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  • Resolved

BQ24172: Battery current has no limit

Part Number: BQ24172

Hello

Please find my schematic attached to this post.

We are trying to develop a 3-cell Li-ion charger with this part. There are quite some issues that are present.

1. With a Vref = 3.3V , the voltages with the dividers at ISET, ACSET should be 0.8V, but I measure as 0.65V (all resistors are 1% and accurate)

2. I have set the CELL/FB at 10V (for checking) but with a resistor load i get around 7V or lesser still. Yesterday I got 4V there. With a capacitive load I get similar voltages.

3. STAT is constantly blinking on resistive load, but i believe that is bound to happen. Since the chip is expecting a battery connected at the output.

4. With a 3-cell battery connected at the output and a 16V/10A source(fixed voltage and current)  there was no limit to current, all 10A was flowing in the battery. I immediately shut off input power to prevent further       damage.

5. If i limit the input current to 2A, there is around 100mA current flow in to the battery.

6. I am not using the System output anywhere, I just need the battery output, which is going on to another cell balancing part ISL94203 (Currently it is not connected)

What is the problem? Please advise

CHG_BQ24172.pdf

  • In reply to Abhijit Jagtap8:

    Hello Abhijit,

    Can you please let us know which pins are damaged? Does this happen on one board or multiple boards?

    We first need to locate the damaged area for further debugging. 

    Please use the BQ24172EVM schematic for reference. I have looked into your schematic, besides the BATFET connection and TS connection, for ACVV, we suggest to only add a 10ohm resistor for the AVCC rising slew rate control. 

    Regards,

    Jing Zou

    Application Engineer, Battery Charging Products

    Please click "This resolved my issue" button if this post answers your question.

  • In reply to Jing Zou:

    Damaged pins are PVCC and AVCC
    My sch is based on the evm .
  • In reply to Abhijit Jagtap8:

    Abhijit,

    We typically need to run an FA on the IC to allocate where the first failure comes from on the IC. 

    There are several possibilities.

    1. As previously all the 10A current passes through from input to the battery. When it is turned off, due to the parasitic inductance on the path, it is highly likely the voltage of the can spike up to exceed the voltage rating for AVCC and PVCC.

    2. Can you please check if the 10ohm resistor connect in series with AVCC is damaged or not?

    3.  Have you tried on a fresh board that has not been tested before?

    Regards,

    Jing Zou

    Application Engineer, Battery Charging Products

    Please click "This resolved my issue" button if this post answers your question.

  • In reply to Jing Zou:

    Hi Jing

    I got 4 more boards assembled.

    There was a severe bug on our boards which somehow got overlooked. In one of the layers, the output inductor L1 from SW pin was acting as a direct short link to the shunt resistor R24. We removed this short circuit physically by cutting the track and then set current as 0.78A , and 0.78A started flowing!!

    Although on the same board , when we tried to increase the ISET current by adjusting Viset voltage by increasing R17, the ISET pin somehow got damaged. It now presents a 0v and shows a resistance of 124R. Naturally there is no current flow. I am trying to understand why this pin got damaged, since we did not do nothing more than change a resistor there! Is i so sensitive to ESD? if we assume that ESD damaged it?

    On another board , we again assembled and set the current to 1.5A and FB voltage of 12.6V . Current flows, tapers when voltage nears 12.5V , never reaches 12.6 since Iref of 10% of Iset reaches sooner and the current is cut off.

    So it behaves perfectly and as expected!

    Please comment on the cause of the damage , after which i will mark this thread as resolved!!

    Thanks for the support

  • In reply to Abhijit Jagtap8:

    Hello Abhijit,

    Regarding on the ISET pin damage, it is hard for us to pin point the cause without an FA to locate where the first failure was introduced. Based on your description, it is highly likely the ISET ESD is damaged.

    Please refer to the datasheet ESD rating section for our ESD spec. Our device has been tested and pass the ESD level specified in the datasheet.

    Regards,

    Jing Zou

    Application Engineer, Battery Charging Products

    Please click "This resolved my issue" button if this post answers your question.

  • In reply to Jing Zou:

    <p>Thanks Jing</p>

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