ADS1299 Temperature sensor

Derek Xie

Other Parts Discussed in Thread: ADS1299

Hi Team:

My customer is using the ADS1299 in the EEG. And right now, they try to use internal temperature sensor and find the data is wrong.

The software setting is below:

WREG(CONFIG1,0x96);

WREG(CONFIG2,0xD0);

WREG(CONFIG3,0xE0);

WREG(LOFF,0x00);

WREG(CH1SET,0x05);

WREG(CH2SET,0x05);

WREG(CH3SET,0x05);

WREG(CH4SET,0x05);

WREG(CH5SET,0x04);

WREG(CH6SET,0x04);

WREG(CH7SET,0x04);

WREG(CH8SET,0x04);

WREG(BIAS_SENSP,0x00);

WREG(BIAS_SENSN,0x00);

WREG(LOFF_SENSP,0x00);

WREG(LOFF_SENSN,0x00);

WREG(LOFF_FLIP,0x00);

WREG(GPIO,0x00);

WREG(MISC1,0x00);

WREG(MISC2,0x00);

And they read back the data is 05A311（hex）= 369425 (Dec)

Calculate is 369425*4.5/（2^23-1） = 0.198175V = 198175uv

It looks like the temperature is quite high.

They have check the temperature is not high. So do you have any idea which will cause this issue

over 7 years ago

0 Brian Pisani over 7 years ago

TI__Mastermind 38745 points

Hey Derek,

Firstly, which channel are they reading from? It looks like some of the channels are set to measure the temperature sensor and some are set to measure the test signal. Second, what is the expected temperature? Figure 14 in the data sheet shows the offset error which could contribute to an error in temperature reading.

Regards,
Brian

0 Derek Xie over 7 years ago in reply to Brian Pisani

TI__Genius 12255 points

Hi Brian:

Thanks for your response.

1. They read as you can see the resgister setting channel 5- 8 is used for temperature reading. The expected temperature should be normal temperature like 25 degree C.

2. What will cause the offset error? They set the input connect the internal Temperature Sensor and internal test signal.

WREG(CH1SET,0x05);

WREG(CH2SET,0x05);

WREG(CH3SET,0x05);

WREG(CH4SET,0x05);

WREG(CH5SET,0x04);

WREG(CH6SET,0x04);

WREG(CH7SET,0x04);

WREG(CH8SET,0x04);

0 Derek Xie over 7 years ago in reply to Derek Xie

TI__Genius 12255 points

Hi Biran:
Could you help me to check whether the register setting is right? And is it possbile casue by the hardware? Thanks.

0 Brian Pisani over 7 years ago in reply to Derek Xie

TI__Mastermind 38745 points

Hey Derek,

Offset error is a device characteristic that is inherent to the hardware. However, it seems like they are seeing temperatures that are larger than offset error would produce if the die were at 25 C. One thing to note here is that the sensor measures the die temperature - not the PCB temperature or the ambient temperature. It could be that after the device has been consuming power for a few minutes, the die is at a higher temperature than the air around it.

It's also worth noting that we do not specify any performance on this sensor. If accurate temperature sensing needs to be done in this application, I recommend using a dedicated temperature sensor.

Regards,
Brian

0 Derek Xie over 7 years ago in reply to Brian Pisani

TI__Genius 12255 points

Brian:

Thanks. So the customer register setting is right?

0 Brian Pisani over 7 years ago in reply to Derek Xie

TI__Mastermind 38745 points

Derek,

Yes it is.

Brian

0 Derek Xie over 7 years ago in reply to Brian Pisani

TI__Genius 12255 points

Hi Brian:

Thanks. The customer have checked the chip, it isn't very hot. So whether the hardware issue will cause this?

I attached the customer schematic.NU1000v1.1.pdf

0 Brian Pisani over 7 years ago in reply to Derek Xie

TI__Mastermind 38745 points

Hey Derek,

Let me check with the design team. Their schematic looks fine.

Regards,
Brian Pisani

0 Brian Pisani over 7 years ago in reply to Brian Pisani

TI__Mastermind 38745 points

Derek,

I checked with design. The temp sensor should be pretty accurate.

Is R29 populated on their board? If so, have them depopulate it and check again.

Regards,
Brian

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ADS1299 Temperature sensor