BQ27426: AverageCurrent Measurement

Robert Whalley

Part Number: BQ27426
Other Parts Discussed in Thread: BQ24092, BQSTUDIO

I am using the BQ27426 embedded in a target system with a 10 mΩ external sense resistor and with a BQ24092 charger. I have configured the Design Capacity, Design Energy, Termination Voltage and Taper Current appropriate for the battery and the charger. The input to the BQ24092 is a standard laboratory power supply.

From the BQ24092 data sheet, the calculated charging current for a 1K resistor on the ISET pin, should be 540 mA. My laboratory power supply shows a current of 554 mA when charging, which includes the expected system load current and which I therefore believe.

The AverageCurrent() reported by the BQ27426 is 1212 mA.

When not charging, the system load consumes about 8 mA and the AverageCurrent() reported by the BQ27426 is about -38 mA.

Any suggestions would be very welcome.

over 7 years ago

0 Onyx Ahiakwo over 7 years ago

TI__Guru* 76230 points

Hi Robert,
Go to the calibration window on bqstudio and perform current calibration. Apply a known current and then type the value in the field provided, check the box and hit the calibrate gauge button.
thanks
Onyx

0 Robert Whalley over 7 years ago in reply to Onyx Ahiakwo

Prodigy 200 points

Hi Onyx,

When I've done that, the value of CC gain and CC delta has changed. I assume that I can then generate a new golden image, checking the option to include CC gain in the OTFS file?

Rob

BTW do you happen to know what format the CCGain is, because it doesn't appear to be IEEE 754 binary32, The default value of 0.238 in IEEE 754 is 0x3E73B645, but the gauge has 0x7E73B645, so the exponent is wrong.

0 Onyx Ahiakwo over 7 years ago in reply to Robert Whalley

TI__Guru* 76230 points

Hi Rob,
The TRM will have that information
thanks
Onyx

0 Robert Whalley over 7 years ago in reply to Onyx Ahiakwo

Prodigy 200 points

SLUUBB0 makes absolutely no mention of the format in which the floating point numbers are stored. Sect 7.2 merely provides minimum and maximum values (which, incidently don't agree with the published IEEE 754 binary32 values) and which suggest that an alternative encoding is being used. All I am asking is details for that encoding. If it is in a different document, then by all means provide me with a hyperlink. I am using the msp430-elf-gcc C compiler for my application and uses IEEE 754 binary32 numbers, so I will have to write a conversion routine.

Many thanks.

0 Onyx Ahiakwo over 7 years ago in reply to Robert Whalley

TI__Guru* 76230 points

Here are a couple of e2e postings that may help.

thanks
Onyx

0 Robert Whalley over 7 years ago in reply to Onyx Ahiakwo

Prodigy 200 points

Those postings do indeed help - many thanks Onyx.

I am sure that I am not alone in finding it very strange that TI adopted this format instead of using the IEEE 754 binary32, but it is what it is, and I'm glad I understand it now.

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BQ27426: AverageCurrent Measurement