LMP91002: LMP91001/2 with N02 SGX sensors

Hi Jalen

Thank you for your reply, sorry for my late reply.

I have attached the datasheet for my sensor, please advice me if i need any further information to crate a sensors part on the WEBbench tool? I am new to using such sensor, and would need to some help in creating a new part in the tool with the information provided in the datasheet.

So that i get a feel of this tool, i have selected a random sensor(N02-A1) from the list, but is there a guide on how to progress foward in the tool? Do you offer a screen share support?

0652.DS-0228 (SGX-4NO2) V1.pdf

Anyone who can help me get started?

Dear Jalen 

Thank You for your reply.

I will contact the sensor manufacture if there is more information on the Capacitance and resistance.

I have managed to create the custom sensor as shown below. I am going the the steps from 1 to 9.

1. I select my sensor.

2. "Modes of operation"- As shown below: What is the difference in status and lock options?

3. "External Reference"- I have kept to use a the internal Vref, which i believe will be VDD 3.3V(output of the LDO). Am i correct in saying that Vref should be 3.3V as my ADC is 3.3

4."VREF Devider" As my Vref is going to be 3.3V, it does not need to be divided as my ADC will read 3.3V, therefore the setting will be in bypass mode as shown below. Is this correct?

5."Variable Bias", As per extra information from the following attached PDF, it seems that the SGX-4N02 output bias is negative, but what should BIAS be set to?

6. How do i determine that correct TIA GAIN for the sensor?

7. How do i determine that correct RLOAD the sensor?

8. Is shorting FET required?

With exception of points 6-8. i have added as much information as possible and kept the defaults for point 6-8. I now come the following screen.  What must i do next, as its not very clear?

What i aim to achieve is the setting for i2C, so that device simply output an Voltage that my ADC can continuously read to determine N02 levels in the air. Am i correct in believing that is what this device will help me achieve?

I have also attached my schematic below. It looks fairly simple, but do i need to set R9 and C9 to particular values for this sensor?

DAS768835AA-ECVQ-EK3-User-Guide-V4.pdf

HI Jalen

I will read the documents and update you on any query.

I will also update my schmaticso that Vref is also 3.3V.

What i wanted to ask was ,does the tool also produce  a list of register or what i need to do in terms of i2c?

When you say " So please determine what system sensitivity you would need for your ADC and choose the proper RTIA for your application. " what does this refer to ? I am using an Atmel AVR ADC. IS there certain parameters i need to look out for?

Thanks

Dahrmesh,

Yes, there is a Register Map icon above the block diagram that along with reading the datasheet should help you with the register map.

As mentioned, please take time to read through the datasheet and application note I provided in my previous post. These explain your questions pretty well.

Jalen

Hi Jalen

In regards to your first post, about "if you have information about the resistive/capacitive elements of the sensor", i have been sent the following. Which values from the image would i need to add into tools parameter.

Thanks

Hi Jalen 

Great, Thanks.

I have started working on the layout. The datasheet mentions it best to keep the sensor away from high frequency, which i am. But my looking at the reference design, it seems that LMP9100 device was kept underneath the sensor. My Sensor does not have any clearance below it, therefore i have kept the ic on the side, with a ground pour around all the traces. Does it look ok? Or should it be underneath it?

Thanks

Thanks

Unfortunately could not place it below, but close as possible. 

Is there away to test if LMP91000 is setup correctly without the sensor? e,g, placing a resistor between two points etc. I presume to fully test it i need to be in the environment i am hoping to test?

If i want to find what the ADC reading equals to in terms of ppm, do i need to ask the manufacture or is standard formula? 

Regards

Dharmesh,

Yes you will need to be in the environment you are hoping to test to verify operation of LMP91000. 

Is your question here how to make sure the ADC can read the sensitivity of the output of LMP device?

Jalen

Yes i would like to insure LMP device is able to output properly(set correctly) for my ADC to read it. Would like to avoid be exposed to what i am trying to test as well.

Dharmesh,

You need to be sure that the LSB (least significant bit) of your ADC can is smaller than the system sensitivity. The LSB is the smallest signal that the ADC can convert. If your sensor sensitivity is smaller than the LSB, then your ADC will be unable to detect the incremental output voltage per ppm.

For example,

The TIA has a gain of R_TIA for 3-lead Amperometric Cell mode. (this is where selection of  R_TIA comes into play)

Your sensor gain is 600 nA/ppm or 6 x 10^-7

If your gain is 14 x 10⁴ then your system sensitivity becomes (6 x 10^-7 )x (14 x 10⁴ ) = 84 mV/ppm.

Your LSB for ADC needs to be greater than this number.

Hope this helps,

Jalen

Hi Jalen

My ADC is 10-bit adc that comes with my uC. 

So if i am correct the LSB will be: 3.3/1023, =0.0032V, therefore should be able to detected the voltage.

What i was trying to ask was , is it possible to place the device in some form of test or simulation mode, just to insure everything with exception of the sensor is working correctly?

Dharmesh,

One way you could check operation of LMP91000 is by reading the temperature sensor output from Vout pin. This would require setting the device in Temperature Measurement mode, which is explained in the datasheet.

Have you checked out the LMP91000EVM ? It will help to evaluate the performance and operation of the LMP91000.

Jalen