PWM Signal Voltage Translation

Discussion in 'General Electronics Chat' started by sarbhatia2005, Feb 3, 2011.

  1. sarbhatia2005

    Thread Starter New Member

    Feb 3, 2011
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    Hi,

    I am trying to translate a 0-3.3V PWM signal to a 0-5V PWM signal using a ADG3300 translator chip. The translator chip translates bidirectionally, and I am using the 3.3V - 5V translation direction.

    At the moment a 0-3.3V PWM signal is being input to the chip, however right at the output pin, a 3.3(low)-5(high)V signal is being generated. Additionally, when I put an oscilloscope probe to the end of a wire connected to the pin, the signal is mashed up so to speak in that is a fuzzy waveform at about 3.3 V, i.e. not a PWM signal.

    I tried switching wires/connections but to no avail.

    Inputs A1-A4 work fine for my stepper motor connections, which just translate a 3.3V signal to 5V. I am using A6 input for the PWM signal, A5, A7, and A8 have been soldered to the ground pin.

    Any help at all would be greatly appreciated.
    Thanks.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Do you have 0.1uF bypass capacitors from Vcca to GND and Vccb to GND, as close as possible to the IC?

    What is the A6 output driving? If you have a long wire connecting to a MOSFET gate that has a high gate charge, you will likely have problems.

    What is your input PWM frequency?

    Can you post a schematic of your circuit, and a photo of the layout you are using?
     
  3. sarbhatia2005

    Thread Starter New Member

    Feb 3, 2011
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    I have connected 100nF capacitors from Vcaa and Vcyy to GND. The A6 output is driving a Firgelli 'I' type linear actuator, where the duty cycle of the PWM signal determines the distance moved by the actuator.

    The frequency of the PWM signal is 1 kHz.

    The input signals are coming from I/O pins on a microcontroller with a MSP430f169 processor. I have tried using a different pin on the voltage translator to transmit the signal but I get the same output: 5V(high)-3.3V(low) PWM signal at the pin that mashes together along the length of the wire.

    I will post schematics and picture as soon as I can.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Well, I believe that this is the Firgelli Automation home page:
    http://www.firgelliauto.com/
    However, I really do not wish to expend the effort to locate a datasheet that probably won't be an exact match for what you have.

    You need to be more specific about the actuator model and accessories that are relevant to it's controls.
     
  5. sarbhatia2005

    Thread Starter New Member

    Feb 3, 2011
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    The actuator has an on board controller which allows it to be controlled with a single digital output pin from an external microcontroller. In addition, it is connected to a DC power supply (GND and V= +6V).

    However at the moment my wire from the voltage translator is not connected to the actuator. I am measuring the signal with an oscilloscope and I am not recieving the correct output. I have connected GND of the oscilloscope to GND of the microcontroller (which provides the input to the voltage translator).
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    OK then, what does the PWM signal look like on the input side on A6? Are you getting a 0v to 3.3v swing, with a pretty decent looking square wave?

    If that looks OK, have you tried the A5, A7 or A8 inputs to outputs?

    Perhaps your translator IC has a bad channel, or perhaps you damaged it.
     
  7. sarbhatia2005

    Thread Starter New Member

    Feb 3, 2011
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    The input to A6 looks like a normal square wave 0-3.3V.

    I have tried the other A inputs to outputs and I get the same output when I use A6. As I said before, the pins work fine for translating a 3.3V constant level to 5 V for my stepper motor, or when it is low, keeping it low.

    But for some reason when I am trying to translate the PWM signal, it continues to not get translated the way I wouldve thought, with 5V high and 0V low. instead it is 5V high and around 3V low.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    You said that you had a wire connected to the B6 output.
    Have you tried removing the wire, and just looking at the pins' output?
    Try using a pull-down resistor; perhaps 10k.
     
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