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PGA900: PGA900 resistive bridge compatibility + temperature measurement

Tobias_1
Prodigy 40 points
Part Number: PGA900

Dear TI-Team,

I'm currently evaluating the PGA900 and I would like to ask some questions which I couldn't clarify via the data sheet.

1) Compatibility of external resistive bridge and analog front end

a. Which resistance range of the sensor element is supported by the PGA900? I a 3 kOhm bridge possible?

b. Which offset of the bridge signal is supported by the PGA? => e.g. a signal span of 50 mV and a negative offset of -30 mV, is this possible?

2) Temperature measurement via an external diode

a. In the data sheet there is temperature measurement via an external element mentioned but only with a thermistor (PTC is mentioned)

b. Is it possible to use a diode as a temperature sensor element and measuring the voltage drop over the diode (with a constant current, one terminal of the diode connected to ground as described on p. 35 in the data sheet)?

Best regards

Tobias

  • 0
    TI__Mastermind 31655 points

    Hi Tobias,

    1.

    a. The only restriction to the resistance of the bridge is in the current limit of the excitation voltage supply. There is a 1.5mA current supply limit, so you can calculate the minimum resistance using this and whatever excitation voltage you plan to use. For example, at 2.5V, your bridge can be a minimum resistance of 1.6kohm before running into the current limit.

    b. The common Mode at P Gain Input and Output has two constraints: (a) The single-ended voltage of positive/negative pin at the P Gain input must be between 0.3 and 1.8 V. (b) The single-ended voltage of positive/negative pin at the P Gain output must be between 0.1 and 2 V. 

    That offset should be fine, but you may need to use a smaller gain to not violate the output constraints of the PGAIN amplifier and you'll leave a little bit of your output range on the table.

    2.

    There shouldn't be any issue with this. The INTP can be configured to act as a current source, and you can measure in single-ended mode as you mentioned.

    Regards,