I have a PCB with an OPA552 opamp. I have a tina model that works well.
Here is the pinout of the opamp pins.
1-4-5 > -9v
7 > + 41V
2 > through 10K ohm to ground
3 > receives 0-4 V square wave at ~.25Hz
6 > output with a 100K pull down resistor and 25K to pin 2
8 > flag through 100K ohm to ground

My anticipated output should be 1+ 25K/10K. I am running non-inverting positive input.
I get all this with Tina as I expect.
With my o-scope, I get 0V with a 1.3MHz 4v ripple with no variation over a few seconds on the output at pin6.

There is more to the story.
The -9v and + 41v are provided by a separate power source than the input signal. It is possible that the opamp could receive a signal with no power.
Also, the opamp could receive both powers with no signal. The signal and two power supplies are switched separately but the three share a common ground.

The pricey opamp is rated at +/- 30V and my limited knowledge is that they can withstand any delta power supply less than 60V.

A schematic of my circuit from tina is attached and it works in the virtual world.
I am hoping that by stating my issue and having outside reviewers look at these values, I could find out why I have no output wrt the .25 Hz signal.
Any help will be greatly appreciated. While I am waiting for a response to this posting, my diagnostics will involve looking at the voltage spikes on the PCB while the switch toggles that connects the -9 and +41v power supplies.
Thanks.

 

This part is speced at 60V total between positive and negative pins, but only
30 V max any power pin to ground, I believe.



Also the power sequencing matters as you have a direct connection between V+
and prior stage output. Is that stage powering up before you power up the 552 ? Might
be possible the input stage is getting broken down due to breakdown of input stage
when its + and - supply pins at 0V......not sure.

Regards, Dana.

 

I have 4- 24vdc switching power supplies. They are turned down to ~20v.
Two are wired to give 40v.
So I have 4 wires feeding my pcb.
+40, +20, -20 and GND.
There is a relay in a PLC that switches them on.
The PCB has a 7809 and a 7909 voltage regulator.
My PCB then has -9v, +9v, +41v.
There is also a FPGA demo board that has +3.3v and 5v.
So my PCB has 5 different voltages and a common ground.
My FPGA board also has a USB and a rj45.
I could add the power supply line of the FPGA demo to the relay bank.
Now my PLC could turn on all the power at the same time.
Would it be okay to leave the USB and Ethernet connected?


I saw an Australian guy giving a youtube lecture about opamps and I gathered that as long as the sum was less than the max, I was okay. I guess that is not the case because my driving voltage is not in the middle, I will look for another opamp. Hopefully, I can find one with the same 8SOIC footprint.

 

I saw some contradiction but I have a pdf with the following that I highlighted.


"The OPA55x may be operated from power supplies of ±4 V to ±30 V, or a total of 60 V with excellent
performance."

My output max is only 30V and if I can find a rail to rail, I may be okay.

 

Dana,
In the spec sheet I saw the following on page 17:

"For applications that do not require symmetrical output voltage swing, power-supply voltages do not need to be
equal. The OPA55x can operate with as little as 8 V between the supplies or with up to 60 V between the
supplies. For example, the positive supply could be set to 50 V with the negative supply at –10 V, or vice-versa."

It looks looks like -9 to +41 should work. I just changed the +41v to +24 v for testing.

 

Thanks fmrPIC for pointing that out, interesting possibilities for applications.

Would it be okay to leave the USB and Ethernet connected?

No way of categorically answering this. Quick method would be to take a multi-
channel DAQ and look at the interfaces during power up. Or take the respective
datasheets and look at interface constraints under no power, ramp up conditions.
Tedious, would not be surprised if you found inadequate datasheets that do not
fully cover the topic, their parts behavior.

Regards, Dana.