Are all the 7660 chips this fragile?

[dennism]

I've built several pedals of the old positive ground circuits (FF, Buzzaround, TB, etc) with charge pumps to allow using a standard power supply (My power supply is a Boss brand).   They seem to have a high failure rate.   Often after just a few days or weeks of playing, the 7660 chip will fail.   I socket them and so it's just a matter of swapping in a new one, but it's still frustrating.   So, am I buying the wrong ones?   I normally buy them in lots of 10 or so from ebay sellers.   Are there some available out there, for more money maybe, that are more hardy and less prone to failure?

[R.G.]

The 7660 is not particularly prone to failure. Possible issues are:
(1) your source; ebay sellers can be OK, but having been burned a few times by ebay, I consider it a last resort for semiconductors
(2) your setup; which Boss supply, what is your power filtering and connection schematic, are there any protection diodes, etc.?

The LT1054 is much more robust in general, if more expensive. It's probably not more expensive than using a rotating magazine of 7660s, though.

[dennism]

This is the layout I've been using, I think I'd need to mod it for the LT1054.   I suspect that cheapness is my issue here, so I may need to try the LT1054 or find a more reputable source for the 7660's.

http://www.sabrotone.com/?attachment_id=523

[Govmnt_Lacky]

(2) your setup; which Boss supply, what is your power filtering and connection schematic, are there any protection diodes, etc.?

Good question....

And I would like to add.... Is it regulated? Some BOSS supplies put out as much as 15-17VDC. Very bad for some of the charge pump chips.

[MrStab]

I think I'd need to mod it for the LT1054.

afaik you just need to clip off or isolate pin 1 for an LT1054 conversion, which is optionally connected to V+ on the 7660S to keep the oscillator frequency above the audio range, but isn't necessary with the 1054 (i assume you're using the 7660"S" variant).

at least, i hope so, as i've just done this twice over the last fortnight...

[dennism]

Yes, I just looked at the LT1054 datasheet (TI) and it says, Pin-to-Pin Compatible With the LTC1044/7660.

So is the output voltage for the LT1054  something around 9V(-), so it would be suitable for 9V powered effects like the 7660 and the MAX1044?   I couldn't find (or saw and didn't comprehend) that info in the datasheet.

[MrStab]

the LT1054 is suitable for use with 9V input effects and will work in much the same way as the other chips. it allows for more current draw than the others - 1.1V drop over 100mA - so is actually better in that way.

i've used the LT1054 in a circuit designed for 7660S chips (pin 1 & 8 shorted) before, and it worked fine, but the datasheet suggests you shouldn't, as pin 1 serves a totally different function from the other chips. See page 5 here: http://cds.linear.com/docs/en/datasheet/1054lfh.pdf .

i've heard of heterodyning issues when using the LT1054 with certain circuits containing oscillators, but the IC's oscillator frequency can be lowered by a cap (if needed) as per the datasheet.