Data Sheet

LT8349

analog.com

Rev B

24 of 29

The output capacitors, along with the inductors and input capacitors, should be placed on the same side of the

circuit board, and their connections should be made on that layer. It is recommended to make the layout identical

between the two channels to improve the current sharing (refer to Figure 32).

Place a local, unbroken power ground plane under the application circuit on the layer closest to the surface layer.

The SW1, SW2, BST1 and BST2 nodes should be as small as possible. Keep the FB and RT nodes small so that the

ground traces will shield them from the noise generated by the SW1, SW2, BST1 and BST2 nodes.

To keep the thermal resistance low, extend the ground plane as much as possible, and add many thermal vias to

additional power ground planes within the circuit board.

Thermal Considerations

Care should be taken in the layout of the PCB to ensure good heat sinking of the LT8349. The power ground plane

should consist of large copper layers with thermal vias; these layers spread heat dissipated by the IC. Placing

additional vias can reduce thermal resistance further. The maximum load current should be derated as the junction

temperature approaches its maximum temperature rating. Power dissipation within the IC can be estimated by

calculating the total power loss from an efficiency measurement and subtracting the inductor loss. The junction

temperature can be calculated by multiplying the total IC power dissipation by the thermal resistance from junction

to ambient and adding the ambient temperature. The LT8349 includes internal overtemperature protection that is

intended to protect the device during momentary overload conditions. The overtemperature protection shuts down

the IC when the junction temperature exceeds 170°C (typ). The internal soft start is triggered when the junction

temperature drops below 165°C (typ). The maximum rated junction temperature is exceeded when this protection is

active. Continuous operation above the specified absolute maximum operating junction temperature (see Absolute

Maximum Ratings section) may impair device reliability or permanently damage the device.