Structural Features, Pin Functions and Application Scope of Brushless Motor Driver THMC40/41

“THMC40/41 is a two-phase DC fan brushless motor driver; can be used for the control of 12V cooling fans that require PRM rate control.

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1. Features of THMC40/41

THMC40/41 is a two-phase DC fan brushless motor driver; can be used for the control of 12V cooling fans that require PRM rate control. This drive has the following characteristics:

Structural features, pin functions and application scope of the brushless motor driver THMC40/41 ●It can control the speed of the DC fan without external power drive, and can reduce the number of components, save space and reduce costs.

●Adopt a unique method of adjusting motor winding power level to control fan speed.

●By changing the operation cycle of VPWM voltage, the fan speed can be adjusted by PWM control in the range of 11% to 100%.

●Low power consumption, the typical current value in sleep mode is only 300μA.

●With the function of shutdown and automatic retry, it can effectively protect the locked rotor.

●With speed signal or locked rotor detection signal output.

●With low noise Hall sensor signal conditioning.

●With thermal shutdown protection function, it will automatically shut down when the chip junction temperature exceeds 165℃.

2. Internal composition and pin function

2.1 Internal structure

THMC40/41 driver consists of 23kHz PWM oscillator, PWM generator, tachometer, high-side gate driver, low-side gate driver, Hall sensor comparator, startup and sleep detection circuit, locked rotor detection and automatic restart circuit , thermal management circuit, high and low-end switches, synchronous switch circuits and power supply circuits and other parts, as shown in Figure 1, its internal structure block diagram.

Structural features, pin function and application range of brushless motor driver THMC40/41 The difference between the two chips of THMC40/41 is that the function of pin 2 is different. The output of pin 2 (TACH) of THMC40 is the open-drain tachometer signal output. It can be used to monitor and measure the actual speed of the fan; the output of pin 2 (RD) of THMC41 is the open-drain motor rotor lock detection output, which can be used as an alarm when the motor is locked. However, both drivers are driven motor windings with RDS=0.4Ω, rated current of 1A, high- and low-side PWs are the same as DMOS drive circuits, and are connected from pin 5 (VOUT), pin 11 (PHA) and pin 10 (PHB) output, therefore, no external power drive circuit is required. The THMC40/41 controls the fan speed by adjusting the power level of the motor windings.

2.2 Pinout and Function

THMC40/41 adopts dual-row 14-pin package, and its pin arrangement is shown in Figure 2. The function description of each pin is as follows:

Pin 1 (Cosc): External oscillation capacitor connection, possibility to design the frequency of PWM oscillator. The internal 180μA current source and current sink connected to pin 1 are used to charge and discharge the oscillator capacitor to generate a triangular wave voltage signal from 0.5 to 2.3V on pin 1.

Pin 2 (TACH): Open-drain tachometer signal output (THMC40 only), which can be used for monitoring and measuring the actual speed of the fan. For THMC41, its pin 2 (RD) is the open-drain motor rotor lock detection output, which can be used to give an alarm when the motor is locked. The corresponding relationship between the state of pin 2 (TACH) of THMC40 and the input state of pin 13 (H+), pin 12 (H-), pin 11 (PHA) and pin 10 (PHB) is listed in Table 1.

Table 1 Correspondence between pins 2 of THMC40 and pins 10 to 13

H+ H- PHA PHB THAC (THMC40)

+ – High(OFF) LOW(ON) High(OFF)

– + LOW(ON) High(OFF) LOW(ON)

Pin 3 (CP): The connection terminal of the external charge storage capacitor is used to generate the gate driving voltage required by the VOUT output high-end DMOS transistor.

Pin 4 (VPWR): driver supply voltage input.

Pin 5 (VOUT): The high-end PWM drive output of the motor winding.

Pins 6 (NC) and 8 (NC) are empty ends.

Pin 7 (PGND), pin (AGND): respectively the power ground and module ground of the driver.

Pin 10 (PHB), pin 11 (PHA): The low-end driving pins of the motor B-phase and A-phase windings respectively. Can be used to drive commutation (which can be controlled based on rotor position monitored by Hall effect position sensors).

Pin 13 (H+), Pin 12 (H-): are the positive and negative input pins of the sensor comparator respectively.

Structural features, pin functions and application range of brushless motor driver THMC40/41 3. Electrical parameters

The main electrical parameters of THMC40/41 are as follows:

●The highest input voltage VPWM: 18V;

●High-end PWM drive output maximum voltage VOUT: 18V;

●Low-end driving voltage VPHA, VPHB: 40V;

●Sensing comparator sensing input voltage VH+, VH-: 7V;

●PWM duty factor control input voltage VPWM: 7V;

● Open-drain tachometer signal output voltage V7ACH (only THMC40): 7V; ● Open-drain motor rotor lock detection output voltage VRD (only THMC41): 7C; ● Oscillation capacitor voltage Vcosc: 7V;

●Charge pump capacitor voltage VCP: 30V;

●High-end PWM drive output current IOUT: 1.5A;

●Low-end PWM drive output current IPHA, IPHB: 1.5A;

●Power consumption PD: 1022mW;

●Working temperature range Tc: -30～+80℃;

●Storage temperature range Tstg: -55～+150℃;

●Maximum junction temperature Tj: 150℃.

●Welding temperature (10s) TLEAD: 300℃.

4. Application

THMC40/41 are mainly used for the drive of variable speed DC brushless fan motors. Its application areas include desktop computers, workstations, servers, printers, laboratory testing instruments, and laboratory power supplies.

Figure 4 is the schematic diagram of the application circuit of THMC40/41. In the figure, the 12V DC voltage is added to the pin 4 (VPWR) of THMC40/41 through the diode CR1 as its working voltage, and its working current is about 5μA. The capacitor C4 connected to the pin 4 is a bypass capacitor, and the function of C5 is to eliminate the current spike that appears on the input power supply when the motor is commutated. C2 is the PWM oscillator frequency setting capacitor, and C3 is the charge pump energy storage capacitor.

By applying the high-end drive output of pin 5 (VOUT) of THMC40/41 to the common terminal L of the motor winding, the PWM signal generated inside the chip can be used to provide a controllable power to the motor, thereby controlling the speed of the motor. When the PWM drive signal is on, the motor current increases; when the PWM drive signal is off, the motor current decreases. When the rate control input on THMC40/41 pin 14 (VPWM) is open, the fan can be controlled by a 1-10MΩ resistor. The VPWM voltage can be used to determine the duty cycle of the PWM waveform output on VOUT. VPWM can be either a DC control voltage input or a digital control input. Compare the VPWM voltage with the triangular wave voltage generated on pin 1 (Cosc), so that the output duty factor of the PWM comparator inside the chip is proportional to the voltage VPWM. When the voltage on pin 14 is VPW