ADC range

[MiCo_4221156]

Hi there,

i am using current sensor (LSTR) that translate current into voltage, most of the reading is between 2.5 - 3.125 , how can i adjust the ADC range to be between  2.5 - 3.125 ?

thank's

Michael

[NoriTan]

I am assuming you are going to use LEM's "Current Transducer LTSR 6-NP"  Please let me know if this is not.

The transducer has a reference pin which can be used for reference voltage input or output.

I recommend to use a differential input sigma delta ADC connecting the OUT to the positive input and the REF to the negative input.  The gain is determined by the ADC's input range.

Regards,

Noriaki

[MiCo_4221156]

Hi Noriaki thank you for your answer!

I am using "LTSR 25-NP" and I assuming that they the same in general.

Maybe I didnt explain what I am trying to do correctly, so i will do it.

in 8 bit ADC the range will split to 255 segments so if the range is vssa-vdda (i.e. 0-5v) the range will split to 255 segments.

since my range is 2.5 to 3.125 , I want to adjust the ADC rage, so 2.5 to 3.125 will split to 255 segments.

there are 4 options for the range :

• vssa-1.25
• vssa-2.5
• vssa-vdda
• vssa -7.5

I am not sure if i got you right, can you please explain in more details?

Thank you!

Michael

[NoriTan · Accepted solution]

I am assuming you are going to use an ADC_DelSig component.

If the ADC is used as single end as you said,

The usable ADC range will be vssa-6*vref (6.144V)

I don't recommend vssa-vdda because the vdda is not suitable for the reference voltage.

When the ADC is used in 8-bit resolution, the voltage resolution is 24mV/LSB

If the ADC is used as a differential input,

The maximum difference between Pin_POS and Pin_NEG is 3.125-2.5=0.625

So, the range +/-vref (+/-1.024V) can be used.

When the ADC is used in 8-bit resolution, the voltage resolution is 8mV/LSB

Which is 3 times fine resolution comparing to the singled ended mode.

In addition it is expected to have a shorter conversion time and the differential input can measure the negative current..

Regards,

Noriaki

[MiCo_4221156]

Noriaki,

Thank you very much!