As more and more systems are becoming electrified, system thermal management has become more critical. Many systems utilize temperature measurement for managing the system thermal performance. While this is adequate for many systems, for systems with rapidly changing temperature, this could be difficult. This is due to the thermal equilibrium principle which temperature measurement is based on. For systems with potentially rapid changing temperature, measuring the system current may enable a faster method for predicting and managing the thermal performance of the system.
System thermal management
Whether it is the electrification of motor vehicles, the proliferation of the Internet of Things (IoT), or Industry 4.0, more electronic systems are in the world today that are expected to be available 24/7. To ensure these systems continue to operate optimally, the systemís thermal performance needs to be monitored and managed. For many systems, a thermistor or temperature sensor integrated circuit (IC) is used to perform this monitoring. This thermal management is performed typically for one of the following use cases:
- Long-term system reliability
- Real-time system performance and utilization
- System safety
- Fault identification and prevention
As I discussed in Signal Chain Basics #86: Fundamentals of Temp Sensors, these devices work on the basic principle of thermal equilibrium, two bodies thermally connected will reach a common temperature based on the thermal mass of each. In electronic terms, this is a relatively slow process. This temperature increase is normally due to an increase of the system current flow. Systems that may be exposed to rapid increases in temperature may struggle to best manage their thermal profile if using a temperature measurement system. Therefore, measuring current may be a better alternative, especially for addressing system safety or fault identification and prevention use cases.
If left unchecked, increasing load current eventually causes key components in a system to exceed the absolute maximum junction temperature ratings. In the most severe case, the IC can actually ignite from the heat. This type of catastrophic failure is rare, but the consequences can be costly in terms of system damage, and potentially could lead to bodily injury. Monitoring the current can enable the management system to identify possible issues well before they become dangerous and allow it to take preventive actions. In the most adverse of conditions, it can simply shutdown the system with the goal of reducing current flow to below dangerous levels.
An example of prevention of bodily injury would be in the personal vaporizer. The heating of the liquid is intended to be very rapid to optimize the user experience. However, if the liquid gets too hot, the resulting vapor could cause burns to the user. By monitoring the current flow to the heating element, a current sense amplifier can allow the management system to prevent the temperature of the vapor from exceeding the recommended safe levels.
Fault identification and prevention
If a system has a fault such as a short to power or ground, serious system failures and damage are possible. Therefore, it is critical to detect faults as early as possible. Clearly waiting for the corresponding increase in temperature related to the sudden increase in current that results from a short may be too late to prevent damage. For example, many integrated gate bipolar transistors (IGBTs) used in motor control systems or DC/DC converters have integrated temperature sensing elements. However, the slowness of the reaction time of this measurement is only fast enough in high-power systems to limit the destruction to the IGBTs themselves. Using current measurement techniques to detect the rapidly rising current could enable the management system to prevent the destruction.