TMP468: temp sensor circuit

Timothy Tran2

Part Number: TMP468

Hi,

1) If using a NPN diode connection as shown in Fig 1, does the TMP468 provides/outputs constant current source on these pins (D1+ through D8+)?

2) is that more accurate to use two NPN transistors connected in series with their respective base and collectors short-circuited? see below drawing, for example

Thanks,

Tim

over 6 years ago

0 David Vaseliou over 6 years ago

TI__Expert 6820 points

Hi Tim,

Your images did not upload correctly. Can you please upload images as attachments?

Thanks,
David

0 Timothy Tran2 over 6 years ago

Intellectual 420 points

Hi Daivd,

Here it is per attached. It’s from datasheet page 1 per attached link below…

https://www.ti.com/lit/ds/symlink/tmp468.pdf

Thanks,

Tim

Fig1.PNG

0 Timothy Tran2 over 6 years ago

Intellectual 420 points

#2, is the circuit FigA better accuracy than FigB as shown in the attached screent-shot?

Thanks, Tim

2xNPN vs 1xNPN.PNG

0 David Vaseliou over 6 years ago in reply to Timothy Tran2

TI__Expert 6820 points

Hi Tim,

The first image from the datasheet that you reference looks to use PNP transistors. In this configuration NPN cannot be used.

As for your second image, we recommend using Fig. B as mentioned in the datasheet on page 31.

Thanks,
David

0 Timothy Tran2 over 6 years ago

Intellectual 420 points

Where is the answer?

0 David Vaseliou over 6 years ago in reply to Timothy Tran2

TI__Expert 6820 points

Hi Tim,

Please see above response. If there are any concerns I missed or more explanation needed please let me know.

Thanks,
David

0 Timothy Tran2 over 6 years ago

Intellectual 420 points

David,

Sorry, I couldn’t see where the response is. Can you email it to me or point it out to me?

Thanks

0 Timothy Tran2 over 6 years ago in reply to David Vaseliou

Intellectual 420 points

Are these pins D1-D8 of TMP468 current sources? and why it can't be used with NPN?

0 David Vaseliou over 6 years ago in reply to Timothy Tran2

TI__Expert 6820 points

Hi Tim,

This is what my answer was:

"The first image from the datasheet that you reference looks to use PNP transistors. In this configuration NPN cannot be used.

As for your second image, we recommend using Fig. B as mentioned in the datasheet on page 31."

Thanks,
David

0 David Vaseliou over 6 years ago in reply to Timothy Tran2

TI__Expert 6820 points

Hi Tim,

The D1-D8 pins are current sources that are applied to the remote sensor.

NPN transistors can only be used in the diode-connected configuration as seen on page 31 of the datasheet. This is because the TMP468 uses Vbe to determine the temperature, thus the D+ and D- pins must be connected to these two terminals of the NPN. For an NPN in transistor-connected configuration the emitter needs to be connected to ground to ensure operation.

Thanks,
David

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TMP468: temp sensor circuit