BQ34Z100-G1: Internal Temp Sensor Way Off

Sam Evans

Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100EVM, BQSTUDIO, , BQ34Z100

We are set up to use an internal temperature sensor. I have a 10k pulldown on the TS line. When we set the configuration to use the Internal Temp Sensor and calibrate, our read temperature is way off.

When our set temp is 22C, our read calibrated temp is ~45C

When our set temp is 2C (which is known to be wrong, our room is actually 22C), our read calibrated temp is closer to ~25C

I am curious why there is this massive offset and why we have to lie to the chip in order to get the temperature sensor within an acceptable range?

The error is not even close to within tolerance given by the datasheet

over 7 years ago

0 dMax over 7 years ago

TI__Genius 14985 points

Hi Sam,
You should be fine without calibrating either the internal or external temp sensor.
What was the error before you did calibration?
Is this on your custom board or on the bq34z100EVM?
Also, if you can extract a .gg.csv file from the board in question using the Data Memory plugin from bqStudio and attach it to your post it will help.
Finally, can you use the Registers tab and log the values reported for a minute or so, we can see if anything else looks odd.

0 Sam Evans over 7 years ago in reply to dMax

Prodigy 150 points

This is on my custom board.

Is having a 10k pulldown to ground the right setup? I have a note on my schematic that I should either have a 10k pulldown or leave it open. We removed the resistor and the behavior is the same if it were an open circuit. It is still off by ~20C.

I am attaching the .gg.csv

sisterboard_calibrated_1.gg.csv.zip

0 Jasper Yi over 7 years ago in reply to Sam Evans

TI__Intellectual 1365 points

You have to connect 10Kohm between TS and REG 25. However, internal temp is not related the temp offset. It should be very close to real temp

0 Sam Evans over 7 years ago in reply to Jasper Yi

Prodigy 150 points

Thank you Jasper. This is probably the solution. The datasheet talks about being able to use the internal temp sensor, but I don't see info on having to connect the 10k resistor. Can you show me where this info came from (datasheet, app note, eval board, etc.)?

Thanks for the reply!

0 Jasper Yi over 7 years ago in reply to Sam Evans

TI__Intellectual 1365 points

The description is in the bq34z100-G1 datasheet.

Page 37.
When an external thermistor is used, REG25 (pin 7) is used to bias the thermistor and TS (pin 11) is used to
measure the thermistor voltage (a pull-down circuit is implemented inside the device).

EVM schematic has a complicated circuits but you can see RT1 is connected to between REG25 and TS pin.

0 Sam Evans over 7 years ago in reply to Jasper Yi

Prodigy 150 points

This is explaining when an external thermistor is used. What about for the internal temp measurement? Something without the RT1 external thermistor?

Or are you saying the way to use the internal temp sensor is to just fake the external thermistor? It isn't really clear in the datasheet how to use the internal temp sense functionality.

Thank you for taking the time, Jasper!

0 Jasper Yi over 7 years ago in reply to Sam Evans

TI__Intellectual 1365 points

Internal Temp sensor is integrated in the bq34z100. So, the external thermistor is not related to the internal temp measurement.
If internal temp has a hugh offset value, it would be the device problem.
Internal temp is selected in Pack configuration[TEMPS] bit configuration.

0 Sam Evans over 7 years ago in reply to Jasper Yi

Prodigy 150 points

how should I have the TS pin hooked up if I am using internal temperature sensing, though?

0 Jasper Yi over 7 years ago in reply to Sam Evans

TI__Intellectual 1365 points

We recommend to connect 10Kohm between REG25 and TS.

0 Sam Evans over 7 years ago in reply to Jasper Yi

Prodigy 150 points

yes. I understand that in talking to you now.

But is there anywhere in the datasheet or app note that would have told me that BEFORE I built the board? It isn't clear how to use the internal temp sensor in the documentation provided for the part.

0 David Hien over 7 years ago in reply to Sam Evans

TI__Genius 10830 points

Hi Sam,
We checked with our designer and there is no external components required for an internal temperature sensor measurement.

Regards,
David

0 Sam Evans over 7 years ago in reply to David Hien

Prodigy 150 points

Thank you, David. So the answer for us is to not have any external components attached to the TS line? Leave it floating if you want to use internal temperature sensor?

0 David Hien over 7 years ago in reply to Sam Evans

TI__Genius 10830 points

hi Sam,
We verified with our design engineer that there would be no external components required for an internal temperature sensor measurement.

Regards,
David

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BQ34Z100-G1: Internal Temp Sensor Way Off