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Help with shunt resistor

jgauthier

Mar 22, 2013
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This is most likely an Ohm's law question, but I feel like I need a little help with it. I have this circuit that I use on a low voltage low current system in order to measure the current.
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My device load is 5V around 3A (peak, not sustained).
I'm just looking for some advice on the resistor (1 Ohm pictured). I don't want to use a giant shunt resistor, but I also want to make sure I don't overload the resistor since they are commonly 1/8W rating. It doesn't need to be surface mount, but I really don't want something large either. There may be some consideration I am not taking into this as well. I'm also concerned about voltage drop and need to keep it close 5V.

Thanks!
 
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Bluejets

Oct 5, 2014
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Normal approach would be to use 10th of an ohm resistor.
@3A , 1ohm would create too much losses.
A 0.1ohm would do the same job only use a multiplication factor by measuring the voltage drop across it.
What is the load...??
Concerned about change of voltage, put any regulator after the current sense.
 

Harald Kapp

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Nov 17, 2011
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The datasheet shows specs for a sense voltage (VP - VM of 50 mV (with a max. of 100 mV). Therefore 50 mV is a good operating point for the sense inputs.
With a 3 A load this equates to Rsense = 50 mV / 3 A = 17 mΩ.
SInce 3 A is peak only, you may also chose Rsense = 100 mV / 3 A = 33 mΩ.
The max. voltage drop will then be 50 mV or 100 mV, respectively.
 
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