SLLSEK2A June   2014  – March 2017 DRV8846

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 PWM Motor Drivers
      2. 7.3.2 Micro-Stepping Indexer
      3. 7.3.3 Current Regulation
      4. 7.3.4 Decay Mode
      5. 7.3.5 Blanking Time
      6. 7.3.6 Protection Circuits
        1. 7.3.6.1 Overcurrent Protection (OCP)
        2. 7.3.6.2 Thermal Shutdown (TSD)
        3. 7.3.6.3 Undervoltage Lockout (UVLO)
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Stepper Motor Speed
        2. 8.2.2.2 Current Regulation
        3. 8.2.2.3 Decay Modes
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.3 Current Regulation

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.

Table 4. Fixed Off-Time Selection

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:

Equation 1. DRV8846 eq_IFS_LLSEK2.gif

where

  • IFS is the full scale regulated current
  • VREF is the voltage on the VREF pin
  • RISENSE is the resistance of the sense resistor
  • TORQUE is the scaling percentage from the torque DAC.

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.

Table 5. Torque DAC Settings

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.

Table 6. Torque DAC xISENS Trip Levels (VREF = 3.3 V)

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