Replacement by RC4580 to OPA2188

Hi Stewart,

The schematic didn't come through. Can you please try again to include it? Use the "Insert Media" icon to the left of the paperclip. Many popular media formats are supported; JPEG, TIF, etc.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello Stewart,

I reviewed the schematic in relation to replacing the RC4580 with the OPA2188. I had some difficulty finding information about the HG302A Hall effect device, but think I have enough to verify it will be okay with the OPA2188. I was a little concerned about the C3 - 10 nF load on the output of IC1B, with regard to the OPA2188 stability. There is R10 inseries with the IC1B output, before C3 is encountered and that should help isolate the 10 nF load from the output. I did a stability analysis using a TINA Spice simulation to be sure that wouldn't be an issue. The results of the analysis indicate that the phase margin should be about 78 degrees indicating the circuit should be completely stable. You can see the simulation results below.

Do note that the bandwidth and slewing rate of the OPA2188 are lower than that of the RC4580, but this doesn't appear to be a wideband application. Everything else looks good and the circuit should benefit from the higher dc precision of the OPA2188.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas,

Thanks for qucik reply and advice to me!!.

We check it your advice.

Thansk. Stewart.

Hi  Thomas,

Could you please advice to me below quastion.

We are R&D team used the very old production machine of Current Sensor products.

So We want the recommad you and your team for new measurement.

1. Response time measurement of Open & Closed Loop current sensor

2. Frequency characteristic measurement of Open & Closed Loop current sensor

3. Waveforms measurement of Open & Closed Loop current sensor

Thanks and B/R.

Stewart Jeon.

Hi Stewart,

We have a TI Precision Design on the subject of a closed-loop current sensor circuit design. It may be of some interest to you:

For a more general discussion of closed-loop and open-loop current sensors I find this DigiKey article useful:

I didn't find anything specific about the response time and frequency characteristics of open-loop and closed-loop current sensors.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Tomas,

This is Stewart .

Long time no communication.

Thanks and B/R.

Stewart Jeon.

Hello Stewart,

Okay, we are going to need more information regarding the OPA188 application and the failure mode the customer is incurring after about 1 week of aging. The circuit schematic looks okay on the surface, but certainly, there is something going on in the actual circuit that is leading to the device failure.

Some questions:

• The U1 circuit does not appear to have any dc feedback, which would indicate that it is running open loop at dc and low ac frequencies. What are the characteristics of the signals applied to the H1 inputs, +IN and -IN? I need to make sure the common-mode range, or some other limit isn't being exceeded. 

• Do the +15 V and -15 V power supplies come up together upon power on? Have they been checked with a DSO to make sure the voltage levels are within the safe range during startup and when operating? 

• It seems that the OPA188 is working as expected initially, but then sometime in that 1 week period it stops working. Once that happens, what is the behavior of the OPA188? Is the device completely dead, or is it simply not working as expected? 

• What are the conditions of the aging test? 

The OPA188 and LM201A are very different operational amplifiers in terms of their technologies, designs and electrical characteristics. The OPA188 is a precision CMOS chopper op amp, while the LM201A is a more conventional, general-purpose bipolar op amp. That said I would expect both to perform reliably in the application circuit unless there is an unexpected voltage condition to which they might be vulnerable.

About the only suspect difference I find in their datasheets at this point is the OPA188 has an absolute maximum supply voltage of ±20 V, while the LM201A is rated at ±22 V, and that might only be a concern if there is an electrical over-stress (EOS) condition in the circuit.

I would like to hold back from suggesting an OPA188 replacement until I have answers to the questions and I have had an opportunity to assess the situation.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Tomas,

My comment as belows and can you reply to me ASAP.

•The U1 circuit does not appear to have any dc feedback, which would indicate that it is running open loop at dc and low ac frequencies. What are the characteristics of the signals applied to the H1 inputs, +IN and -IN? I need to make sure the common-mode range, or some other limit isn't being exceeded.
-. We applied DC feedback to R14(27K) and C3(120pF) it's not??
-. H1(HW302W) is Hall sensor, +Out(+15V) and –OUT(-15V) , +IN(122~204mV), –IN(-122~204mV)

•Do the +15 V and -15 V power supplies come up together upon power on? Have they been checked with a DSO to make sure the voltage levels are within the safe range during startup and when operating?
-. Yes, used the +15V and -15V

•It seems that the OPA188 is working as expected initially, but then sometime in that 1 week period it stops working. Once that happens, what is the behavior of the OPA188? Is the device completely dead, or is it simply not working as expected?
-. OPA188 is completely dead.

•What are the conditions of the aging test?
-. Test conditions is input the 土122~204mA from Hall sensor(H1) , it's room temperature is 25C not special chamber.

Currently Our customers do not want to use the OPA188.
Pls give me the new replacement TI Parts.......

Thanks and B/R.
Stewat Jeon.

