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I am analyzing an open-source BMS project based on a BQ76920 from Texas Instruments and checking its datasheet to understand their features and applications. The schematic of the project seems to be consistent with the datasheet but my question is: Could I use it for only 3 cells in series instead of 5? what should I do for only using 3 cells instead of 5 cells?

Reading the datasheet I think I should pull down the VC5 and VC4 to VSS (GND) with a 10 kΩ resistor according to the text highlighted in yellow:

enter image description here

Do you think that is correct? or is there something I am not considering? Thank you!

winny
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imt_blake
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    The note (1) you've highlighted in yellow only applies to the TS1 pin. You'll notice on the end of the description for that pin there's a (1) in superscript and not on any of the other pins. – brhans Mar 13 '23 at 17:48
  • That is correct! So do you think is it possible to use only 3 cells instead of 5? The datasheet also says: Up to 5 cells so I guess it should be possible to use only 2 o 3 for example – imt_blake Mar 13 '23 at 17:55

1 Answers1

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As pointed out in the comments, the highlighed note applies to the (1) in the description next to the Thermistor description. It does not apply to all pins.

According to the datasheet device comparison, your device does support use with 3 to 5 cells, so it should be possible to use it with just the three.

Device Comparison

Later in the datasheet it describes how to connect fewer cells than specified. This is documented in section 9.1.8 on page 39:

Connections for fewer cells

So for 3 cells, you short the pins VC4, VC3 and VC2 together, and connect them to the node in the battery pack between cells 2 and 3.

Tom Carpenter
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