# ADS1230 shows a large offset

I'm using an ADS1230 for measuring the output of a pressure sensor (MPXM2053). The schematic of the circuit is shown below and some voltages are as follows:

AVDD = 3.304V

DVDD = 3.304V

Common-Mode input = 1.690V

AINP - AINN = 0.0002 V

GAIN is 128 (only R2 is used and R1 is not used)

The problem is that the output of ADS1230 has a large offset. Its typical value is around 389000 (5EF88 hex) while the differential input is 0.0002V. I expect an output around 0.0002 * (2^19 - 1) / (0.5 * Vref / GAIN) = 8134 (1FC6 hex). You can see in the following table the relation between the input signal and the output of the ADS1230 (from datasheet):

A sample of the ADS1230 data (DOUT signal) along with SCLK signal is shown in the following image (SCLK is yellow and DOUT is blue):

I also should mention that I calibrate the ADS1230 after power-on using 26 pulses on SCLK.

What have I done wrong?

Thank you

• The circuit diagram can't be right; with R1 and R2 both being 0R, you are short-circuiting +3.3 to ground. Apr 20, 2022 at 8:14
• As I mentioned in my question only R2 is used and R1 is not used Apr 20, 2022 at 8:26
• The offset may well be an accurate representation of the voltage being output by the sensor. Do you have a voltmeter accurate enough to corroborate what the ADC is measuring? Apr 20, 2022 at 9:53
• @Kubahasn'tforgottenMonica Your point is correct. I need an accurate reference. Previously, I measured it using a [KYORITSO 1009 multimeter ](kew-ltd.co.jp/en/products/detail/00911) and it showed 000.2 mV. It means the the ADS1230 should generate a number near 0.0002*(2^19-1)/(0.5*3.3/128) = 8134 (here Vref =3.3 , GAIN = 128), while it generates a number near 440000 (i.e 10mV) . The accuracy of the multimeter is ±0.6%rdg±4dgt, which I think its error should be less than 1mV. Apr 21, 2022 at 12:02
• Later, I measured it using a scope (Analog Discovery 2) and its resolution is 0.32mV. The scope measured the differential voltage equal to 1.4mV while the ads1230 showed a result of 270000(= 6.6mV). Again, it seems the ads1230 has a large offset. Apr 21, 2022 at 12:02