12.1.1 Mounting and Temperature Conductivity

Alternatively, the LMT70 can be mounted inside a sealed-end metal tube, and can then be dipped into a bath or screwed into a threaded hole in a tank. As with any IC, the LMT70 and accompanying wiring and circuits must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate at cold temperatures where condensation can occur. If moisture creates a short circuit from the TAO output to ground or VDD, the TAO output from the LMT70 will not be correct. Printed-circuit coatings are often used to ensure that moisture cannot corrode the leads or circuit traces.

The LMT70's junction temperature is the actual temperature being measured. The thermal resistance junction-to-ambient (R_θJA) is the parameter (from Thermal Information) used to calculate the rise of a device junction temperature due to its power dissipation. Equation 1 is used to calculate the rise in the LMT70's die temperature.

Equation 1.

where

• T_A is the ambient temperature.
• I_Q is the quiescent current.
• I_L is the load current on V_TEMP.

For example, in an application where T_A = 30°C, VDD = 3 V, IDD = 12µA, V_TAO = 943.227 mV, and I_L = 0 μA, the total temperature rise would be [187°C/W × 3 V × 12 μA] = 0.007°C. To minimize self-heating, the load current on TAO pin should be minimized.