undersatnding External ADC

[varuntejavarma]

Hello,

I have to interface an external ADC to PIC mcu through SPI with load cell as input transducer. In this interfacing process i have come across some terms which i am a bit confused. I have already searched in internet but am not cleared.

1. the voltage source range of my adc is -0.3 to 3.6. So, can i use a Vref out of this range like 0-5v ??

2. what is LDO output voltage selection mean??

3. why is DC offset input voltage used??

I have attached the datasheet of my ADC

Any kind of help is appreciated. IT would be good if someone could tell me what to know and look out in this interfacing process. As, I am a newbie in this field. still learning. so, kindly go easy on me. cheers

 

[horace1]

what voltage supplies do you have?

 

[ftsolutions]

You need to specify what power supply voltages are available for use in your system. Also, it is fairly likely that you will want to have some op amps for signal conditioning and filtering and reference biasing between the load cell and the ADC - the selection of these is also tied into the power supply voltages and how close to the power supply rails (+Vdd, -Vss, GND) you need the input to the ADC to swing (most likely you will want to select rail-to-rail capable op amp, like an MCP601, for example).

One typically uses a DC offset or reference voltage bias with op amp circuit to bias the signal coming into the ADC so that one can detect, for example, both positive and negative variations on the transcuder's output while keeping the signal level within the working voltage limits of the system and ADC. For example, if you pick an ADC that is 0-to-5V maximum input, you might bias the input to the ADC at 2.5V if you need to detect both positive and negative outputs from the transducer, thus you could handle inputs from -2.5V to +2.5V in amplitude, with the "0" or unloaded case being 2.5V instead of "0". But, if your application will never see or have to deal with negative values, or values below the input range of the ADC, then you might not need to do this biasing, or could use a lower level bias voltage, if you need to deal with low level noise in the ADC measurement circuit and/or if the ADC isn't linear enough or lacks monotonicity at low level inputs.