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  • TI Thinks Resolved

INA301EVM: ina301evm ,shunt resistor

Part Number: INA301EVM

i have INA301 with A3 chip and 100 gain evaluation board. i need to set 500 mili ampere threshold current.

so according to calculation, i need 50 mili ohm shunt resistor.

suggest me a perfect resistor fro my evm board.

type of resistor i can user as a shunt resistor?

smd type? through hoe type or which one?  what are the requirements? smd type resistor can work satisfying? I need to control maximum 5 Ampere current.

suggest me a link of resistor where i can buy it online?

  • Hello Mehul,

    I assume you are using the EVM's standard comparator threshold of 2.528V, which is set by R3 = 31.6kOhm.

    Anyway you may want to use the shunt resistor (R6) footprint to solder down a SMD resistor for best accuracy. R6 looks to be a 2010 (5025 metric) footprint so if you want to use an SMD you can use a 2010 SMD resistor. If the max load current can be 5A, then your resistor will need to have a 1.25W rating (5A*5A*0.05Ohm). However, it does not look like has a 1.25W 2010 50mOhm SMD resistor here:

    You could very well use a through-hole that connects across J4 (the IN+ and IN-) header. The MR3FT50L0 resistor is also an option:

    Peter Iliya
  • In reply to Peter Iliya:

    yes thanksAccording to my understanding when i connect INA 301 and give supply 5v and pass current through shunt resistor. i can not get any voltage at Vout pin. why?

    Vout is the voltage output according to current set by shunt resistor. right?

     i do not get any output voltage. why? 

    my connections are,

    vcc 5v


    Resistor 50Mili ohm in between IN+ and IN-.

    when i connect only VCC 5V and my input is off then Vout pin shows 5v and alert led was turned on. explain me the logic of working of  INA 301 with A3.

  • In reply to mehul patel:


    I'm sorry to hear this. Could you please send some pictures of your setup or explain it a little more? How are you connecting the 50mOhm resistor the the INA301EVM? How are you generating the bus current? What is the common mode voltage (voltage at Vin+) when you're measuring current? Could you start debugging by measuring the differential input voltage. It should be 25mV if shunt is 50mOhm and current is 0.5A.

    When you say the input is off I assume you are disconnecting the inputs from your external circuit correct?

    Peter Iliya
    Current Sense Applications
  • In reply to Peter Iliya:

    Hello sir, i have sent you my full circuit diagram. 

    i have to monitor the current given to the laser diode driver. I m connected the shunt resistor in series from the pin LDA ( current going to laser from this pin ).

    IC haus is my load .Functional Block Diagram for INA301.pdf please rotate the photo and check.

  • In reply to mehul patel:

    Hi Mehul,

    I'm assuming the following:
    - The ammeter is not connected while you are running this circuit in normal operation or that, if it is connected, the sense resistor is disconnected whenever the ammeter is connected.
    - The ground pin of the INA301 is connected to the ground of the power supply.

    Are these assumptions correct?

    1. What are you connections for the ALERT, RESET, and LIMIT pins?
    2. Is the laser diode driver/rest of your circuit operating correctly even though the INA301 is not?
    3. Can you measure the differential voltage across Rsense during circuit operation?

    Peter Iliya
    Current Sensing Applications
  • In reply to Peter Iliya:

    yes sir, I have switched to select either ammeter or INA301.

    -when i m using INA circuit ammeter will be disconnected.

    all grounds are common to the power supply that i must have checked.

    i have already connected jumper J2 to pin 2 to 3 for the transparent mode of operation and J1 for enable alert led.
    i cannot connect reset, alert and limit pins. i think these pins are internally connected.

    is it necessory to connect ALERT , RESET AND ALL OTHER PINS shown on the boards?
    when i measure current with ammeter mode it works well.

    but when i connect INA 301 circuit my load laser will turn on but at OUT pin of INA301 it shows only 30 mili volt.
    i have set 50 mili ohm shunt resistor for 500 mA current to pass but when i connect supply and shunt resistor and ground i can not get alert led on after 500 mA current reached. i have already attached jumper to enable alert dioide on. then why is it happening???

    i have another question.

    i need to sense my current and if it is over current then threshold then it must be shut down. is there any evaluation board available for overcurrent protection?
    my requirement is when overcurrent flows from the supply EVM will detect and it shut down my input and it will protect my system from damage. current rating maximum 2A.

    how can i do it with INA301?

    my input is from the regulated dc power supply, my load is a laser driver.

    i want to give my driver 500 mA current. if it rises above 500mA then iNA 301 sense it and alert me but i want to save my laser diode.
  • In reply to mehul patel:


    You must not have changed the threshold setting resistor (R3) on EVM. This resistor connects to the LIMIT pin and sets the threshold. The INA301EVM comes with R3 = 31.6kOhm, which means you threshold is set at 31.6kOhm*80uA = 2.528V.

    Thus, if you are using INA301A1 (gain = 20V/V), then your output at 500mA is 500mA*0.05Ohm*gain = 500mV, which will not trip the internal comparator and thus not pulling the ALERT pin low and flashing the red LED. If you want the ALERT pin to go low at 500mA load current, then place a 6.25kOhm resistor at R3. R3 = 500mV/80uA = 6.25kOhms.

    As for the other pins it seems like you already have the connections correct. You are pullling up the ALERT pin by jumping J2 and you are pulling RESET pin low by jumping pins 2 and 3 of J1, to put the system in transparent mode. I would suggest jumping pins 1 and 2 of J1 to pull RESET high and thus put the part in latch mode, so if load current does exceed 500mA then ALERT will go low and stay low.

    Please measure the current drawn by your IC and check if it is even exceeding 500mA. Also measure the differential voltage across your 50mOhm shunt resistor when system is on. Have these measurements will help with debug process.

    Peter Iliya
    Current Sense Applications
  • In reply to Peter Iliya:

    If i used this module in Latched mode. Then it is periodically checking the current right?

    how much time will it take to start monitoring and stop? how do I know about which time period it will scan current?

    Give me an explanation about the latched mode and how it works in latched mode?

  • In reply to mehul patel:

    Hello Mehul,

    If the INA301 is in Latch Mode ( RESET = high), then during an overlimit condition (current is greater than 500mA) the ALERT pin will go low and stay low regardless if the current is still above the 500mA threshold. In order to reset the ALERT pin, the RESET pin must be pulled low for at least 100ns. If the INA301 is in Transparent Mode, then during an overlimit condition the ALERT pin will go low, but will go back high once the overlimit condition is over.

    The part is technically always continuously scanning or sensing the current for both latch and transparent modes. If the part is in latched mode and there is an overlimit condition, then ALERT pin will be stuck low even if you have shut down your bus current of 500mA. So it only takes one occurence of the current exceeding 500mA for the ALERT pin to go low and stay low. After this occurence, the part is effectvely not scanning for an overcurrent condition. Thus, if you want the part to begin scanning for an overcurrent condition again, you will need to pull the RESET pin low for 100ns.

    The reason I suggested putting your part in Latch mode (RESET = high) is so that you can know for sure that the system is working. If you have it in transparent mode (RESET = low), then you might be missing the overcurrent condition and not realize it or it is happening for a brief moment in time.

    These modes are explained in the INA301 datasheet section 7.3.2.


    Peter Iliya

    Current Sensing Applications Support

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