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BQ24780S: Compatibility with 24V Adapter and VCC Overvoltage Threshold Issues

Cho Lena
Prodigy 80 points
Part Number: BQ24780S
Other Parts Discussed in Thread: BQ24735,

Hi, Sir,

We are using the BQ24780SRUYR charge IC on our motherboard. Our application requires the use of a 24V adapter.
However, we noticed in the datasheet that the minimum VCC overvoltage rising threshold is listed as 24V.
Our customer pointed out that 24V adapters typically have a tolerance of +/- 5%, meaning the maximum input voltage can reach 25.2V. Indeed, during our testing with a 25.2V input, several boards experienced a shutdown issue (we confirmed this was not caused by insufficient wattage).
We have the following questions:
1. Given that the maximum VCC operating voltage is 24V, but the VCC overvoltage rising threshold minimum is also 24V, is it feasible to use a 24V adapter with this IC?
2. If a 24V adapter is supported, what circuit modifications can we make to prevent triggering the VCC overvoltage rising threshold (min 24V)?

schematic is below:

image.png

  • 0
    TI__Mastermind 37481 points

    Hello Cho,

    Cho Lena said:
    1. Given that the maximum VCC operating voltage is 24V, but the VCC overvoltage rising threshold minimum is also 24V, is it feasible to use a 24V adapter with this IC?
    2. If a 24V adapter is supported, what circuit modifications can we make to prevent triggering the VCC overvoltage rising threshold (min 24V)?

    It should work with an input of 24V, but as you mentioned you are seeing this issues at 25.2V. We do not have a workaround for this device to support greater than 24V.

    If you need to use an input of 24V, you could use BQ24735, this is similar to BQ24780s and pin to pin compatible, but the ACOV shutoff is set using ACDET pin not the actual input voltage. So you can configure it to support 25.2V.

    Best regards,

    Christian. 

  • 0 in reply to Christian Moyer
    Prodigy 80 points

    Hi, Christian,

    I checked the datasheet of BQ24735, but it is not pin-to-pin compatible with the BQ24780s.Are there any other solutions that are pin-to-pin compatible with the BQ24780s?

    If we want to increase the OVP threshold to 25.5V, can we add two diodes in series as shown in the figure below?
    By doing this, we aim to create a voltage drop so the VCC pin detects a lower voltage than the actual input. This would prevent the IC from entering OVP protection when the adapter output is at 24V + 5% (approx. 25.2V). Is this an acceptable design?

  • 0 in reply to Cho Lena
    TI__Mastermind 37481 points

    Hello Cho,

    Cho Lena said:
    we want to increase the OVP threshold to 25.5V, can we add two diodes in series as shown in the figure below?
    By doing this, we aim to create a voltage drop so the VCC pin detects a lower voltage than the actual input. This would prevent the IC from entering OVP protection when the adapter output is at 24V + 5% (approx. 25.2V). Is this an acceptable design?

    This should work. I don't see any obvious issues with this implementation. 

    Best Regards,

    Christian.