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THS6222: Facing thermal Issue and also drawing lot of current.

Part Number: THS6222
Other Parts Discussed in Thread: THS6212

Hello,

I have used this part in one of my project, and input is 1Vp-p, with a gain of 10, but it's drawing lot of current ( +VS= +16V and -VS=-16V, 350mAat each supply)when I connect it to my output circuit at output of the THS6222. Also heating up a lot because of thermal issue current is also slowly increasing as temperature increases.

Exposed Pad(EPAD) I have connected to Negative supply and connected to exposed copper with through via. I have not poured copper in bottom layer. Copper is present in Top layer and layer 4 but not present in bottom.

Please help on this.

Thanks

Regards,

Vinayak Chabbi

  • Hello Vinayak,

        At 350mA current drawn from each supply current, the part will heat up exponentially due to the very high amount of current drawn. If you followed the layout guidelines and examples in section 10 of the datasheet, the heat should dissipate through the thermal vias to the internal copper negative supply plane. The issue in your case seems to be the connection to the output circuit increasing the supply current over normal conditions. Would you be able to share the schematic of the THS6222 and the connection at the output?

    Thank you,

    Sima

  • Hello Sima,

    Thank you for the reply.

    Here is the schematic snapshot for your reference. 

    When I connect the BJT schematics to THS6222, it starts taking current upto 450mA, and also we have made a mistake of not pouring copper in inner layers for EPAD to dissipate heat, we have poured copper on Layer 4.

    Please let me know if you need any further information and can I get the layout file of THS6222 EVM board?

    Thanks,

    Regards,

    Vinayak Chabbi

  • Hello,

     In EVM Layout, for EPAD copper poured on top and bottom layers since only 4 layer board, but in case of 6 and more layer board, do I need to pour copper in all layer under the EPAD and place PTH vias? If I pour on all layer will the heat dissipated cause the problem? 

    Regards,

    Vinayak Chabbi

  • Hello Vinayak,

        Sorry for the late response. There really should not be a problem since it seems like both outputs are driving AC coupled capacitors; there is no differential to ground at these outputs. From your schematic, you seem to have each stage connected to separate power supplies. Are you reading this high supply current of 350mA from only the power supplies to the THS6222 when you connect the output stage to the device? Would you be able to share more insight on the application, especially at the output stage of the THS6222 and the BJT part numbers? 

         For your thermal layout concerns, you could have vias only going through the internal layers for where the negative voltage plane is located. In high power/temperature concerns, it would help to run them though to the bottom layer which will dissipate the heat faster; but, this is not the most significant factor in dissipating the heat. It depends more on surface area of the copper plane, the number and size of the vias. If you would like more information on the topic, here are some app notes with more insight: Thermal Design, PowerPad, Layout, PowerPad Brief.

    Thank you,

    Sima

  • Dear Sima,

    Thanks for the response.

    Will the absence of differential ground affect the performance of the device?

    I'm using two amplifiers, THS6212 with +-12V supply, which driving the THS6222 (+-16V supply) and output of TH6222 is given to BJT circuit, same +-16V is shared with this circuit also but I have provided the supply to this circuit through jumper.

    When THS6222 not connected with output BJT circuit it's taking current around 95-110mA ( increasing the current as temperature increases); when I connect BJT circuit , current is going to ~450mA.

    BJT Part numbers are 2SCR574D3, 2SAR574D3, 2SCR554P5 and 2SAR554P5, also attaching better quality snapshot for your reference.

    If any further info needed please let me know.

    Awaiting your response.

    Regards,

    Vinayak

  • Hello Vinayak,

        It should not be an issue in affecting the performance of the device; it was more of an indication that you should not be having a problem at the connection of the output stage. Your application does seem like it has unusually high output current even without the connection to the output stage; since, normally it should be within 20-30mA. This suggests there could be a problem within the first two stages. Would you be able to measure the input and output signal of the THS6222? Thank you for the higher quality image and the part numbers!

    Thank you,

    Sima

  • Hello Sima,

    Input to THS6222 is 600mVp-p sine wave, and output I'm getting 6Vp-p, without BJT circuit.

    Regards,

    Vinayak

  • Hello Vinayak,

        That does seem reasonable. Below, I have attached a datasheet characterization of quiescent current vs temperature. It should still be around 20-30mA at those temperatures with no loading. So, even if your board is thermally heating up due to the mistake you brought up earlier, it should still be in that range. Did you try other THS6222s with the same outcome? If not, would you be able to try another THS6222? Also, I would suggest testing only the THS6222 in the same configuration as your schematic (input of 600MVpp and same gain) on another pcb board. 

                  

    Thank you,

    Sima

  • Hi Vinayak,

    I think you should improve your cooling management. Can you show pictures of the four layers of your layout?

    Kai

  • Hello Kai,

    Sorry for the late reply.

    Please find the attached file for layout snapshots of THS6222.

    Currently we have added copper in all the layer with vias for better heat dissipation, waiting for the board to arrive, will update it soon.

    Sima : I have tested on 4 boards, all 4 THS6222 gave almost similar readings. I have tested along with THS6212 as input circuit to THS6222.

    ARCH1_REVB_THS6222_Layout_TI.docx

    Regards,

    Vinayak

  • Hi Vinayak,

    you should not route a copper trace directly under the THS6222. As consequence you loose two vias. That's not good. Move this single copper trace away from the vias and add the two vias again.

    Also, you should add a copper plane for cooling in layer 3 and especially in the bottom layer. And you should considerably expand the copper plane in layer 4.

    All these measures will massively improve the cooling.

    Kai