INA290: Need design review

Shyam Thillainathan

Prodigy 150 points

Part Number: INA290
Other Parts Discussed in Thread: LM5069

Need design review for INA290, want to make sure the current rating and voltage will drop across:

over 2 years ago

0 Javier Contreras4 over 2 years ago

TI__Mastermind 26475 points

Hello Shyam,

For the Max Current of 36.7A the output of the INA290 will not be valid.

with INA290A2 is 50 V/V

Vout at max current = 36.7A *2mΩ* 50V/V = 3.67V which is larger than Vsupply and will not be valid.

Max Vout = 3.3V- 0.025V(Swing High) = 3.275V

Therefore the max current is calculated below with the specifications. Please keep in mind the tolerances where not included. Normally the largest tolerance is normally the resistor value.

3.275 / 50V/V / 2mΩ = Max Current measurement valid = 32.75A

0 Shyam Thillainathan over 2 years ago in reply to Javier Contreras4

Prodigy 150 points

Hi Javier,

LM5069 current limit is set at 36.7A, for worst case scenario, however, the actual current doesn't go over 33A. Here is the calculation:

Also, the 2mR I am using is part number: KRL6432E-M-R002-G-T1 (3W). Do you see any potential issue due to the wattage rating of the resistor?

0 Javier Contreras4 over 2 years ago in reply to Shyam Thillainathan

TI__Mastermind 26475 points

Hello Shyam,

Just recall you will not be able to get up to 3.3V if your supply is 3.3V due to swing high limitations. As for the resistor you are correct that the resistor can handle the current at room temperature. Please be aware that the resistor degrades with ambient temperature. Also the resistance will change with the temperature change at 100ppm/°C. I could not find the package dissipation of the resistor but if you are not running at max current you should not have issues. The only thing is to verify the accuracy of the resistor in your application and temperature range.

0 Shyam Thillainathan over 2 years ago in reply to Javier Contreras4

Prodigy 150 points

Got it, lets say, if I have designed it for 33A, but for some reason my current goes higher to 35A, will the output show 3.3V and saturate then?

0 Javier Contreras4 over 2 years ago in reply to Shyam Thillainathan

TI__Mastermind 26475 points

Hello Shyam,

Yes but the saturation will be more 25mV below your supply voltage of 3.3V. So it could go higher but our limit is 25mV below the supply voltage with no current draw. Like I calculated above your max Vout is 3.275V. Once you draw current from the output that voltage degrades. More details here for swing limitaitons. https://www.ti.com/lit/an/sboa519/sboa519.pdf

0 Shyam Thillainathan over 2 years ago in reply to Javier Contreras4

Prodigy 150 points

Got it, so will change my calculations to reflect 3.275V as my maximum. Thank you so much. Just want to make sure this circuit won't create issues like voltage drop, and when powering a capacitive load as high as 1500uF etc.,

+1 Javier Contreras4 over 2 years ago in reply to Shyam Thillainathan

TI__Mastermind 26475 points

Shyam,

Normally changing a capacitor will not be an issue even if the fast transient current will spike and create a larger current for a small time it only saturate the input for small time then it will recover. If the current is larger than your calculated current. As long as the setup does not go beyond the "Absolute Maximum Ratings" for you case I don't think you will ever get 30V(Max differential of the INA290) across the 2mΩ.

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INA290: Need design review