Designers often need to measure and manage power consumption of low-voltage, high-power ICs such as FPGAs and GPUs to manage performance or anticipate problems. But this simple-sounding task has some implementation complexity and operational subtlety. The challenge is compounded when there’s also a need to know total energy use, which is a function of the aggregate (integral) of the instant-by-instant power value.
To address this problem, Microchip Technology developed the PAC1932/3/4, which are two, three, and four-channel power- and energy-monitoring ICs, respectively. Using a high-voltage multiplexer, this monitor continuously digitizes the dc rail (bus) voltage as well as the voltage across an external current-sense resistor, both with 16 bits of resolution. It then digitally computes the instantaneous power as a product of the two voltage readings (since the current can be inferred from the voltage across that resistor) and provides the results via I2C/SMBus interfaces, including an eight-sample average for reading stability.
The user-supplied sense resistor is chosen so that the maximum current to be measured reaches 100-mV full scale, with a 0- to 32-V common-mode voltage range. The IC can also be set to measure bidirectional current corresponding to a ±100-mV input scale, if needed, which is useful for charge/discharge applications. Measurement accuracy is 1% over a wide dynamic range. The ICs can measure voltage rails under 1 V to as high as 32 V. Thus, designers needn’t reconfigure the measurement resolution when going between low- and high-current load events.
The two-channel PAC1932 IC from Microchip enables simple inclusion of power- and energy-use measurement into circuit designs, which are needed to monitor these vital and often limited resources. The three- and four-channel versions are very similar, but support higher channel count.
The PAC1932 series provides more than just instantaneous power readings. Its offers on-chip accumulation to 28 bits of power results for energy measurement, with a 48-bit power accumulator register for recording accumulated power data and a 24-bit accumulator count.
Sampling rates are user-programmable at 8, 64, 256, and 1024 samples per second, allowing for up to 17 minutes of power data accumulation at 1024 samples/s and over 36 hours at 8 samples/s. The sampling rate and energy-integration period can be controlled via the SMBus or I2C interfaces, which can also be used for active channel selection, one-shot measurements, and other configuration control.
The ICs require a 2.7- to 5.5-V supply, and have a separate VDD I/O pin for digital I/O. They come in 4- × 4- × 0.5-mm UQFN packages, as well as a 2.225- × 2.17-mm WLCSP package for the four-channel PAC1934. The two-and three-channel PAC1932/33 work with Linux and Windows 10 software drivers. The PAC1932/33 is register-compatible with the ADM00805 evaluation board, which can be used to start development with a graphical user interface reporting sensed voltage, bus voltage, power, and accumulated power. Both the basic PAC1932 power-monitoring IC and the three-channel PAC1933 are available now, priced at $0.78 and $0.94 each, respectively, in 10,000-unit quantities.
