Hello.I have some problems with the MAX232.In some cases, when I pluga and turn on the system (with contains the max232), the IC will be inoperated and overheat too much.In other cases, the RX will work OK, but TX not work.I don't know wich's the cause of my troubles...I hope help me.Best Regardsfede
This is very odd; please supply more information.
How many MAX232 units have overheated? Are they permanently damaged?Does this happen when the RS232 cable is unplugged? Do the 'system' with MAX232 and device on other end of the cable share the same ground?
The MAX232 should not overheat unless it is damaged by electrical overstress or electrostatic discharge.
In reply to Ron Michallick:
Some max232 are overheated.... it's very frequent . Of 10 system, one or two have this problems.
If I turn off the system at time (when overheated), the max232 aren't permanently damaged.I take few minutes, turn on again, and max232 will work ok.
This happen when I turn on my system with the RS232 cable IS PLUGGED.
The system with Max232 and other device share the same ground.
I checked that the DB9 Chassis are not grounded.
OT: Today I replace the max232 with the TRS232ECN, but my system have some problem at start up. In my system have an RTC. When I change the Max232 for TRS232ECN, ocurred the RTC data loss. The RTC datasheet note the negative voltage glitches... but it's is another problem.
In reply to Federico Couzelo:
Do you have a oscilloscope to measure to MAX232 pins.
Let me describe the expected signals.
C1+ is square wave 5V to 9V C1- is square wave 0V to 5V
C2+ is square wave 0V to 9V C2- is square wave -9V to 0V V+ is +9VV- is -9VVCC is 5V without large rippleDOUT pins +7V or -7VRIN pins unknown
All numbers are approximate; look for differences between good and bad devices.Is your application close to that in data sheet figure 4? The +/-8.5V labels are for information only, they do not connect to external circuitry.
Ok, i will check it.
My application is the same at the figure 4, but I have ommited the Cbypass 1uF.
Do you know why my system don't work when I replace the max232 for TRS232ECN??
This is most interesting. Only today, I have been working on an application where I too experience the MAX232 overheating along with the 7085 that is providing power. Initially I observed it to be intermittent. I stripped out the capacitors one by one but still intermittent heating up when i power up the circuit. Further investigation found that if you place a short on the capacitor between pin 2 and ground for a fraction of a second and the thing takes off. I removed all the caps and it still does it. I then checked with a circuit i built several years ago and placed the short on ground and then quickly removed it. Sure enough the MAX232 takes off and heats up, drawing considerable current and making the 7805 way too hot to touch.
I suspect that my intermittent fault may be down to a bad cap but I am now concerned that I could be sitting on a small time bomb. I haven't experimented yet but perhaps a resistor in series with the supply might limit the current if it starts to do whatever its doing??
Dave - G4UFS
In reply to David Pearson:
The plot thickens. After a little more digging and looking at other peoples circuits. I noted that all of them had the capacitor on pin 2 going to Vcc. This could be the problem with MY circuit and could be root cause of others.
The datasheet I have been working to was the first hit on google (see below) and it clearly shows the cap going to ground :-
Yet a further search which brings up another datasheet shows the cap on pin 2 going to Vcc :-
I will check my circuit later but perhaps it could explain the observation of others??
The C1 capacitor can be terminated to ground or VCC. The charge pump works equally well either way.I will test the temporary short effect in the lab later this week.
I tested shorting the V+ pin with and with out capacitors installed. The short current was very high, over 600mA, because there is an internal diode from VCC to V+.There was not any current gain that would suggest a possible latchup condition. When the short was removed the current level returned to normal.
I was not able to recreate the overheat condition.Regards,Ron Michallick
This is most interesting. I have reproduced the fault on three chips now. Just to be clear, this is pin 2 to ground. Something else i noted, when the chip heats up, removing power and then repowering has to be done after it cools otherwise it heats again
Any one else have the problem?
I experience the MAX232 overheating too.
My application is a little different that Figure 4. I have nonpolarized ceramic capacitors (1 uF) and the capacitor C3 (Vs+) is connected to VCC.
I turn off the system at time (when overheated). The max232 aren't damaged because if a turn on again, the circuit works!
Anyone else have the problem?
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