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SM72442: SM72442, Reading I2C reg1

William Conley
Prodigy 135 points
Part Number: SM72442
Other Parts Discussed in Thread: SM72441, SM72445

In reference to reading the I2C registers from the SM72442, more specifically REG SM72442 and "Current in". Where is the  SM72442 taking these measurements from?

As an example: where is the SM72442 taking the "SM72442' measurements, which external components and/or when SM72442 PINS?

  • 0
    TI__Guru* 78675 points
    The measurement is taken at AIOUT those four pins: AIOUT, AVIN, AIOUT, and AVOUT. The other four pins A0/2/4/6 basically set references, and together with the resistor divider a the four measurement pins, the device can scale the voltage and current readings.
  • 0 in reply to Youhao Xi
    Prodigy 135 points

    I am using the SM72442 and having issues communicating via I2C.

    I have a question reference the minimum I would need to get my Microcontroller to communicate to the SM72442.

    - I Have +5vdc and GND applied to the SM72442

    - I have RESET HIGH

    - I have my microcontroller I2C bus connected to the SM72442's I2C bus. 

    - I have I2C0 HIGH, I2C1, I2C2 set low.

    This is some of the data on my I2C analyzer: E0 03 FF FF FF FF FF FF FF FF

    Is there any other hardware lines on the SM72442 that I would need to connect to allow for I1C communications? What would impede the SM72442 from communicating via the I2C bus?

     

  • 0 in reply to Youhao Xi
    Prodigy 135 points
    This make no sense? You indicate 4 pins: "AIOUT, AVIN, AIOUT, and AVOUT", but "AIOUT" is mentioned twice?
  • 0 in reply to William Conley
    TI__Guru* 78675 points

    Sorry for the obviously a typo.  It should be AIIN, AVIN, AIOUT and AVOUT.

  • 0 in reply to William Conley
    TI__Guru* 78675 points
    I need to ask a digital engineer to answer your question. Hope to get back to you soon.
  • 0 in reply to Youhao Xi
    Prodigy 135 points

    I'm using your reference design.

    Can you please tell me what your full scale values are for AIIN, AVIN, AIOUT and AVOUT.? I'm looking to display true floating point values and I need to calculate the engineering units but I'm not 100% sure what the full scale units are. I think AIOUT is 0-35vdc? What I will be doing to reading these values via the I2C bus then formatting the values to display actual Analog Voltage IN, Analog Voltage OUT, analog Current IN and analog Current OUT. 

    I'm assuming:

    AVIN =  Voltage being produced by the PV

    AIIN =  Current being produced by the PV

    AIOUT = Current consumed or draw by the battery

    AVOUT = Voltage at the battery

    Correct?

  • 0 in reply to William Conley
    TI__Guru* 78675 points

    Hi William,

    Very sorry for the delay.  I really want to help and I have been trying hard but I am not able to identify a right digital engineer to answer your I2C questions. When I was using the SM72441/42 in 2008-2009 in designing the Power Optimizers SM1230 and SM3320, the controller was internally called LM25091 (never official released in this part number to the market).  All related ICs were given new SMxxxxx part numbers when the Solarmagic group became a separate business unit inside National Semiconductor.  In designing these two Optimizers I just followed our digital engineers' recommendations to setup A0-A6 pins, and I myself never used the I2C interface. After releasing these two Optimizers, I returned to our product line.  The digital engineers that I used to consult are no longer with the company, and my memory become very vague after so many years.

    Regarding your question:  the full scale of AVIN, AIIN, AIOU and AVOUT is the VDDD voltage, which normally is 5V.  You need to scale the real input/output rail voltages and currents for the controller.

    Basically,  A0 is the voltage ref voltage for the maximum voltage, which is determined by the resistor divider at the A0 pin, scaled from the VDDD voltage.   This ref voltage is checked against the real output voltage feedback resistor divider.   Namely, (Pls ref to the SM3320-RF-EV Schematic)

    Vomax = [ VDDD x R38 / (R28+R38)] x [(R53+R51+R52) / R153]

    Use the same ref voltage and method to decide AVIN divider.

    Pin A4 sets  reference to program the maximum current, and you need to take into account the current sense gain from the driver IC. Note: AIOUT does  not use the driver internal current sense amplifier. Instead, an external current amplifier is used.  It is mainly because the internal current sense amplifier requires a minimum 5V rail common mode voltage to operate, hence it becomes blind if the output port is shorted.

    Ioutmax = [ VDDD x R40 /(R40+R30)] / (R63 /R58) / R10

    Use the same ref voltage to select AIIN divider. The input current uses the driver's internal current sense amplifier and the gain is determined by R56/R8.

    Hope this helps.

    Best Regards,

    Youhao XI,  System and Applications Engineering, APP-BMC-BCS, TI

  • 0 in reply to Youhao Xi
    Prodigy 60 points
    Hi, Mr. Youhao XI

    I'm Duc.Chu and i also used SM72445 for my design, i'm reading datasheet but inform for AVin pin it's so meager. Your reply is helpful but, I have a little confuse for this:
    "Basically, A0 is the voltage ref voltage for the maximum voltage, which is determined by the resistor divider at the A0 pin, scaled from the VDDD voltage. This ref voltage is checked against the real output voltage feedback resistor divider. Namely, (Pls ref to the SM3320-RF-EV Schematic)
    Vomax = [ VDDD x R38 / (R28+R38)] x [(R53+R51+R52) / R153]
    Use the same ref voltage and method to decide AVIN divider."

    Is this mean the AVin also ref to Voltage in A0 pin? Am I right?

    Thanks so much for your time

    Regards,
  • 0 in reply to duc chu
    TI__Guru* 78675 points
    Yes AVIN also references to A0 pin voltage.
  • 0 in reply to Youhao Xi
    Prodigy 60 points

    Hi Youhao Xi.

    Thanks for your quick reply.

    One more question, How to set the switching frequency and dead-time of SM72445?

    Regards,

  • 0 in reply to duc chu
    TI__Guru* 78675 points
    Please refer to the datasheet Page 5: there are three frequency to choose by programming at A2 pin. Dead time is described on Page 10.