Accurate measurement of power is an essential part of reliable and energy-efficient (green) system design. Measuring the voltage and current of low voltage (1.8V to 36V) power supplies is straightforward, but higher voltages present more challenges. In this video we introduce the LTC2945 wide range I2C system monitor. The device monitors current, voltage and power from any 0V to 80V supply rail, and the rail-to-rail current input allows the sense resistor to be placed on the high or low side of the supply. The LTC2945's wide operating range makes it ideal for a wide range of applications, including 48V telecommunications equipment, advanced mezzanine cards (AMC) and blade servers. The LTC2945 utilizes a 12-bit ΔΣ
ADC to measure current and voltage, calculate power, and store all this information along with minimum and maximum values in registers accessible through I2C. Measurement accuracy is ±0.75% over the entire operating temperature range. If any parameter exceeds user-programmable limits, the LTC2945 flags the alarm register and pin according to the SMBus alarm response protocol. The 400kHz I2C interface features 9 device addresses, a blocking bus reset timer, and a branched SDA pin, which simplifies optical isolation.