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BQ25703A: general questions

Amr Elhadidy
Expert 1005 points

Part Number: BQ25703A
Other Parts Discussed in Thread: BQ25703, BQ40Z50-R2

Hello,

first thanks for the great support as I have seen in other solved Questions. there are some Points that I want to make sure I rightly understood from the datasheet and some other General Questions.

- is there any available Signal from BQ25703 that indicate that charging is complete?

- OTG_Voltage and OTG_Current, are they a Limit for each or are they the value that the converter regulates resp. the OTG voltage and current at?

- can one send the following values to the microcontroller; inputvoltage, Inputcurrent, OTG voltage and OTG current, Vbat, Ibat from the Registers in the BQ25703? or should external circuitry be used. for example, one can connect pin 9 (IBAT) to the microcontroller but I would prefer to read it from the Register, is this possible and is there any difference in the readings?

- if I rightly understood, one can set the Input current Limit using the Ilim_HIZ pin. if this Limit it set through the Hardware, can one deactivate this Setting and set some other Setting through Software while hardwired Ilim_HIZ still connected?

Thank you very much.

Kind reagrds,

Amr

  • 0
    TI__Mastermind 25800 points

    Hey Amr,

    Amr Elhadidy said:
    - is there any available Signal from BQ25703 that indicate that charging is complete?

    This charger does not terminate or complete a charge cycle. This is something the host must determine and disable itself, typically determined with a battery fuel gauge. 

    Amr Elhadidy said:
    - OTG_Voltage and OTG_Current, are they a Limit for each or are they the value that the converter regulates resp. the OTG voltage and current at?

    That is correct. The OTG current limit is only hit if you overload the converter in OTG mode. 

    Amr Elhadidy said:
    - can one send the following values to the microcontroller; inputvoltage, Inputcurrent, OTG voltage and OTG current, Vbat, Ibat from the Registers in the BQ25703? or should external circuitry be used. for example, one can connect pin 9 (IBAT) to the microcontroller but I would prefer to read it from the Register, is this possible and is there any difference in the readings?

    The charger has an integrated 8-bit multi-channel ADC to read many of these values for your MCU and pass them via I2C. The IBAT, PSYS, and IADPT are optional analog outputs for greater accuracy.

    Amr Elhadidy said:
    - if I rightly understood, one can set the Input current Limit using the Ilim_HIZ pin. if this Limit it set through the Hardware, can one deactivate this Setting and set some other Setting through Software while hardwired Ilim_HIZ still connected?

    Yes, if disable the EN_EXTILIM bit in the ChargeOption2() register, you will be able to disable the external ILIM pin function an rely solely on the IIN_HOST() register based input current limit setting.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Expert 1005 points

    Hi Joel,

    thanks for the answers. Mostly all are clear. For the second Question if I rightly understood, OTG voltage Setting is the voltage set Point that one obtain but OTG current is a current Limit. is this so Right?

    is there please a link for an adviced battery fuel gauge?

    Thank you.

    Regards,

    Amr

  • 0 in reply to Amr Elhadidy
    TI__Mastermind 25800 points

    Hey Amr,

    Yes, the OTG voltage is the regulation voltage for VBUS in OTG mode. The charger will remain at this voltage until the load on the OTG output exceeds the OTG current limit, at which point the regulation voltage will droop, similar to a current limited power supply. However, as long as the load is regulation sufficiently to prevent the OTG voltage from dropping below the VVBUS_OTG_UV threshold (found in the EC table), the charger will continue to provide a current up to the programmed OTG current limit.

    As far a gauge, if you have a multi-cell application, I typically recommend the BQ40z50-R2. You can post a separate new thread asking about gauging recommendations as I mostly support TI's chargers. 

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Expert 1005 points

    Hi Joel,

    thanks alot for your answer and the recommendation. 

    there are some other Questions please related to the charger;

    - does Vbus serve also as a Vcc for the chip?

    - when the System is powered up from the battery, without the dc source, the batfet on the very Right in the first page of the datasheet turns on. Does Q4 in this case stays off? 

    - batfet seems to be on for charging and also for discharging the battery. is it Right that batfet is only disabled when no charging is required anymore for any reason? is there some Register thru which the batfet can be turned off?

    Regards,

    Amr

  • 0 in reply to Joel Hernandez II
    Expert 1005 points

    Hi Joel,

    thanks alot for your answer and the recommendation. 

    there are some other Questions please related to the charger;

    - does Vbus serve also as a Vcc for the chip?

    - when the System is powered up from the battery, without the dc source, the batfet on the very Right in the first page of the datasheet turns on. Does Q4 in this case stays off? 

    - batfet seems to be on for charging and also for discharging the battery. is it Right that batfet is only disabled when no charging is required anymore for any reason? is there some Register thru which the batfet can be turned off?

    Regards,

    Amr

  • 0 in reply to Amr Elhadidy
    TI__Mastermind 25800 points

    Hey Amr,

    VBUS does serve, indirectly, as an internal power rail for the charger, as does VSYS. 

    In battery only mode, if you have not programmed OTG operation, the entire power stage is not enabled, so all of power FETs are off.

    Yes, the BATFET is only off when charging is disabled. You can disable the BATFET using the BATFETOFF_HIZ bit in the ChargeOption3() register, but in reality the body of the MOSFET will allow forward conduction to SYS in any scenario.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Expert 1005 points

    Hi Joel,

    in battery only mode, will the System be supplied from the battery (i.e. SRN pin)?

    regards,

    Amr

  • 0 in reply to Amr Elhadidy
    TI__Mastermind 25800 points

    Hey Amr,

    The SYS rail is tied to the battery via the BATFET, so yes.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Expert 1005 points

    Hi Joel,

    yes I remembered the Diode. Fine.

    Thanks very much for your support. was very fine.

    Regards,

    Amr