OPA2890: Op-amp operation during shutdown has high Vout

Hi Fairuz,

when the OPA2890 are powered down and PIN1...4 are inputs, where is the 2.33V coming from 

I hope the input voltage of OPA2890 is also 0V when the OPA2890 are powered-down

Kai

Hi Fairuz,

If you disconnect the DUT VDDIO wire, do the op-amps disable properly? I'm wondering if some interaction with the DUT pin is pulling up the disable line.

Best,

Sam

As you can see, the DUT on the right is just empty. for illustration purposes i had to draw the empty boxes. Maybe someone from TI could verify the findings.

Hello Kai, i did try as below:

with Shutdown bit set to 0V :

With VDD 9V & VSS -3V : 2.33V

Remove VDD & VSS : ~0V

Remove VDD & remain -3V VSS : ~ -1V

Remove VSS & remain 9V VDD : ~3.38V

Does this happen in real life OPA2890? i was hoping 0V when the device shutdown.

Hi Fairuz,

I think this is just some harmless floating. Connect a resistor from each output to signal ground.

And decrease the feedback resistor to 0R.

Kai

Hello Kai, do you mean something in the picture below (simplified to single opamp for discussion)?

1. does it make any degradation if I have resistor after opamp (R1 ) there? and yes i can see the Vout is at uV now.

2. about the feedback to 0R, i guess this type of opamp is OK with 0R? normally i am using 300-1kohm (because stated in datasheet unity gain stable?)

Hi Kai, thanks for the prompt feedback. so should I design the circuit with shunt 10k ohm after the opamp before the RC or without is OK since it is harmless.

thanks!