SNOAAB5 October   2025 TMP461-SP , TMP9R00-SP , TMP9R01-SEP

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Comparisons
  6. 3Remote Application Use Cases
  7. 4Default Remote Considerations
  8. 5Beta Error
  9. 6Calibration
  10. 7Layout Techniques
  11. 8Summary
  12. 9References

6 Calibration

TI remote temperature sensors can correct for errors through calibration registers. This feature allows to match with a variety of different BJTs. As stated previously, n-factor represents the error of how closely the base emitter junction follows the ideal diode equation. N-factor and offset can be corrected within the I2C registers of TI remote temperature sensors. To reduce these errors, the following steps must be performed. The equipment needed for adjusting the n-factor and the offset are the following: a controlled temperature environment, a reference temperature measurement, and the remote/junction setup.

  1. Verify the connection pins to confirm the presence of a diode by measuring the forward voltage drop, which can be approximately 0.7V.
  2. Place remote/junction setup in a controlled temperature environment like an Oil Bath or an Oven. A reference temperature reference needs to be setup within the environment. Oil bath or an oven reference must not be used. The preferred reference is to use a Platinum Resistance Thermometor (PRT) or a Resistance Temperature Detector (RTD) as close to the remote junction as possible. Another reference option is the using the local temperature die of the remote sensor.
  3. Collect temperature of remote, local, and reference data across temperature within the controlled environment. The range of temperature needs to be users desired range of the product.
  4. Load collected data into the Remote Calibration Tool to optimize the value needed for n-factor and offset.
  5. Write new n-factor and offset values into I2C registers.
  6. Confirm improved performance by repeating step three.

An example of improved accuracy with the Remote Calibration Tool is shown, first highlighting the raw data with no changes in the configuration, then, highlighting the improvement in accuracy with changes in the configuration.

Effects from Changing Offset and N-factor Figure 6-1 Effects from Changing Offset and N-factor
Table 6-1 Calibration Settings
Nfactor Offset
0.994661626 -17.875C
0x1C 0xF710

When n-factor and offset are the only sources of error, the following equations can also be used to optimize the remote device. Nexpected value is 1.008.

Equation 9. E r r o r   =   ( T   +   275 . 15 )   ×   N a c t u a l - N e x p e c t e d N e x p e c t e d R e p o r t e d   T   =   ( T   + 273 . 15 )   ×   N a c t u a l N e x p e c t e d - 273 . 15 N a c t u a l = ( T r e p o r t e d + 273 . 15 )   ×     N e x p e c t e d T   +   273 . 15

Our temperature sensors also have, automatic series resistance cancellation. Series resistance cancellation in remote temperature sensors is an important technique used to enhance measurement accuracy, especially in applications where long cable runs are involved and connecting to SOCs. When sensors are placed at a distance from the measurement system, the resistance of the connecting wires can introduce errors in temperature readings due to voltage drops along the wire. Any resistance in the junction signal path can cause a voltage drop between the actual VBE at the transistor and the measured VBE at the temperature sensor, which results in a temperature offset. To mitigate this effect, internally remotes can cancel resistance on the DXP/DXN signals to cancel out resistance error from the wire and allow the addition of noise filtering without increasing the temperature error. A total of up to 1kΩ of series resistance can be canceled by the device. Series resistance cancellation allows direct connections to embedded and discrete junctions. The equation below highlights the additional error to the Vbe measurement when resistance in in the D+ and D- path. The first term is the added error from the series resistance.

Equation 10. ∆ V B E = I S R s   +   η k T q ln I C 2 I C 1