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MAX3232E: EMC caused by 1Mhz charge pump

Zach Zhu
Intellectual 2520 points

Part Number: MAX3232E

Tool/software:

Hi expert,

MAX3232EIDR is drop-replacement with MAX3232IDR. However, customers reported that charge pump frequency of the MAX3232EIDR was 1Mhz, which could easily cause EMC problems and the EMC test could not be passed. 

Could you pls help give some comments or any other P2P device recommended?

Thank you!

BR,

Zach

  • 0
    TI__Guru* 78221 points

    Zach,

    We don't characterize the charge pump's frequency so I don't know which devices have which frequencies. 

    The MAX3232IDR is still an active device. If the switching frequency is a concern, can't they just keep the original device instead of replacing it?

    -Bobby

  • 0 in reply to BOBBY
    TI__Intellectual 2520 points

    Hi Bobby,

    Thanks for your reply. I have a question needed for your help.

    The charge pump is for converting Vcc to 3.3V or 5V, right? So I guess the switching frequency is set to be fixed. 

    Is there something wrong with my understanding?

    BR,

    Zach

  • 0 in reply to Zach Zhu
    Guru 320520 points

    The charge pump outputs are regulated to about ±5.4 V, so I would expect their frequencies to change depending on the load.

  • 0 in reply to Zach Zhu
    TI__Guru* 78221 points
    Zach Zhu said:

    The charge pump is for converting Vcc to 3.3V or 5V, right? So I guess the switching frequency is set to be fixed. 

    Is there something wrong with my understanding?

    The charge pump will take in the Vcc voltage and try to step it up/down to +/-5.4V (VoH/VoL of driver in datasheet)

    There is going to be some max frequency where it can't switch any faster. But my understanding of how the charge pump circuit works is it looks at the voltage on the pumps and will turn on/off it's charge based on the current voltage it's at. If it drops below 5V it will try to charge it up to 5.5V. If it charges over (example value) over 5.8V it will disable the charge. This basically loops over and over to try to regulate it to the +/-5.4V target.

    -Bobby