Sensor AFE : LMP91000
Parameters : Programmable TIA gain, Internal Zero selection (Reference voltage), variable BIAS voltage, FET switch
I am trying to figure out the proper settings for various toxic gas sensors using LMP91000 eval board. I can read/write configuration registers through I2C interface and was able to verify them with the logic analyzer. I would like to verify the effects of these configuration register settings like programmable internal zero, programmable TIA gain, and variable bias on the LMP91000 eval board before placing any actual sensor. The only parameter i was able to verify is the programmable internal zero which shifts the output scale at the Vout pin. Could someone explain me how these parameter settings affect the 3 electrode pins and help me with simulating a small input range and playing/verifying with these programmable registers in the stand-alone mode ?? I also have the two interface boards -- SPIO4 and ADC161S626BEB for interface with the computer through usb and configured using the WEBENCH graphical user interface.
let me try to explain.
What you can program with the LMP91000 is
May I ask you, why you try to do these measurement?
Hope I could help you.
Thanks for the explanation Andreas,
With the bias voltage, i still could not see the bias voltage between the WE and CE pins. It always remain at the same potential (basically (vdd - internal zero)).The reason i am trying to do the measurements is that, I do not want to place a toxic gas sensor with improper configuration settings. I just wanted to understand how each parameters work on the board before testing. Could you help me with this bias voltage measurement? Thanks again!
that sounds strange. I am attaching a picture here, how I did the measurement. Vbias was set to 10% of Vref = 0.4096V, which is what I measure.
My mistake was, I did not short the CE and RE in the J_CE_RE_GND jumper. Thanks a lot for the info.
Also, it would be good to have a custom configuration setting that could be saved on the chip in addition to the default setting (FAB default) during power on. In that way, it could work standalone without a need for the microcontroller to configure everytime when it is powered on.
about the configuration setting. Unfortunately this is not possible with the LMP91000. It would require internal non-volatile ,e,ory, which the LMP91000 does not have. It may be possible to include this in future parts, if technology allows.
It is possible to reconfigure the lmp91000?
What I do is:
1) Configure lmp91000 at start up
2)go into lmp3
What I want to do is between 2) and 3) reconfigure lmp91000, is this possible?
Solve it!! Time between configurations
not sure if I understand correctly, you problem is solved?Andreas
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