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bq24032a: problem about system's supplying current from USB and BAT

Jiang Boqian
Intellectual 655 points
Other Parts Discussed in Thread: TPS61032, BQ24032A

Hi,

I am currently using bq24032a to power my little motor control system( motor driver IC's supply voltage directly from bq24032's OUT pin, and control logic from an one-cell Li-Ion booster tps61032 powered uC) while charging a 3.7 volt Li-Ion battery.

I set PSEL to LOW, ISET2 to HIGH and connect ISET1 to 3k resistor. So when USB plugged in without system load, I will get approximately 330mA charging current to battery, and that's also what I measured using an multimeter.

But I got confused when running my system, with USB plugged in, battery presented. I measured USB port supplys 250mA and battery supplys 160mA approximately. I also measured the battery's supplying current without USB plugged, it is 450mA approximately. I don't understand, 450mA is not reaching 500mA current limit. I read the datasheet about DPPM, so I think I should have a 500mA USB supplying current, most of them( 450mA) goes to system, while the rest of 50mA charging my battery. Is my understanding right... I don't think so, but cannot figure out why, and if it is necessary to modify my circuit.

Answers desired, thanks :)

  • 0
    Intellectual 655 points

    My USB port can deliver 460mA approximately, with only USB presented. I measured this using my system simply drives a dc motor, with 4.79 volt on USB pin.

  • 0
    TI__Expert 7730 points

    Hello, Boqian,

    Your understanding about the DPPM is correct. The charge current will reduce when there is a system load. If the input cannot provide enough power to the load,  the battery will supplement the current to load.

    330mA sounds right with 3k resistor to ISET1. The 460mA from USB is also correct as the 500mA is the maximum limit so any input current between 400mA to 500mA is reasonable. The above two data points can probably tell that the chip itself is functional as expected.

    What you observed with your system doesn't seems normal though. Can you provide more information about your setup like the input voltage, battery voltage, system voltage, etc? Also, when you got the 460mA from USB, did you run the same system that you were running with the battery earlier? In other words, with the battery, you were only able to see 250mA from USB, but without battery, the USB can provide 460mA to the system?

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Intellectual 655 points

    Thanks for reply Wenjia,

    I will measure and update more information about my system's setup on Monday.

    But from now, I can reply some of your questions.

    Wenjia Liu said:
    Also, when you got the 460mA from USB, did you run the same system that you were running with the battery earlier?

    Yes, it is the same system. I try only USB presented, only battery presented and both USB and battery presented separately, IIRC... The current readings come from a multimeter. Also, I will start another new but same test when back to lab... in case of my bad memories...

     

    Wenjia Liu said:
    In other words, with the battery, you were only able to see 250mA from USB, but without battery, the USB can provide 460mA to the system?

    Yes, that is right.

     

    I am thinking if the behavior is caused by my motor driver IC. The motor may has a large starting current, which may exceed 500mA( the stable current is 460mA, so 500mA is reasonable)... But that doesn't make sense... Why USB has a 250mA current when both are presented...