LB1927

No.6197-10/11

[Precautions for wiring layout design]

Since the crystal oscillator circuit operates at high frequencies, it is susceptible to the influence of floating

capacitance from the circuit board. Wiring should be kept as short as possible and traces should be kept narrow.

When designing the external circuitry, pay special attention to the wiring layout between the oscillator and C3

(C2), to minimize the influence of floating capacitance. The capacitor C4 is quite effective at reducing the

negative resistance (gain) at high frequencies. However, care is required to avoid excessive reduction in the

negative resistance at the fundamental frequency.

(2) External clock input (equivalent to crystal oscillator, several MHz)

When using an external signal source instead of a crystal oscillator, the clock signal should be input from the XI pin

through a resistor of about 5.1k

Ω connected to the pin in series. The XO pin should be left open. Signal input level

Low : 0 to 0.8V

High : 2.5 to 5.0V

6. Speed lock range

The speed clock range is

±6.25% of the rated speed. When the motor rotation is within the lock range, the LD pin

becomes Low (open collector output). When the motor rotation goes out of the lock range, the ON duty ratio of the

motor drive output is varied according to the amount of deviation to bring the rotation back into the lock range.

7. PWM frequency

The PWM frequency is determined by the capacitance connected to the PWM pin.

f PWM ≈ 1/ (14400×C)

PWM frequency in the range 15 to 25kHz is desirable. The ground side of the connected capacitor must be

connected to the GND1 pin with a lead that is as short as possible.

8. Hall input signal

The Hall input requires a signal with an amplitude of at least the hysteresis width (42mV max.). Taking possible

noise influences into consideration, an amplitude of at least 100mV is desirable. If noise during output phase

switching disrupts the output waveform, insert capacitors across the Hall signal inputs (between the + and - inputs),

and position those capacitors as close as possible to the pins.

9. Forward/reverse switching

Forward/reverse switching of motor rotation is carried out with the F/R pin. If this is performed while the motor is

running, the following points must be observed :

• Feedthrough current during switching is handled by proper circuit design. However, the VCC voltage rise during

switching (caused by momentary return of motor current to power supply) must not exceed the rated voltage

(30V). If problems occur, the capacitance between VCC and GND must be increased.

• If the motor current after switching exceeds the current limiter value, the lower-side transistors go OFF but the

upper-side transistors go into the short brake state, which causes a current flow. The magnitude of the current is

determined by the motor counterelectromotive voltage and the coil resistance. This current may not exceed the

rated current (2.5A). (Forward/reverse switching at high speed therefore is not safe.)

10. Motor restraint protection circuit

To protect the IC and the motor itself when rotation is inhibited, a restraint protection circuit is provided. If the LD

output is High (unlocked) for a certain interval in the start condition, the lower-side transistors are turned off. The

length of the interval is determined by the capacitance at the CSD pin. A capacitance of 10

μF results in a set

interval of about 3.3 seconds. (Tolerance approx.

±30%)

Set interval (s) ≈ 0.33×C (

μF)

If the capacitor arrangement is subject to leak current, possible adverse effects such as setting time tolerances must

be taken into consideration.

When the restraint protection circuit has been activated, the condition can only be canceled by setting the system to

the stop condition or by turning the power off and on again (in the stop condition). When wishing not to use the

restraint protection circuit, connect the CSD pin to ground.

If the stop time when releasing the restraint protection is short, the capacitor charge will not be fully dissipated.

This in turn will cause a shorter restraint protection activation time after the motor has been restarted. The stop time

should therefore be designed to be sufficiently long, using the equation shown below (also when restarting in the

motor start transient state).

Stop time (ms)

≥ 15×C (μF)