Fujitsu MHU2100AT Product Manual page 70

Theory of Device Operation
(5) Spindle motor control circuit
The spindle motor control circuit controls the sensor-less spindle motor. A
spindle driver IC with a built-in PLL(FLL) circuit that is on a hardware unit
controls the sensor-less spindle motor.
(6) Driver circuit
The driver circuit is a power amplitude circuit that receives signals from the
spindle motor control circuit and feeds currents to the spindle motor.
(7) VCM current sense resistor (CSR)
This resistor controls current at the power amplifier by converting the VCM
current into voltage and feeding back.
4-14 C141-E202-01EN