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MAX3237E: DIN5 6V output

Shuji Ishiwata
Mastermind 7855 points
Part Number: MAX3237E

Tool/software:

Hi All,


I have a question about the MAX3237.

I confirmed that there was a voltage of about 6V from the DIN5 pin when there was no input signal.

Is it possible that the charge pump voltage is output from the DIN5 pin?


Best Regards,
Ishiwata

  • 0
    Guru 317370 points

    The DIN pins are high-impedance CMOS input and should never be allowed to float.

    It is not possible to measure the voltage of a floating pin. Try measuring the resistance between DIN5 and GND/VCC.

  • 0
    TI__Guru 73971 points

    Clemens is correct, since the pin is high impedance, there should not be an active voltage on the pin if there is no input signal.

    Shuji Ishiwata said:

    Is it possible that the charge pump voltage is output from the DIN5 pin?

    It's unlikely, unless the device was damaged.

    Are you able to capture the 6V signal you are seeing from an o-scope? 

    -Bobby

  • 0 in reply to BOBBY
    Mastermind 7855 points

    Hi Clemens, Bobby,

    The resistance between DIN5 and GND was high. No shorts or other issues were found.

    The same was true between DIN5 and VDD.

    I have sent the waveforms to you via private message, so please check them.

    Can you check this with an EVM? I would like you to reproduce the same phenomenon.

    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    Guru 317370 points

    Your circuit must not allow the DIN5 input to float. If the MCU's output might ever be disabled (which is likely during power up), then you have to add a pull-up resistor. Do you still see strange voltages with the pull-up?

  • 0 in reply to Shuji Ishiwata
    TI__Guru 73971 points

    Ishiwata,

    It's not possible for our device to step up the voltage like that. It is a high impedance input pin. 

    To me it looks like the CPU reset is causing leakage into the net/pin and pushing the voltage up. 

    As Clemens pointed out. A resistor on this pin may help to allow the leakage to flow somewhere else and prevent it from stepping up like this. 

    You can try adding a pull up resistor or a pull down resistor. I would suggest trying 4.7k first. 

    -Bobby

  • 0 in reply to BOBBY
    Mastermind 7855 points

    Hi Clemens, Bobby,　　

    A customer reported that 6V was output even when DIN5 was open and not connected to the CPU.
    Also, when a 10kΩ pull-down resistor was installed, the output was 0.2V.
    There seems to be a leakage current.

    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Guru 73971 points
    Shuji Ishiwata said:
    A customer reported that 6V was output even when DIN5 was open and not connected to the CPU.

    Is it possible the Vcc of the device is deregulating and pushing the rail higher than 6V?

    Shuji Ishiwata said:
    Also, when a 10kΩ pull-down resistor was installed, the output was 0.2V.
    There seems to be a leakage current.

    Is adding a pull down resistor something that the customer can do as a workaround?

    -Bobby

  • 0 in reply to BOBBY
    Mastermind 7855 points

    Bobby,

    Thank you for your support.

    We have informed the customer that floating is prohibited.
    We have also explained that the 0.2V caused by the insertion of a 10kΩ pull-down resistor is due to a leakage current of 18uA.
    As of now, we have not received any feedback from the customer.

    Best Regards,
    Ishiwata