LTM8025

15

8025f

APPLICATIONS INFORMATION

Thermal Considerations

The LTM8025 output current may need to be derated if it is

required to operate in a high ambient temperature or deliver

a large amount of continuous power. The amount of current

derating is dependent upon the input voltage, output power

and ambient temperature. The temperature rise curves

given in the Typical Performance Characteristics section

can be used as a guide. These curves were generated by a

board. Boards of other sizes and layer count can exhibit

different thermal behavior, so it is incumbent upon the user

to verify proper operation over the intended system’s line,

load and environmental operating conditions.

The junction to air and junction to board thermal resis-

tances given in the Pin Configuration diagram may also

be used to estimate the LTM8025 internal temperature.

These thermal coefficients are determined for maximum

output power per JESD 51-9 “JEDEC Standard, Test Boards

for Area Array Surface Mount Package Thermal Measure-

ments” through analysis and physical correlation. Bear in

mind that the actual thermal resistance of the LTM8025

to the printed circuit board depends upon the design of

the circuit board.

The die temperature of the LTM8025 must be lower than

the maximum rating of 125°C, so care should be taken in

the layout of the circuit to ensure good heat sinking of the

LTM8025. The bulk of the heat flow out of the LTM8025

is through the bottom of the module and the LGA pads

into the printed circuit board. Consequently a poor printed

circuit board design can cause excessive heating, result-

ing in impaired performance or reliability. Please refer to

the PCB Layout section for printed circuit board design

suggestions.

The LTM8025 is equipped with a thermal shutdown that

will inhibit power switching at high junction temperatures.

The activation threshold of this function, however, is above

125°C to avoid interfering with normal operation. Thus,

it follows that prolonged or repetitive operation under a

condition in which the thermal shutdown activates neces-

sarily means that the internal components are subjected

to temperatures above the 125°C rating for prolonged

or repetitive intervals, which may damage or impair the

reliability of the device.

Finally, be aware that at high ambient temperatures the

internal Schottky diode will have significant leakage current

increasing the quiescent current of the LTM8025.