NCP631 Datasheet, PDF (7/10 Pages) ON Semiconductor – 3.0 A Linear Voltage Regulator with Soft Start

NCP631
Reverse Current
Some situations might occur were the output pin is raised
to a voltage while the input pin is at zero volts. This situation
will not damage the device.
If the output voltage is raised to a higher voltage than the
input voltage a diode is recommended from output to input
with the anode connect to the output pin.
Thermal Considerations
This series contains an internal thermal limiting circuit
that is designed to protect the regulator in the event that the
maximum junction temperature is exceeded. When
activated, typically at 155°C, the regulator output switches
off and then back on as the die cools. As a result, if the device
is continuously operated in an overheated condition, the
output will appear to be oscillating. This feature provides
protection from a catastrophic device failure due to
accidental overheating. It is not intended to be used as a
substitute for proper heatsinking. The maximum device
power dissipation can be calculated by:
PD
+
TJ(max) *
R_qJA
TA
(eq. 7)
The devices are available in surface mount D²PAK
package. The package has an exposed metal tab that is
specifically designed to reduce the junction to air thermal
resistance, R_qJA, by utilizing the printed circuit board
copper as a heat dissipater. Figure 13 shows typical R_qJA
values that can be obtained from a square pattern using
economical single sided 2.0 ounce copper board material.
The final product thermal limits should be tested and
quantified in order to insure acceptable performance and
reliability. The actual R_qJA can vary considerably from the
graphs shown. This will be due to any changes made in the
copper aspect ratio of the final layout, adjacent heat sources,
and air flow.
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