TMP442 datasheet(49/63 Pages) TI2

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9.2.2 Detailed Design Procedure

The ideality factor (η) is a measured characteristic of a remote temperature sensor diode as compared to an

ideal diode. Compensating for ideality factor differences is simple if the diode manufacturer specifies the n-factor

in the respective data sheet. If the ideality factor of the transistor is not specified, the manufacturer can be able

to provide the n-factor value by a special request.

Typical ideality factor specification differences cause a gain variation of the transfer function. The TMP4719 is

calibrated for the ideality factor of 1.004, so use η-Factor Lookup Table to compensate for a target ideality factor

that differs from 1.004.

For example, if MMBT3906FZ-7B bipolar transistor, which has an ideality factor of approximately 1.008, is

selected for this design example, 15h with a ideality factor (η) of 1.0079 is the closest value that can be

programmed to compensate for the differing typical ideality factors. Referring to I2C and Register Map, the

controller then sends a write command to the address of the target (4Dh) followed by the register pointer (27h)

and finally the data (15h) to η-Factor_Ch1 Register.

The design calls for the high temperature limit of 88°C at device power up, which is programmed using I2C.

Referring to I2C and Register Map, the controller sends a write command to the address of the target (4Dh)

followed by the register pointer (07h) and finally the data (51h) to THigh_Limit_Remote_Ch1_High Register.

START

Target Address

R/W

ACK from Target

THigh_Limit_Remote_Ch1_High

STOP

ACK from Target

Data to Register (88 C)

Target controls SDA line

Controller controls SDA line

Figure 9-2. Application Example: Program Using I2C to Set Temperature High Limit

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

created by fast digital signals, and noise can corrupt measurements. The TMP4719 device has a built-in, 65kHz

low-pass filter on the inputs of D+ and D– 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 100pF and 1.5nF. 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 1kΩ. If filtering is

required, suggested component values are 470pF and 50Ω on each input; exact values are application-specific.

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TMP4719

SBOSAJ7A – OCTOBER 2025 – REVISED DECEMBER 2025

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TMP442 Datasheet(PDF) 49 Page - Texas Instruments