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TMP461-SP

SBOS876B – SEPTEMBER 2017 – REVISED FEBRUARY 2020

www.ti.com

Product Folder Links: TMP461-SP

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Copyright © 2017–2020, Texas Instruments Incorporated

7.3.2 Series Resistance Cancellation

Series resistance cancellation automatically eliminates the temperature error caused by the resistance of the

routing to the remote transistor or by the resistors of the optional external low-pass filter. A total of up to 1 kΩ of

series resistance can be cancelled by the TMP461-SP device, thus eliminating the need for additional

characterization and temperature offset correction. See Figure 5 (Remote Temperature Error vs Series

Resistance) for details on the effects of series resistance on sensed remote temperature error.

7.3.3 Differential Input Capacitance

The TMP461-SP device tolerates differential input capacitance of up to 1000 pF with minimal change in

temperature error. The effect of capacitance on the sensed remote temperature error is illustrated in Figure 6

(Remote Temperature Error vs Differential Capacitance).

7.3.4 Filtering

Remote junction temperature sensors are usually implemented in a noisy environment. Noise is most often

created by fast digital signals that can corrupt measurements. The TMP461-SP device has a built-in, 65-kHz filter

on the D+ and D– inputs to minimize the effects of noise. However, a bypass capacitor placed differentially

across the inputs of the remote temperature sensor is recommended to make the application more robust against

unwanted coupled signals. For this capacitor, select a value between 100 pF differential and 1 nF. Some

applications attain better overall accuracy with additional series resistance. However, this increased accuracy is

application-specific. When series resistance is added, the total value must not be greater than 1 k

Ω. If filtering is

required, suggested component values are 100 pF differential and 50

Ω on each input; exact values are

application-specific.

Additionally, a digital filter is available for the remote temperature measurements to further reduce the effect of

noise. This filter is programmable and has two levels when enabled. Level 1 performs a moving average of four

consecutive samples. Level 1 filtering can be achieved by setting the digital filter control register (read address

24h, write address 24h) to 01h. Level 2 performs a moving average of eight consecutive samples. Level 2

filtering can be achieved by setting the digital filter control register (read address 24h, write address 24h) to 02h.

The value stored in the remote temperature result register is the output of the digital filter, and is the value that

the ALERT and THERM limits are compared to. The digital filter provides additional immunity to noise and spikes

on the ALERT and THERM outputs. The filter responses to impulse and step inputs are shown in Figure 11 and

Figure 12, respectively. The filter can be enabled or disabled by programming the desired levels in the digital

filter register; see Table 5. The digital filter is disabled by default and on POR.

Figure 11. Filter Response to Impulse Inputs

Figure 12. Filter Response to Step Inputs