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LSF0204: Channel-to-channel skew

Dice-K
Mastermind 6330 points
Part Number: LSF0204
Other Parts Discussed in Thread: ADS9120, TXB0104

Hello.

Does LSF0204 have the specification of "Channel-to-channel skew"?

I use LSF0204 as shown below.

In order to connect with the ADS9120, it is necessary to secure setup time and hold time.

For example,
TXB0104 has the following specification.

SCES650I  Page-10
"6.13 Switching Characteristics: VCCA = 1.8 V ± 0.15 V"
Channel-to-channel skew  0.5ns  MAX

Regards,
Dice-K

  • 0
    TI__Guru* 96591 points
    Hi Dice-K,
    The LSF0204 is not an active device, so it does not have this type of specification. It acts like a switch, and the skew will be very dependent upon your system design.

    For example, if channel 1 has a load of 50pF, and channel 2 has a load of 5pF, it's very likely that channel 1 will have a 10x slower rising edge on the 5V side.

    I would recommend watching our video series on the LSF family of translators to understand how they work. The key to matched timing is to ensure that your loads are matched on the higher voltage side of the LSF.

    training.ti.com/LogicMinute
  • 0 in reply to Emrys Maier
    Mastermind 6330 points
    Hello Emrys,
    Thank you for your reply.

    Does the timing depend on the load on the higher voltage side if it is used only in the direction from the higher voltage side to the lower voltage side?

    If the input capacitance of the CLK pin of the ADS9120 is equal to the input capacitance of the CNV pin, is it the same timing?

    Best regards,
    Dice-K
  • 0 in reply to Dice-K
    TI__Guru* 96591 points
    Hi Dice-K,
    If your are only translating from 5V to 3.3V, then the 5V side load will not affect the delay.

    The pin capacitance is one part of the equation -- you must also know the parasitic capacitance from the traces and other connections. It looks like one of the ADS9120 pins is fanning out to 2 pins of the LSF0204. It's likely that the loading isn't equal because of this.

    If it were my system, I would ensure that I had equal length traces for all connections from the ADS9120 to the LSF0204, and I would ensure the total capacitance of each trace was the same -- ie, for any trace that branches, it would likely need to have half the trace width to maintain the same capacitance at the same trace length.