LB1872 Ver la hoja de datos (PDF) - SANYO -> Panasonic

Número de pieza

componentes Descripción

Fabricante

LB1872

Polygon Mirror Scanner Driver IC

SANYO -> Panasonic 

LB1872

4. Reference clock

Any one of the following three techniques can be used to input the reference clock used for speed control.

• Crystal oscillator generated clock

Use the following circuit, consisting of a crystal element, capacitors, and resistors, as a crystal oscillator circuit.

C1 and R1: Used for oscillator stabilization.

C3: Used for oscillator element coupling.

C2: Used for overtone prevention.

R2: Improves the oscillator margin.

Sample External Component Values

Oscillator frequency (MHz)

1 to 3

3 to 5

5 to 7

7 to 10

C1 (µF)

0.1

0.1

0.1

0.1

C2 (pF)

47

18

—

—

C3 (pF)

220

100

47

33

R1 (Ω)

220 k

100 k

47 k

10 k

R2 (Ω)

—

—

—

4.7 k

This circuit and these component values are only provided for reference purposes. Consult with the manufacturer of

the crystal element concerning the influence of such factors as the characteristics of the crystal element itself and the

stray capacitances due to the printed circuit board wiring pattern to assure that problems do not occur.

(Notes on printed circuit board wiring)

Since crystal oscillator circuits are high-frequency circuits, they are easily influenced by stray capacitances due to the

printed circuit board wiring. Therefore, lines for external components must be kept as short as possible and lines must

be made as narrow as possible. In this external circuit, the connection between the oscillator element and C3 (and C2)

is particularly subject to influence by stray capacitance, and requires special care.

• External clock (crystal oscillator equivalent: a few MHz)

If a signal equivalent to a crystal oscillator signal is input from an external signal generator, input that signal

through a series resistor of about 13 kΩ to the XI pin. Leave the XO pin open.

• External clock (FG frequency equivalent: a few kHz)

If a signal equivalent to the FG frequency is input from an external signal generator, set the N2 pin to the middle

level (or open) and input that signal to the N1 pin. In this case, the motor will remain in the stopped state (short-

circuit braking operation) even if a start input is applied when no clock is input. However, since IC heating due to

the large output drive currents that flow in the short braking state (since the lower side transistors in all phases are

driven) care is required if the braking state must be held for extended periods.

5. Hall input signals

Even if the amplitude of the Hall sensor input signals is changed by the motor, the influence on the output will be

suppressed by the AGC circuit. However, if there are discrepancies between the amplitudes of the three phases, the

output phase switching timing may be shifted.

The output current will be cut off by a protection circuit if a start signal is input when there are no signals applied to

the Hall inputs.

The maximum operating frequency of the Hall inputs is affected by the saturation state of the outputs. While there are

no problems for frequencies of under 1 kHz (the frequency in a single Hall phase), if a higher operating frequency is

required, it can be advantageous if the outputs remain unsaturated. If the outputs remain in the unsaturated state, this

IC can be used up to frequencies of about 2 kHz.

Since motors with higher speeds have higher operating frequencies, we recommend using motors with four motor

magnet poles.

6. LD output

The LD output goes on when the phase is locked. Phase lock is determined not by the speed error but by the phase

error only. Therefore, the speed error when the LD output is on, during, for example, lock pull-in, will change with

the acceleration of the FD signal. (The speed error will be smaller for lower accelerations.) If it is necessary to

No. 5625-10/11

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