Hello, I want to scale a current value(Icurr) (in Amperes) to a corresponding 12 bit value. The to-be scaled current value(Icurr) and a 12-bit ADC value(Iact) are given as inputs to a PID controller as actual(Iact) and expected(Icurr) values. I am not sure how to approach the scaling. My idea of approach is to : For example take a 1V=4A value as an input to ADC and find the corresponding 12bit value. Take it as reference to scale Icurr accordingly. But I am also not familiar reading from a ADC data sheet to find the approximate 12bit value for an input voltage/current. Any suggestions?
First question: Is your question related to FPGA, Verilog or VHDL? If so: how? Wil wrote: > Any suggestions? What hardware? > But I am also not familiar reading from a ADC data sheet to find the > approximate 12bit value for an input voltage/current. What ADC? > For example take a 1V=4A value So you have a "device" that forms 1V out of 4A, meaning 2A result in 0.5V?
typical: Vin = Vref : Out = xFFF Vin = 0 : Out = x000 Vin = Rshunt * I Out = Vin * (xFFF / Vref)
Schlumpf wrote: > Out = Vin * (xFFF / Vref) But the slope of this calculation is 1/4096 wrong. But you can ignore the deviation if you want... ;-) For a 12 bit ADC this formula is correct: Out = Vin * (x1000 / Vref)
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Edited by Moderator
Lothar M. wrote: > First question: > Is your question related to FPGA, Verilog or VHDL? > If so: how? > Yes, I want to implement the scaling in VHDL > Wil wrote: >> Any suggestions? > What hardware? > Altera Cyclone IV >> But I am also not familiar reading from a ADC data sheet to find the >> approximate 12bit value for an input voltage/current. > What ADC? > LTC1407 12bit ADC >> For example take a 1V=4A value > So you have a "device" that forms 1V out of 4A, meaning 2A result in > 0.5V? Yes, A Dual Op_Amp gives out 1V=6A (seeing from the layout)
Schlumpf wrote: > typical: > > Vin = Vref : Out = xFFF > Vin = 0 : Out = x000 > > Vin = Rshunt * I > > Out = Vin * (xFFF / Vref) So here to get a 12 bit value, Should I just consider Vin=1V (irrespective out of the 4A i.e. 1v=4A ?). Or do I need to calculat the correspoding voltage for 4A? (V= 4*Rshunt) How do I find Rshunt from the datasheet? The datasheet for LTC1407 says Vref=2.5V. So for Vin=1 Out should be 1638.
Wil wrote: > The datasheet for LTC1407 says Vref=2.5V. > How do I find Rshunt from the datasheet? Because at Imax you want full scale inputof 2.5V for the ADC you have to calculate Rshunt = Imax/2.5V Buuuuuut(!): This will only work if you can accept 2.5V voltage voltage drop over your shunt...
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