DRV10983_15 Datasheet, PDF (36/57 Pages) Texas Instruments – DRV10983 12- to 24-V, Three-Phase, Sensorless BLDC Motor Driver

DRV10983
SLVSCP6B – JULY 2014 – REVISED FEBRUARY 2015
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9.4.11.2.1 Two-Byte Register Read Back
Several of the registers such as MotorSpeed report data that is contained in two registers.
To make sure that the data does not change between the reading of the first and second register reads, the
DRV10983 implements a special scheme to synchronize the reading of MSB and LSB data. To ensure valid data
is read when reading a two register value, use the following sequence.
1. Read the MSB.
2. Read the LSB.
Figure 38 shows the two-register readback circuit. When the MSB is read, the controller takes a snapshot of the
LSB. The LSB data is stored in one extra register byte, which is shown as MotorSpeedBuffer[7:0]. When the LSB
is read, the value of MotorSpeedBuffer[7:0] is sent.
MotorSpeed[15:8]
MotorSpeed[7:0]
Read
MotorSpeed[15:8]
MotorSpeed
Buffer[7:0]
I²C send out motor speed.
Read
MotorSpeed[7:0]
Motor Speed Read Back
Figure 38. Two-Byte Register Read Back
9.4.11.3 Motor Electrical Period Read Back
The motor operation electrical period is automatically updated in register MotorPeriod1 and MotorPeriod2 while
the motor is spinning. MotorPeriod1 is the MSB and MotorPeriod2 is the LSB. The electrical period is measured
as the time between calculated BEMF zero crossings for phase U. The electrical period of the motor is denoted
as d as ‘t_{ELE_PERIOD} (µs)’ and is calculated as shown in Equation 8.
t_{ELE_PERIOD} (µs) = {MotorPeriod1:MotorPeriod2} × 10
(8)
As an example consider the following:
MotorPeriod1 = 0x01;
MotorPeriod2 = 0xFF;
t_{ELE_PERIOD} = 512 (0x01FF) × 10 = 5120 µs
The motor electrical period and motor speed satisfies the condition of Equation 9.
t_{ELE_PERIOD} (s) × Velocity (Hz) = 1
(9)
9.4.11.4 Motor Velocity Constant Read Back
For any given motor, the integrated value of BEMF during half of an electronic cycle will be constant, Ktc (refer to
Lock2: Abnormal Kt).
The integration of the motor BEMF is processed periodically (updated every electrical cycle) while the motor is
spinning. The result is stored in register MotorKt1 and MotorKt2.
The relationship is shown in Equation 10.
Ktc (V/Hz)= {MotorKt1:MotorKt2} / 2 /1090
(10)
9.4.11.5 Motor Estimated Position by IPD
After inductive sense is executed the rotor position is detected within 60 electrical degrees of resolution. The
position is stored in register IPDPosition.
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