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# [FAQ] Selecting Integrated FET/control BLDC Motor drivers based on Motor Datasheet

Other Parts Discussed in Thread: DRV8313, DRV8312, DRV8332, DRV10964, DRV10970, DRV10974, DRV10975, DRV10983, DRV10983-Q1, DRV10987

Understanding the parameters of a motor is very important in selecting a motor driver as the rating of the FETs and control method of the Motor driver depends on motor parameters and construction. A motor has electrical and mechanical parameters listed in the datasheet as it is an electro-mechanical machine that converts electrical energy to mechanical energy.

Electrical circuit model of a Brushless DC (BLDC) Motor showing electrical and mechanical parameters is shown in Figure 1.

Figure 1. Electrical Circuit Model of BLDC Motor

The following table lists and explains the electrical and mechanical parameters of a BLDC motor.

 Electrical Parameter Typical Symbol Unit Definition Rated voltage Vm Volts Rated voltage that is applied to the motor phases. Rated current i Ampere Current drawn by the motor when the motor is loaded at rated torque. No load current inl Ampere Current drawn by the motor when there is no load on the motor shaft. Peak current/stall current ipk Ampere Current drawn by the motor when the motor shaft gets locked. Back EMF constant Kt v/Hz or v/rpm or v/rad/sec Induced voltage Vt on stator windings at 1 Hz or 1 rpm or 1 rad/sec. Stator/Winding resistance R Ω Resistance across two phases of the motor. Stator/Winding inductance L H Inductance across two phases of the motor. Mechanical Parameter Typical Symbol Unit Definition Rated Speed Hz or rpm or rad/sec Rated speed of the motor. Rated Torque Tm Nm Torque generated by the motor at rated speed. Stall Torque Ts Nm Maximum load torque at which the rotor gets locked. Rotor inertia J Oz-in-s2/N-m-s2 Rotor moment of inertia. This is useful to determine the acceleration and deceleration rates, the dynamic response of the system and to calculate the mechanical time constant of the rotor.

Table 1. Electrical and Mechanical parameters of a BLDC motor.

How to select a BLDC motor driver based on the information available in Motor Datasheet?

Determining voltage and current rating of the integrated FETs based on the motor voltage and current rating is the first step in selecting a Motor driver.

Below are the parameters in the motor datasheet that should be considered when selecting a Motor driver with integrated FET architecture.

• Rated Voltage Vm
• Peak current ipk

Power supply voltage Vs (Abs max) and peak output current is of the integrated FET device (listed in table 2) should be compared with rated voltage Vm and peak current ipk of the motor. Vs and is should be slightly greater than Vm and ipk.

Below are the parameters in the motor datasheet that should be considered while selecting a Motor driver with integrated control architecture.

• Rated Voltage Vm
• Peak current ipk
• Rated current i
• Back EMF Constant Kt
• Stator resistance R
• Stator inductance L

Similar to integrated FET devices, Vs and is of integrated control devices should be slightly higher than Vm and ipk. Motor parameters such as R, L and Kt are used in the motor control algorithm of integrated control devices. R, L and Kt in the motor datasheet should be within the applicable range of R, L and Kt (listed in table 2) that the integrated control device can support.

 Device Architecture Power Supply voltage Vs Peak Current is Motor phase-phase resistance Motor phase-phase inductance (mH) BEMF Constant Kt (mV/Hz) Abs Max Abs Max Min Max Min Max Min Max DRV8313 Integrated FET 65 3 N/A N/A N/A DRV8312 Integrated FET 70 6.5 DRV8332 Integrated FET 70 13 DRV10964 Integrated Control 5.5 0.875 5 20 0.05 1 1 100 DRV10970 Integrated Control 18 1.5 N/A N/A N/A N/A N/A N/A DRV10974 Integrated Control 20 2.5 2 40 0.07 5 150 DRV10975 Integrated Control 18 2 0.6 24 0.07 1 1800 DRV10983 Integrated Control 28 3 0.6 38 0.07 1 1800 DRV10983-Q1 Integrated Control 28 3 0.6 38 0.07 1 1800 DRV10987 Integrated Control 28 3 0.6 38 0.07 1 1800

Table 2. Integrated FET and Integrated Control device parameters.

For more details, please refer to the Brushless-DC Motor Driver Considerations and Selection Guide.