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BQ77915: 3S Design Review

M.Joula
Prodigy 10 points
Part Number: BQ77915
Other Parts Discussed in Thread: BQ77905

Hello,

We are going to design 3S PCM 8A.

1. Could you please check our schematic design6562.3 Cell.pdf? Are there any problems with the design?

2. We have used two pairs of NVMFD5C466NL. The datasheet recommends about RCHG and RDSG that adjust this parameter to the desired FET fall/rise value and also the number of FET parallels. So how should calculate that? could you give an example or explain with our MOSFET, please?

4. Is D1 with 30V suitable for the design?

Thanks in advance,

  • 0
    TI__Guru* 81034 points

    Hi,

    I reviewed the schematic and most connections and components look okay. I did notice a couple things:

    - I am not sure I understand all of the FET connections. It looks to me like PACK- and BAT- are always connected around the FETs.

    - The sense resistor value seems high for an 8A application. You also need to consider your desired current limits for OCD and short circuit detection to make sure they are with the SRP/SRN voltage range of -200mV to +800mV. The design example in datasheet section 10.2.2 is really helpful for calculating your sense resistor value.

    - I think the diode you selected for D1 should be okay.

    This app note is helpful for your questions about multiple FETs and fall/rise times: http://www.ti.com/lit/an/slua773/slua773.pdf

    This app note was written using a very similar device, the BQ77905. 

    Best regards,

    Matt