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Original question:

TCAN4550-Q1: TCAN4550-Q1 vsTCAN4551-Q1

TCAN4550-Q1: Difference

Ray Vincent Aranzaso
Mastermind 18180 points
Part Number: TCAN4550-Q1
Other Parts Discussed in Thread: TCAN4551-Q1, TCAN4550

Hi,

Good Day. I found several posts on the difference between the TCAN4550-Q1 and TCAN4551-Q1.

But my customer has some clarifications about the difference. Please see below.

I have just one extra doubt related to the differences which are not mentioned in the forums and it is almost not noticeable within the datasheet: TCAN4550 has GPIO1 but TCAN4551 has GPO1; is that right? Doesn't TCAN4551 have any input pin? Not that we are thinking now about a case where we would need it in our application, but we are considering the differences.

I also have a hardware design question. We are going to use a 2-layer PCB. The top layer has all components and routing and the bottom layer is going to be almost fully flooded cooper ground:
1. Should we also flood the top layer with Cooper ground?
2. Components on the top layer, will have each, one via to connect to the ground bottom layer to reduce inductance. Should the flooded cooper gound on top also connect to the top vias?

Best Regards,

Ray Vincent

  • 0
    TI__Guru 74252 points

    Ray,

    The customer is correct, TCAN4551-Q1 only has GPO1, not GPIO1 and GPO2 like the TCAN4550-Q1. 

    1. I recommend putting any empty space on the PCB with GND for any device. This will just improve thermal performance and noise mitigation.

    2. If they are both connected to the GND net, then yes, they should be connected to both GND layers.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    TI__Mastermind 18180 points

    Hi Eric,

    Good Day.

    Now I have a question related to the theoretical value of the series resistor between OSC1 and crystal. The chosen 40Mhz crystal has a theoretical max resistance of 40ohms, shunt capacitance of 3pF max, and Cload capacitors should be 12pF.

    My calculations leave me with a value of 25.6 ohms. Should I start with that theoretical resistor value?

    Is a 0402 (63mW) resistor size ok? I tried to find information in the "TCAN455x Clock Optimization and Design Guidelines" but I couldn't find information about resistor sizing.

    Best Regards,

    Ray Vincent

  • 0 in reply to Ray Vincent Aranzaso
    TI__Guru 53555 points

    Hi Ray,

    The actual value of the required series resistor may vary depending on the paracitics introduced from other parts of the application. Typically, we will see designs start with a small value (or 0-ohms) and increase it as needed based on testing across operating condition - namely temperature. This would prevent you from having to guess in which direction to move the value in the case that the theoretical value sees vailures.

    0402 sizing is fine here. The smaller package will decrease other impedance parasitic and keep the overall oscillator traces short. I would only recommend a larger package if you plan to replace the value often such as on a test board, but even in this case you would want it to be as similar to the end-application as possible.

    Regards, 
    Eric Schott