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DRV8860 Questions?

Kathleen Ritter
Prodigy 70 points
Other Parts Discussed in Thread: DRV8860

I wanted to know on the DRV8860 if I need to have the 2 capacitors 10uf and 0.1uf on every VM pin of every chip or if you can you just put one set of capacitors for each set of chips serialized together.

I also want to know if there is a max number of chip you can put in series.

Thanks,

Kathie

  • 0
    TI__Guru** 114905 points

    Hi Kathie,

    It is recommended to place one bulk 10uf and one 0.1uf cap around each DRV8860.

    I have to get back to you on the maximum number of chips in series? Do you have an estimate on how many you would like to use in series?

    If you have not done so, it is recommended to go to www.ti.com/tool/drv8860evm and examine the documentation available. The schematic, layout, and BOM of the TI EVM available at the estore can be used as an example. The files can be found under the software section and in the folder Board Files.

  • 0 in reply to Rick Duncan
    Prodigy 70 points

    Hi Rick,

    I will probably not be putting more than 15 chip in series.  I am planning to use it drive solenoid valves.

    I did look at the EVM board which have been useful.  I just wanted to make sure about the caps because there will be around 30 driver chips on the board.

    Kathie

  • 0 in reply to Kathleen Ritter
    TI__Mastermind 26065 points

    Hi Kathie

    There is no theoretical limit of the MAX devices in daisy chain. In practice, it is a trade off between the number of devices and the output shifting speed in synchronous because there will be signal delay from one to another.

    I don't think there will be any problem with 15pcs. I have seen 24pcs in chain at customer side and work very well. 

    There is a recommendation to have 1k to 3k resistor to all the input pins when many devices are in daisy chain. Because if distribution boards for each DRV8860 are used, the ground wire connection may cause great +/- voltage bouncing during the output current ON/OFF. The limit resistors for inputs can protect the input pins from the bouncing voltage.

    Thanks.

  • 0 in reply to Wilson Zuo
    Prodigy 70 points

    I am going to design my own PCB layout with these chips and I am going to use a NI USB-6501 OEM to drive 3 different sets of serial drivers.   The USB-6501 has a internal 4.7k resistor between the +5V and the port Pad.

    So when you are talking about the 1K to 3k resistor to the input talking about to GND, +5V or inline.

    If there is a large bouncing problem when you turn the outputs on/off should a diode be put in parallel with the solenoid valves?

    For me space is a limiting factor on this project, so ever part I put on the board it less space I have to work with.

    Thanks,
    Kathie

  • 0 in reply to Kathleen Ritter
    TI__Mastermind 26065 points

    Hi Kathie

    If you are using the same big duck PCB board with unified GND plane for all the DRV8860s, you can ignore my recommendation.

    The bouncing I meant is more related to the ground wires connection in a multi-board distribution system with each small PCB for every DRV8860. The backing current though the ground wires will cause other boards in this chain have a ground bouncing.

    The limit resistors are supposed to add to the DIN, DOUT, SCLK, LATCH, and EN pins which you also have the long wire to control it in a distribution system.

    Thank.   

  • 0 in reply to Wilson Zuo
    Prodigy 70 points

    Since I am a bit confused by your statement I going to do a little reiteration to make sure I understood it correctly.

    Since I am going to use one big PCB with a single ground plane.  I do not need to worry about the limit resistor from the bound back. You are just talking about if I am linking multiple PCBs together in series?


    Thanks

    Kathie

  • 0 in reply to Kathleen Ritter
    TI__Mastermind 21320 points

    Hi Kathleen,

    I believe you understanding is correct. In Wilson's application they use distributed PCBs with lengthy wire connections (introduces alot of inductance and noise). In this applications steps must be taken to manage this.

    In your design, with a single PCB, proper ground plane, and proper signal/power routing I don't believe this step is needed.