Hi Stewat,

•The U1 circuit does not appear to have any dc feedback, which would indicate that it is running open loop at dc and low ac frequencies. What are the characteristics of the signals applied to the H1 inputs, +IN and -IN? I need to make sure the common-mode range, or some other limit isn't being exceeded.
-. We applied DC feedback to R14(27K) and C3(120pF) it's not??
-. H1(HW302W) is Hall sensor, +Out(+15V) and –OUT(-15V) , +IN(122~204mV), –IN(-122~204mV)

If the capacitor C3 is placed in series with a resistor R14, the capacitive reactance will be extremely high at low ac frequencies and look like an open at dc. Therefore, the circuit will run open-loop which is not a linear operating condition. A similar situation exists for C4 and R26 and no dc path is provided there either.

•Do the +15 V and -15 V power supplies come up together upon power on? Have they been checked with a DSO to make sure the voltage levels are within the safe range during startup and when operating?
-. Yes, used the +15V and -15V

Okay, that is as it should be.

•It seems that the OPA188 is working as expected initially, but then sometime in that 1 week period it stops working. Once that happens, what is the behavior of the OPA188? Is the device completely dead, or is it simply not working as expected?
-. OPA188 is completely dead.

The OPA188 is fully tested and must meet all TI quality requirements in order to be shipped to customers. A scenario where it is completely failing within a week suggests that it is being exposed to an electrical overstress (EOS) condition in the application circuit. Under normal, safe operating conditions the OPA188 should operate for many years without failing.

•What are the conditions of the aging test?
-. Test conditions is input the 土122~204mA from Hall sensor(H1) , it's room temperature is 25C not special chamber.

I don't understand where the Hall effect current +/-122 to 204 mA flows in the input circuit. Does it flow through an external current sense resistor? If this current were forced to flow through the OPA188 internal input circuit, the op amp would be damaged. It has a maximum input rcurrent rating of +/-10 mA.

Currently Our customers do not want to use the OPA188.
Pls give me the new replacement TI Parts.......

I think it is important to determine why the OPA188 is failing in the system before suggesting switching to a different op amp. There may be a detrimental electrical condition that is causing the OPA188 to be damaged. This could very well happen to another, different op amp as well. I suggest connecting 10x DSO probes at the inputs  (outputs of H1) and supply lines of the OPA188 and then run the system through its start-up, operating, and shutdown sequences. You may need to look at other circuit points as well to see if an EOS situation is present.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Tomas,

Customer tested your recommend  value for C3 and R10. 

Test result is good to around 4V and 400mV but  test result for 40mV is not good. it's appear to be noise to customer old schemtic.

pls refer to the attached "Word file" and advice to me the drop in the noise.

Thanks and B/R.

Stewart.

Stewart Jeon.docx

Hi, Tomas,

Hello Stewart,

When I compare the OPA277 and OPA188 electrical specifications they are close in many ways. The primary difference is the OPA188 is a bipolar op of a more conventional design, while the OPA188 is a CMOS chopper amplifier. The input bias current of the bipolar op amp is significantly higher than that of a CMOS op amp, but that should make any real difference in this circuit's performance. Do note that the common-mode voltage range of the OPA277 is (V-) + 2 V and (V+) - 2V and a bit more limited compared to the OPA188, but that doesn't appear that will be an issue in this application.

Both the OPA188 and OPA277 have low input voltage noise density, around 8 nV/rtHz, so the internally generated op amp noise is low. In the images you provide for the 4 V, 400 mV and 4 mV ranges noise becomes more evident as the range is lowered. That is normal becuase the signal-to-nose ratio (SNR) is decreasing as the signal level is decreased relative to the noise level which is more constant. I suspect that the noise you are observing is extrensic noise being introduced into the circuit and not that being contributed by the op amp.

Based on the information that you have provided the OPA277 should be a good choice for this application.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Stewart,

Please see the other response I posted today.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Tomas,

Please give me the answer to another question sent to 6/28.

And there is another question:

-. How can use the +24V input voltage ==> +5V output voltage(max. 0.3W) solution.

Cannot be used Buck IC because the PCB size issue.

PCB size is 2x2cm with OPA2188, TPS60400 and so many R and C.


Thanks and B/R.
Stewart Jeon.

Hi Stewart,

I do not find a specific question in your 6/28 post; however, I did provide a response on 6/29 to your discussion points. It is normal to see a degradation in the SNR if the noise remains constant and the signal level is reduced. Please see my 6/29 response for more information.

The application is coming closer to requiring an ideal op amp the further the circuit requirements are examined; however, as you know there are limits to what all the different op amps can provide. My suggestion is to consider the OPA2192 and OPA2197, which have a typical 25 C voltage offset of +/-5 uV (+/-25 uV max) and +/-25 uV (+/-250 uV max), respectively. Their noise voltage is a very low 5.5 nV/√Hz, typical. The common-mode range extends to 0 V, and (Vs+) -2 V from the positive rail for a single, positive supply. If the output is lightly loaded the output should swing within a few tens-of-millivolts of the supply rails.

The one parameter that  comesclose to the limit is the power. The typical Iq is 1 mA, but can be 1.2 mA for the OPA2192, and 1.3 mA for the OPA2197, at 25C. The power will be the product of (Vs+)( Iq), and the 0.3 W limit might be exceeded depending if Vs+ is high and at temperature extremes.

www.ti.com/.../opa2192.pdf

Regards, Thomas

Precsion Amplifiers Applications Engineering