MN3007 pinout discrepancy

[julessouren]

The datasheet (http://www.experimentalistsanonymous.com/diy/Datasheets/MN3007.pdf) or the BBD Manual by Panasonic, list pin 1 as GND and pin 5 as Vdd (supply). However, multiple designs using the MN3007 (http://www.hollis.co.uk/john/zombie.jpg, http://www.madbeanpedals.com/projects/Collosalus/Collosalus2015.pdf, etc.) have these pins reversed.

Is there any reason for this, and do any other BBD chips suffer from the same issue? After creating symbols for the BBD chips from the datasheets, I noticed this discrepancy so thankfully I haven't fabbed any boards / fried any chips yet. If you can't trust the datasheet, what else is there?

[alanp]

Vdd is negative 15V, not plus 15V, that's why.

[julessouren]

Thanks for your reply. I hadn't checked the supply voltages from the datasheet, and they indeed show a typical supply of -15V. But when I look at the schematics, the zombie chorus has pin 1 tied to ground, and pin 5 to +9V. Is this a case of 'yes, but relative to +9V, pin 1 is at -9V'? The collosalus has pin 1 tied to +15V. It seems to me that pin 1 is at a higher potential than pin 5, which would be the same as pin 5 being at a lower potential than pin 1.

I guess what I'm saying/asking is, why not/can you use a voltage inverter, and tie the ground to pin 1 and the negative supply to pin 5? That way the BBD has a negative voltage supply with respect to ground (as I would expect) and all other circuitry is referenced to +9V and ground. I hope that makes sense, as I'm thoroughly confused. 

[Scruffie]

Is this a case of 'yes, but relative to +9V, pin 1 is at -9V'?

Yup, the chip doesn't know the difference.

And sure you can feed negative voltage to pin 5 but an inverter makes the circuit more expensive/complicated and when most of these pedals were designed originally wasn't very prevalent so a transformer would be required (like in the DMM) or you had a pedal without the standardized +9V DC power supply.

[greaser_au]

But when I look at the schematics, the zombie chorus has pin 1 tied to ground, and pin 5 to +9V. Is this a case of 'yes, but relative to +9V, pin 1 is at -9V'? The collosalus has pin 1 tied to +15V. It seems to me that pin 1 is at a higher potential than pin 5, which would be the same as pin 5 being at a lower potential than pin 1.

I guess what I'm saying/asking is, why not/can you use a voltage inverter, and tie the ground to pin 1 and the negative supply to pin 5? That way the BBD has a negative voltage supply with respect to ground (as I would expect) and all other circuitry is referenced to +9V and ground. I hope that makes sense, as I'm thoroughly confused. 

Both posted schematics have the MN3007  pin 1 to circuit V+, and pin 5 to circuit GND/0V.     Yes, 0V IS negative with respect to +9V - however I would like to offer that thinking like this is an excellent way to be very confused if you're not used to it... 


Pin names are just convention, and depend on the architecture of the device - in this case it's P-channel FET process so the 'drain supply' (Vdd) is negative of chip ground (and appropriate to show it that way).   Interestingly, the posted datasheet shows the manufacturer's reference application on page 4 (shown as '-37-') that ALSO has chip Vdd (5)  tied to circuit 0V and chip GND (1) to circuit +15V.   Use it as shown in the schematics and enjoy (of course, making sure your PCB libraries are correct!!!) 

If you were to create a negative supply for the 3007 - aside from the added unnecessary complications (like additional current draw and electrical noise) everything that had DC connectivity to the BBD would in theory need to have their GND pins connected to -15V, and their + supply to 0V, so as to not exceed the pin ratings of the BBD device (more confusion for young players!).  In basic terms, the individual devices of many ICs are grown into a substrate (forming Junction devices), and if your input pins  fall below ground, the internal junctions become forward biased and the device will not work (or worse)...

david