Advanced Automotive Thermometer with External Diode Sensors for Multi-Channel Monitoring

Microchip has recently unveiled a new line of 10 automotive-grade multi-channel temperature monitoring ICs. These ICs utilize external diodes, transistors, or substrate diodes as sensors. Known as the MCP998x family, they are capable of communicating over a serial bus and feature a pair of discrete output pins.

The accuracy of these ICs is impressive, with a maximum deviation of ±1°C (typical deviation of ±0.2°C) when the IC and probe diodes are within the temperature range of +20°C to +85°C. Furthermore, these ICs can operate at different temperatures. However, when the IC and external probe diodes are anywhere from -40°C to +125°C, the accuracy degrades to ±2.5°C (typical deviation of ±0.4°C). It is important to note that these measurements are based on a supply voltage of 3.3V, although the ICs can function within a range of 1.7V to 3.6V. Additionally, the resolution of these ICs is 0.125°C in all cases.

Out of the ten sensors in the MCP998x family, five of them are equipped with a 'D' suffix. These sensors have an output called 'sys-shdn' that is specifically designed to shut down external hardware. What makes this feature unique is that it cannot be stopped through software, whether maliciously or due to a program flow upset. The 'sys-shdn' output is set between 77°C and 112°C by external resistors. Interestingly, these resistors are also used to pull-up the open-drain 'sys-shdn' and 'alert/therm' outputs, creating a 6-bit binary number between them. On the other hand, the sensors without the 'D' suffix have 'alert' and 'therm' outputs instead. All four of these outputs have multiple functions, and the data sheet provides detailed information on the various options.

"With up to five channels of monitoring and several alert and shutdown options for security, this product family can support systems that supervise more than one thermal element," said Microchip.

Some of the ICs in the MCP998x family offer the option to connect pairs of anti-parallel diodes to certain inputs. The advantage of this configuration is currently being investigated. Additionally, diode-connected transistors, such as a 2N3904 emitter-based junction with collector-base shorted, are expected to be commonly used as sensors. To address this scenario, beta compensation is available on some input pins via a register, as well as an adjustment for the 'external diode ideality factor.' Furthermore, a register-based correction ('REC') is provided to account for errors caused by the resistance of wires and PCB tracks between the IC and the sensed junctions.

The MCP998x family is available in two package options: 2 x 2mm WDFN MSOP-8 or 2 x 2.5mm VDFN MSOP-10. For development purposes, Microchip offers the EV23P16A evaluation board.

These devices are particularly well-suited for automotive applications where operating temperatures for electronics play a crucial role. Microchip states that the sensors are designed to support various functions, including HID lamps, driver-assistance systems, automotive servers, infotainment systems, seat controls, and power windows.

The MCP998x family data sheet can be found here. It provides comprehensive information on the IC's internal workings and the compensation techniques employed to address non-linearity.