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LMZ31710: PH Connection

Carr Jim
Prodigy 10 points
Part Number: LMZ31710

I'm not sure what to do with the PH pins. The datasheet says "These pins must be connected to one another using a small copper island under the device for thermal relief." It looks like the sample layout only has vias surrounding the PH of pin 42. The other PH pins (10, 13-19) don't appear to be connected to the island of pin 42. Further, where are all the vias connected? They are just through the board with no connection to anything? I don't know how this provides thermal relief. Thanks.

  • 0
    TI__Guru 50120 points

    Hi Carr,

    I've attached the typical Top-Layer Layout from the datasheet for reference. 

    Here you will notice that Pin 10 (left pin close to CIN3) and Pin 13-19(pins bottom of the big pad) are connected in one single island. Continuing through Figure 46- 48 you will see there is a copper island in the middle of the PCB board for PH. The vias on the large pad on Top-Layer are all interconnected through to Layer 2,3, and Bottom Layer.

    This adds additional copper area to the pin and allows more heat to dissipate throughout the layers between the device and PCB. 

    Regards,

    Jimmy