at the PWM frequency during motor control, and if that frequency is in the audible range, that resonation may result

in audible noise. If the PWM frequency is too high, the output transistor switching loss will increase. The external

resistor must not have a value under 30 k

Ω.

7. Hall Input Signals

Input signals with an amplitude greater than the hysteresis (60 mV, maximum) are required for the Hall inputs. An

input amplitude of 100 mV or greater is desirable, taking noise and other considerations into account. The Hall input

DC voltage must be set to fall within the common-mode input voltage range specifications.

8. Forward/Reverse (F/R) Switching

The F/R pin can be used to switch the motor direction. The direction can be switched with the F/R pin even if the

motor is turning. The IC circuit is designed to compensate for the through currents that occur when the direction is

the power system instantaneously) during direction switching. If this is a problem, try increasing the capacitance of

the capacitor connected between the power supply and ground.

9. Brake Switching

The LB1821M implements a short braking technique in which the upper side transistors (the external transistors) for

all phases are turned on. (The lower side transistors for all phases are turned off.) This means that the output current

not function. Thus caution is required. During braking, the upper side transistors operate at a 100% duty, regardless

of the motor speed. The braking function can be operated and released in the start state. Thus motor start and stop

control can be performed from the brake pin with the S/S pin at the low level, i.e., with the system in the start state. If

the startup time is a problem, the motor can be started with a shorter startup time by using the brake pin for motor

start/stop control than it can with the S/S pin. (This is because the stop state is a power saving state, and restarting

from this state requires waiting the time required for the VCO circuit to stabilize.)

10. Constraint Protection Circuit

The LB1821M includes an on-chip constraint protection circuit to protect the IC and the motor in motor constraint

mode. If the LD output remains high (indicating the locked state) for a fixed period in the start state, the upper side

(external) transistors are turned off. This time is set by the capacitance of the capacitor attached to the CROCK pin. A

time of a few seconds can be set with a capacitance of under 0.1 µF.

<Set time (s)>

≈ 44 × C (µF)

To release the constraint protection state, the LB1821M must be set to either the stop state or the brake state, or

power must be reapplied. The CROCK pin must be connected to ground if the constraint protection circuit is not

used. However, note that the clock disconnection protection circuit described later cannot be used in this case.

11. Clock Disconnection Protection Circuit

If clock input stops with the LB1821M in the start state, this protection circuit operates and turns off the (external)

upper side output transistors. If the clock is reapplied, the IC resumes operation.

12. Low-Voltage Protection Circuit

The LB1821M includes a low-voltage protection circuit to protect against incorrect operation when power is first

falls under about 3.75 volts, and this function is cleared at about 4.0 volts.

13. Power Supply Stabilization

Since this IC is used in applications that draw large output currents, the power-supply line is subject to fluctuations.

Therefore, capacitors with capacitances adequate to stabilize the power-supply voltage must be connected between

power supply connection, since this makes the power-supply voltage even more subject to fluctuations, even larger

capacitors will be required.

14. Ground Lines

The signal system ground and the output system ground must be separated and a single ground point must be taken at

the connector. Since the output system ground carries large currents, this ground line must be made as short as

possible.

No. 5686-9/16

LB1821M