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BQ25601D: Tech request for portable standalone device (RPi) with LiPo and charger and UPS behavior

FFabio
Expert 1455 points
Part Number: BQ25601D

Hi Team,
I've to design a UPS/charger board for a RPi portable equipment for a my custmer.

The requirement are the followings:

- use as external charger a wall mount power supply rated for 5V - 2A
- use a LiPo battery pack 10000 mAh
- power the RPi at the 5V pins of the GPIO by the UPS/charger

our system have a microcontroller so I'm able to drive the I2C charger BQ25601D, my following questions is to better understand if this charger IC is the right choice for my application or I've to move to other TI charger IC that may be better and up to date.

QUESTION #1
In order to use this IC I'm thinking to put the D+ line connected to D- (shorted) in order to setup the DCP mode and then have the 2.4 A maximum charging current available, this can work with a power supply able to setup a maximum of 2 A and also a load attached to the OUT/SYS pin of the charger (in othr word the charger is able to manage automatically the current balance from load/battery and maximum available from the source) or I've to set a maximum charging current less than the difference from the maximum current available from my wall mount power supply and the needed current for the load (the Raspberry)?

QUESTION #2
Raspberry require 5V power supply voltage. If I correctly understand, because the BQ25601D is a power-path charger, this one will provide power supply to my load through the OUT/SYS pin, but seems that this voltage has a range between 3.5V to 4.2V (it track the battery voltage) so I think that I need to use a boost DC-DC section on the OUT/SYS to have the requested 5V in every condition, I'm right?

QUESTION #3
Because my card have also to act as UPS and then perform a safety shutdown of the Raspberry I need to know when the battery have a voltage that is too low or the battery is going to be not operative and then inform the system to perform the shutdown, are this information available through the I2C registers of the charger or I've to discovered by myself when the battery need to be recharged?

QUESTION #4
If the system is powered by the external power supply, from the charger register (I2C) I can know that?

QUESTION #5
Suppose that the battery bank is not fully charged and externally the power supply is connected to the board, the charger will detect it what is the logic to manage the power path to the battery and to the load? In other word suppose that the load will drawn less current that the maximum current limit set for charging the battery this difference into the current is used to recharge the battery at the same time that the load is also powered? When the current of the load is more than the one that can be supplied from the wall mount power supply the excess of the request current is get from the battery? I kindly ask some details about this point.

Thank!

Best regards!

  • 0
    TI__Mastermind 25800 points

    Hey Fabio,

    For #1, you may either set as a DCP by shorting D+ and D- pins together, in which case the adapter 2A current limit will be < IINDPM limit of 2.4A. If the adapter becomes overloaded, the integrated VINDPM will regulate the input voltage as the adapter voltage begins to droop, and this feature will automatically perform the charge current limiting action you are describing. You may also later reprogram the IINDPM setting after the D+D- detection is complete to 2A in order to prevent the adapter voltage from drooping.

    For #2, that is correct. 

    For #3, you will need to determine this information on your own to perform the shutdown. However, while the charger is charging, there is a Charging Status to inform you that we are in the pre-charge region (i.e. VBAT < 3V). However, if charging is disabled, this will not be case.

    For #4, there is a register bit that determines if an adapter is applied to VBUS.

    For #5, refer to question #1 response. This is the dynamic power path management feature of the charger. You can refer to section 9.4.2 Dynamic Power Management of the datasheet for more details.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Expert 1455 points

    Hi Joel,

    thank for your time!

    Could you please let me know somethings more about your answer at my Question #3, what is the mean "if charging is disabled", the IC charging feature can also be disabled?

    Thank and best regards!

    F.

  • 0 in reply to FFabio
    TI__Mastermind 25800 points

    Hey Fabio,

    The charging function is controllable either through the /CE pin externally or the CHG_CONFIG bit in REG01. These can enable or disable charge. Additionally, any faults will also disable charging.

    My point for #3 is that the charger may not be a reliable way for your host controller to determine if the battery voltage is too low. If charging is disabled by the above cases, you cannot determine if the charger is in the pre-charge region (VBAT < 3V) or not. 

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Expert 1455 points

    Dear Joel

    thank for your very useful information about this point!

    Searching about this stuff inside the datasheet (SLUSDA2 –JULY 2018) keep me landing on the paragraph 9.5.4.3 Interrupt to Host (INT) at page 28/66.

    Concerning the SOC estimation or at least to performing a rougly but safe estimate of the SOC of the battery in order to proper issue a safe shutdown of the system what may be the best solution? Using a microcontroller I can read the battery current by a current sensor and then perform the I*t calculation on charging and discharging (Coulomb Counting Algorithm), also reading the voltage may be useful to detect some threshold but there are some other integrated solution, IC's, that could facilitate this task?

    Best regards

    F.

  • 0 in reply to FFabio
    TI__Mastermind 25800 points

    Hey Fabio,

    So I only work with the charging devices. I would recommend posting a new thread requesting a gauging IC. We have plenty of fuel gauging products for single and multi-cell batteries, each with their own algorithms and extraneous features like temperature compensated SoC calculations and integrated protection. Someone from our gauging team can provide you with a good recommendation.

    Regards,

    Joel H 

  • 0 in reply to Joel Hernandez II
    Expert 1455 points

    Thank you Joel!

    Best regards.

    F.