MAX3232 consuming problem - Page 1
Forum section: electronics / projects

author: Katanara
author_rank: Contributor
timestamp: November 02, 2022, 09:50:09 am
content: Hello! There is a critical problem with RS232 receivers. I need to run one system (it's pump actually) with a microcontroller. So, for a lot of regulars it should be simple. But I have an issue.When I connect the 232 plug, the supply current is increasing (MCU can be off or not). And it's not working. At first I used two different models of chinese adapters (based on SP3232). Then was soldered the MAX3232 scheme. It's original one of Texas. In all cases there was the same problem.As the supply I use the LDO (<100mA). When current is rising, voltage (3.3 or 5V) can be dropped to less. Input voltage is 24, current supply near 60 mA (1.5W only on 3232 consuming). I have tried to replace the LDO to more powerful - chinese adapters became very hot then! Without 232 connector the supply power is less than 0.2 W. If I remove or swap TX and RX of 232 then current stable to normal too.One would think that it's about the pump's controller problem (there, among other things, the supply and ground contacts are used). But ringing is good and more importrant: I also use an USB to 232 converter (CH340), and the system is fully working.Datasheet:https://www.ti.com/lit/ds/symlink/max3232.pdf?ts=1667382138609&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FMAX3232%252Fpart-details%252FMAX3232IDThe scheme was based on this ds. I also highlight the image of this from there. The capasitors are 0.1uF, supply is 3.3V.Thank you!

author: geggi1
author_rank: Frequent Contributor
timestamp: November 02, 2022, 07:39:05 pm
content: Try to increase the charegump capacitors C1 to C4.In the past I had problems with the MAX232 would not do the level convertion propperly.As far as I remember i did multiply the capacitor values by 10.

author: mikerj
author_rank: Super Contributor
timestamp: November 02, 2022, 08:08:16 pm
content: Quote from: Katanara on November 02, 2022, 09:50:09 amThat sounds like you have a bus collision i.e. you have connected TX to TX rather than TX to RX.

author: Katanara
author_rank: Contributor
timestamp: November 02, 2022, 08:35:12 pm
content: Unlikely, but possible. In this case I also failed to start interface, but maybe there was another reason for it.A good point for rechecking.

author: celkins
author_rank: Newbie
timestamp: November 03, 2022, 03:12:08 am
content: Folks,I have experienced this same problem, and after 3 or 4 chips in the bin, I managed to find a reference to this..The issue is that the chip suffers from latch up if any of the charge pump outputs go to the wrong polarity : the fix is to strap then with suitable diodes to prevent this. Since fitting diodes to my board, I’ve had no problems at all.I don’t appear to have kept the link to the errata for this, and can’t take this offline at the moment, but I’ve used 3 Schottky diodes, just can’t see which pins they are on.I’ll try to find this sheet, or failing that, take mine down to check, but it’ll be tomorrowGoogle found it (this isn’t an identical chip, but it isfunctionallythe same, an RS232 tx/rx):https://assets.maxlinear.com/web/documents/an218_sp50x-rs232-latch-up-prevention_041213.pdf