Notes on the LB1971V and External Components

1. Three-phase full-wave sensorless drive

The LB1971V is a 3-phase full-wave sensorless motor driver that provides a reverse torque braking function and is

appropriate for CD and MD players spindle motor drive. Furthermore, since this driver does not require the use of

Hall-effect devices, it can contribute to miniaturization, thinner form factors, and lower power in the motor system.

2. Power supply

motor speed control to be implemented by connecting a power supply that varies according to the speed control.

output can be made to have a low saturation voltage and a highly efficient motor operation can be achieved by

Capacitors with an adequate capacitance for stability must be inserted between each of the power supplies and

ground.

3. Soft switching drive

This IC adopts a soft switching drive technique to minimize motor noise. When the output transistors switch between

phases, a two-phase excitation state is created, and the output current is switched gradually to suppress motor noise.

The two-phase excitation state is determined by the amplitude of the CSLP pin waveform, and that waveform

amplitude is determined by the value of the capacitor connected at the CSLP pin and the motor speed. Note that while

the soft switching operation increases as the amplitude of the CSLP pin voltage decreases, drive efficiency is reduced

and timing problems may occur if this amplitude becomes too small. Therefore, the CSLP pin amplitude should be at

least 200 mVp-p at the maximum motor speed.

4. Position detection comparator circuit

The position detection comparator circuit uses the back EMF generated during motor rotation to detect the position of

the rotor. The position information acquired by this circuit is used to determine to which sections of the output block

power will be applied. Problems that occur during startup due to noise in the VS line can be prevented by inserting

capacitors between the FCOM pin and the UIN, VIN, and WIN pins. However, the timing with which power is

applied during high-speed motor operation may be delayed and efficiency reduced if these capacitors are too large.

5. Startup oscillator circuit (OSC pin)

This oscillator circuit creates the commutation logic timing required to start a sensorless motor.

A capacitor and a resistor are connected in parallel to ground. Use a high resistance of about 1.5 M

Ω for this resistor.

The value of the capacitor depends on the characteristics of the motor: select a value such that the time required to

reach the target speed is minimum and the variation in the startup time is as small as possible. If the capacitance is too

large, the variations in startup time will increase, and if it is too small the motor may be prevented from starting up

normally.

6. CX oscillator circuit

This oscillator circuit creates the reference clock used for the sensorless motor logic system. Insert a capacitor to

ground. The oscillator frequency increases as the capacitance decreases. The oscillator frequency must be less than 60

Hz. (The recommended capacitance is 470 pF.)

7. FG output circuit

The FG output is created from the position detection information acquired from the back EMF waveform. This output

has a frequency three times that of the switching frequency. The output circuit is an open collector circuit. The output

is pulled up with a resistor.

No. 6214-5/9

LB1971V