TMP468: questions about the series resistance cancellation of TMP468

hui zhang

Part Number: TMP468

Hi,expert.

When i reading TI'guide SBOA173-Optimizing Remote Diode Temperature Sensor Design，about TMP468 series resistance cancellation shown as below，I have questions：

1. what △VBE1 and △VBE2 stand for？

2. what the value of K1, K2, K3 , K4 and K5?

3.what the value of m? 6 or 16

Thanks.

over 6 years ago

0 Amit Ashara over 6 years ago

TI__Guru**** 244400 points

Hello Hui,

The △VBE1 stands for the difference in VBE for I1 and I2 and △VBE2 stands for the difference in VBE for I2 and I3 currents.

The constants K1-K5 & m1 are handled by the device. I can check on their calculation.

0 hui zhang over 6 years ago in reply to Amit Ashara

Intellectual 280 points

Hi,Ashara

As you say,if '△VBE1 stands for the difference in VBE for I1(1*I) and I2(6*I) and △VBE2 stands for the difference in VBE for I2(6*I) and I3(16*I) currents.

then△VBE1=VT*ln(6)+5*IR,△VBE2=VT*ln(16/6)+10*IR,

I can't find the valid value K1 and K2 for (△VBE2-K1*△VBE1)/K2*I=R.

Thanks

0 hui zhang over 6 years ago in reply to Amit Ashara

Intellectual 280 points

can you give me the K1-K5 & m1 value,pelease

0 Amit Ashara over 6 years ago in reply to hui zhang

TI__Guru**** 244400 points

Hello Hui,

I am working on the same. Please give us sometime to ascertain the data behind the equations,

0 Amit Ashara over 6 years ago in reply to hui zhang

TI__Guru**** 244400 points

Hello Hui,

The value for the constants provided in the application note cannot be disclosed. The application note aims to highlight how 3 excitation currents can be used to compensate for series resistance cancellation as long as the Rs (series resistor) does not exceed the value as specified in the datasheet for the part.

For information, for TMP468 the maximum recommended Rs is 1 k ohm.

0 hui zhang over 6 years ago in reply to Amit Ashara

Intellectual 280 points

Hi Ashara. Thans for you reply.

Are you sure △VBE1 stands for the difference in VBE for I1 and I2 and △VBE2 stands for the difference in VBE for I2 and I3 currents ?

can it be △VBE1 stands for the difference in VBE for I1 and I3 and △VBE2 stands for the difference in VBE for I2 and I3 currents.

Thanks

0 Amit Ashara over 6 years ago in reply to hui zhang

TI__Guru**** 244400 points

Hello Hui,

It depends on which set of current sources are used for the computation for the △VBE

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TMP468: questions about the series resistance cancellation of TMP468