max232epe gets hot , real hot

[richard]

Another possibility is bad chips, where did you get them? EBAY?

chips came from three separate supliers (farnell aka element14 ,rs components and a local supplier) they all look identical so I can't tell which is which any longer ,
the rs232c inputs are floating and the rs232 outputs are not connected to anything for the test process .according to the data sheet the cmos/ttl level inputs have no internal pullup and need to be not left floating , the rs232 inputs have internal pull down resistors so I'm assuming these can be left o/c (surely). I got a bunch of soic (smd) pack ones on ebay too but these have not been tested yet.
I have only tried 1uF caps but three different types. I'm at a loss to understand why they sometimes fail to work but after a few power on/off attempts they work (for days ) until the next power up

[HenrikOlsson]

Hi,
Well, with chips from three different, well known, suppliers fake/bad chips probably isn't the cause.
Thinking out loud:
What does the supply voltage look like, ristime etc? Perhaps the internal chargepumps doesn't start up properly or something.

/Henrik.

[richard]

that seems to be the issue, the slightest waver in vcc as the charge pumps fire up stalls the osc and then the excess current causes the ps to hiccup then the chip just sits there getting hot (it only takes a millisec ) . I can get it to fail at every switch on now . I will try moving the bypass cap closer to the vcc pin . these epe's are touchy

[richard]

bypass did not help, could it be contact bounce on the power switch ? . I get the same result using the 3amp regulated bench supply

[Ioannis]

I would mark the chips, say by a number, and see if the same chip is always the one to heat up. If this is true, then you know what to do...

Ioannis

[richard]

I have tried 5 epe with the same result all are subject to failure to operate ( none have been destroyed yet) and 5 of the 232n variety they never fail . if I leave the sw on and turn the bench supply on/off the chips always work ,if the sw is used to turn the board on then it may or may not work. increasing the ps smoothing cap made things worse . I have tried driving inputs high and low at power up nothing seems to satisfy these beastly chips

[Dave]

I personally would also check the value of the caps I was using as well as the polarity as connected to the MAX-232. I have used these level converters for over 20 years and have never had a problem with them. Although now that I remember, I did have one that did not have an very robust negative supply.