RTP devices

Littelfuse Reflowable Thermal Protection (RTP) device is a low resistance, robust surface mountable thermal protector. It has a set open temperature and can be installed using reliable, lead-free, Surface Mount Device (SMD) assembly and reflow processes.

The RTP device described in this overview can withstand the demanding environmental, life, and reliability requirements of automotive and industrial applications, including shock, vibration, temperature cycling, and humidity exposures. In the field, the RTP device opens if its internal junction exceeds the device’s specified open temperature. Temperature increases can have multiple sources, one of which is component failure (i.e. when using power components such as a power FET, capacitor, resistor, triac, etc.). The RTP device open temperature is selected so that the device does not open within normal component operating windows, but it does open in a thermal runaway event and before the melt temperature of typical lead free solders.

To simplify installation, improve reliability, and optimize thermal coupling with the PCB, the RTP device is surface mountable. No special SMD installation is required. Instead, after installation, the RTP device utilizes a one time electronic arming process to become thermally sensitive. Before the arming procedure, the device can go through installation temperatures up to 260°C without going open. After arming, the device will open when the critical junction exceeds the open temperature. Arming can occur during test, or in the field.


  • Helps provide protection against thermal runaway for power FETs and other components if failure occurs in applications such as automotive HVAC, ABS, power steering, DC/DC converters, PTC heaters, etc. or IT servers, telecom power, converters, etc.
  • Other DC thermal protection


  • Helps prevent failed components from smoking, and or de-soldering in case of a thermal event
  • Allows use of standard surface-mount production methods with no special assembly costs
  • Low power dissipation and voltage drop
  • Supports DC electronic circuits
  • Suitable for rugged environment applications (automotive and industrial)
  • Green design
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