Part Number: INA233
Hi all,I am trying to use an INA233EVM to measure the current and energy usage of a battery operated device.
I am able to read and write all registers, and from the data sheet I calculated the shut resistor value and the corresponding calibration register value for my application.At this point I am reading reasonable voltage and current values, and I can also read values from the Power and Energy registers.
The problem is that I am not sure what scaling factors are used internally by the INA233 to compute these values in order to roll them back to Watts and Joules.
I followed the "Current Sensing Video series" and particularly the video 3.3 which shows the exact computations to do, but showing formulas that contain two constats (C and D).For the values of these constants the video tell to refer to the specific device data sheet.
Unfortunately I coudn't find any useful data from the data sheet to convert the Power and Energy registers reading into SI units.
As an example I am reading:Vreg=3982Ireg=16With the Voltage scaling of 1.25mV/digit and a Current_LSB of 15.6uA this means V=4.97V and I=250uAWith these values the actual Power should be 1243uWInstead the Power register shows a value of 3 and sometimes 4.
Of course this is due to the internal scaling, but what factor is used?Can anyone help?
As a side note I saw that the energy register increments on average by 3.07 per sample, so it seems to be a simple "power" accumulator without scaling (or with a scaling factor of 1).
The information you are looking for is in section 7.5.2 of the datasheet, as highlighted below:
So, for your example, the Power_LSB would be 25*15.6u=390u. Therefore, the power when it shows 3 is 3*390u=1170uW, and the power when it shows 4 would be 4*390u=1560uW. These values match up nicely with your expected value.
Mitch M, TI Sensing Products Applications Support
If this answered your question, please click below.
Getting Started with Current Sensing Video Training Series
TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.
In reply to Mitch M:
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.