AD22157

The AD22157 is a mixed signal magnetic field transducer designed for applications where both speed sensing and direction sensing of a ferrous target wheel are required over a wide speed range.

The device operates from a 2 wire high compliance current loop and is suitable for continuous operation from -40C to 150C with supplies up to +20 Vdc. The sensor is designed to remain functional during voltage transients up to +27V.

The sensor output format is a current pulse from 7mA to 14mA (the quiescent bias is 7mA) whose rising edge is accurately placed relative to the edges of the target wheel. The pulse width is determined by both target wheel direction and field strength. The output pulse is coded in multiples of a well defined time interval depending on direction and field strength in conformance with industry standards currently being promoted by leading systems manufacturers.

Pulse widths corresponding to differential magnetic fields measured at the sensor of B >4mT (normal operation),2mT<B<4mT (low field range), and B<2mT (very low field range) are provided. Direction is indicated in the normal and low ranges.

A fail safe stop signal repeating at approximately 1.5Hz is provided initially at power on, if the target wheel is stopped, or if no dynamic signal is detected for some other reason.The sensor combines integrated bulk Hall cell technology and instrumentation circuitry to minimize temperature related drifts associated with Hall cell characteristics. The sensor is compensated to work optimally with SmCo magnets. The architecture maximizes the advantages of fine line CMOS and high voltage DMOS allowing the device to operate accurately in demanding environments.

Principle features of the AD22157 include an adaptive differential zero crossing detector which accurately determines the position of target wheel edges. This architecture eliminates the effects of package and thermal stress on the Hall sensor array resulting in 2% repeatability of the time interval from rising edge to rising edge of the sensor output.

The sensor takes 4 edges from either power on or a stopped condition to achieve full accuracy. The architecture employs digital signal processing to provide robust functionality and eliminate spurious or missing pulses under extreme conditions of EMC.

The AD22157 is housed in a 5 lead single-in-line (SIP) package suitable for mounting with a back biasing magnet in a typical wheel speed sensor assembly.