Low-side I/V sensing IC, with internal power calculation

April 12, 2016 // By Graham Prophet
Maxim Integrated has posted details of the MAX44299, a low-side current, voltage, and power monitoring circuit that provides an analogue output current proportional to the measured current, voltage, and the internally calculated instantaneous power. The power monitor offers high precision and integration in tiny size.

Instantaneous power is calculated internally by multiplying the load current and a fraction of the load voltage set by an external resistive divider. All three outputs are scaled to a full-scale current of 100 µA. An additional output current of 100 µA is available at the reference (REF) output; this current can be used to create a reference voltage for the ADC that is being used to measure the power, voltage, and current signals.

 

By providing the ADC with both the measured signals and the input reference voltage, the ADC can make a ratiometric measurement, allowing improved accuracy. The use of currents, rather than voltage, to convey the measured signals to the ADC eliminates any errors caused by voltage drops across the parasitic resistance of PCB, which can be significant for high-current systems. To allow full-system calibration, the CAL bump provides a way to calibrate gain and offset for the ADC.

 

The device measures load current by using a precision, auto-zeroed current-sense amplifier (CSA), which due to its ultra-low offset voltage allows precise measurement of full-scale voltages of 5 mV, 10 mV, and 20 mV. The load voltage is measured via a user-selectable resistive network, dividing the input voltage down to a full scale of 1.00V.

 

The wide supply voltage range of 3V to 5.5V allows the simple sharing of supplies with either the ADC or a microcontroller. The device can be powered down and the outputs will then go high impedance. The device is available in a 2.4 x 2.4 mm, 16-bump wafer-level package (WLP) and is specified for the 0°C to +85°C temperature range.

 

MAX44298 is a very similar product with a choice of 50 µA output current and alternate pinout. An evaluation kit (EV kit) provides a proven design to evaluate the MAX44299 current, voltage, and power monitor. The EV kit PCB is preconfigured with the CSA full-scale input voltage range (VSENSE) of 10 mV and 100 µA of output current ranges, but can be reconfigured to 10 mV/5 mV of FS VSENSE or 50 µA of output current by changing a few jumpers. The EV kit comes with a MAX44299EWE+ and a voltage divider to provide a forced full-scale VSENSE of 10 mV range at the CSA inputs installed.

 

Maxim Integrated; www.maximintegrated.com/en/products/analog/amplifiers/MAX44299.html

 

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