recommendation for a tiny opamp

Hi Brian,

This is tough set of requirements! Let me look into this a bit - I think your requirement for a high supply voltage is going to making finding the package size you need tough.

Here is a list of all shutdown parts that have 15V supplies:
www.ti.com/.../products.html

Can you clarify the shutdown requirement? You want it so that when the shutdown pin is pulled low, the device is turned off?

Do you have an Iq threshold you'd like to stay under?

-Paul

Hi Brian,

As a first start, have you looked at the OPA171? It comes in our DRL package which is 1.7mm x .1.7mm (www.ti.com/.../mpds158c.pdf)

Can you clarify this statement as well:
"Or, if no shutdown pin at all, it would need to have very low Iq and, with the inputs at V-, not output any current as the V+ rail decayed down to zero (which is something that I can't determine looking at the datasheets)."

I'm not sure that what you are asking is possible of any device because the op-amp will have a minimum output voltage that is higher than V-, meaning that there will be some current flow (even if very small) until the V+ is low enough that the device is off. The only way there won't be any current flow is if there is no load on the output of the op-amp.

Finally - do you have any bandwidth requirements?

-Paul

Hi Paul,

Thanks for looking into this for me. Yes, I know it is a tough set of requirements, so that is why I am reaching out for some help to see if out of the 1000s of opamps out there I can find one or two that could do the job. It seems that shutdown is typically only built into low V+ parts.

I will look through your list, and at the OPA171.

On the shutdown, yes we want low means the part is off. If high means the part is off, the current into that pin combined with the Iq in shutdown needs to be low. It is a low duty cycle battery application, so this will probably be the major consumer of battery charge.

Regarding the BW, anything that meets the SR will probably be okay.

If no shutdown, we will disconnect the load so the output will see high impedance. But if the part does anything weird as the supply goes down, like all of the sudden when V+ gets below 1V it spikes up to the positive rail, that will be bad as it will still capacitively couple into the load across the SS switch. That is what I would need to understand with a part that has no shutdown. But a no shutdown part has other issues that will make the operating Iq more important, as we won't be able to turn it off and on in one of the modes of operation.

With a shutdown capability, operating Iq would hopefully be < 1mA, but 2 or 3 would be okay if everything else could be found.

If 12V supply and 10 mA output would get a part that fits everything else, it may work so if there is a really good fit there I could look at that also. But the parts down at 5 or 6V are definitely not on the table. But I think that 12V is really the lowest we could consider, and if we could find 15V and 20 mA it would be better.

We are trying to do something quick that we would normally do in an ASIC because these kinds of requirements are so unusual. But with all of the modern tiny packaging that has been driven primarily by the cell phone industry I am hoping that we can do this without going the ASIC route.

Thanks again.

Brian

You're welcome. If I come up with any other suggestions I'll follow up. Please post back if you determine that the TLV2370 won't meet your needs.

Best,
Paul