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Original question:

BQ2980: BAT resistor functionality

BQ2980: Maximum resistance of Rbat on BAT pin

David Ewing
Prodigy 25 points
Part Number: BQ2980

Hi,

The RBAT value is shown as 20 ohms in the application information. This puts the short circuit power for the resistor at ~0.9W for a single LI-ion cell. So RBAT would need to be larger than a 1206 to handle a continuous short. Is it possible to raise this value to at least 40 ohms? What is the typical current requirement for the BAT pin?

  • 0
    TI__Guru 54715 points

    Hi David,

    The BAT pin has no separate current specification, it is averaged into the INORMAL specification for the supply current.  The BAT pin is sampled for OV and UV measurement, see the mux in the BQ2980 data sheet section 8.2 Functional Block Diagram.  As the RBAT resistor is increased the sample current will have an increasing effect and can cause a shift in the thresholds, so the recommendation is to use 20 ohms.  You can use a larger resistor if it is suitable in your system.  The data sheet does not indicate the current into the pin I would expect you would not see a difference at 40 ohm, but you should test over your expected temperature range and knowing there will be some variation in parts as well as resistor tolerance you may want to test with a resistor twice as large as you intend to use to provide some margin.