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Shunt Resistors - few questions about selecting the Shunt Resistor for INA282

user4353247
Prodigy 165 points
Other Parts Discussed in Thread: INA282

I have few questions about selecting the Shunt Resistor for INA282.

1)

If V+ = 5V chosen for INA282 then output voltage swing range is 0.4 < Vout < 4.6

Input sense range [ 0.4V/50v/v  < Vin < 4.6V/50v/v ]   (Gain (INA282) = 50v/v), which is [ 8 mV < Vin < 92mV ]

According to my calculation, the maximum shunt resistor is

Rshunt = Vshunt / max Current

for my application,

max expected current is 5 A

So,

Rshunt = 92mV / 5A  = 18.4 mOhm  ,  I decided to choose with 15 mOhm (due to resistor's tolerance).

2) I wonder the 15 mOhm is  very small because even the wire consist this tiny resistance. Also it is difficult to find in the local shop. 

3) What is shunt resistor, is it normal resistor (with 2 terminal or 4 terminal) or is there any specific resistor called as shunt resistor ?

Thank you for your comments and answers.

  • 0
    TI__Genius 14825 points

    15mOhm is an appropriate value for a shunt resistor.  Precision, low-ohmic resistors are easy to find online at digikey or mouser or similar stores.  There are types that are simple resistors in standard surface mount packages, and some that are very fancy with different types of package bodies and some are 4-wire resistors, with a high current path and low current, kelvin connected sense lines.

    I found 79 surface mount, .015ohm resistors in stock at digikey in this section.  I hope that helps.

  • 0 in reply to Jason Bridgmon
    Prodigy 165 points

    Thank you. Mr. Jason Bridgmon

    Now, I have the another issue.

    Suppose if I want to purchase the 15mOhm, when I thinking about the Power Dissipation.

    Pd = ILoad (max)<square> * Rsh = 5A * 5A * 15 mOhm =  375 mW  

    Does it mean the resistor I choose that should not exceed 375mW ?

    Because, There are some Watt value mentioned on the resistor as I found some resistor around 15mohm with 1W and 1% . In this case, should I consider the resistor's 1W or Can I use this resistor?

    Please help! 

  • 0 in reply to user4353247
    TI__Mastermind 26475 points

    Hello,

    With regards to the resistor power rating it is the maximum power that it can dissipate.  Therefore with your calculation you would need a resistor that has a power rating higher than 375mW. 

    So a 1W or greater resistor should work. 

    Regards,

    Javier