• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 49 subscribers
  • Views 445 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

INA326: 3-Decade , Load-Current Sensing Circuit issue consult

Kyle Gu
Prodigy 30 points
Part Number: INA326

The doc sboa210 describe the INA326 design. See below schematic.

The first step calculate R1, Why the Vimax value is 250mV. How can I get the Vimax value? See below pic.

  • 0
    TI__Expert 6250 points
    Hi Kyle,
    The Vimax value of 250mV was likely selected to set a reasonably low voltage drop across the sense resistor while requiring a reasonable amount of gain from the INA to achieve the desired output swing. If you have a maximum allowable voltage drop for your application, you could use this in place of Vimax to calculate the required shunt resistance.
  • 0 in reply to Alexander Davis
    Prodigy 30 points

    Hi Alex,

    Above picture is SBOA310, which described Iimax current is 10mA. How can I get the Vimax value? I don't understand the circuit.

    Thanks a lot!

  • 0 in reply to Kyle Gu
    TI__Expert 6250 points

    Hi Kyle,

    Here's how I would approach this design:

    1. Determine the minimum and maximum currents you need to measure, as well as your maximum acceptable voltage drop your design can tolerate.
    2. Determine the required output voltage range from the instrumentation amplifier - this should be kept within the linear range of the amplifier, and will likely be determined by the input range of the ADC you use to measure it.
    3. Using the maximum voltage drop and maximum current from (1), calculate your shunt resistance as R_shunt = Vdrop_max / I_imax. This is the largest shunt resistance you can use without creating excessive voltage drop at maximum current.
    4. At this point, make sure that I_imax ^2 * Rshunt is a reasonable power dissipation. If this power dissipation is excessive ( >1 watt, for instance), you may want to scale the shunt resistor down to lower power dissipation. Keep in mind that decreasing the resistance also decreases the voltage generated at low currents.
    5. Using R_shunt, I_imax, and I_imin, calculate your minimum and maximum input voltages: V_imin = I_imin * R_shunt, V_imax = I_imax * R_shunt.
    6. the circuit from SBOA210 uses two selectable gain ranges - one to handle very low currents up to I_imin, and another to handle large currents up to I_imax. Settings for these two gain ranges can be calculated as shown in SBOA210 design step 2 (page 2)