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BQ24104: TS and VTSB pin have low(near short) internal resistance to GND pin.

Deniel Go
Intellectual 365 points
Part Number: BQ24104

Hello,

We were trying to debug the issue with our charging circuit not functioning. Our charging circuit is shown below. We have two boards that have have a non functioning charging. There was no indication of short in the Vcharger PIN to GND and VBAT PIN to GND and the charger circuit was functional and was used a number of times prior. There is no output on the charger. when battery and 12V Power Adapter is plugged in. One board (BOARD A) shows STAT1 LED blinking when the 12V Adapter is plugged in while the other board (BOARD B) has no LED Turned ON. 

After measuring the resistances of ICs pin to GND, we found the TS pin with RC14 and RC15 still connected to it, to measure around 40-50ohms on Both BOARD A and BOARD B. Board B also had VTSB read  low resistance of 23ohm with respect to GND pin. We then removed RC14, RC15 and CC4 to check if the short was with the external components or with the IC.

The LOW Resistance measurements were still present

Summary of Resistance Readings

BOARD A

TS to GND: 54ohm

VTSB to GND: 30kohm

BOARD B

TS to GND: 43.4ohm

VTSB to GND: 23ohms

We would like to know what might have caused this issue. Is there any thing in our schematic that would have caused it? We have a couple more boards the have the same schematic and layout and we have been using them as well but they did not show this issue. 

Prior to the pins shorting internally. with the resistors still on the PCBA, we were measuring near 20kohms at the VTSB pin and near 10kohms at the TS pin. 

We look forward to your response. 

Thanks,

Deniel

  • 0
    TI__Mastermind 35475 points

    Hi Deniel,

    I notice you are right on the maximum specification of the charge current, do you see the same problem when the maximum fast charge and precharge current is lowered to say 1.75 A and 175 mA?

    As for the rest, we need to isolate this issue as best as possible:

    1. What is the battery voltage applied?

    2. What are both STATx LEDs doing in these cases?

    3. What specific action instigated this observation?

    4. Under what conditions has the VLOAD circuit been verified and are there any issues with it?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Intellectual 365 points

    Hello Mike,

    Thank you for the response. We have not tried it with a 1.75A fast charge. We do have a circuit that can bring down our fast charge rate to 1A and that did not have any issues. But by default it is set to 2A and we have always been using 2A fast charge. Is there any issues with setting the fast charge to 2A? Can this have an effect to the TS and VTSB pins?

    Answering your questions

    1. We are using a 2S4P Lithium Ion Battery. We were not able to measure the battery voltage during the time of failure. But we can estimate that it was between 7.4 to 8V We have also done verifications at the lower battery voltages of 6.5V and charged it until it was full (indicated by STAT2 Green LED)

    2. In one board, that had a low internal resistance to GND on both VTSB and TS pins, STAT1 and STAT2 LED was OFF. For the other board that had only a low internal resistance on the TS pin, STAT1 LED was blinking. We were not able to get a waveform of it. STAT2 LED was OFF.

    3. Specific Action: We wanted to charge the battery. We were using our circuit the previous work day and wanted to charge the battery the following morning. The battery was fully drained. As mentioned in number 1. It might have been around 7.4 - 8V. We applied 12V and saw the STAT LED1 blinking and no current draw was coming from the power supply. We checked another board and it had a working charging circuit.

    4. There is no issues with the VLOAD. There were no indications of shorts in the path. VLOAD also gets disconnected from the charger during charging by the SPDT Relay. VLOAD was not drawing current during that time the 12V was applied to VIN. The only thing connected to the battery and charger was VSYSTEM and that also was not drawing current prior to connecting the 12V. There was also no short in the VSYSTEM path.

    Let me know if you more context and information about our system.

    Thanks,

    Deniel

  • 0 in reply to Deniel Go
    TI__Mastermind 35475 points

    Hi Deniel,

    The current is still within bounds I was just seeing if any faults had occurred on lower charge currents. Please continue to observe this and if it happens to another charger note what charge current was used.

    One thing I would change as a side note would be to increase your pullup resistance for the STATx pins. With 12 V input and 220 ohm resistance you see about 55 mA when the open-drain FET is on. In our typical application we use 1.5k Ohm or a 8 mA current into the open-drain. This will reduce some stress on the STATx switches.

    Can you send me your layout so I can make sure nothing is wrong there?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Intellectual 365 points

    Hello  Mike,

    Thanks for the your response. We will make the changes with the STATx pins pullup resistance. We will also try to test the board continuously at the lower charge rate. For the layout of the charging circuit, can I send it to you via the Private Message?

    Thanks,

    Deniel