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Other Parts Discussed in Thread: REF5050,

Hi team,
We are using ADS1119IPWT to read the analog values from a sensor.
The DVDD is set to 3.3V.
The AVDD is set to 5V.
my input voltage is in the range of 0 -5V.
1). Can I use the internal 2.048 reference voltage for the measurement of a 0 -5V signal?.
2). The maximum voltage to the REFP pin is AVDD, so can I use the voltage reference IC REF5050 (5V) for a 5V AVDD to the ADC IC?. THe REFN pin is grounded.

• Hi Shibin,

my input voltage is in the range of 0 -5V.
1). Can I use the internal 2.048 reference voltage for the measurement of a 0 -5V signal?.

The ADS1119 voltage FSR is +/-2.048V (AINP relative to AINN) for the internal reference.  So you will not be able to measure 0 to 5V with the internal reference.  The input range is limited to 300mV above AVDD and 300mV below AGND.  So for single ended measurements (relative to AGND) you would measure the positive full-scale only or 0 to 2.048V.

2). The maximum voltage to the REFP pin is AVDD, so can I use the voltage reference IC REF5050 (5V) for a 5V AVDD to the ADC IC?. THe REFN pin is grounded.

I would recommend using a good linear LDO for the analog 5V and connect both the AVDD and the REFP input to the same 5V source.

Another possible option is to make the measurement a pseudo-differential measurement using a 2.5V reference and also connecting the reference to one of the analog inputs.  Here the measurement would utilize the entire full-scale range, but will reduce the number of available input channels.  The way this would work is you would add 2.5V to your measurement result.  A 0V input would be -2.5V output result from the ADC and adding 2.5V is 0V.  A 2.5V input results in a 0 output code result where 0 + 2.5V is 2.5V.  A 5V input is positive full-scale, or 2.5V plus 2.5V equals 5V.

Best regards,

Bob B

• Hi Bob,
1). I am planning to provide a 5V at the AVDD pin and a 5V reference from REF5050 reference IC to the REFP pin. Hope this will work fine.
2). I need all 4 channels of the ADC. If I want to configure it as pseudo-differential, my available channels will be only 2. I hope my belief is correct. Please correct me if I am wrong.
3). Can I use ADS1119IPWT directly to measure a 4-20mA current signal by dropping it across a 100Ohms resistor?.

• Hi Shibin,

1). I am planning to provide a 5V at the AVDD pin and a 5V reference from REF5050 reference IC to the REFP pin. Hope this will work fine.

Here you need to be a little careful.  The specification has a maximum reference input voltage of AVDD.  There could be a slight difference in the voltage level output of the 5V supply and the REF5050.  In the end this may create a problem if the AVDD supply is lower than the output of the REF5050.

2). I need all 4 channels of the ADC. If I want to configure it as pseudo-differential, my available channels will be only 2. I hope my belief is correct. Please correct me if I am wrong.

You are correct.  If you need all four input channels then you will not be able to use the pseudo-differential method.

3). Can I use ADS1119IPWT directly to measure a 4-20mA current signal by dropping it across a 100Ohms resistor?.

This would be an indirect measurement as the ADC outputs a code value relative to a voltage reference.  To determine the current you first calculate the input voltage and then divide by the value of the shunt resistance.

Best regards,

Bob B