[SOLVED] Unused bjt from dual package? Leave not connected or tie to supply voltage?

[d123]

Hi,

Sorry to ask this cringeworthily "simple" question but it's not an op amp nor a logic device, it's a dual PNP, so I can see pros and cons to both approaches (not connected pins or tying to appropriate voltage level), but maybe someone can suggest what is the most suitable so as to not interfere with the other BJTs functioning.

Can the unused BJT pins be isolated from the board or is it better practice to tie the base to V+ and e.g. put a large value resistor (2M) to ground on the collector?

I ask as I have the doubt that an unused BJT in a dual package may affect the used BJT and make the experiment with that IC pointless.

Circuit function is just to approximately compare power supply independence and temperature independence of a couple of BJTs compared to simulations. Bad drawing is planned PCB layout.



Thanks.

 

[KlausST]

Hi,

I don´t expect much problems. Only ESD on the unused BJT could cause problems.

It depends on the inner circuit:
If there are two independend dice, then you may leave it floating. Unlikely that ESD wil damage something.
If both BJTs are on the same die, then I strongly recomend to connect both emitters. Because ESD on the one device may brake isolation barrier to the other BJT.

What to do with B and C? (E1 is connected to E2 anyway)
You may completely parallel both BJTs: B1 - B2, C1 - C2.
Or you may disable the unused BJT by connecting all pins. E2 - B2- C2

Klaus

 

[FvM]

Most dual transistors aren't ICs rather than multiple chips in a package. The datasheet should tell.

In case of a monolithic chip, it's important not to forward bias substrate junctions. Floating the unused transistor terminals should be fine anyway.

 

[d123]

Hi,

Thanks very much for your replies, they are very helpful and I've learnt a few more things with them. The datasheet doesn't say (just checked), I'll see if I can find the app note I had related to an overview of type of dual bjts in case it says anything, if not it seems a safe risk to leave it unconnected/isolated pins, which I'd prefer to do if possible.

Really, thank you both very much.