Question
The application we are using this device in has a maximum operating temperatureof +75degC. Our modelling of power dissipation in this device is showing it isgetting hot.The ADM2682E/ADM2687E datasheet (Rev. B) PCB Layout section on page 24, lastparagraph provides some limited recommendations on removing some of the heatdissipation in the device into the PCB by using enlarged pads around the fourground pins and connecting these via multiple vias to the solid ground plane.Is there any data available to estimate how much thermal relief this willprovide? I assume this will equate to the area of the enlarged pads and thearea of the ground plane it is connected to.Secondly the absolute maximum rating of the Thermal Resistance is quoted as 52degree C per Watt. Can you confirm that this is correct for the ADM2687EBRIZ@device? This is the worst case value, but is there any “typical” ThermalResistance data against ambient temperature available.
Answer
Yes, the 52 C/W thermal impedance is correct for the ADM2687E device.Thermal impedance for the ADM2687E was measured on a JEDEC standard 4-layerPCB, with no cooling airflow over the package.Sorry we don’t have any additional thermal impedance data.
While the IC may be getting hot, this should not affect it’s thermalreliability in normal operation.The junction temperature at maximum bus loading should be ~ 110C. This is belowthe max allowable junction temperature for the device.
TJ = TA + èJA*PDISSTJ = 75C + 52C/W*0.675W = 110.1C