LTM8061
17
8061fa
For more information www.linear.com/LTM8601
input voltage, possibly exceeding the LTM8061’s rating
and damaging the part. If the input supply is poorly con
-
trolled or the user will be plugging the LTM8061 into an
energized supply, the input network should be designed
to prevent this overshoot. This can be accomplished by
installing a small resistor in series to V
IN
, but the most
popular method of controlling input voltage overshoot is
to add an electrolytic bulk capacitor to the V
IN
net. This
capacitor’s relatively high equivalent series resistance
damps the circuit and eliminates the voltage overshoot.
The extra capacitor improves low frequency ripple filter
-
ing and can slightly improve the efficiency of the circuit,
though it is physically large.
Thermal Considerations
The temperature rise curves given in the Typical Perfor
-
mance Characteristics section gives the thermal perfor-
mance of the LTM8061. These curves were generated by
the LTM8061 mounted to a 58cm
2
4-layer FR4 printed
circuit 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 sys
-
tem’s line, load and environmental operating conditions.
The junction to air and junction to board
thermal resistances
given in the Pin Configuration diagram may also be used to
estimate the LTM8061 internal temperature. These thermal
coefficients are determined for maximum output power per
applicaTions inForMaTion
JESD 51-9, “JEDEC Standard, Test Boards for Area Array
Surface Mount Package Thermal Measurements” through
analysis and physical correlation. Bear in mind that the
actual thermal resistance of the LTM8061 to the printed
circuit board depends upon the design of the circuit board.
The internal temperature of the LTM8061 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 LTM8061. The bulk of the heat flow out of
the LTM8061 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, resulting in impaired performance or reliability.
Please refer to the PCB Layout section for printed circuit
board design suggestions.
The LTM8061 is equipped with a thermal foldback that
reduces the charge current as the internal temperature
approaches 125°C. This does not mean that it is impos
-
sible to exceed the 125°C maximum internal temperature
rating
. The ambient operating condition and other factors
may result in high internal temperatures.
Finally, be aware that at high ambient temperatures the
internal Schottky diode will have significant leakage current
increasing the quiescent current of the LTM8061.
