OPA211: Problems with Shutdown Pin

Hello Kanan,

Lets examine this a section at a time.

The shutdown pin seems to output a voltage from the chip at around 19.5V if measured while floating. - The OPA211 is not intended to have the enable/shutdown pin float as stated in datasheet Section 7.4.1

- This pin must be connected to a valid high or low voltage or driven, and not left open-circuit.

Attaching 24V to the shutdown pin does not cause the output to turn off. Just to try, we tried to attach 30V to the shutdown pin to see what would happen, and the power supply output hit the set current maximum of 200mA and dropped 26V. I would have imagined this pin to be high impedance so we thought this was strange. Pulling the pin to ground also does nothing, as expected.

- The OPA211 normally goes into shutdown mode when a valid high voltage level of (V+) - 0.35 V to (V+) is applied to pin 8. It is a high impedance pin within its specified operating voltage range. If 30 V is applied to pin 8 when V+ is 24 V, an internal ESD protection diode connected between pin 8 and V+ may become highly forward biased. The diode in only rated at 10 mA and it is possible that it would be damaged by the event if the current becomes much higher than the rated maximum. That event would likely damage the OPA211 enable/shutdown circuitry as well. The datasheet Section 6.1 Absolute Maximum Ratings lists the maximum Input voltage (V–) – 0.5 and (V+) + 0.5 V.

The component markings show "1125 OBCM". I have confirmed the footprint, connections, and orientation of the component. We are trying it on a PCB so though we have tried this across multiple components, their implementation is identical. 

- I do need to see how the "1125 OBCM" is marked on the devices. I do not have access to detailed lot code information, but I do know what the marking arrangement is supposed to be. Please capture some images of the OPA211 device markings and post them here as an e2e response.

Note that the OPA211MDGKTEP is an Enhanced Product, OPA211-EP, produced by another organization within TI. If it turns out there is an issue with the devices the Enhanced Product group will be the one to assist you in obtaining a resolution. 

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas, thank you very much for your response.

My apologies, I thought I had seen 1125 but it apparently says T125. 

The Pin was only left in an open circuit temporarily, we asserted the 24V for the valid V+ signal and did not see the expected response. The output would momentarily stutter (this could have been just the oscilloscope adjusting) and lose some of its DC offset but the AC signal would still propagate through with no problem.

When we placed 30V onto the pin, we did not use that unit for further testing. I would not doubt that it fried something internal to the chip, we just wanted to see if maybe somehow our expected V+ signal on the shutdown Pin was somehow not asserting the shutdown state.

Is this Enhanced Product group a separate forum?

Best,

Kanan

Hello Kanan,

Thank you much for the image of the OPA211MDGKTEP device. I am trying to find someone in TI's Enhanced Products group that assist you with this issue. Since that group is in a different time zone, they wouldn't be available at this time of the day. I will make some calls tomorrow and see who I can find to assist you.

Regards, Thomas

Precision Amplifiers

Yes, I tested this on two different boards, ie two different chips. With one, i was not gentle and probably fried it looking at the 30V response. The other, I never tried more than 24V and 0V. They both produced the same response on the output which I described in my second post.

I'm going to order some more of these chips and bread board them for a sanity check but this problem is pretty strange. I, personally, can't think of a reason why this wouldn't work.