Can MAX232 powered at 5V and connect to tx rx(TTL) on ESP8266

I created a PCB to read data from my MPPT charging controller and it having RS232 communication. I'm using ESP 8266 and MAX232 CPE IC (To create RS232 converter). i input 5V to the MAX232 IC and connected it TX RX to ESP8266 RX TX, PCB is currently working and communication between the MPPT device and ESP8266 is working question is.

  1. ESP8266 TX RX pins are in 3.3V logic level. will it be a issue if i powered MAX232 IC, at 5V.(MAX232 is not working at 3.3V need to give above 5V to working) MPPT controller side is using MAX3232 CSE IC for its RS232 communication. And this ic is powered at 3.3V.but im using MAX232 and powered it at 5V,will it be a issue to the controller


Noted that(there is no place to buy MAX3232 IC in the local market)

From the datasheet for the MAX3232...

Accepts 5-V logic input with 3.3-V supply

Generally all pins on a microcontroller have clamping diodes for protection. That means that in practice, anything over ca. Vcc + 0.6V is clamped to Vcc. Conversely, that means that if you apply 5V to a 3.3V uC pin, the following might happen:

  • Clamping diodes on the uC conduct excessive current, causing damage to the die (local overheating).
  • The clamping current is sourced by the device that applies the excessive voltage, exceeding maximum ratings of said device.
  • The 3.3V power supply is being forced to sink current through its positive terminal with unknown effects on the PSU.

So you tell me - risk it, or perhaps stick to the ratings of each device in the chain?

Thank yoo.

Yes, i agreed, if i used Arduino UNO, problem solved on microcontroller side. what about your idea of RS232 side.

My MPPT device having Max3232 SMD ic ,powered at 3.3V.and I'm using Arduino Uno and RS232 my converter IC is Max232 powered at 5V, will it be a issues to my MPPT controller.

@Riva actually looked it up in the datasheet. I didn't bother fact-checking that. You might if you're not sure.

The RS232 side will not be a problem; typical RS232 output level +/- 8V, maximum RS232 input level +/-30V.

  1. RS232 levels are defined by specification. You if you MPPT controller (what ever that is) expects RS232 voltage levels then it irrelevant what the respective MAX's are power with.

  2. The 5V supplied MAX will output something in the order of 3.5 to 4.5 volts (going to the ESP8266). You can simply put a 10k between the MAX rx and the ESP8266 to limit the "fault" current. Some folks don't like this approach but it has worked for a lot of folks.

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.