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BQ21040: Package thermal considerations

John Anhalt
Prodigy 20 points
Part Number: BQ21040

Section 11.3 of the datasheet describes a thermally enhanced package with a thermal pad for that device.  It then goes on to say that pad on the PCB should be connected to VSS.  The current package drawing (DBV variant) does not show any thermal pad.  What should its dimensions be?  I am assuming one should solder the device pad to the PCB.  If not, are you recommending one use a heat and electrically conductive epoxy or something else?    

  • 0
    TI__Guru* 75556 points

    Hello

    Unfortunately this is an error in section 11.3, BQ21040 does not have a thermal pad.  Package is a SOT-23 type with limited thermal performance.  Best approach is to connect pins to large thermal area as indicated in figure 29.

    The BQ2404X family of devices do have thermal pads and provide better thermal performance. 

  • 0 in reply to Bill Johns
    Prodigy 20 points

    Thank you for the prompt reply.

    Does that mean the Thermal Information (Table 7.4) for Junction-to-board thermal resistance and Junction-to-board characterization parameter, which are both 45.5°C/W, are also errors?

    I was surprised that value was so low for an SOT-23(6) package.  If that value is correct, I can live with it and enlarge the copper area around the pads as shown in Figure 29.  Otherwise, I will switch to a device with a thermal pad.

    Regards, John

  • 0 in reply to John Anhalt
    TI__Guru* 75556 points

    Hi John

    Table 7.4 is OK, this info was updated and does apply to the SOT-23(6).  Problem with section 11.3 is it was reused from another device but not updated to reflect the new package.  I will work on an update to data sheet.