Datasheet

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Power-Up Characteristics
t − 10 ms/div
V
I
(1 V/div)
V
O
(1 V/div)
I
I
(1 A/div)
Current Limit Protection
Thermal Shutdown
PTH04070W
SLTS227B – SEPTEMBER 2004 – REVISED OCTOBER 2007
When configured per the standard application, the PTH04070W 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 PTH04070W 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.
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