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  • TI Thinks Resolved

LMH6517: SPI problem

Prodigy 90 points

Replies: 14

Views: 716

Part Number: LMH6517

Hello!

I am trying to program the gain of the LMH6517 via SPI using a beagleboard, but that does not seem to work. I already checked the communication lines on the oscilloscope and everything seem fine, so I would like to know if anyone can help identify what the problem is.There is some fixed gain there because I get an amplified signal out of it, but it does not change. The latch pin should not matter when spi is in use so I wonder what could be happening.

This would be the python code:

from Adafruit_BBIO.SPI import SPI

spi = SPI(1,0) #configure device and bus at beagleboard

spi.msh = 10500000 #clock
spi.bpw = 16 #bits per word

spi.open(1,0) #opens it

spi.xfer2([128,0]) #transmits data

Thank you,

JPL

  • Hi JPL,

    What is the voltage on the ENA and ENB pins? If they are grounded instead of floating, it would explain the behavior you describe.

    Best regards,

    Sean
  • In reply to Sean Cashin:

    Hi Sean,

    The configuration pins are set to:

    ENA = +3.3V

    ENB = +3.3V

    LATA = GND

    LATB = GND

    MOD0 = GND

    MOD1 = +3.3V

    Best regards,

    JPL

  • In reply to JPL:

    Does either parallel or pulse mode work for this device? Also, is the device powered with 5V?
  • In reply to Sean Cashin:

    The supply is +5V on the designed board and I also tested it on a modified evaluation board LMH6517EVAL-R1 which works for pulse/parallel. There it didn't work either.
  • In reply to JPL:

    Did you try a different device to see if a damaged part is the issue?
  • In reply to Sean Cashin:

    I have two parts here that I used for testing and I get the same issue. Maybe the way I am programming it is wrong?
  • In reply to JPL:

    How are you programming it?
  • In reply to Sean Cashin:

    I am using a beagleboard black and programming in python which I am not very experienced with. Signals for clock, cs, sdi and sdo were checked on oscilloscope and apparently seem ok. The basic code is the one I send above and I wonder if the problem lies on the way I send the bits over spi.xfer2 or some other configuration that could be missing.

  • In reply to JPL:

    Oscilloscope images when sending spi.xfer2([1,254]), maybe it can help. I cannot understand the issue yet.

    Here I am using a slower clk than the maximum 10.5MHz specified in the datasheet.

    CS and SCLK:

    MOSI and SCLK:

    MISO and SCLK:

    And these are the signals at input (1) and output (2). This gain never changes when set to SPI mode:

  • In reply to JPL:

    I noticed the high level of the MOSI is actually low. This could be it, I will try: e2e.ti.com/.../1137694

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