• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 34 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

[FAQ] BQ2980: Protector Behavior for Severely Depleted Battery (0V Charging)

BQ2970: Charging during UVP

Mark Timieski
Prodigy 10 points
Part Number: BQ2970

Tool/software:

We are having issues charging batteries that have fallen below the UVP threshold when using the BQ2970DSER.  We've implemented the design per the BQ29700EVM-610 with the Q1/Q2 replaced with a DMN3135LVT-7 dual FET.  We are using the design with a small 85mAh Li-Po battery.

We have discharged the battery to 2.447V, which is below the 2.8V UVP setting.  We see DOUT go low as expected.

The charger is then connected (Pack+ to Pack-).  We do not see DOUT return high.  I would expect that DOUT would need to be high to allow the battery to charge.

I'm trying to go through the specifications and make sure that everything is in order but am getting confused on some of the descriptions and diagrams.

Section 9.4.3 (Over-Discharge Status) makes reference to a number of voltages, for example "V- is lower the -0.7V".  What is the negative reference for these measurements reference?  BAT? VSS? 

I'm having the same issue with the VUVP_Hys specification in section 7.6.  There are references to the voltage at BAT and V- but not sure what the negative reference should be.

In looking at the timing chart in section 8.1, I see that the DOUT is shown low after the charger is connected but also indicates that the battery voltage begins increasing.  How would the battery voltage increase if the ground reference to the charger is effectively disconnected with DOUT in a low state?

Do I need some accessory circuit to enable charging if the battery should fall below the Vuvp limit?

  • 0
    TI__Expert 5065 points

    Hi Mark, 

    Apologies for the delay on getting back to you , support queue is higher than expected so answers are slower than usual. 

    Once the device crosses the UV threshold of the D/S, the DSG will turn off to prevent further discharge of the battery, as you mentioned above as expected. The pack can still be charged through the body diode of the discharged FET. DSG will turn on, once the battery voltage exceeds the over-discharge detection voltage again. No external circuitry will be needed. 

    Regarding the voltages, the part transition to a standby mode while the battery is in under discharged mode (over discharge detection status) where the V- is internally pulled to BAT and has a detection circuit internally of 0.7V, to detect if a charger is connected and then allow the BQ chip to exit this low power mode and allow the battery to charge. For simplicity and for your query, you can potentially ignore this thresholds as they are just saying how to the charger detection voltage works inside the part. 

    Hope this helps. 

    Regards, 

    Arelis G. Guerrero