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.

Adjust the S-S pin voltage gradient by means of the capacitance of the oscillator between the S-S pin and 5VREG. Recommended capacitance is 0.1 μF to 1 μF.

Figure 3. Soft-Start Timing (V_VTH < V_RMI)

Adjust the S-S pin voltage gradient by means of the capacitance of the oscillator between the S-S pin and 5VREG. Recommended capacitance is 0.1 μF to 1 μF.

Figure 4. Soft-Start Timing (V_VTH > V_RMI)

7.3.3 Lock Detection

When the rotor is locked by external means or load conditions, The lock detection feature helps to protect the circuit by not allowing the current to rise beyond control. A hiccup mechanism is also provided. The lock detection is enabled by a connection to the lock detection capacitor (see *10 in Figure 5) The constant current charge and discharge circuits cause drive stop when the pin voltage rises to 3 V and unlocking the drive when pin voltage falls to 1.1 V. If lock detection feature is not desired in the application, this pin needs to be connected to ground.

7.3.4 Current Limit

Current limit resistor is connected in a return path of H Bridge connection. This input is connected to the SENSE pin where the Current is limited when the voltage across this resistor crosses 200-mV threshold. The device enters in lower regeneration mode (see *8 in Figure 5) If not used, this pin needs to be connected to ground.

7.3.5 Minimum Speed Setting

Minimum speed setting (see *6 in Figure 5) feature is use with the RMI pin in the device. Connect to 5VREG with a pullup resistor if not used.

7.3.6 Speed Output

The speed of the motor while running can be observed at the FG pin which is an open collector output and needs to be pulled high for using it.

7.3.7 Drive Frequency Selection

The P channel switches in the device are switched with higher frequency whose duty cycle is decided by the speed control input. The frequency of the operation can be decided by the capacitor connected at the CPWM pin. As this is used also for the current limiting canceling signal, be sure to connect the capacitor even when speed control is not used.

Table 1. Drive Lock Truth Table ^{(1) (2)}

Table 2. Speed Control Truth Table ^{(1) (2)}