I am using TI-ADS1258 24-bit Sigma Delta filter in battery monitoring systems. It is communicated with TMS320F2808x through SPI communication.
I have configured the ADC in fixed channel mode. Configuration of registers are like this:
CONFIG0: 0x3200 : CONFIG1 : 0x7000 : MUXSCH: 0xDC00 (13th channel as ADC positive and 12th channel negative - grounded).
ADC sensing circuit has 2 stages:
1. Differential Amplifier with a gain of 0.09.
Output of differential Amplifier is given to ADS1258. As per my understanding the ADC MUX will be pointing to channel 13(+ve) and channel-12 (grounded).
2. There is an external Signal conditioning circuit which is connected to the ADC pins ADCMUXP and ADCMUXN. External sensing circuit has an instrumentation Amplifier. As per my requirement, I need to increase the gain of instrumentation Amplifier to a value 11. If I increase the gain from unity, the output voltage of instrumentation Amplifier which is going to ADC IC (ADCINP and ADCINN) is coming properly. But ADC raw value is coming less(say for example if Output of Instrumentation is coming 2.2V, ADC raw value is coming 1.85V). Is it a problem with ADC configuration or some hardware issue.
NOTE : Reference to the ADC IC is 4.096V
