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BQ76920EVM: Question about D1, refering to the BQ76920EVM

Paul K52
Intellectual 640 points
Part Number: BQ76920EVM

Hello,

I have a question about D1. D1 is depiced in the datasheet of the BQ76920EVM on page 36.

I have build a batterymanagmentsystem based on the plan of the bq76920evm.

I think there is a short cicuit between J2 the diode D1 and J3, when I connect the battery to the input pins.

What do you think about this thought and why is it nessecary that this diode D1 is placed on this position?

Is D1 a zener-diode?

Thanks for help

  • 0
    TI__Genius 10830 points
    Hi Paul,
    Thank you for your interest in our products. A BMS expert has been assigned to your question.

    Regards,
    David
  • 0 in reply to David Hien
    TI__Guru 54715 points
    Hi Paul,
    There has been some confusion with the EVM and power supply since the positive is at the bottom of the page and the "bottom" of the EVM. This kept the signal line and trace from un-necessarily crossing other paths, but it is opposite from how people think of voltages on a graph.
    The bq76920EVM D1 is a TVS diode intended to limit transients across cells from inductive switching during evaluation. Some designers will implement this type of component, some don't want it since it is a single point failure opportunity which could short the inputs. The EVM component had a 28V working voltage and would not conduct at a 25V typical maximum input. On the EVM it also had the effect of preventing reverse voltage if a current limited supply was connected in reverse. Certainly TVS diodes are rated for pulse power and current rather than continuous, so it is not obvious how much current it would take.
    See the EVM user guide in the tool folder or http://www.ti.com/lit/slvu924 for the component part numbers and schematic.
    If you have implemented a TVS, be sure it was installed with the proper polarity. There are bi-directional TVS devices typically on the same data sheet, they have a different part number. In the case of the EVM the part used was SMCJ28A while the bi-directional part would be SMCJ28CA