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How to design the CLK Pin

Sora Choi
Prodigy 70 points
Part Number: TPS92661-Q1

I design the 9 LEDs Matrix circuit, so I use the 1 TPS92661-Q1 chip as below.

I have a question about how to design CLK pin using external oscillator(not microcontroller unit, e.g. crystal).

I think oscillator need the 2pins but TPS92661-Q1 has just 1 CLK pin.

and Please check if the Tx pin design is correct.

Thanks.

  • 0
    TI__Genius 13700 points
    Hello Sora,

    Regading your oscillator question. There are a number of oscillators available that an simple single output pin devices such as these from digikey:www.digikey.com/.../172
    The devices that need two pins like X1/X2 are bare crystal oscillators.

    The pull up on your TX line looks good. The question I have is about R52. Is the LMM_TX net a very long net that could have other voltages couple in and damage the TX pin? Unless this wild fluctuation is a strong concern I am not sure if the inline 100ohm resistor is needed on the TX, RX, or EN lines.
  • 0 in reply to Ryan May
    Prodigy 70 points

    Thanks, Ryan

    I redesign the circuit below and use the oscillator you recommended. Is it OK?

    Also, I have a question about register. I just control the LED ON/OFF except for LED Dimming. How do i control the register map? If you can, Please example of source code.

  • 0 in reply to Sora Choi
    TI__Prodigy 710 points

    Hi Sora,

    The MAX7375 has +/-4% initial accuracy at 25C/5V.  This is not accurate enough for asynchronous communications.  You need to maintain +/-2% accuracy.  A part I have used in the past that easily meets this is SiT2024.  You can power that directly from the VCC pin of the TPS92661.  It is automotive rated and not that much more expensive than quartz.

    You have to manipulate LEDON, LEDOFF, ENON, and ENOFF to manipulate the LEDs through the fully range of duty cycles and to allow phase shifting.  What do you mean by "control the register map"?

    There is a single 10-bit register for LEDxON (or LEDxOFF).  There are 2 ways to address this register, and update its value.  As an example, I will use LED1ON.

    • Perform a 5-byte (can also do 10 or 15-byte) write to register address 0x00 with the 8 LSbits in the first data byte and the 2 MSbits in the fifth data byte's [1:0] position.  The MCU will have to track the other pixels (LED2-LED4) as well, and write to them with the remaining bytes/bits of the packet.
    • Perform a 5-byte (or 10 or 15) write to register address 0x40 with the same formatting as above.

    Both of these writes result in the exact same outcome in the hardware.  The first mapping just places all of the LEDONs together, then the LEDOFFs together.  The second mapping interleaves the LEDONs and LEDOFFs.  It is up to you which mapping (or both) you use.  They are provided as a convenience, but both map to the same piece of physical memory.

    Best Regards, Mike

  • 0 in reply to M. Drake
    Prodigy 70 points

    thanks a lot, Mike

    I have two question.

    First, If LED Driver IC supply 600mA, Is it right  that LED input current is 600mA ?

    I saw the datasheet about  TPS92661 output current range. What does it mean?

    1) TPS92661 can supply max 2A. So, LED input current is "LED Driver IC supply current + TPS92661 supply current"

    2) TPS92661 can control max 2A. So, if LED Driver IC supply over 2A, TPS92661 doesn't work..

    Last, Is it correct ?

    Default = 1~9 LED ON

    1. LED1OFF : 1Packet send = address : 0x20, data : 0x00(led1), 0xC8(led2~4)

    2. LED1ON : 1Packet send = address : 0x00, data : 0xC8(led1), 0xC8(led2~4)

    3. LED1OFF & LED5OFF : 2Packet send = address : 0x20, data : 0x00(led1), 0xC8(led2~4) address : 0x25, data : 0x00(led5), 0xC8(led6~8)

     

  • 0 in reply to Sora Choi
    Prodigy 40 points
    Please how can i get the pspice model of TPS92661??