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Original question:

BQ25713: SCAP charging behaviour

BQ25713: Set and reset HIZ mode using the I2C interface on the BQ25713EVM-017

user4186954
Prodigy 70 points
Part Number: BQ25713

I have a BQ25713 charger, which gets the initial supply from the VBUS to charge super capacitors. In order to charge the SCPs fast, the BATFET source is shorted to the BATFET drain.
According the point 9.6.5.1 in the data sheet, BQ25713 needs to stay in the HIZ mode till the configuration is completed. I found out, that BQ25713 starts the charging sequence before I am able to enable the HIZ by I2C interface. Is there a way to enable the HIZ mode from the begin and to release the HIZ mode later per I2C cmd? The goal is it, to save a cpu pin for controlling the HIZ mode. 

  • 0
    TI__Mastermind 25800 points

    Hello, 

    HIZ mode can be controlled using the ILIM_HIZ pin pulled to ground. When pulled to ground, the converter is placed in HIZ mode.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 70 points

    oscilloscope.pdf

    Hello Joel

    Thanks for answer. I know with the Pin ILIM_HIZ I am able to enter and leave the HIZ mode, but  I do not like to spend a pin on the CPU side for this function.

    The attachment includes three measurements:
    1. Charging behavior with an active BATFET: It can be seen that VSYS gets  powered till the I2C configuration starts.
    2. Charging behavior with a shorted BATFET: This looks how i like it to have, but I am not sure if the BQ25713 is fine with this configuration?
    3. Charging behavior with a shorted BATFET and the use of the ILIM_HIZ signal: BQ25713 is fine with this configuration. But as I mentioned, I do not like to spend a CPU pin to drive the ILIM_HIZ signal.

    Please let me know, if the 2. configuration is aloud or if it damages the BQ25713 with the time?

    Regards,
    Adi

  • 0 in reply to Joel Hernandez II
    Prodigy 70 points

    0777.oscilloscope.pdf

    Hello Joel

    Thanks for answer. I know with the Pin ILIM_HIZ I am able to enter and leave the HIZ mode, but  I do not like to spend a pin on the CPU side for this function.

    The attachment includes three measurements:
    1. Charging behavior with an active BATFET: It can be seen that VSYS gets  powered till the I2C configuration starts.
    2. Charging behavior with a shorted BATFET: This looks how i like it to have, but I am not sure if the BQ25713 is fine with this configuration?
    3. Charging behavior with a shorted BATFET and the use of the ILIM_HIZ signal: BQ25713 is fine with this configuration. But as I mentioned, I do not like to spend a CPU pin to drive the ILIM_HIZ signal.

    Please let me know, if the 2. configuration is aloud or if it damages the BQ25713 with the time?

    Regards,
    Adi

  • 0 in reply to user4186954
    TI__Mastermind 25800 points

    Hey Adi,

    I apologize. I understood that you had the option of using a spare GPIO on your CPU to do this.

    If a hardware implementation does not function, you will have to go the software route. This route will have gap when your supercapacitors are completely discharged. Here you would use the EN_HIZ bit to enable HIZ mode before you plug in your input. However, again the issue is the scenario with a dead supercapacitor bank and no input applied. Here, all settings be revert to their default states. 

    I also noticed you are shorting across the BATFET in this implementation. If you keep the BATFET in place, you can disable charge much easier, or keep the charging current at the very least, down to 128mA when the caps are depleted. 

    Regards,

    Joel H