ADJUSTABLE-SPEED SINGLE-PHASE FULL-WAVE PRE-DRIVER FOR MOTOR

AM4967

Data Sheet

10

Oct. 2008 Rev. 1. 2

BCD Semiconductor Manufacturing Limited

Operating Diagram

Note 3:

1. Minimum Speed Setting Mode (Stop Mode)

When fan rotate at low speed, its lowest speed is settable

by VMIN pin voltage. If not, fan motor stops.

2. Low Speed to High Speed Setting Mode

PWM control system works by comparing the voltage of

VPWM and COSC (1.0V to 3.0V). When VPWM voltage

is low, the transistors of the upper and lower side outputs

are ON. On contrary, when VPWM voltage is high, the

upper side transistors are OFF. And coil current re-circu-

lates in a lower side transistor. Therefore, as the VPWM

voltage becomes lower, output ON duty becomes large.

Sequentially, coil current increases and the motor runs at

high speed which is monitored by FG output while rota-

tion-stop state is monitored by RD output.

3. Full Speed Rotation Mode

When VPWM voltage drops to 1.0V or lower, motor fan

will run at full speed. (If the speed is not controlled,

Figure 9. Operating Diagram 1 of AM4967 (Speed Control, Note 3)

VPWM Voltage

f

VMIN Voltage

COSC Voltage

0V

Minimum Speed Setup

Rotation (Stop Mode)

Low

Speed

PWM Adjustable

Speed

High

Speed

Full Speed

FG

ON-Duty-Large

ON-Duty-Small

3.0V

1.0V

RPM