DC motor speed controller
VISHAY

The Si9961A is a linear actuator (voice coil motor) driver
suitable for use in disk drive head positioning systems. The
Si9961A contains all of the power and control circuitry
necessary to drive the VCM that is typically found in 31/2-inch
hard disk drives and optical disk drives. The driver is capable
of delivering 1.8 A at a nominal supply of 12 V.
The Si9961A provides all necessary functions including a
motor current sense amplifier, a loop compensation amplifier
and a power amplifier featuring four complementary
MOSFETs in a H-bridge configuration. The output crossover
protection ensures no cross-conducting current and true Class
B operation during linear tracking. Externally programmable
gain switch at the input summing junction increases the
resolution and dynamic range for a given DAC. The head
retract circuitry can be activated by either an undervoltage
condition or an external command. An external resistor is
required to set the VCM current during retract.