The following sections provides recommendations for board layout, solder reflow profile and power supply bypassing when using LMK62XX to ensure good thermal / electrical performance and overall signal integrity of entire system.
The LMK62XX is a high-performance device. Therefore, pay careful attention to the device configuration and printed-circuit board (PCB) layout with respect to power consumption. The ground pin must be connected to the ground plane of the PCB through three vias or more, as shown in Figure 9, to maximize thermal dissipation out of the package.
Equation 1 shows the relationship between the PCB temperature around the LMK62XX and the junction temperature.
To ensure that the maximum junction temperature of LMK62XX is below 105°C, it can be calculated that the maximum PCB temperature without airflow should be at 81°C or below when the device is optimized for best performance, resulting in maximum on-chip power dissipation of 0.36 W.
For best electrical performance and signal integrity of entire system with LMK62XX, TI recommends routing vias into decoupling capacitors and then into the LMK62XX. TI also recommends increasing the via count and width of the traces wherever possible. These steps ensure lowest impedance and shortest path for high frequency current flow. Figure 9 shows the layout recommendation for LMK62XX.
TI recommends following the recommendations set by the solder paste supplier to optimize flux activity and to achieve proper melting temperatures of the alloy within the guidelines of J-STD-20. Processing LMK62XX with the lowest peak temperature possible while also remaining below the components peak temperature rating as listed on the MSL label is preferred. The exact temperature profile would depend on several factors including maximum peak temperature for the component as rated on the MSL label, board thickness, PCB material type, PCB geometries, component locations, sizes, densities within PCB, as well as the recommended soldering profile from the manufacturer, and capability of the reflow equipment to as confirmed by the SMT assembly operation.