IC monitors input power
By Paul Rako, Technical Editor -- EDN, April 2, 2009
International Rectifier has introduced the IR3725 input-power-monitoring IC. The device communicates with a host system over the I2C (inter-integrated-circuit) bus to monitor input power, voltage, and current for power supplies operating on 8 to 23.5V inputs. Current-monitoring accuracy is 1%, and voltage-monitoring accuracy is 1.5%. Worst-case power-measurement error is 2% over the full temperature range and 1.5% over a 0 to 85°C range. A PSI (power-state-indicator) interface provides the ability to maximize efficiency at light loads. The IC operates from a 3.3V bus, and you can set up a programmable open-drain-alert pin to indicate when power exceeds a programmable level.
The device can use a discrete current-sensing resistor or the DCR (dc resistance) of the power inductor in the buck regulator it is monitoring. It includes an internal thermal-compensation circuit that accounts for the varying DCR of the power inductor. You can program the averaging interval of the measurement through the I2C bus.
The IR3725 provides input power monitoring for energy-efficient CPU, server, and storage applications. It comes in a 12-pin DFN package, operates in the −10 to +150°C temperature range, and sells for $1.25 (10,000).
