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Power-Up Characteristics

t − 10 ms/div

Current Limit Protection

Thermal Shutdown

Output On/Off Inhibit

PTH04070W

SLTS227 – SEPTEMBER 2004

When configured per the standard application, the PTH04070 power module produces a regulated output voltage

following the application of a valid input source voltage. During power up, internal soft-start circuitry slows the

rate that the output voltage rises, thereby limiting the amount of in-rush current that can be drawn from the input

source. The soft-start circuitry introduces a short time delay (typically 10 ms) into the power-up characteristic.

This is from the point that a valid input source is recognized. Figure 10 shows the power-up waveforms for a

PTH04070W, operating from a 3-V input and with the output voltage adjusted to 1.8 V. The waveforms were

measured with a 2-A resistive load.

Figure 10. Power-Up Waveforms

The PTH04070 modules protect against load faults with a continuous current limit characteristic. Under a load

fault condition, the output current cannot exceed the current limit value. Attempting to draw current that exceeds

the current limit value causes the output voltage to be progressively reduced. Current is continuously supplied to

the fault until it is removed. Upon removal of the fault, the output voltage will promptly recover.

Thermal shutdown protects the module internal circuitry against excessively high temperatures. A rise in

temperature may be the result of a drop in airflow, a high ambient temperature, or a sustained current limit

condition. If the junction temperature of the internal components exceeds 150

°C, the module shuts down. This

reduces the output voltage to zero. The module will start up automatically, by initiating a soft-start power up when

the sensed temperature decreases 10

°C below the thermal shutdown trip point.

For applications requiring output voltage on/off control, the PTH04070 power module incorporates an output

on/off Inhibit control (pin 5). The inhibit feature can be used wherever there is a requirement for the output

voltage from the regulator to be turned off.

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

whenever a valid source voltage is connected to Vin with respect to GND.

Figure 11 shows the typical application of the inhibit function. Note the discrete transistor (Q1). The Inhibit control

input.

11