MAX232 circuit design guideline
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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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.
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
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Basic Circuit diagram:
Here is the basic circuit diagram according to the datasheet.
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.
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:
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.
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.
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.
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