Max232 is one of the most popular RS232 communication ICs in the electronics arena. Straightforward circuit and very easy to use too. Anyone can implement the circuit within few minutes. But there are some issues I found in products. If you are using the MAX232 IC as your product and that product will be used for years, you must have to maintain some protections. In this article, I’ll discuss MAX232 failure protection and MAX232 circuit design guideline.

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Table of Contents

About MAX232:

The MAX232 device is a dual driver/receiver with a capacitive voltage generator to supply EIA-232 voltage levels from a single 5-V supply.
Each receiver converts EIA-232 inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of 1.3 V and a typical hysteresis of 0.5 V
and accept ±30-V inputs. Each driver converts TTL/CMOS input levels into EIA-232 levels. The driver, receiver, and voltage-generator functions are available as cells in the Texas Instruments LinASIC library.

MAX232

This is the pin configuration of MAX232. There are two sets of Tx & Rx pins. For RS232 communication, this IC is the most popular.

Download the Datasheet of MAX232

Basic Circuit diagram:

Here is the basic circuit diagram according to the datasheet.

The basic diagram of MAX232

The manufacturer recommends this circuit diagram. But there is something else you must take care of. As the MAX232 IC doesn’t have any ESD protection, so you must take care of that. Here are some common issues with this IC.

Common troubles:

There are some common troubles with this IC that happens in long run.

  • IC Heating issue
  • No communication issue
  • IC burning issue

All of these issues happen due to some minor mistakes. Here are some guidelines to solve those issues.

Circuit design Guidelines:

Heating issue:

The MAX232 IC can be heated by anything from powering up. This can happen due to the overlay of trigger signals. As there are boost converters inside, a small overlay can heat the IC. We can solve this issue by using a power switch like MOSFET/BJT to trigger the IC’s power just before starting the communication. But there are some related linked issues you must maintain too.

No Communication issue:

No communication issue is found if there is any missing capacitor. There are 4 capacitors used for the boost converters. If anyone is missing or the connection is missing, duplex way or simplex way miss-communication will happen.

IC burning issue:

This is linked with the IC heating issue. If the IC is heating for a long time, it will be burnt. But why this happens? It can happen for several reasons. All are related to missing the timing of the signals. Using a resettable fuse can give a good result.

A long-lasting circuit diagram:

After gathering experience for a long time using this IC, I recommended this modified circuit diagram which I implemented in my products which are running 24×7 for years without any issues.

MAX232 circuit design guideline
Recommended circuit diagram

Here, I got the best result using ceramic non-polar capacitors (SMD). Two series resistors of 330 Ω and two bidirectional TVS (Transient Suppressor Diode) diodes are used as ESD protection. This simple modification solved all issues with MAX232 troubles.

Conclusion:

In this article, I’ve shared my experience troubleshooting some issues with MAX232 IC with MAX232 circuit design guidelines. I hope this will help others to keep the IC protected as well as the products or the circuits will get long service life. If you have any questions, please comments below.

I hope this project was helpful to you. If you make one for yourself, it will be a great pleasure for me. Anywhere you need help, let me know. Please share this project and subscribe to my blog. Thank you.

For Professional Designs or Help:

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MKDas

Mithun K. Das; B. Sc. in EEE from KUET; Head of R&D @ M's Lab Engineering Solution. "This is my personal blog. I post articles on different subjects related to electronics in the easiest way so that everything becomes easy for all, especially for beginners. If you have any questions, feel free to ask through the contact us page." Thanks.

8 Comments

ibra · 02/06/2022 at 12:43 pm

thank you in advance. Your explanation is very easy to understand. i want to ask you about what is the value used by the tvs diodes?

    MKDas · 05/06/2022 at 11:55 am

    Thanks. Use 16V bidirectional.

      khalid · 25/07/2022 at 4:23 pm

      thanks you for this explanation , can you to explains why this modification for 330 ome , 100nF and TVS. or how to know this modification ??

        MKDas · 26/07/2022 at 12:19 pm

        well, R&C forms a RC filter and TVS protects from spike.

        Balwan Singh · 20/08/2022 at 4:37 pm

        I was facing the same heating/ burning problems with max3232 IC.
        I did many experiments to solve the same problem.
        1) First I had a doubt on PCB layout as the tracks were very thin and a long route of tracks without any decoupling capacitors.
        2) capacitors were used of 0.1uf for 5 volt operation.
        3) But datasheet of this product recommends different capacitor values as per voltage range of operation.
        4) I was using a regulated variable linear power supply of good quality so there was no doubt of interference.
        5) I found that when I applied voltage to the ic directly from the banana plugs,
        It latched every time and got hot or burnt if kept for a longer time of period.
        6) if I connected IC with supply and turned the supply mains switch on then it worked fine.
        It shows that a ramping voltage avoids latching of IC.
        7) this all was happening without connecting the ic outputs to any device.
        8) then I connected IC to the input/output devices.
        9) when input/ output devices were kept unpowered and ic (max3232) was turned ON, it created problem.
        10) when input/output devices were already powered and then ic was powered it worked normally.
        11) lastly I came down from 5 volt supply to 3.3 volt and added 330 ohm resistances as suggested by you now I m confident it is working fine.
        Thanks for an excellent idea.
        Now let me know the exact nomenclature of TVS you used for ESD protection in this circuit.
        If it is smd type would be more suitable.
        Thanks a lot
        Balwan

          MKDas · 20/08/2022 at 5:39 pm

          Like you, I suffered a lot with this stuff. But now it’s all working fine. Pleased to know your problem was also solved. Now, you can use any TVS between 16V~32V. but, in my design, I’ve been using 16V bi-directional.

Eyub · 06/08/2022 at 8:16 pm

Hello

Thank you for your suggestion. I would have two questions:
1. How many volts should the TVS diode be and can you give an example series?
2. How can we avoid signal loss for long range cable?

Thank you

    MKDas · 08/08/2022 at 11:36 am

    1. RS232 has a voltage range of +/- 15V so you can use over 16V to 30V.
    2. Each cable and protocol have a range of distance, keep your distance within that limit to minimize the signal loss. And if you still need to extend, then use a signal booster in the mid. Like use a receiver in the cables end and transmit again that same signal to another cable. Which will actually boost the signal strength.

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