HIP4081 Driver coupling problem

Discussion in 'The Projects Forum' started by bytraper, Apr 15, 2011.

  1. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    With the help of sargentwookie (and no help from me) I now have a great little PWM generator!

    Now I've come across a couple of problems and I'm stuck.

    I'm trying to run the output of the PWM into the inputs of a HIP4081 mosfet driver IC, and bluntly, its not working.

    Firstly I tried to drive the output of the little pwm generator into either the ALI or BLI (forward or reverse inputs) and nothing happened. Then I got clever and used a pull up resistor to the +5v and kind of got a response, but not at all what I was expecting.
    When i turn the pot which adjusts the duty cycle of the pwm it does nothing to a point, then goes to full on.

    I think it might have something to do with the fact that the 4081 inputs for the ALI and BLI inputs are logic level ? but I don't know enough to be sure.

    I am also not sure what I need to do with the DISABLE input (pin 3), the application data for it is confusing with jumpers and other things I don't need? But as far as I can understand it, it basically makes sure the top and bottom mosfets aren't on together at power up thus preventing shoot through. Is this right?
    Can i put a resistor and capacitor or something there?

    This diagram shows what I am trying to do:

    I currently have a 100 ohm diode from the disable input to ground, but I don't think that's right

    [​IMG]
     
    Last edited: Apr 15, 2011
  2. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    did you read the datasheets for the driver ICs?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The HIP4081 accepts logic level inputs. Vin <= 0.8v is a logic low. Vin >= 2.7v is a logic high.

    You have AHI and BHI wired to +12v, which means you're trying to turn both high sides of the H-bridge on continuously.

    If you then put high either ALI or BLI, you will have a dead short across the power supply, which will likely result in smoke.

    You should not have both high side MOSFETs on.

    In order to charge the boost cap on the A side initially, you need to have ALI high, and AHI low.
    In order to charge the boost cap on the B side initially, you need to have BLI high, and BHI low.
    If you don't charge the caps initially, it may take the high-side MOSFETs quite a while to turn on.

    You will need resistors from the MOSFET gates to the AHO, ALO, BHO, BLO outputs. I suggest 22 Ohms for starters.

    I am not going to have time to help you with this.
    There are several archived threads dealing with the HIP4081.
    I was trying to help someone with that IC over the course of the last few weeks, in this thread: http://forum.allaboutcircuits.com/showthread.php?t=51588
     
    Last edited: Apr 15, 2011
  4. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    Hi Sarge,

    You misunderstand, if you set the AHI and BHI high then the control is taken from a PWM input to either the ALI or BLI (but not both at the same time. You get a dead shorts between the fets if you try and run PWM inputs to both at once).

    Its the PWM mode switching part of the chip. When i run a signal generator PWM signal to either the ALI or BLI to get (forward or reverse), and adjusting the duty cycle I get 0-100% speed from a motor I have hooked up to it and it works perfectly.

    The h-bridge side of the circuit is all done and working well and I know the pwm circuit you designed is working too, but the problem is the mismatch between the output of the PWM generator you worked out for me to the input to of the HIP 4081 chip.

    I guess my question should be how do I turn the output from the PWM generator into a logic level output that the inputs of the 4081 can understand ?
     
    Last edited: Apr 15, 2011
  5. sgardner025

    Active Member

    Nov 5, 2009
    79
    4
    The disable input is active high, so it needs to be tied low for normal operation.
     
  6. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    126
    4
    Hi gardener,
    At the moment I have the disable pin working so that's no longer an issue.
    I just need to work out how to get the output of the Pwm circuit matched up to the Ali and bli logic inputs of the 4081. I'm just not sure how to properly connect the two circuits I posted together, but just joining them up doesn't work.
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,019
    1,542
    @ bytraper - in this link; http://www.intersil.com/data/fn/fn3659.pdf on page 3 it shows what your trying to do.

    In your schematic where you have the red dotted lines, it looks like you need to add a inverter IC. In the link look where it says "PWM input", the triangle with a bubble on the output is the symbol for a inverter. A 7404 is a TTL inverter. Your PWM signal is already 5V so it is already TTL level and the inverter will connect to your 5V circuit also.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    OK, try changing R6 to 2.7k, and instead of Vcc, connect the high side of R6 to 12v.

    12v/2.7k = 4.4mA, which is within the specifications of the LM2903/LM339 type comparators.

    5v should really be OK though; the datasheet shows 2.7v being a logic high.
     
    Last edited: Apr 16, 2011
  9. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You need to provide complementary PWM signals on the ALI and BLI inputs in order for the driver to drive the MOSFETs properl. This is to charge the bootstrap capacitors. Another way to drive it, is to drive one of the xBL pins high and apply PWM to the other.
     
  10. PerunaPete

    New Member

    Mar 17, 2011
    22
    1
    Can you post up images from an oscilloscope? You really need something identical to the circuit in the application notes. it may seem unnecessary, but it's essential to have a complementary input as mentioned above.
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The complimentary input is what the inverter in the link(data sheet) I provided gives.
     
  12. sl001

    New Member

    Jun 11, 2011
    1
    0
    Hi there, was a solution found to this problem? I to have built a similar circuit using a PIC to drive the ALI and BLI inputs. I have tied the AHI and BHI to +12V. The problem I have is the same as the original post in that, pwm input to either input has no effect. Note: if I tie AHI low and BHI high or vice versa, all works as it should. It is just the PWM input that has no effect. Scopeing the pwm input reveals it is being pulled low when connected to the HIP4081. I have read through these posts and I see several references to the circuit on the data sheet that suggests using a complementary input to both inputs, however I don't feel this is necessary as: A) other circuits that I see using this IC are simply driving it directly with a micro and B) how would you then select direction?. Any advice would be very welcome.
    (my circuit is based on the following:http://www.hvlabs.com/hbridge.html you will see there is no inverter in sight)
     
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