0 V

CPWM

FG

VTH voltage

RMI voltage

3 V

1.1 V

f = 30 kHz (CP = 220 pF)

PWM control

variable speed

Full speed

Rotation set to

minimum speed

(stop mode)

Low speed

High speed

ON Duty Cycle

100%

0%

TMP815

www.ti.com

SLDS153B – MAY 2009 – REVISED NOVEMBER 2015

7.3 Feature Description

7.3.1 Speed Control

The speed control functionality is obtained by VTH pin of the device. For pulsed inputs, the user can supply a 20-

kHz to 100-kHz frequency input (20 kHz to 50 kHz recommended) on the pin with a current limiting resistor in

between.

If not used, this pin needs to be connected to ground for full speed.

A.

Minimum speed setting (stop) 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 5VREG), the motor stops.

B.

Low

↔ high-speed. PWM control is made by comparing the CPWM oscillation voltage (1.1 V ↔ 3 V) and VTH

voltage. Both upper and lower output TRs are turned ON when the VTH voltage is low. The upper output TR 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 cycle increases, causing an increase in the coil current, raising the motor rotation

speed. The rotation speed can be monitored with 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. The full-speed mode becomes effective when the VTH voltage is 1.1 V or less.

Set VTH = GND when the speed control is not used.

Figure 2. Speed Control Timing

7.3.2 Soft-Start

The speed control functionality is obtained by S-S pin of the device. Connection to the soft-start setting capacitor

(see Figure 5) is through this pin. Connect the capacitor between S-S and 5VREG to set the soft-start time,

according to the capacitance that is chosen (see Figure 3 and Figure 4). If the soft-start feature is not intended to

be used, then the this pin needs to be connected to ground.

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