Signal system ground ... Ground for the IC and the IC external components

passing a current through an external resistor. A stable voltage can be generated by setting the current to value in the

current + output current <source> requirements) and they must have voltage handling capacities in excess of the

motor power-supply voltage. Since the heat generated by these transistor may be a problem, heat sinks may be

required depending on the packages used. If the IC power-supply voltage (4.4 to 7.0 V) is provided from an external

connected to ground.

16. FG Amplifier

Normally, the FG amplifier is used to construct a filter amplifier such as that shown in the application circuit to reject

noise. Since a Schmitt comparator is connected after the FG amplifier, applications must set the amplification so that

the amplifier output amplitude is at least 250 mV p-p. (However, a setting that results in an amplitude of 1 to 3 V p-p

required for bias voltage stabilization and to generate the initial reset pulse for the internal logic. The reset pulse is

17. Integrating Amplifier

The integrating amplifier integrates the speed error pulses and the phase error pulses and converts them to a speed

command voltage. At the same time it also sets the control loop gain and frequency characteristics using external

components. The integrating amplifier output (pin 1) is normally connected to the TOC pin (pin 44) by an external

line. Separating the integrating amplifier output and the PWM control circuit allows applications to switch the

integrating amplifier constants using an external operational amplifier, analog switch, or other circuit. This is useful

in applications that require integration constant switching due to a wide range of variability in the motor speeds that

must be provided.

18. VCO Filter Amplifier

The VCO filter amplifier converts the VCO system PLL output to the VCO voltage. The amplifier input resistor

(about 10 k

Ω) is built in. Therefore, the gain and the frequency characteristics are set by the feedback resistor and the

feedback capacitor. Since the range of frequency variation supported becomes narrower as the gain is reduced, it is

desirable to set the gain of this amplifier to be 1 or higher.

19. Startup Techniques

If the motor is started and stopped repeatedly over a short period, the charge accumulated on the integrating

amplifier’s external capacitor may become a problem. (This can result in abnormal speed overshooting at startup and

other problems.) The circuit shown below can be effective at resolving this problem.

No. 5686-10/16

LB1821M

Added circuit

S/S signal