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TXB0108: TXB0108 as SPI buffer

S L61
Intellectual 780 points

Part Number: TXB0108
Other Parts Discussed in Thread: SN74LVC245A, SN74LVC244A, SN74LVC16245A

Hi everyone,

I have a question about TXB0108 as voltage buffer. I know TXB0108 is a level shifter and I used it before. Now I want to use it as a voltage buffer but not sure if it can work like that.

Here is the situation:

  1. A SPI master (like Raspberry PI) needs to drive 12 or more slaves
  2. CLK speed: 5MHz
  3. Each slave needs 3 wires (CLK, MOSI and MISO) to be buffered, totally 36 wires (assume 12 slaves). So 5 voltage buffers (TXB0108) are added between master and slaves
  4. Both sides are working at 3.3V
  5. The trace is about 20-30cm

Will the method above cause potential problem? Or is it necessary?

Any suggestion is helpful.

Sean

  • 0
    TI__Guru* 97666 points
    The TXB0108 isn't really the best solution for this.

    I would recommend using a bus buffer such as SN74LVC244A, SN74LVC245A (both are 8-channel buffers, 245 is a flow-through architecture with direction control pin).

    Each output can drive up to 15 slave device (as a rule of thumb).

    If you need to fan-out to more channels, you could go for something like the SN74LVC16245A (16-channel version) or the SN74LVC32245A (32-channel version).
  • 0 in reply to Emrys Maier
    TI__Guru* 97666 points
    Sorry, I didn't address the question of 'is it necessary' -- that will depend on the load capacitance and the driver's strength. Most FPGAs (& many MCUs) have weak drivers and will require additional buffering for an application like this.