F2967

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R109-036.a



CONTROL TIMING CHART

(1) Minimum speed setting (stop) mode

Input of PWM-IN 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

While the input pin of PWM-IN 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.)