LTC4015 INTVCC issue

Hello!

I'm having an issue with the LTC4015 chip. I integrated the design into dev PCB that I'm working on, and used the reference application circuit in the data sheet (application circuit 1). I made the following modifications

- replaced M3 with the following: https://www.digikey.ca/en/products/detail/texas-instruments/CSD18534KCS/3674879?s=N4IgTCBcDaIMIGUAiBGAHAVgMwBYDSiIAugL5A

- Removed the circuitry for UVCLFB and  connected it to 2P5VCC with a 10k resistor.

I've also configured the chem and cell pins for an 8-cell li-ion battery.

The issue I'm having is rather strange. I have the board running from a wall power supply at 28V, no battery connected. I can confirm that at this point INTVCC is 5V. However, when I enable the measurement system with force_meas_sys_on, it drops to 3.5v. This leads me to believe that the internal LDO isn't able to output enough current to operate the circuit and the ADC, however this seems very strange to me as I'm using the reference design nearly verbatim. I don't believe it is an issue with my power supply, as I can confirm that it is not hitting a current limit, and after enabling the measurement system, the chip reports reasonable values for everything (vsys and vin are ~27-28v, IIn is consistent with the expected load for the board).

A few other strange issues

- drvcc_good is reporting 0 despite it being connected directly to INTVCC in the design

- no_rt is set, although from other forum posts I believe this is normal when the chip is not charging a battery

Any suggestions for likely culprits or any additional information about the chip to help my debugging would be greatly appreciated!.

Thanks,
Adam

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  • 0
    •  Analog Employees 
    on Aug 26, 2021 6:14 AM

    Hi Adam,

    Hope you are doing well.

    I might need more info so I'll ask some questions on this. Is this a recurring issue when no battery is connected? When you try to connect a battery, does this occur again? Also, when you try to force_meas_sys_on, what is the state that your battery into (battery detection or charger suspend)? I'm thinking that this is the response of trying force_meas_sys_on without a battery connected, the INTVCC is forced to go into a UVLO state to suspend charging. Can you confirm this by checking the state of your charger? The drvcc_good reporting as 0 is a result of directly tying to the INTVCC since the value at which the DRVCC will servo is around the voltage of the INTVCC(in your case 3.5 which is in UVLO).

    Regards,

    Siglo

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  • 0
    •  Analog Employees 
    on Aug 26, 2021 6:14 AM

    Hi Adam,

    Hope you are doing well.

    I might need more info so I'll ask some questions on this. Is this a recurring issue when no battery is connected? When you try to connect a battery, does this occur again? Also, when you try to force_meas_sys_on, what is the state that your battery into (battery detection or charger suspend)? I'm thinking that this is the response of trying force_meas_sys_on without a battery connected, the INTVCC is forced to go into a UVLO state to suspend charging. Can you confirm this by checking the state of your charger? The drvcc_good reporting as 0 is a result of directly tying to the INTVCC since the value at which the DRVCC will servo is around the voltage of the INTVCC(in your case 3.5 which is in UVLO).

    Regards,

    Siglo

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