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STP24DP05 (I don't get it)

Discussion in 'Electronic Design' started by Jon Slaughter, Jan 23, 2009.

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  1. http://www.st.com/stonline/products/literature/ds/14714/stp24dp05.pdf

    How are the outputs controlled? It has a serial input but I don't understand
    how one can control the output(or maybe you can't?)?

    It says that it can be used for high resolution LED panels

    "for high serial data rates enabling responsive image rendition" ...

    "The driving current of 5-80mA per LED channel is adjusted using one
    external resistor per color group of eight outputs, allowing the maximum
    brightness of red, green and blue channels to be optimized independently."

    "Using this device to drive video displays and signage comprising large
    numbers of high-brightness LEDs saves bill-of-materials costs compared to
    conventional devices with fewer outputs. By allowing closer spacing of
    pixels and constituent LEDs, the driver also enables higher display
    resolution. Major applications will include full-color RGB video display
    panels for indoor or outdoor use, LED advertisement billboards, graphic
    boards, colored traffic signs, and variable message signs."

    I can't for the life of me figure out how this chip works ;/ 5mA min
    current per driver??? Does that mean I can't drive an LED to ~0
    brightness?(or even close)

    No where do I see what the data format is for the input or what the input
    commands are or what they control. (this is the main problem as I have no
    idea how to use the thing. (I am either hoping to be able to turn a driver
    completely on or off using serial comm. or send bits to specifiy amount (255
    = full on, 0 = full off or something similar)

    It says that it can drive an LED matrix but how? If I can't control
    individual LED's then it will be impossible to control individual rows ;/

    -----------------

    What I want to do is hook up a driver to the cathodes of 24 LED's and send
    info to the chip to program the currents. I'd ultimately like to have a
    matrix where I will cycle through the rows, each time programming the chip
    to give the appropriate currents for the LED's on that row.

    I don't know if pages are missing from that datsheet or if I'm just being
    completely retarded but I can't find anything in it that makes any real
    sense on how to use it.
     
  2. Guest

    from a very quick scan of the datasheet, this is what the chip will
    do:

    you can set the output current for each set of 8 LEDs with and
    external resistor.

    clocking in a 24 bit "word" one bit for each output you can either
    turn it on or
    turn it off

    you cannot control the current in each led, just in each group and
    that is done
    with the external resistors

    only way to dim a specific led would be to PWM it by continously clock
    in data
    turning it on and off

    -Lasse
     
  3. Can you tell me what page told you this? No where do I see any mention of
    turning on or off an output. I do not see any mention of the protocol. They
    do have at timing diagram though but it doesn't mention anything about this.

    Seems like your guessing or I'm missing a page... Not that your wrong but
    I'd like to be 99.9% sure. Maybe this is just suppose to be common
    knowledge?

    what if I only clock in 8 bits? is the first bit the last driver or the
    first? I guess I should be able to figure it all out by just looking at the
    schematic given?

    Basically just a shift register where bit's flow in and flow out? When I
    latch it copies the register to the data latch and uses that to turn on/off
    the corresponding drivers?
    I want to control the current using pwm.
    This is what I want to do.
     
  4. JosephKK

    JosephKK Guest

    I browsed through the data sheet. It was perfectly clear to me. He
    can PWM it by reloads or by external means. The chip won't break, but
    it might complain about intermittent opens in the output load.
     
  5. JosephKK

    JosephKK Guest

    Really. And what is the total datarate for a 320 by 240 size display
    done this way with your rate feeding a row fraction of 8 pixels? This
    is way more than OP's required resolution BTW, i just want to make a
    point.

    240 rows of 40 modules at 16384 updates / s of 48 bits. What is the
    data rate?
     
  6. JosephKK

    JosephKK Guest

    That is exactly my point. Rather than feed that many modules like
    that do something different. The data rate would be insupportable.
     
  7. JosephKK

    JosephKK Guest

    I will have to work that one out some more. My proposed array of 320
    by 240 may be a lot bigger than OP's target. I certainly respect
    jumbotrons a lot better now. For the first cut i would use an array
    of smaller units say 8 pixels by 8 pixels. Then i would have to look
    at architectures that talk to enough of these modules, most likely on
    some kind of tree fed meta array model. I would have to think really
    deeply about what i wanted to display and how fast. So, no, i do not
    have a complete design to hand. Not much more than an approach to a
    problem that may be different from OP's problem.
     
  8. For a decent range of intensity you generally need 12 bits of raw greyscale capability, with a gamma
    correction curve from 8 bit source data.
    Look at the Macroblock MBI5031 driver - this is used in a lot of large LED screens
    www.mblock.com.tw
     
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