SNAS890 Data sheet

SNAS890A February 2025 – June 2025 HDC3120-Q1

PRODUCTION DATA

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)

DEF|8

Thermal pad, mechanical data (Package|Pins)

Orderable Information

7.4.1.2 Heater Electrical Behavior

The on-chip heater of the HDC3120-Q1 operates as a resistive element with a positive temperature coefficient (PTC)—its resistance increases with temperature. The heater resistance can be estimated using Equation 6 as a function of the junction temperature (TJ):

Equation 6.

R_{H E A T E R} (T_{J}) \approx R_{25 - H E A T E R} ∙ [1 + α (T_{J} - 25 ° C)]

At 25 °C, the typical resistance (R_25-HEATER) is approximately 168.4 Ω, and the temperature coefficient α is roughly 0.00326 °C⁻¹. When HEAT_EN is asserted, the heater draws current from V_DD according to Ohm’s law: I_HEATER ≅ V_DD / R_HEATER. Note while the resistance increases linearly with temperature, the actual junction temperature—and thus heater resistance—varies depending on environmental conditions, airflow, PCB layout, and duty cycle.

With the heater resistance estimated, the heater power can then be approximated using Equation 7:

Equation 7.

P_{H E A T E R} (T_{J}) \approx \frac{{V_{D D}}^{2}}{R_{H E A T E R} (T_{J})} \approx \frac{{V_{D D}}^{2}}{R_{25 - H E A T E R} ∙ [1 + α (T_{J} - 25 ° C)]}

Table 7-4 summarizes typical heater current and power values at 25 °C ambient. These values represent the initial heater power draw, prior to thermal ramp-up. Heater resistance increases as the die warms, so current draw decreases slightly over time during a heating cycle. However, during the initial 1–2 seconds, when the heater is still cool, the current draw is at the maximum.

Table 7-4 Estimated Heater Current and Power at 25 °C

Supply Voltage (VDD)	Heater Current (typ.)	Heater Power (typ.)
1.8 V	≅10 mA	≅18 mW
3.3 V	≅19 mA	≅62 mW
5.0 V	≅28 mA	≅138 mW
5.5 V (maximum)	≅30 mA	≅165 mW

Note:

Due to these varying factors, estimating exact junction temperature from resistance or power is generally not practical. Therefore, users must focus on heater enable timing and system-level thermal behavior, rather than relying on theoretical resistance models.

Always design your power supply and system thermal envelope to accommodate the peak heater current observed during startup. This verifies stability and avoids brownout conditions, especially at higher V_DD levels.