SLUAAY5 December   2024 UCC21551-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Automotive PTC Heater Module Overview
    1. 2.1 Automotive Heating Architectures
      1. 2.1.1 Positive Temperature Coefficient Heaters
      2. 2.1.2 Heat Pumps
    2. 2.2 Automotive Heating Architectures
    3. 2.3 PTC Heater Topologies
  6. 3Design of Automotive PTC Heater Controller
    1. 3.1  Block Diagrams
    2. 3.2  Designing the Power Supplies
    3. 3.3  Picking Low-Dropout Regulators
    4. 3.4  Designing of the Communication Interface
    5. 3.5  Implementation of the Digital Isolator
    6. 3.6  Implementation of the Microcontroller Unit
    7. 3.7  Designing of the Switch Driver Stage
    8. 3.8  Selection of the Power Switches
    9. 3.9  Considerations of the PTC Load
    10. 3.10 Designing the Load Current Monitoring
    11. 3.11 Selection of the Temperature Sensing
  7. 4Summary

3.11 Selection of the Temperature Sensing

Temperature sensors measure the heat from either the power switches or the PTC load and feed the information back to the MCU within a specified accuracy.

When picking a temperature sensor, the first factor a designer may want to look for is accuracy. A temperature accuracy within 2°C-3°C may be sufficient for PTC load and power switch temperature. An attribute that greatly impacts accuracy is the device's power consumption. The device's "self-heating" can negatively impact the measurement read and fed back to the MCU. The TMP235-Q1 has a maximum temperature accuracy of ±2.5°C, so it provides a great balance of cost and accuracy.

Another factor to consider is the package size of the sensor. The smaller the package, the faster the response time. If your system requires a fast response time, in conditions such as rapid overheating of the power switches, the PTC load suddenly going past its power rating and so forth, consider the package size of the temp sensor. Regarding fast power switches temp response, you can use a device like the ISOTMP35-Q1. This is an isolated temp sensor that lets you connect to the HV power switches for instant response.

If the goal of the application is to achieve the lowest cost PTC module possible, a designer can use a negative temperature coefficient (NTC) sensor. However, if the designer wants more accurate temperature measurements without having to use a linearization circuit, as well as less resistance tolerance variation than what traditional NTCs can provide, a PTC thermistor like the TMP61-Q1 can be a good choice. This sensor also comes with a fast response time of 0.6s, enabling the PTC heater control module to respond to overtemperature conditions quickly.

Placement is one of the most important factors when implementing this component in your PTC heater module. Proper placement is critical for accurate readings. Air is by far the worst medium for measuring temperature, so place the temperature sensor as close to the power switch or PTC load as possible to provide proper ambient temperature sufficient measurement. One can measure hotspots of the power switches to help maximize the performance without getting overheated. However, capturing this usually requires more expensive temperature sensors.