max232epe gets hot , real hot

[richard]

has anybody got any clues why my max232epe's get hot and draw excess current nearly 400ma but only sometimes at other times they are fine . several power ups are sometimes required before the chips will run properly.
there are no floating inputs and there is no external load on the +/-`10v supplies . I have tried tant / electro and npo caps they all have the same issue. if I replace the epe version with a 232n all is good problem gone (except you can't buy them any more). the max232epe's appear to be genuine Maxim devices and were supplied by a reputable supplier . I know the epe's have no internal pullups on the cmos / ttl inputs but none of these are left floating (once the pic sets the tris regs anyway). I'm mystified

[Archangel]

If it's getting hot, obviously that power's going somewhere, I'm guessing you have an input / output state conflict between it and whatever is connected to it. I suggest some current limiting resistors and trace out the logic to resolve this issue, or it could just be fried

[richard]

If it's getting hot, obviously that power's going somewhere, I'm guessing you have an input / output state conflict between it and whatever is connected to it. I suggest some current limiting resistors and trace out the logic to resolve this issue, or it could just be fried

that's not the case a max232n in the same socket works fine , a max232epe works sometimes

[Archangel]

that's not the case a max232n in the same socket works fine , a max232epe works sometimes

. . . and you bought these from a reputable source?

[HenrikOlsson]

Hi Richard,
I haven't looked into the difference between N and EPE but are they both supposed to have the same value capacitors as you're using? I know some needs 1uF while others need 0.1uF for example.
Another possibility is bad chips, where did you get them? EBAY?

/Henrik.

[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.