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Topic: Calculate the ideal current sense resistor (Read 759 times) previous topic - next topic

combib

I am using the AD8207 in a circuit and need to select the ideal current sense resistor for several ranges. My ranges are (up to 500ma, 500ma to 1A, 1A to 5A, and 5A to 10A) is there a calculation to select this resistor correctly?

Magician

I think, selection of resistor 'd be based on power you willing to lost at 10A, setting P = 1 W,
V = P / I = 0.1 V , or just 100 mV.
Next, you look in data sheet at "Offset Voltage drift" for IC, which is -+1 uV/C.
Setting commercial temp. range to -15 +85 or 100C span, offset worst case scenario -+100 uV.
From the ratio 100 mV / 100 uV = 1000 ( 0.1%)  obviously precision couldn't be better than 10-bits.
That in next term it drops to 1000 / ( 10 A / 500 mA) = 1000 / 20 = 50 ( 2% ) for 500 mA .
If you o'k with 2% than R = 100 mV / 10 A = 10 mOHm.
If not, than you have to use better precision PGA at first stage.

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