OPA2991: SHDN Pull Down Resistor

Benjamin Bawkon

Part Number: OPA2991

Hello TI,

Do you have any information for the value of the internal pull-down resistor on the SHDN pin on OPA2991S? I intend to use a simple P-Channel Mosfet to disable (pull-up) the SHDN pin(s), but I would like to be confident that an additional pull-down resistor isn't required to overcome mosfet leakage current. Space is non-existent on this design.

Thank You,
Ben

over 1 year ago

0 Ashley Kang over 1 year ago

TI__Genius 11660 points

Hi Ben,

I will check with the internal team and get back to you on this.

Thank you!
Best Regards,
Ashley

0 Caro Walter over 1 year ago in reply to Ashley Kang

TI__Mastermind 18887 points

Hey Ben,

We have a similar question on a different part but similar shutdown circuitry question:

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1106222/tlv9152-pull-down-value-on-shdn-pin

To answer your question directly, its "shutdown circuitry" of which I am not allowed to specify more.
Luckily, we may leverage the electrical characteristics table and work backwards:

I would use the threshold voltages along with the Iq to see if a resistor is required:

All the best,
Caro

0 Benjamin Bawkon over 1 year ago in reply to Caro Walter

Expert 1075 points

Caro,

Perhaps I'm just running low on my coffee intake today, but I'm having a hard time wrapping my head around how the amplifiers Iq has any direct relationship to the pull down strength on the SHDN pin. Could you elaborate?

Thank You

0 Clemens Ladisch over 1 year ago in reply to Benjamin Bawkon

Guru 268120 points

I_Q is defined as the current that flows into V+ and out of V−. So it does not include the pull-down.

The SHDN pin current is specified as 150 nA when pulled down and 500 nA when pulled up externally. So your PMOS leakage would have to be much less than 500 nA.

+1 Caro Walter over 1 year ago in reply to Clemens Ladisch

TI__Mastermind 18887 points

Thanks Clemens for the assist, you're absolutely right.

Ben,

I was trying to tie together where Ron (from the previous post) got the 500uA but then I realized his post actually says 0.5uA. Sorry for the confusion, please follow Clemen's suggestion.

All the best,
Caro

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OPA2991: SHDN Pull Down Resistor