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DRV8846: Lack of nRESET control on DRV8846

Andrew V
Intellectual 270 points
Part Number: DRV8846
Other Parts Discussed in Thread: DRV8825,

What is the difference between DRV8846 and DRV8825 in terms of enabling, disabling, and resetting the indexer? DRV8846 doesn't have the nRESET input, while DRV8825 has it. Is it redundant on both parts?

  • 0
    TI__Genius 14485 points

    Hi Andrew,

    For DRV8846, Table 10 in the datasheet should answer your question for that device. Bringing nENBL low will ignore the STEP input, but it shouldn't reset the indexer. Bringing nSLEEP low will reset the indexer.

  • 0 in reply to James Lockridge19
    Intellectual 270 points

    Thank you for the pointer. I am evaluating the DRV8846 and comparing it with a previous design based on DRV8825. Am I right in thinking that DRV8825 allows to disable the operation without re-initializing the indexer? DRV8846 doesn't seem to offer this option. I've summarized the differences in the following tables

    DRV8846          
      nSLEEP nENBL Hbridge VINT Indexer
    Operating  1 0 Operating Operating Operating
    Disabled 1 1 Disabled Operating Operating
    Sleep 0 X Disabled Disabled Disabled. Indexer is initialized when nSLEEP = 1

    DRV8825          
      nSLEEP nENBL nRESET Hbridge Indexer
    Operating  1 0 1 Operating Operating
    Disabled 1 1 1 Disabled Disabled, indexer
    is not initialized
    Sleep 0 X 1 Disabled Disabled, indexer is imitialized when nSLEEP = 1
    Reset X X 0 Disabled Disabled. Indexer is initialized when nRESET = 1
  • 0 in reply to Andrew V
    TI__Genius 14485 points
    Andrew,

    I've asked my design team how nENBL affects the indexer in the DRV8825 since the datasheet is not super clear on this use case.

    The DRV8846 allows you to disable it without losing your place in the indexer. When nENBL is HIGH, only the H-bridge outputs are disabled. When you bring nENBL low again, the indexer will be in the same place you left it (unless you sent step signals when nENBL was HIGH).
  • 0 in reply to James Lockridge19
    TI__Genius 14485 points
    Andrew,

    My design team confirmed that the DRV8825 retains the indexer state when nENBL toggles.