INA230 shunt resistor choice

Hi Barry,

You are correct, there are other trade-offs that needs to be considered when selecting the shunt (sense) resistor. This training video will walk you through the process of selecting the appropriate resistor value for your application. 

Please watch Video #4:

 

Ok good to see you have videos on these parts but sure would like to see one specific to this one.  I am still trying to get grips on this - I have to admit I haven't yet seriously looked at the software. I want to be sure I wire up the EVM correctly and really there is not a clear diagram of how to do so.  

1)Figure 10 in the EVM - you should label all the connections as to what they are on the EVM board (T#'s etc.). 

2)What is Vbus - is that Vbus off USB and valid when J2 is set to internal? I wouldn't think you would support bringing this in through the SM-USB-DIG cable and in fact above Figure 5 it describes the ezhook connections as external Vbus.  So why have J2 if power is always sourced external?  I don't get it.

I remain confused on the design aspects.  Seems like you choose a sense resistor for power, cost, or accuracy.  Then you have to worry about the calibration register and how the current LSB is factored by 25 for the power register value. There is discussion about setting Calibration for easy to convert units for the system processor.  So this is rather hidden - you must also do factorization in the system uC code to get the correct decimal unit values.  This can be done by measuring the actual current and then playing with factoring to get the correct system reading.  Is this basically the process - really two calibrations? 

Hi Barry,

Follow the following steps to wire up the EVM correctly:

1. Connect the two PCBs of the EVM together (INA230 Test Board and SM-USB-DIG) @ J1.

2. You have two options for VS power source:

     Internal- J2 on the INA230EVM set to the INT position. When set to the INT position, the SM-USB-DIG Platform provides the supply for the INA230.

     External- J2 set to the EXT position, an external supply voltage can be connected to terminal strip T2 to provide the supply for the INA230.

3. Connect the desire Vbus. The source for Vbus is not included with the kit. Connect your external power source to terminal 3 (T3).

4. Set I2C address. Jumpers 3 through 6 control the I 2C address pins for the INA230. These jumpers can set the address for A0 and A1 to either supply, ground,       SCL, or SDA. 

5. Figure 5 of the EVM User Guide shows an example of low-side shunt scenario. Refer to this picture for shunt resistor placement across VIN+ and VIN–.

6. If you don't have any shunt resistor at the moment and want to do a quick test of the EVM you could apply a differential voltage between VIN+ and VIN– pins.

7. Calibrate the software.  

Calibration:

We have a video (tutorial) that also explains the calibration process of our Digital output devices. Please take a look at this video for a detailed explanation. It is Video #15 Programming Power Settings

The EVM GUI is very helpful! Please give it a try. The configuration tab will help you understand the setup process required to configure the device and some of the different setups that can be done. The Calculations tab gives a flow chart of how the calculations within the INA230 occur. 

Looks like my previous reply got lost somewhere.

Anyway, I've made good progress.  I discovered my 10m Ohm sense resistor really is 16.5m Ohms, thus the readings I was getting didn't make sense and the software refused to keep my calibration and current LSB settings. If others get confused and screwed like I did they might want to just check a reading with a DVM or this kit of the drop across the sense resistor with a verified load. This was staring me in the face.  I had measured the sense resistor out of circuit and thought it correct - but it is not.

My first issue was that although the board is recognized and software seems operational I had to cycle power using the GUI button to get things talking correctly (was getting communication errors). 

It is also easy to plug the module in the board or ribbon cable upside down or off by a pin.  This should have been a more robust and keyed connection. 

The Tx screw connections are too small for applications using this board.  You can't really get more than one wire into the connection hole.

The "0A" you see as a default in the CurrentLSB window is not a hex value it is zero Amps.  Units for sense resistor are also decimal ohms or "m" milliohms. "uA" for microamps.

Could you go over how the Read and Write register, and AutoWrite buttons work as to how new manually entered data values become permanent.  I had occasions where values set in the Configuration page were not updated in the Calibration page.

Does the Continuously Poll button need to be set to see new value readings or is there a manual way preferred?

Advise customers to see/use the "Help w/reg" button in the Registers page.

Spoke too soon. Tried a 25mohm resistor and cannot get the software to work right. I need to talk with someone on the phone.

Hi Barry,

"Could you go over how the Read and Write register, and AutoWrite buttons work as to how new manually entered data values become permanent.  I had occasions where values set in the Configuration page were not updated in the Calibration page."

The Auto-Write feature is enabled by default. This feature automatically updates the register table whenever a change is made. You can disable the Auto-Write feature and use the Read All Reg and Write All Reg buttons. You can change the register values by highlighting the Register in the Register Table (Register Tab). Modify the bit to match your desire register value and press Write All Reg. Then Press Read All Reg and you should be able to see the set value in the Register table.  

When you changed your resistor to 25mOhm, did you updated the Configuration Register (Step 5) to match this change? You might be running out of range? The EVM/Software worked well in your earlier experiment...with the 16.5mOhm? Or it never work correctly?

Please send me your contact info to mayrim.verdejo@ti.com so we can schedule a call. 

Regards,

 

Wonderful, all of US tech support closed for a meeting....

Here's what threw me off: I tried one of those metal strip type of sensors, marked .025 ohms.  I couldn't get it to work with the software at all.  Now I found a 50 mOhm SMT part.  When I put it in series with the electronic load set to (CC) 100mA I get a drop across of 6.1xx mV.  So if I set the Resistance window in the "Current LSB" page to 61m and then Current LSB to 30uA and go to the "Calibration Register" page and set to 2798 I get a pretty nice 100.1mA. But if I go back to the Current LSB page and set the Resistance to 50 mOhms - which is marked on the part itself, nothing changes. I click "Read all Registers" - still ok. I go to Calibration Register page, still good. Now I turn Power off with GUI button and back on. Register data entries are lost and need to be re-entered. I enter 50mOhms, 1A max., and 30uA Current LSB. Now Current reads 120.2mA. So I go to Calibration Register page - says enter 3413 for 50m. I click Read all Registers and Auto-write off/on, no change - Current still says 120.x mA. Whatever I now enter in the Calibration window doesn't change the Current reading.  Wrong. I go back to Current LSB and now it says Current LSB is 51.2uA.  Why? Current reading still wrong. Basically I can't get it to read correctly 100mA now. This looks to me like a software bug on your part.

Hi Barry,

I am not sure I am following what is happening on the software side. I'd like to schedule a WebEx if possible with you so we work together on the EVM GUI setup. Please send me your contact info to mayrim.verdejo@ti.com so we can schedule a call tomorrow.

Can you go through all this thread and correct my erroneous entry of 320 to 230? Thanks.

Hi Barry,

Thanks for the call!

For other customers benefit:
The current EVM software do not update the resistor value and configuration register automatically. This is a bug in the software and will be fixed ASAP.

You can set the "Resistance value" and the Current LSB value in the Current LSB page. If you have a valid shunt voltage value you should be able to see valid data in the current. So far so good. But if you decide to change the calibration register value you NEED to power cycle the EVM software ( Power off with GUI button and back on). If you fail to do so, the calibration register will not update to the new expected value.



Regards