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BQ25601: setting safety timer for large capacity batteries

Maximilian Hoferichter
Prodigy 60 points
Part Number: BQ25601
Other Parts Discussed in Thread: BQ25606

Hi,

I´m currently getting into LiIon and LiPo charging. I have to design a device that will be powered by a LiPo battery which should be charged via USB. For this I´m thinking of using the BQ25601. However this is a complex device to set up and I´m new to this so I have some issues understanding this.

The settings of the BQ can be edited via I2C. What happens to the settings if the battery will be disconnected (no other power source is conneted) or it disconnects itsself (overdischarge detection). Are the registers volatile and all my settings are gone and am I limited to the default mode settings then?

The thing I´m worried about is the charging safety timer setting. Since I will use a high capacity LiPo cell, charging might take pretty long and even expire the default 10hr safety timer especialy when using just a 500mA USB2.0 input or the pre-charge phase get pretty long.

My battery:

capacity = 7000mAh
maximum charging current = 1C

Any ideas?

Best Regards

Max

  • 0
    TI__Mastermind 25800 points
    Hey Max,

    To your first concern: You are correct. All settings will be lost if there is no power to the device. The registers are set through a state machine, and when there is no power, all settings return to default. Do you expect to disconnect your battery and/or not use a host controller?

    To your second concern: It may not be an issue. If you set the charge current setting to a large value (let's say 2A which is default), but the input source (500mA USB) reaches it's current limit, the device will run in it's DPM loop. When this loop is active, we actually run the safety timer at half the clock rate (or 2x timing), meaning your 10 hours becomes 20 hours.

    Are you expecting to only charge with USB?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 60 points
    Hey Joel,

    thanks for your quick response. I think that will help me for noe.

    I don´t expect to disconnect the battery but the host controller will be turned off.
    Yes, the USB port will be the only source for charging the device.
    Do you have any suggestions for other ICs that might be a better choice for this application?

    cheers

    max
  • 0 in reply to Maximilian Hoferichter
    TI__Mastermind 25800 points

    Hey Max, 

    I think the bq25601 is a good choice. 

    If you don't plan on ever communicating with the charger, you could also consider the bq25606, which is a standalone part.

    However, by setting the ILIM pin appropriately or the PSEL pin, you can still get the same result. 

    I think with any charger you find, the limitation will be the same because of the capability of your input source. However, the 2X safety timer will give the charger time to sufficiently charge the battery.

    Regards,

    Joel H

  • 0
    Prodigy 60 points
    Thanks for your Answer Joel,
    I have some further questions to the BQ25601. How does the PSEL input work? Can it detect Dedicated Charging Ports and how is it connected to the USB line then? The D+/D- input is a nice feature of the BQ25606. Can I realize something similar with the BQ25601 over the PSEL?
  • 0 in reply to Maximilian Hoferichter
    TI__Mastermind 25800 points

    hey Max,

    The PSEL pin works whenever a valid input source is applied to VBUS, the charger measured the state of PSEL, be it HIGH or LOW. The state applied to the PSEL pin is then used to determine the IINDPM register setting. 

    It does not have the logic to detect a DCP nor would it be connected to a USB D+ or USB D- line. Typically, customers will use a host GPIO to drive this pin, or pull it High or Low based what the expected customer input will be. 

    In regards to bq25601 having D+/D- detection, you will need extra logic circuitry plus your host controller running some algorithm to decipher what type of port has been plugged in.

    Regards,

    Joel H