LB11681H

No.A0665-9/11

Explanation of LB11681H and External Parts

The LB11681H is three-phase brush less fan motor driver IC that can be operated with 12V signal power supply.

Since this IC is PWM soft switching drive, it is perfect to operate as high-efficiency motor for a low-noise drive.

Also, since this IC incorporates a motor constraint protection function necessary for a fan motor, highly reliable

products can be designed.

To design the system by using the LB11681H, please develop the system that is obtained sufficient characteristics

after reading the following details.

1. Output Drive Circuit

The LB11681H is three-phase brush less type fan motor driver.

A high-efficiency direct PWM drive method is adopted in this drive.

Also, for low-noise drive of motor, 180degrees current-carrying soft switching method is adopted.

2. Hall Amplifier and Bias circuit

Since motor driving current depends on the Hall input waveform, the Hall input amplitude should be set to

appropriate value. To obtain good driving current, please adjust the bias resistance so that the Hall input

amplitude is 100-200mVp-p. When the Hall input amplifier is large, a current-carrying OFF band is made.

Connect a Hall bias resistance between the Hall power supply and plus-side of Hall bias.

Also, connect the minus-side of the Hall bias with the HB-pin (pin 1) directly. (No bias resistance on the minus-

Side ).

3. Current Limitation Circuit

The LB11681H incorporates the current limitation circuit. The value of control current of the current limitation

circuit is determined by I = VRF / Rf. (VRF = 0.21V typical)

The current limitation operation, when the voltage of the RF pin (pin 4) exceeds the limiting value,

The transistor on the sink-side is turned off.

4. PWM oscillation circuit

The PWM frequency of this IC is adjustable by connecting the capacitor between the PWM pin (pin 10) and

GND. We recommend the PWM frequency of 50kHz to 100kHz. When the PWM oscillation frequency is too low,

the ripple amplitude of the coil current becomes large. Also, when the PWM oscillation frequency is too high,

the driving efficiency is reduced.

5. Adjust of the driving current

In order to ensure the soft switching, it is necessary to set the driving current value by the best value with inputting a

proper the Hall input amplitude.

The driving current is set by the IB pin (pin 11).

When the value of the IB resistance becomes small, large amounts of the driving current will flow.

The constants of reference for the IB resistance and the RF resistance are shown below.

RF limited current

RF resistance

IB constant

Controlled gain

0.64(A)

1

Ω 3parallel

8.2(k

Ω)

0.66(A/V)

0.84(A)

1

Ω 4parallel

6.8(k

Ω)

0.88(A/V)

1.05(A)

1

Ω 5parallel

4.7(k

Ω)

1.10(A/V)

1.26(A)

1

Ω 6parallel

3.3(k

Ω)

1.32(A/V)