Maxim Integrated Products has introduced the MAX9928/MAX9929 current-sense amplifiers for monitoring charge and discharge currents. The devices use a rail-to-rail input stage to achieve a wide -0.1V to +28, input common-mode range, which suits them to a wide variety of applications.
Among the features of these devices are ground sensing and high-side current sensing in the same ic with unidirectional or bidirectional (charge/discharge) current-monitoring capability – useful for monitoring batteries in deep discharge. Current sensing is also useful for the supercapacitors that are employed as emergency backup supplies in hybrid cars, whilst a 20microamp quiescent current means the devices can be used for battery-powered handheld devices. The MAX9928/MAX9929 require an independent, +2.5V to +5.5V supply voltage.
Maxim classes these as precision amplifiers as they boast less than 400microvolts of offset voltage, and include on-chip, laser-trimmed, gain-setting resistors to achieve less than 1% gain accuracy.
The MAX9928 is a current-output device and is available in two transconductance gain options: 2microamps/mV and 5microamps/mV. The user can select the output resistor to convert the current to a voltage to match the input range of an ADC. The MAX9929 is a voltage-output device with fixed-gain options of 20V/V and 50V/V.
Both devices include a digital sign output that indicates the direction of current flow, allowing the user to maximise the output-voltage swing and use an ADC's full input range for measuring charge and discharge currents. An internal comparator uses low offset voltage and hysteresis to ensure that the direction of the sign bit is correct and unambiguous.
The MAX9928/MAX9929 are available in 1mm x 1.5mm, 6pin UCSP and 8pin microMAX packages and are specified over the -40oC to +125oC automotive temperature range.