LB11967V

Control Timing Chart

4.55V

1.65V

f=25kHz (CP=100pF)

0V

0V

12V

VCC

CPWM

FG

VTH voltage

RMI voltage

ON-Duty-small

PMW-IN disconnected

Full speed

High speed

Low speed

PWM control variable speed

Rotation set to

minimum speed

(Stop mode)

ON-Duty-large

(1) Minimum speed setting (stop) mode

PWM-IN input is filtered to generate the VTH voltage. At low speed, the fan rotates with the minimum speed set with

RMI pin during low speed. If the minimum speed is not set (RMI = 6VREG), the fan stops.

(2) Low

⇔High speed mode

PWM control is made through comparison of oscillation and VTH voltages with CPWM changing between

1.6V

⇔4.6V.

When the VTH voltage is lower, the IC switches to drive mode. When the VTH voltage is higher, the p-channel FET

is turned off and coil current is regenerated through the low-side FET. Therefore, as the VTH voltage lowers, the

output ON-DUTY increases, increasing the coil current and raising the motor speed.

The rotation speed is fed back by the FG output.

(3) Full speed mode

The full-speed mode becomes effective with the VTH voltage of 1.65V or less. (VTH must be equal to GND when the

speed control is not to be made.)

(4) PWM-IN input disconnection mode

When the PWM-IN input pin is disconnected, VTH becomes 1.65V or les and the output enables full drive at 100%.

The fan runs at full speed. (Refer to the sample application circuit.)

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