SNVSCU2A August 2024 – August 2024 LM5137-Q1
ADVANCE INFORMATION
The useful operating temperature range of a PWM controller with integrated gate drivers and bias supply LDO regulator is greatly affected by the following:
For a PWM controller to be useful over a particular temperature range, the package must allow for the efficient removal of the heat produced while keeping the junction temperature within rated limits. The LM5137-Q1 controller is available in a small 6mm × 6mm 36-pin VQFNP (RHA) PowerPAD package to cover a range of application requirements. Thermal Information summarizes the thermal metrics of this package.
The 36-pin VQFNP package offers a means of removing heat from the semiconductor die through the exposed thermal pad at the base of the package. While the exposed pad of the package is not directly connected to any leads of the package, exposed pad of the package is thermally connected to the substrate of the LM5137-Q1 device (ground). This connection allows a significant improvement in heat sinking, and designing the PCB with thermal lands, thermal vias, and a ground plane to complete the heat removal subsystem is imperative. The exposed pad of the LM5137-Q1 is soldered to the ground-connected copper land on the PCB directly underneath the device package, reducing the thermal resistance to a very low value.
Numerous vias with a 0.3mm diameter connected from the thermal land to the internal and solder-side ground plane or planes are vital to help dissipation. In a multi-layer PCB design, a solid ground plane is typically placed on the PCB layer below the power components. Not only does this action provide a plane for the power stage currents to flow but this action also represents a thermally conductive path away from the heat generating devices.
The thermal characteristics of the MOSFETs also are significant. The drain pads of the high-side MOSFETs are normally connected to a VIN plane for heat sinking. The drain pads of the low-side MOSFETs are tied to the respective SW planes, but the SW plane area is purposely kept as small as possible to mitigate EMI concerns.