Open-load detection for stepper motor drivers

A method, comprising:

• operating a motor driver circuit to provide a drive current to a motor coil of a motor;
• sensing the drive current;
• comparing the drive current to a first current or a second current;
• detecting an open-load condition responsive to a first signal indicating a first operating state of the motor and the comparison indicating that the drive current is less than the first current
• , or detecting the open-load condition responsive to the first signal indicating a second operating state of the motor and the comparison indicating that the drive current is less than the second current;
• and
• generating an open-load fault signal responsive to detecting the open-load condition.

A motor driver circuit for detecting an open-load fault condition, the motor driver circuit comprising:

• driver circuitry comprising driver transistors, the driver circuitry coupled to first and second output terminals;
• detection circuitry configured to generate a first signal at an output of the detection circuitry, the first signal indicating an operating state of the motor driver circuit;
• comparator circuitry having a first input, a second input, a third input, a fourth input, and an output, the third input of the comparator circuitry coupled to the output of the detection circuitry, the fourth input of the comparator circuitry coupled to the driver circuitry, and the comparator circuitry configured to:
• compare a drive current at the driver transistors to a first current sensed at the first input of the comparator circuitry responsive to the first signal indicating a first operating state of the motor driver circuit, and compare the drive current to a second current sensed at the second input of the comparator circuitry responsive to the first signal indicating a second operating state of the motor driver circuit;
• generate a signal at the output of the comparator circuitry responsive to one of the comparisons;
• and
• fault detect circuitry having an input coupled to the output of the comparator circuitry, the fault detect circuitry configured to provide a second signal responsive to the signal at the output of the comparator circuitry.

Motor driver circuitry for detecting an open-load fault condition, the motor driver circuitry comprising:

• driver transistors coupled to first and second output terminals, each driver transistor having a gate terminal;
• gate driver circuitry having outputs coupled to the gate terminals of the driver transistors;
• controller circuitry coupled to the gate driver circuitry;
• a first current source;
• a second current source;
• and
• select circuitry having a first input coupled to the first current source, a second input coupled to the second current source, a select input coupled to the controller circuitry, and an output;
• a comparator having a first input coupled to the output of the select circuitry, a second input coupled to the driver transistors, and an output.