Turning Q1 on applies a low voltage to the Inhibit control pin and disables the output of the module. If Q1 is then

turned off, the module executes a soft-start power-up sequence. A regulated output voltage is produced within

25 ms. Figure 15 shows the typical rise in both the output voltage and input current, following the turn-off of Q1.

resistive load.

For protection against load faults, all modules incorporate output overcurrent protection. Applying a load that

exceeds the regulator's overcurrent threshold causes the regulated output to shut down. Following shutdown, a

module periodically attempts to recover by initiating a soft-start power-up. This is described as a hiccup mode of

operation, whereby the module continues in a cycle of successive shutdown and power up until the load fault is

removed. During this period, the average current flowing into the fault is significantly reduced. Once the fault is

removed, the module automatically recovers and returns to normal operation.

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