Current sense amplifier saves portable space
02 September 2008
The MAX9938 is claimed to be the smallest high-side current-sense amplifier.
The IC from Maxim typically measures battery charge and discharge currents. They also monitor supply rails that may need to be powered down to control heat and power dissipation. The MAX9938 amplifier is packaged in a four-bump UCSP, which at 1mm x 1mm x 0.6mm is x9 smaller than competitive SOT23 devices. It has precision resistors, which eliminate the need for external gain-setting resistors. It is manufactured using Maxim’s proprietary BiCMOS technology, claimed to be responsible for the industry’s lowest quiescent-current consumption and highest accuracy. It has an ultra-low +/-0.5mV Vos and 0.5 per cent gain error for a total error of less than one per cent.
The low Vos allows the use of a lower, full-scale Vsense voltage and smaller Rsense resistor. This creates a device with a minimalised voltage drop loss in the line and power dissipation in the sense resistor to avoid a hot-spot behind the LCD of a notebook computer.
Power consumption is 1µA Iq, compared to typical consumption of 100µA to 500µA Iq. Three voltage gain versions are available, 25V, 50V and 100V. It is also available in a five-pin Sot23 package. Operation is over the -40°C to 85°C extended temperature range.
It operates from 1.6V to 28V input range, suitable for use with battery-operated portable devices, such as smartphones, digital cameras, PDAs, MP3 players and notebook computers, where small size, low quiescent current and high accuracy are critical.
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