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Original question:

BQ40Z80EVM-020: bqStudio not supporting target

BQ40Z80: Several design questions on BQ40Z80

Fabrizio Raggioli
Intellectual 360 points
Part Number: BQ40Z80

Hi,
I'm finishing the schematic design of my board (it is 90% based on the reference EVM).
I have some questions to solve:
1) Can I put the TVSs on each inputs (including the thermistor-in ?)
2) As I understood, the wake-up circuit in the EVM is needed only for development purposes to produce a current flow. I removed from my schema. There is any implication?
3) The precharge current should be the around 10% of the nominal maximum current of charge. So, for my battery pack that has 1.5A I choose 100mA of precharge. Is it correct this approach?
4) In the 6s configuration, where should I put the 4 thermistors on the pack (on the interface of each battery)?
5) For the configurable Pins, if I put the unsed to VSS before the configuration of the board with the new FW, is there a problem of a short circuit if the pin is configured as output and connected to the ground?
6) Can I configure the current on the LED? I have a small LEDs that require 22mA and not the typical 30mA
7) For the Shutdown input, as I understood from the datasheet there is an internal pull-up. So, I don’t put any pull-up network. Is it correct?
8) Can you provide a general feedback on the following schematic, in case of macroscopic error?

9) The fuse pin, can drive with 8V a Led?


Thanks for your support

.

  • 0
    TI__Guru 52115 points

    I will review your schematic and provide answers to your questions.

    Andy

  • 0 in reply to Andy Liu (BMS)
    Intellectual 360 points

    Hello Andy,

    do you have any updates for me?

    Thanks

  • 0 in reply to Fabrizio Raggioli
    TI__Guru 52115 points

    See my comments below.

    1) Can I put the TVSs on each inputs (including the thermistor-in ?)
    I suggest you not put the TVSs on the TS pins.

    2) As I understood, the wake-up circuit in the EVM is needed only for development purposes to produce a current flow. I removed from my schema. There is any implication?
    Yes, it can be removed and a charger is used to wake up the gauge from shutdown.

    3) The precharge current should be the around 10% of the nominal maximum current of charge. So, for my battery pack that has 1.5A I choose 100mA of precharge. Is it correct this approach?
    I would suggest you check the battery manufacturer spec. 100mA seems high for a 1.5Ah battery. I would recommend keeping it around 50mA.

    4) In the 6s configuration, where should I put the 4 thermistors on the pack (on the interface of each battery)?
    The more temp sensors the better to get a more accurate reading of cell temperature.

    5) For the configurable Pins, if I put the unsed to VSS before the configuration of the board with the new FW, is there a problem of a short circuit if the pin is configured as output and connected to the ground?
    By default, these pins are configured as input in the HIGH-Z state. Check Chapter 2 of BQ40z80 TRM.

    6) Can I configure the current on the LED? I have a small LEDs that require 22mA and not the typical 30mA
    You need to add an external resistor to limit the current.

    7) For the Shutdown input, as I understood from the datasheet there is an internal pull-up. So, I don’t put any pull-up network. Is it correct?
    Yes, no external pull-up is needed.

    9) The fuse pin, can drive with 8V a Led?
    It depends on the BAT voltage. If BAT > 8V then it can drive VOH max of 8.65V and follows BAT < 8V. See FUSE drive section of the EC table on page 16 of the datasheet.

  • 0 in reply to Andy Liu (BMS)
    Intellectual 360 points

    thanks for the answers.

    I think that we have to deepen some aspects:

    6) The LED pin seems that has a current generator

    so a resistor doesn't limit the current. If my interpretation is correct, seems that I don't need a limitation (22.5 mA of nominal current is ok for the LEDs)

    9) From the datasheet is not clear the maximum current of the fuse pin: is IAFEFUSE(PU) of maximum 330nA ?

  • 0 in reply to Fabrizio Raggioli
    TI__Mastermind 34775 points

    Fabrizio Raggioli said:
    9) From the datasheet is not clear the maximum current of the fuse pin: is IAFEFUSE(PU) of maximum 330nA ?

    Yes it's for driving the gate of an NMOS FET that blows the FUSE.

    Fabrizio Raggioli said:
    so a resistor doesn't limit the current. If my interpretation is correct, seems that I don't need a limitation (22.5 mA of nominal current is ok for the LEDs)

    You shouldn't for most LEDs based on the brightness. If you LED max current is less that 22.5mA  then you can add series resistor to limit the current.