LB11868V

No.A1915-8/11

Control timing chart

(Speed control)

(1) Minimum speed setting (standby) mode

The low-speed fan rotation occurs at the minimum speed set with the RMI pin.

When the minimum speed is not set (RMI pin pulled up to REG), the motor stops.

If the VHT voltage rises when the lowest speed is not set (RMI pin is pulled up to REG), the fan stops running, and if

the OTS pin capacitor is used, the standby mode is established.

Details of the standby mode are given in the section “Control timing chart (ON-time start, Lock protection).

(2) Low speed

⇔high speed

PMW control is made by comparing the CPWM oscillation voltage (VCPWML

⇔VCPEMH) and VTH voltage.

The drive mode is established when the VTH voltage is low.

Both upper and lower output FET are turned ON when the VTH voltage is low.

When the VTH voltage is high, Pch is turned off, and the coil current is regenerated inside the lower FET. Therefore,

as the VTH voltage decreases, the output ON-DUTY increases, causing an increase in the coil current and raising the

motor rotation speed.

The upper output Pch is turned OFF when the VTH voltage is high, regenerating the coil current in the lower TR.

Therefore, as the VTH voltage decreases, the output ON-DUTY increases, causing increase in the coil current, raising

the motor rotation speed.

The rotational speed can be monitored using the FG output.

(3) Full speed mode

The full speed mode becomes effective when the VTH voltage is VCPWML or less. (Set VTH = GND when the

speed control is not to be made.)

GND

VCPWMH

VCPWML

CPWM

0%

100%

FG

ONDUTY

VTH voltage

RMI voltage

Minimum speed

setting rotation

Low speed

High speed

PWM control speed variable

Full speed

Standby mode