OPAMP recommendation

Hi JH,

Does the customer have any other requirements?

• Noise requirements? 
• Quiescent current/power consumption? 
• What kind of load is it driving (capacitance and/or resistance)?
  • And what is the load's value?
• Does the part need to be automotive qualified? 
• Is there a specific package they want the part to be in? 
• Do they want to have a shutdown pin?  
• How many channels? (1, 2, or 4)

I ask because right now we have a lot of op amps that fit those requirements. Depending on the requirements, some top contenders are TLV9001, TLV9041, and TLV8541, though there are many more. 

Best Regards,

Robert Clifton 

Hi Robert,

Thanks for your reply.

Below are customer responses.

• Noise requirements? 

We don’t have specification for it. But voltage sensing  need to under 30mV in ADC ( = ADS1114).
We think that Noise spec. (Vn at 1 kHz (typ) (nV√Hz) 264)  of TLV8541 is enough.

• Quiescent current/power consumption? No matter for it.
• What kind of load is it driving (capacitance and/or resistance)?
  • And what is the load's value?

Load device is ADS114.

• Does the part need to be automotive qualified? We prefer automotive  part. 
• Is there a specific package they want the part to be in? We prefer small size package that size of TLV8541 is enough.
• Do they want to have a shutdown pin?  No
• How many channels? (1, 2, or 4) 1CH

Please let us know if there is a better product to meet the customer's requirements.

Please include a reference design for the application.

Thank you.

JH

Hi JH,

Thank you for the information! This will help narrow down the options we have. 

Before I go into the op amp selection I want to correct the schematic that you sent over. Using a single channel op amp means that you will have to operate the ADC in a single-ended configuration. So the circuit would look like this: 

Also I have a few other questions: 

• Where did they get the C_diff and C-Single values? 
  • I searched the datasheet and found only the input impedance values. 
• They expect to have a 6Vpp output signal but for that to go into an ADC that's powered with 3.3V? That's going to cause clipping. 

If automotive is preferred then I'd recommend the TLV9001-Q1. 

There's two pieces of content that might help with the design. The first is a fun video found here: Engineer It - How to select an op amp to drive your SAR ADC. It's a bit cheesy but it does help with choosing the correct op amp. 

The second piece of content is the Buffer Op Amp to ADC Circuit Collection which gives a few ideas of how to use a single-ended op amp for an ADC. 

Best Regards, 

Robert Clifton 

Hi Robert,

Below are customer responses.

Before I go into the op amp selection I want to correct the schematic that you sent over. Using a single channel op amp means that you will have to operate the ADC in a single-ended configuration. So the circuit would look like this: 

The voltage given by the sensor is single. So Differential doesn't seem to make sense.

• Where did they get the C_diff and C-Single values? 
  • I searched the datasheet and found only the input impedance values. 

We modified it as follows. Please note. And I honestly don't know if that's right.

Reference is ADS1113/4/5/ Data sheet.

R1 , R2 = 100

Fc = 2Khz (10 times applied to 200 Hz. Maybe it can be changed.(under 2Khz)

Cdiff =  390nF

Ccm1/ Ccm1  = 39nF

• They expect to have a 6Vpp output signal but for that to go into an ADC that's powered with 3.3V? That's going to cause clipping. 

6.0Vp-p is error.  We are modify to 3.0V   

Thank you.

JH

Hi JH,

Also here's the TINA simulation file I used.

 E2E - TLV9001-Q1 OPAMP recommendation.TSC

Best Regards,

Robert Clifton