High speed head fault detection circuit with programmable current mirror

A method of detecting a fault in a head resistance of a hard disk drive, the method comprising:

• generating a mirror current proportional to a write output current, wherein the write output current flows through the head resistance via an H-bridge writer output;
• converting the mirror current into threshold voltages by steering the mirror current through matched resistors using bipolar transistors controlled by a bias voltage;
• comparing differential voltages from the H-bridge writer output to the threshold voltages;
• and
• generating a fault signal in response to detecting a fault condition.

A write driver system for a hard disk drive, the write driver system comprising:

• an H-bridge circuit configured to provide a write output current through a head resistance;
• an impedance matching network coupled between the H-bridge circuit and the head resistance;
• and
• a fault detection circuit comprising:
• first and second voltage sources configured to generate threshold voltages based on the write output current and a parallel combination of the impedance matching network and a head resistance fault threshold;
• first and second comparators configured to compare differential voltages from the H-bridge circuit to the threshold voltages;
• and
• a polarity detector configured to generate a fault signal in response to detecting a fault condition.