Questions About Choosing a Shunt Resistor

chulian

Member
I'm trying to do a power analysis on my target, which runs on 3.3 volts. Without the resistor, the average current while running is roughly 140mA.
I used a 10Ohm resistor as a shunt resistor with a 5V power source. The voltage difference between VCC PIN and GND was measured using a shunt resistor linked between 5V and the target VCC pin. (The decoupling capacitors have been removed.) On the other hand, the oscilloscope lacked a proper power consumption line.
Is there a problem with my setup? Is there any guidance on how to choose a shunt resistor?
 

Dreamed

New Member
If the maximum full-scale output of a current-sense amplifier I use is 4.9V (it will be given in the manual), its gain is 20, and the maximum current signal I want to measure is 0.2A, then the maximum Rshunt value should be:
   (4.9V/20)/0.2A=1.225Ω;
   In other words, the Rshunt value I chose should be <1.225Ω. In order to improve the accuracy of the collected signal, I chose Rshunt=1Ω.
 

Ozumoz66

Well-Known Member
I'm trying to do a power analysis on my target, which runs on 3.3 volts. Without the resistor, the average current while running is roughly 140mA.
I used a 10Ohm resistor as a shunt resistor with a 5V power source. The voltage difference between VCC PIN and GND was measured using a shunt resistor linked between 5V and the target VCC pin. (The decoupling capacitors have been removed.) On the other hand, the oscilloscope lacked a proper power consumption line.
Is there a problem with my setup? Is there any guidance on how to choose a shunt resistor?
Not sure I understand your question. Are you using a 5v supply and trying to drop it to 3.3v by using a resistor? If so, you'd need to drop 1.7v across the resistor. Since you know the current, it'd be 1.7/.14 or about 12ohm.

Not sure that answers your question. Please provide a schematic if it doesn't.
 
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