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LMP91200: Need to verify SCH and Layout from your side before actual incorporation with all circuit wrt product design

Part Number: LMP91200

Hello Team,

want to test pH sensor amplification part before it incorporating to complete design __kindly verify and advice on below details

Q1) Can we use simple any 2 pin Connector for connecting pH Sensor to PCB, with using Coaxial cable and proper Guard and ground connection mentioned in attached design.

Q2) Can we we short Pin 10 to Pin 15,16 because we are using same supply for Tl431_2.5Vdc and LMP91200

Q3) what will be my output voltage range with +2.5v as Vref and +5V as a VDD  (ph Sensor Range -414mV  to +414mV)

  • Hi Rahul,
    Please find my comments below:
    1. As you can read on section 10 (Layout) of the data sheet the recommended connector is a triaxial connector. Your PCB and schematics don't look like like a coax connector, it looks like the one on section 10.
    2- Yes. You should short Pin 10 to pins 13-15-16 since all of the are ground, as shown in your schematics and page 3 of the LMP91200 data sheet - www.ti.com/.../lmp91200.pdf
    3- The Ph Amp is a Unity Gain buffer so it will track the swing from your sensor output and will be referred to the VCM Voltage.

    Regards,
    Jose

  • In reply to Jose Arteaga4:

    Thanks Jose,

    1)  i have taken exactly same tracks and same PCB layout pattern for pH sensor, can you re-verify. kindly Ignore  schematic symbol for triaxial connector just taken for SCH reference and taken care in PCB layout.

    2) Ground point is clear..Thanks

    3)- The Ph Amp is a Unity Gain buffer so it will track the swing from your sensor output and will be referred to the VCM Voltage.

    __Sorry unable to understood above point it means what.

    my pH ouput is -414mV to +414mV

     Vref will be at +2.5V

    All Vcc/VDD is at +5V

    Need Vout range available for ADC =  ?  _______(with respect to mentioned voltages)

    it will help me whether we need to amplify signal with proper gain and another opamp IC or will get amplified version at vout of IC LMP91200 (pin num 12 )

  • In reply to Rahul Joshi10:

    Hi Rahul,

    1) Your PCB layout look exactly the same as the recommend example provided in section 10 of the LMP91200 data sheet. This is for a Triax cable. Can you explain to me what are the differences?

    3) Unity gain buffer means that output amplitude is the same as input.  (-414mV to +414mV)+VCM