I've been using the MAX232A line-level convector for serial communication for quite a while. It requires five 0.1uF capacitors. They're polarized in the reference circuit diagram (https://www.electro-tech-online.com/custompdfs/2008/10/MAX220-MAX249.pdf -- page 17/36).
In my circuits I've used ceramic caps (which are not polarized). Following the reference circuit I've run in to some stability issues. I've had some problems with serial communication connecting it to a PIC micrcontroller. Also in an I2C circuit using an Arduino and a couple MAX232A's, the I2C bus gets messed up after about 5 minutes of transactions.
In both cases I've narrowed the problem down to C4 in the reference circuit mentioned above. C4 is connected to V- on the chip. In the circuit C4 is connected between V- and GND. However, I've found that if I move the capacitor to between V- and +5V, stability becomes perfect. If I measure the voltage on the chip pin in both cases it's around -9V which is proper. If I remove C4, voltage is around -5V and communication gets really flaky.
Am I using the wrong type of capacitors?
Can anyone explain why I'm having these problems and why the workaround works?
I write some electronics tutorials on my website and I don't want to recommend going against the datasheet without some reasoning behind it.
In my circuits I've used ceramic caps (which are not polarized). Following the reference circuit I've run in to some stability issues. I've had some problems with serial communication connecting it to a PIC micrcontroller. Also in an I2C circuit using an Arduino and a couple MAX232A's, the I2C bus gets messed up after about 5 minutes of transactions.
In both cases I've narrowed the problem down to C4 in the reference circuit mentioned above. C4 is connected to V- on the chip. In the circuit C4 is connected between V- and GND. However, I've found that if I move the capacitor to between V- and +5V, stability becomes perfect. If I measure the voltage on the chip pin in both cases it's around -9V which is proper. If I remove C4, voltage is around -5V and communication gets really flaky.
Am I using the wrong type of capacitors?
Can anyone explain why I'm having these problems and why the workaround works?
I write some electronics tutorials on my website and I don't want to recommend going against the datasheet without some reasoning behind it.