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MAX3232E-Q1: Charge Pump, ununsed pin, layout

Dongbao Zhou
Expert 3930 points
Part Number: MAX3232E-Q1

Hello team,

I have some questions about MAX3232E-Q1, that I don't find an answer from d/s and e2e.

1. Charge pump

  • .Why we need two charger pump (positive and negative) integrated into Max3232-Q1？
  • What does V+ and V- stand for? What are the typical value of V+ and V- if Vcc=3.3V?

2. Unused pin

  • For unused receiver port, we can leave input and output open. While for unused driver port, the input pin must have a logic high or low applied,  and the output pin could be left open. Is that correct?
  • Do we need to add pull-up or pull-down resistor in receiver/driver output pin?

Thanks.

Dongbao

  • 0
    TI__Guru 62910 points
    Hi Dongbao,

    The charge pumps are used to generate higher-voltage positive and negative voltage rails that are used by the driver to output proper RS-232 voltage levels (which cover a larger range than just the VCC/GND rails of the IC). You are right that it is OK to leave unused receiver ports open. The driver outputs can be left open as well, and you are right that it is generally best to pull the driver input pin either high or low. (Allowing this pin to float could result in a mid-point bias that could cause excessive current consumption.)

    I hope this helps, and if you have any other questions please let me know.

    Regards,
    Max