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EM1402EVM: Thermal issue on low side of the EMB1499Q

annib copp
Prodigy 30 points
Part Number: EM1402EVM
Other Parts Discussed in Thread: BQ79616

Hi,

we are developing a new board very similar to EM1402EVM, but without the  external 12V supply/battery. In our design a single cell is charged/discharged from/to the entire stack (14cells). The board work good in discharge phase, but in charge phase the temperatures of the main switch (NMOS) and the AUX/CLAMP (PMOS) rise immediately even at low charge current (<1A).

We found this waveforms on the gates of the devices, in yellow the Vgs for the PMOS and in blue the one for the NMOS. 

Cell charging phase:

Cell discharging phase:

These waveforms seem correct in charging phase but incorrect in discharging phase if compared to what is reported in the EMB1499 datasheet. Below the schematic relative to the converter:

Please can anyone help me?

Regards Annibale

  • 0
    TI__Genius 17370 points

    Hi annib,

    The attachments did not work - can you please rettach? I also want to comment this design is very old and so support knowledge on this design is limited especially for custom designs. Can you comment on if the much newer cost effective devices like our bq79606a or bq79616 devices could better support your needs?

    Best Regards,

    Taylor

  • 0 in reply to Taylor Vogt
    Prodigy 30 points

    Sorry for the attachments.

    Below the schematic relative to the converter:

    The new devices bq79606a and bq79616 look similar to the bq76PL455A used in our project, however we are developing an active cell balancing system with a current of a few amps. So we want to solve the thermal problem in charging mode.

    Thank you in advance

    Best regards Annibale

  • 0 in reply to annib copp
    TI__Genius 17370 points

    Hi Annib,

    I would recommend to check the FAULT[2:0] pins on the device to see there is a fault happening. Description can be found in the "Fault Detection and Fault Codes" in the datasheet. 

    You can also use an oscilloscope to compare the signals from the working board and the not working board and identify any differences. Can you compare with EM1402EVM or install 12V like it to see if that may be the cause?

    Regards,

    Taylor