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MAX3232E: Circuit integration.

Andrew Russell
Prodigy 30 points
Part Number: MAX3232E

I'm trying to integrate this into a design project at my University, but I'm having difficulties understanding some of the functions. Does this product amplify through DIN1 or DIN2 pins? From what I can see the purpose of the capacitors is to smooth out the output signals, but do they need to be the capacitors listed on the datasheet? I saw a schematic that had multiple inputs running into the IC, what happens if a signal is connected to the pins that are meant for capacitors? What conversions are the RS232 lines doing? Are there any example circuit designs that can be viewed?

  • 0
    TI__Guru 62910 points
    Hi Andrew,

    This chip is designed to convert between logic-level signals (DIN, ROUT) and RS-232-level signals (DOUT, RIN). This is useful when trying to send data from a low-voltage digital device like a microcontroller or UART (which may operate at supply voltages like 3.3 V or 5 V) over a cable to some other system that is designed to implement the RS-232 interface. Because RS-232 signals swing by fairly large voltages above and below ground, though, the MAX3232E chip also needs to be able to generate these large positive and negative reference voltage to use. That's where the C1/C2/V+/V- pins come in. These are used to implement a "charge pump" which is able to first take the VCC supply and boost it up to a larger voltage at V+ (by charging a "flying" cap up from VCC and then using it to dump charge on a "storage" cap) and then to take the V+ voltage and make a negative copy of it on the V- rail (using a similar technique).

    With this in mind, you can take a look at Figure 7 in the datasheet to get an idea of the typical external components involved. In this case data that is to be transmitted on the line would first be input to the DIN pins and the transceiver would take the data and boost it up to RS-232 levels on the DOUT pins (e.g., for transmission over a cable). At the same time, the transceiver will receive RS-232 levels on the RIN pins and output corresponding logic signals to an MCU/digital device on the ROUT pins.

    Good luck in your project!

    Regards,
    Max
  • 0 in reply to Max Robertson
    Prodigy 30 points

    Using the Caps, does that take out the need for higher rail voltages? If not, do I need seperate rail voltages for this chip to increase the output voltages past the 3.3V or 5V I out? This is inside a digital circuit so everything is running at 5V and gnd currently. Thank you for the help.

  • 0 in reply to Andrew Russell
    TI__Guru 62910 points
    Hi Andrew,

    Sorry for the delay getting back to you. Yes, when using the capacitors there is no need to supply the chip with a voltage rail besides 3.3 V or 5 V and ground. The higher voltages that are needed for RS-232 communication will then be generated by the transceiver's charge pump and can be observed on the V+ and V- pins. In case you would like to learn more about the charge pump operation, you can refer to this blog:

    e2e.ti.com/.../how-the-rs-232-transceiver-s-regulated-charge-pump-circuitry-works

    Let me know if you have any other questions.

    Regards,
    Max
  • 0 in reply to Max Robertson
    Prodigy 30 points
    Thank you for the assistance. I believe I've gotten it to interface properly and it should work great.