Dual, 2-Wire Hall-Effect Sensor Interface with Diagnostics

Industry's First 2-Wire Hall-Effect Sensor Interface Solution Saves Space and Cost in Automotive Applications

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The MAX9921 provides a single chip solution to interface two 2-wire Hall-effect sensors to a low-voltage microprocessor (µP). This device supplies and monitors the current drawn by two Hall-effect sensors, filters the sensed current level, and outputs the corresponding logic level.

The MAX9921 includes input diagnostics and fault protection. These features allow the device to determine fault conditions such as open inputs, inputs shorted to the battery, and inputs shorted to ground. If the MAX9921 detects any of these conditions at either IN1 or IN2, the device shuts off the current to the corresponding input.

The MAX9921 protects the Hall sensors from supply transients up to 60V at the BAT supply. Normal operating supply voltage ranges from 6V to 18V. If the battery voltage is out of range, the MAX9921 shuts off the current to the Hall sensors.

The MAX9921 provides an 80µs blanking time following Hall sensor power-up or restart. The open-drain logic outputs are compatible with logic levels up to 5.5V.

The MAX9921 is available in a small 10-pin µMAX® package and is specified over the -40°C to +125°C automotive temperature range.
MAX9921: Typical Application Circuit MAX9921: Typical Application Circuit Enlarge+

Key Features

  • Withstands 60V at BAT Supply and Hall Inputs
  • 6V to 18V Operating Voltage Range
  • Provides Supply Current and Interfaces to Two 2-Wire Hall Sensors
  • Error Output with Diagnostics of Hall Inputs and BAT Voltage
  • Protects Hall Sensors from Overvoltage by Isolating them from Supply Transients
  • Hall Inputs Protected from Short to Ground
  • Ramps Current to Hall Sensors at 4mA/µs
  • Output Enable Input Allows Multiplexing of Outputs from Multiple MAX9921s
  • Hall Output Filtering
  • Hall Sensor Blanking Following Hall Sensor Power-Up or Restart
  • Low-Power Shutdown, Controlled with OE and DIAG Inputs
  • Operates with ±2V Ground Shifts Between Hall Sensor and MAX9921


  • Door Modules
  • Electric Sunroofs
  • Powered Lift Gate Controllers
  • Powered Running Boards
  • Seat Movers
  • Seatbelt Buckles
  • Window Lifters

See parametric specs for Sensor Interface Devices (11)

Part NumberSensor Interface TypeChannelsVSUPPLY
Low Power ShutdownOper. Temp.
minmaxtypSee Notes
MAX9921 Hall-Effect26181000Yes-40 to +125
$0.92 @1k

Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.

MAX9921EVKIT: Evaluation Kit for the MAX9921
Product Reliability Reports: MAX9921.pdf 
Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C   Material Composition  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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