L6256

The 12 Volt Combo chip L6256 is a combination spindle otor driver, voice coil driver and D/A converter.

the L6256 can be used in,application like HDD.

The VCM amplifiers drive a low impedance coil nd are set up to accept RC compensation, which llows a wide bandwidth with absolute minimum hase lag. The sense resistor/amplifier arrangement llows full current loop operation. The loop ain is changeable by attenuating the VCM DAC oltage amplitude in cascadable stages.

The L6256 is a PWM only voltage loop ith power supply feedforward, driving a 3 phase e sorless brushless DC motor. Since L6256 uses WM operation at full run speed, L6256 has output lew rate control during start and run modes.

There is an inductive clamp circuit to limit flyback oltage transients across the supply voltage during otor phase changes and during the braking

sequence. Only the 2 phase or bipolar commutation attern is produced by the internal commutation ircuitry. A commutation register allows arbitrary inding sequencing during certain operations. ntern l protection against crossover pikes is built in.

3 phase or tripolar commutation can be supported n software during start by writing a commutation attern directly to the preload register.

Tripolar operation requires that more than two hase drivers contribute current simultaneously.  he current limit circuitry reflects this and allows 3% higher current limit, which produces nearlyconstant torque. This is a very high power dissipation ode, meant only for momentary operation n unusual circumstances.

Spindown during a power failure uses the back MF voltage generated by the spindle motor to rovide power to the VCM amplifier. The Spindle otor coasts during the Brake Delay time to allow  ime to park the head actuator. The park circuit is  constant voltage circuit settable externally.

After the head is parked, braking commences.

The brake operates by shorting all 3 windings.

The spindle output stages stay on as long as is equired to bring the motor to a complete stop, ven if no power is applied to the part.

A Power On Reset (POR) function of the L6256 provides pulse tretching for the bidirectional POR\ bus, to ensure hat the processor and clocks are at running peed before allowing them to function.

volt and 12 volt pins are used directly for the undervoltage etect circuit.

L6256 allows direct use internally of both supplies. oltage monitor margining is supported.

An external 3.3V linear regulator is provided and ied into the POR circuit.