floating input in bipolar input mode

Hi SwaminathK 

I have moved this thread to Precision ADCs forum. Someone here should be able to support you.

Hi, SwaminathK .

SwaminathK said:

What would be the output code of LTC2308 when any input channel left open  in bipolar input mode.

A floating input is not advisable. You would not know what the exact output of the ADC is if it is left floating. Thus, it is best to ground any unused pins.

SwaminathK said:

What is is input impedance of of LTC2308  can we interface voltage output of sensor directly to the ADC input channel? The sensor minimum load resistance requirement is 250kohm.

I would suggest that you put an AFE circuit since the load is high. From the datasheet, only a low impedance source (in your case, it is a sensor) can be directly driven to the input of the ADC. Here is a reference you can use on how to design an AFE for your ADC. Front-End Amplifier and RC Filter Design for a Precision SAR Analog-to-Digital Converter | Analog Devices

May I know your application?

SwaminathK said:

Does COM pin require a buffer amplifier to supply Vref/2 voltage in bipolar mode if internal reference 4.096 V is used.?

Based on Figure 6c, there is an LDO that was used to overdrive the REFCOMP pin. Make sure that the LDO that will be used has enough driving capability of current during the conversion and acquisition phase. A buffer is sometimes used to compensate for this driving capability, and it also ensures that the REFCOMP pin is free of noise.

Warm regards,
Jo