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LMP91200: LMP91200 reference design questions

Part Number: LMP91200

Hi Team,

The customer would like to use LMP91200 to measure the PH of the polluted water.

For the E version datasheet, it removes the SPI function. 

He needs to the reference schematic for the PH design.  

Q1: Would you provide a reference schematic to measure the PH  for the E version datasheet?

Q2: For the E version datasheet, I think its content is very brief.

a). For the PH buffer, what are the voltage range for the GUARD1,INP, GUARD2, VOUT and VOCM pins?

b). For the VCM buffer,  what are the voltage range for the VREF, VCM and VCMHI pins?

c), For the PGA, is the GAIN 5V/V? Is this value 5V/V constant?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

6 Replies

  • Hi Team,

    Can anyone support this case? The customer is waiting for my reply.

  • Hi team,

    Does anyone support this case?
  • In reply to Mickey Zhang:

    Hi Mickey,

    Attached the reference schematic:

    The theoretical output of the standard Ag/AgCl pH probe is 59.16 mV/pH at 25°C with 0V out at a pH of 7.00. This output is proportional to absolute temperature.

    So, the input span can vary from 640mV @-40°C to 1.1V @125°C.

    The Gain of the PGA is constant and equals to 5V/V. Unfortunately, without the SPI, you can not access to PGA anymore.

    Please let me know if this replies to your questions.

    Best regards,

    Carmine

  • In reply to Carmine Iascone:

    Hi Carmine,

    Thanks for your support.
    The customer would like to use PT100 for temperature compensation. Now the LMP91200 does not have the SPI interface,
    how to use PT100 for temperature compensation?
  • In reply to Mickey Zhang:

    Hi Mickey,
    following our conversation by email, i'm going to close this thread.
    Let me know if you need further information.
    Best regards,
    Carmine
  • In reply to Carmine Iascone:

    Hi Carmine,

    OK. Thank you for your help.

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