SLLSEK2A June 2014 – March 2017 DRV8846
PRODUCTION DATA.
The current through the motor windings is regulated by an adjustable fixed-off-time PWM current regulation circuit. When an H-bridge is enabled, current rises through the winding at a rate dependent on the DC voltage, inductance of the winding, and the magnitude of the back EMF present. After the current reaches the current chopping threshold, the bridge enters a decay mode for a fixed period of time to decrease the current, which is configurable between 10 to 30 µs through the tri-level input TOFF_SEL. After the time expires, the bridge is re-enabled, starting another PWM cycle.
TOFF_SEL | TOFF Duration |
---|---|
0 | 20 μs |
Z | 10 μs |
1 | 30 μs |
The PWM chopping current is set by a comparator which compares the voltage across a current sense resistor connected to the xISEN pin, with a reference voltage. The reference voltage can be supplied by an internal reference of 3.3 V (which requires VINT to be connected to VREF), or externally supplied to the VREF pin. The reference voltage is then scaled first by the 3-bit torque DAC, then by the output of a sine lookup table that is applied to a sine-weighted DAC (sine DAC). The voltage is attenuated by a factor of 6.6.
The full-scale (100%) chopping current is calculated as follows:
where
Example: Using VREF is 3.3 V, torque DAC = 100%, and a 500-mΩ sense resistor, the full-scale chopping current is 3.3 V / (6.6 × 500 mΩ) × 100% = 1 A.
The current for both motor windings is scaled depending on the I0 and I1 pins, which drive a 3-bit linear DAC, as in Table 5.
I1 | I0 | CURRENT SCALING (TORQUE) |
---|---|---|
0 | 0 | 100% |
0 | Z | 87.5% |
0 | 1 | 75% |
Z | 0 | 62.5% |
Z | Z | 50% |
Z | 1 | 37.5% |
1 | 0 | 25% |
1 | Z | 12.5% |
1 | 1 | 0% (outputs disabled) |
Table 6 gives the xISEN trip voltage at a given DAC code and I[1:0] setting.
Sine DAC Code | Torque DAC I[1:0] Setting | |||||||
---|---|---|---|---|---|---|---|---|
00 - 100% | 0Z - 87.5% | 01 - 75% | Z0 - 62.5% | ZZ - 50% | Z1 - 37.5% | 10 - 25% | 1Z - 12.5% | |
31 | 500 mV | 438 mV | 375 mV | 313 mV | 250 mV | 188 mV | 125 mV | 63 mV |
30 | 500 mV | 438 mV | 375 mV | 313 mV | 250 mV | 188 mV | 125 mV | 63 mV |
29 | 495 mV | 433 mV | 371 mV | 309 mV | 248 mV | 186 mV | 124 mV | 62 mV |
28 | 490 mV | 429 mV | 368 mV | 306 mV | 245 mV | 184 mV | 123 mV | 61 mV |
27 | 485 mV | 424 mV | 364 mV | 303 mV | 243 mV | 182 mV | 121 mV | 61 mV |
26 | 480 mV | 420 mV | 360 mV | 300 mV | 240 mV | 180 mV | 120 mV | 60 mV |
25 | 470 mV | 411 mV | 353 mV | 294 mV | 235 mV | 176 mV | 118 mV | 59 mV |
24 | 460 mV | 403 mV | 345 mV | 288 mV | 230 mV | 173 mV | 115 mV | 58 mV |
23 | 450 mV | 394 mV | 338 mV | 281 mV | 225 mV | 169 mV | 113 mV | 56 mV |
22 | 440 mV | 385 mV | 330 mV | 275 mV | 220 mV | 165 mV | 110 mV | 55 mV |
21 | 430 mV | 376 mV | 323 mV | 269 mV | 215 mV | 161 mV | 108 mV | 54 mV |
20 | 415 mV | 363 mV | 311 mV | 259 mV | 208 mV | 156 mV | 104 mV | 52 mV |
19 | 400 mV | 350 mV | 300 mV | 250 mV | 200 mV | 150 mV | 100 mV | 50 mV |
18 | 385 mV | 337 mV | 289 mV | 241 mV | 193 mV | 144 mV | 96 mV | 48 mV |
17 | 370 mV | 324 mV | 278 mV | 231 mV | 185 mV | 139 mV | 93 mV | 46 mV |
16 | 355 mV | 311 mV | 266 mV | 222 mV | 178 mV | 133 mV | 89 mV | 44 mV |
15 | 335 mV | 293 mV | 251 mV | 209 mV | 168 mV | 126 mV | 84 mV | 42 mV |
14 | 315 mV | 276 mV | 236 mV | 197 mV | 158 mV | 118 mV | 79 mV | 39 mV |
13 | 300 mV | 263 mV | 225 mV | 188 mV | 150 mV | 113 mV | 75 mV | 38 mV |
12 | 280 mV | 245 mV | 210 mV | 175 mV | 140 mV | 105 mV | 70 mV | 35 mV |
11 | 255 mV | 223 mV | 191 mV | 159 mV | 128 mV | 96 mV | 64 mV | 32 mV |
10 | 235 mV | 206 mV | 176 mV | 147 mV | 118 mV | 88 mV | 59 mV | 29 mV |
9 | 215 mV | 188 mV | 161 mV | 134 mV | 108 mV | 81 mV | 54 mV | 27 mV |
8 | 190 mV | 166 mV | 143 mV | 119 mV | 95 mV | 71 mV | 48 mV | 24 mV |
7 | 170 mV | 149 mV | 128 mV | 106 mV | 85 mV | 64 mV | 43 mV | 21 mV |
6 | 145 mV | 127 mV | 109 mV | 91 mV | 73 mV | 54 mV | 36 mV | 18 mV |
5 | 120 mV | 105 mV | 90 mV | 75 mV | 60 mV | 45 mV | 30 mV | 15 mV |
4 | 100 mV | 88 mV | 75 mV | 63 mV | 50 mV | 38 mV | 25 mV | 13 mV |
3 | 75 mV | 66 mV | 56 mV | 47 mV | 38 mV | 28 mV | 19 mV | 9 mV |
2 | 50 mV | 44 mV | 38 mV | 31 mV | 25 mV | 19 mV | 13 mV | 6 mV |
1 | 25 mV | 22 mV | 19 mV | 16 mV | 13 mV | 9 mV | 6 mV | 3 mV |
0 | 0 mV | 0 mV | 0 mV | 0 mV | 0 mV | 0 mV | 0 mV | 0 mV |