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ADS1112: Single Ended

Ray Vincent Aranzaso
Mastermind 18180 points

Part Number: ADS1112

Hi,

Good Day.

The datasheet, page 6, it shows how to calculate output codes for a given PGA gain, number of bits, and differential input (Vin+, Vin-).

What I wish to do, is use single-ended conversion, and calculate the output code from a single-ended Vin connected to Ain0 with PGA gain set to "1". 

Can you indicate the correct way to do this?

Please advise. Thank you very much.

Best Regards,

Ray Vincent

  • 0
    TI__Guru** 113765 points

    Hi Ray Vincent,

    The datasheet table and discussion is a little confusing, and the expression shows the actual output code.  In more recent datasheets the equation relates to a value of a single code (LSB) relative to the full-scale range (FSR).  As this device changes the resolution depending on data output rate, the calculation was expressed in terms min/max code.

    The output of the ADS1112 is in binary 2's complement where the code value is positive if the VIN+ voltage is greater than VIN- representing the positive half of the FSR.  This would be the single-ended case where VIN- is at ground and VIN+ is always above ground. AIN3 (or VIN-) would be connected to ground, and the mux channel selections would be AIN0, AIN1 and AIN2 relative to AIN3.  So there is a maximum of three single-ended inputs when using the ADS1112.

    The voltage input range would be 1/2 of the FSR (+2.048V).  The voltage calculated will be Code returned * 2.048 / GAIN / (Maximum Code) where Maximum Code is from Table 1 on page 6 of the datasheet.

    • 15sps = 32767
    • 30sps = 16383
    • 60sps = 8191
    • 240sps = 2047

    If I apply 2.048V while using gain of 1 and 30sps, the maximum code will be 16383.  The calculated input voltage will be VIN =  16383 (code returned for positive FS from Table2) * 2.048 / 1 / 16383 = 2.048V.  If 1.024V is applied, then the calculation would be (16383/2 which is the conversion result read from the ADS1112) * 2.048 / 1 / 16383 which is 1.024V. Let's say we don't know the input voltage but the conversion result code shows 9428 (0x24D4) the result will be VIN = 9428 * 2.048 / 1 / 16383 = 1.178V.

    I hope that makes it a little easier to follow.

    Best regards,

    Bob B