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BQ77915: 8-series cell configuration with BQ77915

user5503575
Intellectual 800 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ77905

Hi,

I am designing 8-series protection circuit with using bq77915. But I am not sure how will I divide cells between two IC's. Should I connect 5 cells to lower IC and 3 cells connect to upper IC? Or just the opposite?

I think lower IC will drive FET's so it needs more voltage (I mean 5 cell) but I am not sure. 

Also the similar IC bq77905 has EVM schematic which I can take as an example values of components but BQ77915 doesnt have any.

Can anybody show me an example schematic 8 series protection circuit with BQ77915?

Also do you have any offer to make this circuit configurable 7-8-9-10 series?

  • 0
    TI__Guru 54715 points
    Hi User,
    The basic stacking idea for bq77915 with a simple schematic is shown in the data sheet figure 19. Note that the upper device signals and filters should reference its VSS. As you note, the bq77905 is similar, it has an application note on stacking showing a 20S schematic with component values, www.ti.com/.../slua774 . The bq77915 will also have the 10k resistors between stacked devices for the PRES and CBI signals.
    With a 10 series cell design 2 ICs are needed. For making 6, 7, 8, or 9 series reduce one or both IC's cell count. The bq77915 data sheet section 9.3.12 discusses configuring cell count. Generally keep the cell count balanced between devices. When the cell count does not match, section 9.3.13 of the data sheet recommends using the higher cell count on the upper device.
  • 0 in reply to WM5295
    Intellectual 800 points

    Hi ,

    Thank you for your answer. I created a schematic with bq77915 and bq77905 documents :) But I have another question now. I dont want to use two thermistor for two IC. I added one thermistor to lower IC then upper IC's TS pin through to GND with 10K . Is it possible ? I couldnt find any example on bq77915 and bq77905 datasheet,evm,20cell documents. 

  • 0 in reply to user5503575
    TI__Guru 54715 points
    Hi User,
    Yes. If you don't want to use a temperature input connect a 10k resistor in place of the thermistor. The RTS resistor value will not change significantly with temperature and should track the RTS_PU resistor value so there will be no temperature protection on that input. The temperature measurement does not have an enable so you can't just short the TS pin or leave it open.
  • 0 in reply to WM5295
    Intellectual 800 points

    Hi,

    I know that how to disable temperature protection with using 10k resistor between TS pin to VSS but I use two bq77915 IC on 8 series circuit . I want to use temperature protection but in my opinion I dont need two thermistor . I will connect one thermistor to lower device and disable temperature protection of upper device. Is it possible ?

  • 0 in reply to user5503575
    TI__Guru 54715 points
    Hi User,
    Yes, it is possible.