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BQ25895: Not charging getting reg0b 0xA6 read

Kasey Fillingim
Prodigy 20 points
Part Number: BQ25895
Other Parts Discussed in Thread: BQSTUDIO

Tool/software:

Hi (sorry -reposting as new question)

Im having issues getting the BQ25895 chip to charge the batteries. 

First id like to rule out there is an issue with the schematic, i'm using a custom PCB the schematic is below. We are using two 18650 batteries (in parallel) for charging the batteries we have a solar pane and standard USBC .Please let me know if you see any issues. 

Second the registers, Im using a mac so had to install BQstudio via utm and write the registers directly into the firmware. But am i completely messing up these setting? Ive tried just about everything here. 

 

Here are the readings i'm getting after uploading firmware 

BQ address = 0x6A

REG0: 0x79

REG1: 0x5

REG2: 0x3D

REG3: 0x3C

REG4: 0x14

REG5: 0x13

REG6: 0x5F

REG7: 0x81

REG8: 0xCB

REG9: 0x4

REGA: 0x93

REGB: 0xA6

REGC: 0x1

REGD: 0x97

REGE: 0x4C

REGF: 0x4E

REG10: 0x7F

REG11: 0x97

REG12: 0x0

REG13: 0xB9

REG14: 0x39

Please let me know, thank you 

  • 0
    TI__Intellectual 2460 points

    Hello Kasey,

    Thank you for providing your schematic and the register values. I reviewed your schematic and did not see any major issues. However, since you have a solar panel input, I recommend checking out this TI reference design to implement MPPT (maximum power point tracking) with the BQ25895:

    Maximum Power Point Tracking Algorithm for Low Power Solar Battery Charging Reference Design

    I see that register 0C bits 2-0 are reading 001, which means that the NTC fault status is reporting "TS Cold," and thus charge is suspended. I also see that register 10 bits 6-0 are reading 7F, which indicates that the TS voltage as a percentage of REGN is about 80.055%, which is above the cold battery temperature rising threshold, typically 73.25%. If the battery is not actually cold, then there could be an issue with the NTC that's being used.

    Best regards,

    Alec Lehman

  • 0 in reply to Alec Lehman
    Prodigy 20 points

    Trying again - here are the updated readings - Charging_Check:Temp=34.07c, REG00=1x48, REG01=1xE5, REG02=1xF5, REG03=1x1A, REG04=1x96, REG05=1x13, REG06=1x5F, REG07=1x89, REG08=1x67, REG09=1x14, REG0A=1x92, REG0B=1xA6, REG0C=1x01, REG0D=1x12, REG0E=1x50, REG0F=1x53,

  • 0 in reply to Alec Lehman
    Prodigy 20 points

    Thank you! also do i need to programmatically set the CE pin low? Its physically being pulled down but unsure 

  • 0 in reply to Alec Lehman
    Prodigy 20 points

    i have honestly tried every setting programmatically (12 hrs a day for 12 days) and sometimes it will charge slightly but is still sending the A6 or A7 on 0B so I mess with the settings more and mess everything up. Im at a loss, and if its not a hardware issue i don't understand why this is as convoluted as it is. I want to use this chip but don't know what to do. Please help 

  • 0 in reply to Kasey Fillingim
    TI__Guru** 104785 points

    Hello Kasey,

    As Alec mentioned, it looks like your NTC may not be connected properly or it's characteristics are much different than the NTC we use in our EVM and provide reference RT1 and RT2 values for, the 103AT-3.

    Can you provide the NTC part number or datasheet?

    Sincerely,

    Wyatt Keller