SNIA042 November 2021 TMP114 , TMP126 , TMP126-Q1
With a desired system limit of 20 °C/s and a conversion period timing error of 15 %, the Slew Rate Limit setting can be calculated as shown in the following equations. To ensure the warning triggers by 20 °C/s, the ±15 % timing error must be factored into the calculation. Using the below equations we get a Slew Rate Limit of 17.4 °C/s.
With a Slew Rate Limit setting of 17.4 °C/s , minimum and maximum slew rates that will trigger an alert can be determined by Equation 4. A setting of 17.4 °C/s will trigger an alert at a minimum slew rate of 14.79 °C/s, a typical slew rate of 17.4 °C/s, and a maximum slew rate of 20 °C/s. This ensures that the warning will always trigger before reaching the 20 °C/s design requirement.
The second outlined requirement is the system must react within 200 ms to the temperature spike occuring. The list of possible conversion period settings are shown in Table 4-1. From this table it is acceptable to choose between options 31.25 ms (1h), 62.5 m (2h), or 125 ms (3h). This would allow the device to detect and alert the system faster than 200 ms. Setting 0h cannot be chosen as the slew rate warning requires a time delay between temperature conversions.
Setting | Conversion Period |
---|---|
0h (No delay between conversion) | 5.5 ms |
1h | 31.25 ms / 32 Hz |
2h | 62.5 ms / 16 Hz |
3h | 125 ms / 8 Hs |
4h | 250 ms / 4 Hz |
5h | 500 ms / 2 Hz |
6h | 1 s / 1 Hz |
7h | 2 s / 0.5 Hz |
The device settings for this design example are shown in Table 4-2.
Setting | Conversion Period |
---|---|
Slew Rate Limit | 17.4 °C/s |
Conversion Period | 125 ms |