LB8652T, LB8652LP

No.7896-8/9

Points to Take into Consideration When Designing

(1) For shutter control Constant current setting (RFG1, RFG2, OUT1, OUT2)

The constant current when flowing the current from OUT2 to OUT1 can be specified by a resistor connected

between RFG and GND. (In this case, RFG1 is connected to the emitter side of NPN transistor while RFG2 is

connected to the minus input side of constant-current control amplifier.) The reference voltage is generated in the

IC and it is approximately 0.218V. The voltage is controlled in such a way so that the voltage generated at the

resistor used for current detection connected between RFG and GND would be equal to this voltage.

The formula for calculating the output current is as given below. In addition, as a fundamental setting, it is

designed so that the approx. 200mA would flow through the coil when RFG resistor is connected with 1

Ω.

(Current flows from OUT2 to OUT1)

= 0.218V

÷(Resistance between RFG and GND+0.05Ω) - (Drive current of output Tr)

This 0.05

Ω 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.

Also, the drive current of output Tr is equal to 1/hfe (a 80th to 200th part approx.) of the coil current.

The constant current flowed from OUT2 to OUT1 is more accurate than that flowed from OUT1 to OUT2.

Therefore make sure to use this method for shutter closing drive.

(2) For shutter control Open-loop constant current control setting (ILM, OUT1, OUT2)

In order to prevent the high-current flowing when shutter opening, the output current control circuit is

implemented for current flowing from OUT1 to OUT2. The constant current when flowing the current from

OUT1 to OUT2 can be specified by a resistor connected between ILM and GND.

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

(Current flows from OUT1 to OUT2) = 1.36V

÷(Resistance between ILM and GND) ×200 approx.

Due to open-loop control by which feedback signals are not sent, the accuracy of constant current is relatively

inferior. It is used for shutter opening drive.

(3) Phase compensation capacitor (FC)

See and check the capacitor value for FC pin between 0.0015 to 0.033

μF. Choose a capacitance value which does

not cause oscillation problems for output. In particular, when a coil with large inductance is used, it is necessary

to choose a sufficiently large capacitance.

(4) Constant voltage control Oscillation-stopping capacitor (OUT4, OUT8)

When controlling the constant voltages, it is necessary to place capacitors between the OUT pins to stop

oscillation. See and check the capacitance value between 0.01

μF to 0.1μF. Choose a capacitance value which

does not cause oscillation problems for output.

When driving at saturation, there is no need for such oscillation-stopping capacitors.

(5) GND wiring and power line capacitors : (SGND, PGND, VCC, VB)

Connect GND (2 places) near the IC, and place the capacitors as close as possible to each of the power pins.