SBOA603 June   2024 INA700 , INA740A , INA740B , INA745A , INA745B , INA780A , INA780B

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Design Size
  6. 3Performance and Functionality
    1. 3.1 Total Error Comparison for Current ≤ 15A Over Temperature
    2. 3.2 Total Error Comparison for Current ≤ 25A Over Temperature
      1. 3.2.1 Common Mode Voltage ≤ 40V
      2. 3.2.2 Common Mode Voltage ≤ 80V
    3. 3.3 Total Error Comparison for Current ≤ 50A Over Temperature
  7. 4Summary
  8. 5References

3 Performance and Functionality

When using a design to measure current, power, voltage, or Energy, you can either use a Digital Power Monitor with a shunt resistor or an EZShunt™ device. For the first interpretation, the Digital Power Monitor can have a certain accuracy and adding a shunt resistor can include an additional source of error including Shunt drift, and tolerance percentage. The value of these error sources from each shunt resistor can vary based on cost and subsequent performance.

To analyze this performance against our EZShunt™ technology and traditional design sets, we collected benchmarking data by choosing resistors classified to support up to 15A, 25A, and 50A over temperature from three separate providers ranging between Cost and performance. These resistors were then paired with Digital Power Monitors which provide similar performance, functionality, and cost to respective EZShunt™ devices. Although each resistor is classified for specific parameters, a total of 20 resistors from each of the 9 chosen products were hand-measured in an unsoldered state, and 50% were tested after soldering using both hand and reflow methods at 0.5A. Multiple providers were used in sourcing each resistor to make sure variety and measured at 125°, 95°, 60°, 25°, 0°, and -40° Celsius. The main sources of error produced by a sense resistor can be classified between Tolerance percent and Drift.

The tolerance percent for each resistor was calculated using Ohms law:

Equation 1. R   =   V I

Where the voltages at variant temperature ratings were measured at 0.5A of current being implicated upon the system in an unsoldered state. The calculated resistor value was then compared to the nominal resistance value of the shunt to measure the tolerance percentage.

Meanwhile, the drift is calculated using the following formula:

Equation 2. D r i f t   =   R 2 - R 1 T 2 - T 1 R N o m i n a l

Where R2 is the measured current at 125°C, R1 is the measured current at -40°C, T2 is 125°C, T1 is -40°C, and RNominal equates to the nominal shunt value.

In addition, the data was then cross-examined according to Current vs Total error at room temperature (25°C) and 125°C. The total error on both discrete designs and EZShunt™ was calculated according to the following formula:

Equation 3. C R S S   ( % )   ≈ V O S 2 + C M R R 2 + P S R R 2 + G a i n _ E r r o r 2 + L i n e a r i t y 2 + S h u n t _ T o l e r a n c e 2 + B i a s _ C u r r e n t 2

To calculate total Error, only consider a typical use case where the main sources of error on both designs are gain error, gain drift, offset error, and offset drift.