Electronics > Beginners
W27C512 EEPROM Frustrations
CRCLARKE:
I am relatively new to eeprom programming, but i am gaining plenty of experience.... I have been working with the w27c512 and I am having some real struggles with erasing the eeprom. I have built an Arduino breadboard programmer based on Ben Eaters, along with an erasing module, wired it properly and followed the voltage requirements. I tested it and it works well.
The problem is, out of 10 chips, only 3 work properly, 3 won't erase, and 4 went up in smoke during erasing. I am not sure whats wrong, are they defective chips? am I not erasing properly? I do not use the verify algorithm, is it required? 3 erase just fine. I also don't use any timing to erase, just 2 push buttons. One for VPP and the other for CE...... I tried erasing at 12v and it works on the good chips, but had no effect otherwise.
I am once again 1 short on chips and the project is shelved. |O :-[
I have just ordered a 20 pack of w27c512, luckily there pretty cheap but the wait sucks. I really hope I don't have this much trouble with the next batch
Has anyone had this trouble before?
Are there any tips or tricks to erasing these eeproms?
Thanks!
Nerull:
If you're burning chips than you likely do not have something wired correctly.
Ian.M:
The W27C512 datasheet says it requires +14.0V +/-0.25V Vpe to erase on /OE and A9, will draw 30mA from Vpe and the abs. max. voltage those pins can tolerate is only +14.5V.
That's not a lot of margin between a successful erase and blowing the chip, so your Vpe switching circuit must provide clean edges free from overshoot, ringing etc. Also the spec says the /CE pulse to trigger erase is 100ms +/- 5ms, so there's no way you'l meet those specs with a simple pushbutton.
At the minimum you'll need a debounce circuit for the button, an active Vpe switching cicuit that can handle >30mA with negligable voltage drop, and some monostables to sequence Vpe and /CE with correct timing. Best bet would be to do the sequencing and timing with the Arduino.
CRCLARKE:
I am pretty sure it is wired correctly because I have erased several eeproms successfully, and the eeproms that do work I have erased several times successfully.
I am operating within the voltage tolerances, and have even successfully erased at 12v. I am aware of the 100us CE pulse but it does not specifically state a maximum time for VPP or A9. No issues reprogramming the chips, but only the ones that survived erasing made it to reprogram. and they have repeatedly worked as I was expecting. but it is total hit and miss, mostly miss. I feel it has something to do with that A9 voltage. I wish I knew how it worked, I added a current limit resistor to A9, didn't help, though it made the failures less catastrophic.
I can setup some timing for the erase, but I am skeptical about there being a difference....... and I don't think a denounce would help, because so what if it erases multiple times, but I can test it.
3 of the chips work reliably with my setup.... so far anyway, maybe there just tough, but I would expect them all to be identical
I will have to wait till new chips arrive to test because the chips that work, always work and the chip that don't, don't respond to anything so I have no way to differentiate the test
So I got some time to brainstorm till the new ones show up, so lay it on me!
james_s:
Buy a TL866 and use that, they're only about 40 bucks and will easily save you money in the long run if you are blowing chips.
Also where are you getting the EEPROMs? If they're from China they're likely pulls, many might not be EEPROMs at all. I once bought a couple of EEPROMs that turned out to be random 28 pin ICs that had been blacktopped and re-marked, I wiped them with acetone and the black paint came off the top.
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