LT8697
applicaTions inForMaTion
High ꢂemperature Considerations
currentsflowintheLT8697’sV pins, PGNDpins, andthe
IN
input capacitors (C and C ). The loop formed by the
IN1
IN2
For applications with higher ambient temperatures, lay
out the PCB to ensure good heat sinking of the LT8697.
The exposed pad on the bottom of the package must be
soldered to a ground plane. This ground should be tied
to large copper layers below with thermal vias; these
layers will spread heat dissipated by the LT8697. Placing
additional vias can reduce thermal resistance further. The
maximum load current should be derated as the ambient
temperature approaches the maximum junction rating.
Power dissipation within the LT8697 can be estimated
by calculating the total power loss from an efficiency
measurement and subtracting the inductor loss. The
die temperature is calculated by multiplying the LT8697
power dissipation by the thermal resistance from junction
to ambient. The LT8697 will stop switching and indicate
a fault condition if safe junction temperature is exceeded.
input capacitor should be as small as possible by placing
the capacitor adjacent to the V and PGND pins. When
IN
using a physically large input capacitor the resulting loop
may become too large in which case using a small case/
value capacitor placed close to the V and PGND pins
IN
plus a larger capacitor further away is preferred. These
components,alongwiththeinductorandoutputcapacitor,
should be placed on the same side of the circuit board,
and their connections should be made on that layer. Place
a local ground plane under the application circuit on the
layer closest to the surface layer. The SW and BST nodes
should be as small as possible. Finally, keep the USB5V
and RT nodes small so that the ground traces will shield
them from the SW and BST nodes. The exposed pad on
the bottom of the package must be soldered to ground so
that the pad is connected to ground electrically and also
acts as a heat sink thermally. To keep thermal resistance
low, extend the ground plane as much as possible, and
add thermal vias under and near the LT8697 to additional
ground planes within the circuit board and on the bottom
side.
8697p
23
For more information www.linear.com/LT8697
LINEAR_DIMENSIONS [ Linear Dimensions ]
