SNAS758A February   2025  – June 2025 HDC3120

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Device Power-Up
      2. 7.3.2 Device Disable and Enable
      3. 7.3.3 Conversion of the Signal Output
        1. 7.3.3.1 Relative Humidity (RH%) Measurement
        2. 7.3.3.2 Temperature Measurement
      4. 7.3.4 NIST Traceability and Unique ID
      5. 7.3.5 Output Short Circuit Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 On-Chip Heater
        1. 7.4.1.1 Operating Principle
          1. 7.4.1.1.1 Heater Configuration Example
        2. 7.4.1.2 Heater Electrical Behavior
        3. 7.4.1.3 Heater Temperature Increase
        4. 7.4.1.4 Heater Usage Guidelines
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
    3. 8.3 Power Supply Recommendations
    4. 8.4 Rehydration Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
      2. 8.5.2 Layout Example
    6. 8.6 Storage and PCB Assembly
      1. 8.6.1 Storage and Handling
      2. 8.6.2 Product Storage
      3. 8.6.3 PCB Assembly Flow
      4. 8.6.4 Rework Consideration
      5. 8.6.5 Sensitivity to Chemicals and Vapors
      6. 8.6.6 Exposure to High Temperature and High Humidity Conditions
      7. 8.6.7 Recovering Sensor Performance: Bake and Rehydration Procedure
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

8.5.1 Layout Guidelines

When doing PCB for humidity sensors, the most important concept to understand is that the junction temperature of the humidity sensor needs to match the ambient temperature as closely as possible. This is because to obtain an accurate relative humidity result, the temperature measured by the sensor needs to be of the ambient air since relative humidity is dependant on temperature. Practically, this means minimizing the thermal resistance between the HDC3120 and the ambient air, and maximizing the thermal resistance between the HDC3120 and PCB heat sources. To accomplish these goals, TI recommends to:

  1. Isolate all heat sources from the HDC3120. This design means positioning the HDC3120 away from power intensive board components such as a battery, display, or microcontroller. Preferably, the only onboard component close to the HDC3120 is the supply bypass capacitor. See the Layout Example for more information.

  2. Eliminate copper layers below and around the device (GND, VDD) that are connected to other potentially heat generating components on the PCB or carry thermal energy from another source.

  3. A small exposed backside copper layer that is not electrically connected to any signal can be placed underneath the HDC3120 (with the thermal pad soldered). Thermal vias can then be added to better thermally connect the HDC3120 package to the backside copper plane. The purpose of this copper plane is to provide another path for ambient air temperature to reach the HDC3120. The copper plane heats or cools as the plane is exposed to the ambient air, and then pass that temperature change through the thermal vias to the HDC3120. This way the HDC3120 is not only receiving the ambient air temperature through the package body on the topside of the PCB, but through conducted thermal transfer as well.
  4. Use slots or a cutout around the device to reduce the thermal mass and obtain a quicker response time to sudden environmental changes.
    • The diameter of the routing in Layout Example is 6mm. There is not a recommendation on exactly how wide the slot-cut needs to be in the PCB, the user must verify that there is sufficient isolation of external thermal gradients present on the PCB. TI recommends placing as large of a slot-cut as possible around the HDC3120. Other representations of cutouts for thermal relief and additional layout guidelines and information can be found in the Optimizing Placement and Routing for Humidity Sensors application note.
  5. Follow the Example Board Layout and Example Stencil Design that is illustrated in Section 11.
    • TI recommends a multilayer ceramic bypass X7R capacitor of 0.1μF between the VDD and GND pins.
  6. Soldering the package thermal pad to a board pad that is left electrically floating is generally best practice. However, the package thermal pad can be left unsoldered to minimize thermal leakage for maximum heater efficiency. See the HDC3x Silicon User's Guide for more information regarding when leaving the thermal pad unsoldered can be helpful for the user application.