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Driving a 6A Coil with an LMD18201

Discussion in 'Robotics & Mechatronics' started by hybridspecies, Aug 20, 2013.

  1. hybridspecies

    hybridspecies New Member

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    The chip is rated at 3A continuous, but I'd like to use it to drive a coil (electromagnet actually) at 6A continuous in either direction. The specs say I can go that high for a burst, but I want it to be able to do 6A for a prolonged time. I've heard that paralleling can get me a little higher (4A), but I was hoping instead to feed a mosfet from the out pins of the LMD18201 to amplify the current. Problem is I don't know how to account for the directional shifting when PWM goes reverse. Any ideas? Thanks.
     
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    L9958 or SA57
    There are a number of bigger parts.
     
  3. hybridspecies

    hybridspecies New Member

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    RS, Thanks for responding. I'm open to using a different part, but I'd like to avoid registers and more importantly I couldn't tell from the datasheets whether or not those parts support pwm locked-antiphase. With the 18201 I can set PWM at 5V and input my pwm signal to the dir input to get the h-bridge switching at either side of 50%, which is what I need. I'd also like to keep the part through hole if possible not to mention that I already have a couple of 18201s on hand. Is the mosfet amplifier I mentioned a possibility?
     
  4. dave

    Dave New Member

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  5. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Many people use a MOSFET driver (high side and low side) to drive two MOSFETs (4 MOSFETs).
    With external MOSFETs you really have no limit.
     
  6. hybridspecies

    hybridspecies New Member

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    How would I connect the mosfet driver to the 18201's two output pins? Or are you talking about building an h-bridge with the mosfets? I thought about that, but I wouldn't know how to integrate the locked antiphase logic without extensive logic gating. It just seems to me that I should be able to take the signal from the out pins of the 18201 and use them to trigger a mosfet hooked to the coil and V+.
     
  7. ChrisP58

    ChrisP58 Well-Known Member

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    Take a look at the internal logic drawing of the LMD18201. You will see that each of the two outputs pins are tied to the drain of one mosfet and the source of another. The gates of those two mosfets are driven differently.

    In order to connect external mosfets to the LMD18201, you need to drive the external gates with the same signals that the internal mosfets are driven with. While those signals could probably be extracted from the output pins, it would take extra logic to separate them.

    You are much better off with just using a larger h-bridge device, or starting with a bridge driver designed for external mosfets.
     
  8. hybridspecies

    hybridspecies New Member

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    Chris, thanks for the feedback. Are you familiar with a larger h-bridge or external driver that does PWM locked antiphase? There might be many, but I haven't been able to identify a part. If you know of any that can do 6A+ and locked antiphase please let me know the part number. I understand what you are saying about the gating requirements, but do you think if I fed the outputs from the LMD18201 into the inputs of a TLE 5206-2, for example, I could drive the coil that way, or would it still require extra logic? I'd prefer not to have to use both parts, but it is worth considering if nothing else is available. Thanks again.
     
  9. hybridspecies

    hybridspecies New Member

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    This part would be perfect (STK681-332-E) except that I can't tell if it supports locked antiphase.
     
  10. ChrisP58

    ChrisP58 Well-Known Member

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    My experience is in power supplies, not motor control, so I don't really know what locked antiphase is. :(
     
  11. hybridspecies

    hybridspecies New Member

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    Locked antiphase is a way to control motor direction and power using only a single pwm input. Instead of having one input for the pwm signal and another specifying cw or ccw rotation, the single pwm input tells the motor to spin cw if the duty cycle is > 50% or ccw if the duty cycle is < than 50% (or vice versa) while at the same time preserving the ability to modulate power based on duty cycle. I'm trying to keep my circuit simple and prefer not to incorporate a uC or logic gates if I don't have too, which is why I'm looking for something with locked antiphase capabilty. Thanks.
     
  12. Mr RB

    Mr RB Well-Known Member

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    It's a modern trendy term for "driving a motor with PWM and a H-bridge".

    Basically the PWM makes one side of the motor HI and the other LO. If the PWM is 50% then both sides are equally HI and LO and the motor does not turn. If one side is more HI than the other then the motor turns that direction.
     
  13. carrotSnack

    carrotSnack Member

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    What about the HIP4082 with external mosfets.
    All you need is a not gate to control is with a single PWM signal.
     
  14. hybridspecies

    hybridspecies New Member

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    carrotSnack, thanks for the suggestion. I pulled up the datasheet on the 4082, but it doesn't look like it supports pwm locked anti-phase. I want to be able to control the direction and speed of the motor (coil) with just a single pwm input. If I'm wrong about the locked anti-phase pwm let me know, because what you suggest should work otherwise.

    On a side note, I'm waiting on a response from Infineon regarding their TLE 5206-2, which would give me 5A continuous out (I can live with that instead of the 6A I wanted), as to whether or not that chip really supports single input pwm locked antiphase operation. The data sheet says it does, but there are no clear instructions for enabling it like with the LMD 18201.
     
  15. hybridspecies

    hybridspecies New Member

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    ok, so it turns out the inputs of the TLE5206 have to be uP varied (or one side inverted) to achieve pwm locked anti-phase mode. I was hoping to avoid increasing the part count of the circuit, but it appears I have no choice but to add an inverter if I want 6A output capability. I will go with the STK681332E motor driver since it's capable of higher outputs. Thanks to everyone who took the time to respond and I hope this serves as a future reference for others with the same question.
     

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