Human Body Detector - MS8891A

Product Specification

1.General Description

    The integrated circuit MS8891A is an ultra-low power, two channel capacitive sensor specially designed for human body detection. It offers two operating modes: meter mode or switch mode. In switch mode the sensor capacitance is compared with the internal reference capacitance. The sensor output changes polarity if the sensor capacitance falls below or rises above a threshold capacitance. The threshold capacitance can be individually set for both channels.

    The MS8891A can also be operated in meter mode where the absolute capacitance values of the sensor channels are measured. The MS8891A is configured via an I2C serial interface. The comparator outputs are available at circuit pins in switch mode or can be read via the I2C serial interface. The configuration of the various options and the operation of the meter mode are done via the I2C serial interface. After programming the configuration to the one-time programmable (OTP) memory, the MS8891A can be operated in switch mode as a stand-alone solution.

2.Applications

▪ Human body detection (e.g. in-ear phone, finger detection)

▪ Wrist detection (e.g. wearables or medical wearables)

▪ Capacitive sensor

▪ Touch and proximity switch

3.Typical application

4.Features

▪ Two capacitive sensor channels with individual outputs and inputs

▪ One or two channel operation

▪ Meter mode or switch mode

▪ Capacitance meter with 4 measuring ranges covering 0 to 1.6pF with a resolution of 8 bits

▪ Individually programmable threshold capacitance for both sensor channels in switch mode

▪ Programmable measuring interval in switch mode(single trigger, 2 measurements/s, 32 measurements/s, permanent) 

▪ Programmable noise filter in switch mode

▪ Comparator outputs available at pins OUT1 (sensor CS1) and OUT2 (sensor CS2) in switch mode

▪ Polarity of comparator outputs selectable by pin POL

▪ OUT1 and OUT2 can be configured to output logical OR (OUT1) and AND (OUT2) combination of switch mode results

▪ CMOS or open-drain output drivers

▪ I2C serial interface available at pins SDA and SCL

▪ No external components needed

▪ Sensors capacitance can be realized with conductive tracks on PCB or casing

▪ Idle current typ. 50nA

▪ Active current during measurement typ. 11μA

▪ Average current for 2 measurements/s in switch mode typ. 725nA (1 channel, no noise filter)

▪ Voltage operating range 1.8 to 4.5V

▪ Temperature operating range -40 to 85°C

▪ Available in QFN16 3x3mm or CSP12  1.52x1.03mm