Advanced Power
Electronics Corp. APE8970/
Current Limit and Short-Circuit Protection
Thermal Considerations
PCB Layout
5
An input capacitance of ~ 2.2µF is required between the APE8970/A input pin and ground
(the amount of the capacitance may be increased without limit), this capacitor must be located a
distance of not more than 1cm from the input and return to a clean analog ground. Input capacitor
can filter out the input voltage spike caused by the surge current due to the inductive effect of the
package pin and the printed circuit board’s routing wire. Otherwise, the actual voltage at the VIN
pin may exceed the absolute maximum rating. The output capacitor also must be located a
distance of not more than 1cm from output to a clean analog ground. Because it can filter out the
output spike caused by the surge current due to the inductive effect of the package pin and the
printed circuit board’s routing wire.
The APE8970/A series can deliver a current of up to 1.5A over the full operating junction
temperature range. However, the maximum output current must be dated at higher ambient
temperature to ensure the junction temperature does not exceed 125 ° C. With all possible
conditions, the junction temperature must be within the range specified under operating
conditions. Power dissipation can be calculated based on the output current and the voltage drop
across regulator.
PD = (VIN - VOUT) IOUT
The final operating junction temperature for any set of conditions can be estimated by the
following thermal equation:
PD(MAX) = (TJ(MAX) - TA) / RthJA
Where TJ(MAX) is the maximum junction temperature of the die (125 ° C) and TAis the
maximum ambient temperature. The junction to ambient thermal resistance (RthJA) for SOT-223
package at recommended minimum footprint is 75°C/W (please refer Maximum rating table) that
is connected 1 in2 PCB copper area to tap pin.
The APE8970/A used a current sense-resistor to monitor the output current. A portion of the
PMOS output transistor’s current is mirrored to a resistor such that the voltage across this resistor
is proportional to the output current. Once the output current exceeds limit threshold, APE8970/A
would be protected with a limited output current. Further more, when the output is short to ground,
the output current would be folded-back to a less limit.