[SOLVED] MAX232 heat up after a few month

[Ahmad Edi Saputra]

Hello,

i am currently use max232CSE and ch340 to drive a thermal printer for my application. i do some test to my final board, about 10000 transaction a day, it work properly without error. but when i use it in outdoor (water is not the case) after 1 or 2 month it heats up and burn sometimes then can no longer be used. i am sure i use the cap value. i do some searching there are a few people having same problem but none of them was solved. so my question is what is possibly goes wrong with my design? and is there any solution for this problem?

Thanks

 

[KlausST]

Hi,

there have been discussions about this.

A known problem is when unused inputs are left floating.
Others are overvoltage, wrong connectionsdirty supply voltage, wrong signal levels, bad PCB layout.

Klaus

 

[Ahmad Edi Saputra]

Hi,

i don't see any discussion in this forum, or i missed something perhaps,

i already read some advise to pull up floating tx, and i did, but i get same result, even i add some 330 from v+ supply to max232 vcc, still no luck.
dirty power suply, i am not quite sure, i just use USB VCC, but maybe there is some chance this is the cause. i already plan to add external power suply recently, but i haven't done it

what do you mean by bad PCB layout? i know a few practice to design PCB. but if there is any reference you have regarding this problem i would be very happy

 

[KlausST]

Hi,

i don't see any discussion in this forum, or i missed something perhaps,

This forum has a search function.
If you use "max232 hot" you get some useful threads.

Powe supply:
USB or any other supply you need to supply the MAX232 within it's specified range...including noise/spikes on supply.

what do you mean by bad PCB layout?

I recommend to read datasheets. Nowadays almost any datasheet includes some PCB layout considerations or applcatiin informations ... and so does the MAX232 datasheet.

Other possible causes:
* too high load current
* ESD problems
* wiring, grounding, shielding of the RS232 cable (both sides)

Klaus

 

[Easy peasy]

most likely ESD during manufacture, or parts that are not strictly genuine ...

 

[Ahmad Edi Saputra]

i found some good reference, add 330ohm resistor to vcc pin and supply voltage, pull up every TX pin. and in max232 out and in. add 330 resistor before DB9 connector. it works, and i dont know why, now i am not having much problem like before

thanks all

 

[betwixt]

Those sound like bad solutions. Adding resistance in series with the supply pin may cause malfunction of both the transmit and receive parts of the IC and potentially can make them interact with each other. Adding resistance in series with the DB9 limits the current but in doing so makes the rise and fall times of the data waveform slower so it limits the maximum speed you can achieve. You are finding 'work around' solutions rather than curing the underlying problem.

Brian.

 

[Ahmad Edi Saputra]

i know it is a bad solution. but i can't came up with any other solution. for the first time, i think is only because floating condition on TX input max232 so it might caused high frequency noise, i added pull up, doesn't solve the problem, then i add series resistance with DB9, sometime still broke max232. so i added all thoose three solution at one, it does the job. i just have to make sure that input supply is above 5v( not until 6v ), so the voltage in v supply max232 still above 3. i also tried max3232, seem good with no heating problem without any of those bad circuit design, but haven't tried on the field. do you have any other solution?

Best Regards,
Edi

 

[czm_88]

I think you should check you shechmatic, and PCB.