0 V

CPWM

V

CC

FG

0 V

VTH voltage

RMI voltage

4.55 V

1.65 V

PWM-IN disconnected

ON duty small

f = 25 kHz (CP = 100 pF)

ON duty large

PWM control

variable speed

Full speed

12 V

Rotation set to

minimum speed

(stop mode)

Low speed

High speed

TMP814

A.

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

B.

Low

↔

high

speed

mode

PWM control is made through comparison of oscillation and VTH voltages with CPWM changing between 1.6 V

↔ 4.6

V.

Upper and lower TRs are turned ON when the VTH voltage is higher. The upper output TR is turned OFF when the

VTH voltage is lower, and the coil current is regenerated in the lower TR. 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.

C.

Full

speed

mode

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

speed control is not used.)

D.

PWM-IN

input

disconnection

mode

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

The fan runs at full speed (see Figure 1).

Figure 3. Control Timing

Copyright © 2009, Texas Instruments Incorporated

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