DRV10975_15 Datasheet, PDF (15/57 Pages) Texas Instruments – DRV10975 12-V, Three-Phase, Sensorless BLDC Motor Driver

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Device Functional Modes (continued)
Table 2. Motor Resistance Look-Up Table
R_{PH_CT} (Ω)
0.0000
0.0073
0.0147
0.0220
0.0294
0.0367
0.0441
0.0514
0.0588
0.0661
0.0735
0.0808
0.0882
0.0955
0.102
0.110
0.117
0.132
0.147
0.161
0.176
0.191
0.205
0.220
0.235
RM[6:0]
0000000
0000001
0000010
0000011
0000100
0000101
0000110
0000111
001000
0001001
0001010
0001011
0001100
0001101
0001110
0001111
0011000
0011001
0011010
0011011
0011100
0011101
0011110
0011111
0101000
HEX
00
01
02
03
04
05
06
07
08
09
0A
0B
0C
0D
0E
0F
18
19
1A
1B
1C
1D
1E
1F
28
R_{PH_CT} (Ω)
0.264
0.294
0.323
0.352
0.382
0.411
0.441
0.470
0.529
0.588
0.646
0.705
0.764
0.823
0.882
0.94
1.05
1.17
1.29
1.41
1.52
1.64
1.76
1.88
2.11
RM[6:0]
0101001
0101010
0101011
0101100
0101101
0101110
0101111
0111000
0111001
0111010
0111011
0111100
0111101
0111110
0111111
1001000
1001001
1001010
1001011
1001100
1001101
1001110
1001111
1011000
1011001
HEX
29
2A
2B
2C
2D
2E
2F
38
39
3A
3B
3C
3D
3E
3F
48
49
4A
4B
4C
4D
4E
4F
58
59
R_{PH_CT} (Ω)
2.35
2.58
2.82
3.05
3.29
3.52
3.76
4.23
4.70
5.17
5.64
6.11
6.58
7.05
7.52
8.46
9.40
10.3
11.2
12.2
13.1
14.1
DRV10975
SLVSCP2 – JANUARY 2015
RM[6:0]
1011010
1011011
1011100
1011101
1011110
1011111
1101000
1101001
1101010
1101011
1101100
1101101
1101110
1101111
1111000
1111001
1111010
1111011
1111100
1111101
1111110
1111111
HEX
5A
5B
5C
5D
5E
5F
68
69
6A
6B
6C
6D
6E
6F
78
79
7A
7B
7C
7D
7E
7F
9.4.1.2 Motor Velocity Constant
The motor velocity constant, Kt[6:0] describes the motors phase-to-phase BEMF voltage as a function of the
motor velocity.
The measured motor velocity constant (Kt_PH) needs to be converted to a 7-bit digital register value Kt[6:0] to
program the motor velocity constant value. The digital register value can be determined as follows:
1. Convert the measured Kt_PH to a weighted digital value: Kt_{ph_dig} = 1442 × Kt_PH
2. Encode the digital value such that Kt_{ph_dig} = Kt[3:0] << Kt[4:6].
The maximum Kt_PH that can be programmed is 1330 mV/Hz. This represents a digital value of 1920 and an
encoded Kt[6:0] value of 0x7Fh. The minimum Kt_PH that can be programmed is 0.7 mV/Hz, which represents a
digital value of 1 and an encoded Kt[6:0] value of 0x01h.
For convenience, the encoded value of Kt[6:0] may also be obtained from Table 3.
Kt_PH (mV/Hz)
0.00
0.70
1.39
2.09
2.78
3.48
Kt[6:0]
0000000
0000001
0000010
0000011
0000100
0000101
Table 3. Motor Velocity Constant Look-Up Table
HEX
00
01
02
03
04
05
Kt_PH (mV/Hz)
25.1
27.8
30.6
33.4
36.2
39
Kt [6:0]
0101001
0101010
0101011
0101100
0101101
0101110
HEX
29
2A
2B
2C
2D
2E
Kt_PH (mV/Hz)
223
245
267
290
312
334
Kt [6:0]
1011010
1011011
1011100
1011101
1011110
1011111
HEX
5A
5B
5C
5D
5E
5F
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