LB8649FN

No.7893-5/9

3. VCM constant current control for SH/AE, or stepping motor drive.

Input

Output

IN9

IN10

IN11

IN12

INHD

OUT9

OUT10

OUT11

OUT12

Vref

ISH

Mode

L

L

L

L

-

-

-

-

-

-

Stand-by

H

L

*

*

H

L

L

H

*

*

L

H

*

*

H

L

H

L

*

*

L

H

L

L

H

1.0V

SH & AE

H

L

*

*

H

L

L

H

*

*

L

H

*

*

H

L

H

L

*

*

L

H

L

H

Setting

voltage

state

Hold

L

L

L

L

H

-

-

-

-

0.67V

Discharge

Stand-by

• ( - ) is output OFF, and ( * ) is “Don’t care”.

• OUT9 and OUT10 are used for the SH.

Quick charge and quick discharge circuitry allows the stabilization of start-up characteristic.

• OUT10 and OUT11 are used for the AF.

• At the time of stand-by, ISH pin voltage becomes discharge state by the internal transistor and it is set to 0V.

• In addition, when IN1 to 8 are input, ISH pin is in discharge state (for start-up correction).

• When INHD = “L”, Vref voltage is 1.0V. When INHD = “H”, Vref voltage is 0.67V.

Application Design Notes

1. Constant current setting (ISH, IAE, RFG1, 2, OUT9 to 12)

The constant current setting between pins OUT9 and OUT10 is determined from the ISH input voltage and the

connecting resistor of RFG1. As shown in the block diagram, it is controlled in such a way so that the voltage

generated at the resistor used for current detection connected between RFG1 and GND would be equal to the ISH

input voltage. The formula for calculating the output current is as given below.

(OUT9 to OUT10 Output Current) = (ISH Input Voltage)

÷ (RFG1 Resistor + 0.05Ω)

The 0.05

Ω here is for a common impedance of the output Tr emitter which drives constant current in the RFG pin

and the sensing wiring for the constant current control amplifier.

In the same way, the constant current setting between pins OUT11 and OUT12 is determined from the IAE input

voltage and the connecting resistor of RFG2.

Furthermore, as the constant current control block within the IC is connected to PGND, when supplying voltage to

the ISH pin or IAE pin which has been divided by resistors be sure to connect the ground side of these resistors to

PGND.

2. Quick charge/discharge circuitry (FC1, OUT9, OUT10)

Quick discharge circuitry has been built in to the shutter control block (OUT9 to OUT10) to support high-speed

shutter control, quick recharge, quick discharge and consecutive shots.

Quick recharge and quick discharge circuitry has not been built in to the AE control block (OUT11 to OUT12).

Therefore, make sure to use the block (OUT9 to OUT10) for the shutter drive.