BQ27541-V200: Current Sense Tolerance

Hi Lon,
The gauge can measure up to +/- 1mA if the calibration is done.
thanks
Onyx

Hello Onyx,

The context is this: For a given value of CC Gain the voltage measured across RSP-RSN is read by the gauge and converted to a current. What is the tolerance on that voltage reading? In other words, what is the variation in sensed current over production runs of gauges measuring the SAME VOLTAGE across RSP-RSN. I am making a case for changing our test procedure so that instead of JUST MEASURING current sense error to a +/- 1% limit compared to an accurate meter, I want to CALIBRATE current. But to justify changing our test process, the customer needs documentation for the need to do so.
Presumably the CC gain was INITIALLY set to center the distribution. The sense resistor tolerance is +/- 1%. Realistically Rsns is likely well within those limits. But the distribution is wider than +/- 1% so we have some % of units failing the test. The extra variation is within the fuel gauge. But I need a way to quantify that to demonstrate the need to the customer. Surely there is variation between devices within a given lot, and between different production lots of the gauge. I am seeking some quantification so I can make the case to calibrate.

Thank you,
Lon

Hi Onyx,

The variation in current reading is based on voltage, so the variation in current that you describe depends on the value of the sense resistor. What Rsns is assumed in your answer?  In our case it is 20 milliohms.

We are NOT CALIBRATING the gauge at this time. A value for CC Gain was established long ago and that value is programmed into the bq27541-V200.   I am asking for some quantification of the variation in FG current reading from device to device and production lot to lot, specifically due to the FG's tolerance on measuring Vsns.  Another way to express this is for a test current fixed at 1.00A and Rsns fixed at 20.00 milliohms, how much variation will there be in Current measurement from device to device and from lot to lot?.   (There has to be some tolerance on the FG reading of Vsns. That is what I'm seeking. Normally it would be expressed as some % of reading and some % of full scale.)

I want to calibrate current. But to make this change in the test process our customer wants documentation of the need to do so, That is the reason for my inquiry.

Thank you. 

Lon