PCA9306

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Product data sheet

Rev. 6 — 25 November 2010

12 of 26

NXP Semiconductors

PCA9306

11.2.1.1

Example maximum frequency

Question — We need to make the PLL area of a new line card backwards compatible and

need to need to convert one GTL signal to LVTTL, invert it, and convert it back to GTL.

The signal we want to convert is random in nature but will mostly be around 19 MHz with

very long periods of inactivity where either a HIGH or LOW state will be maintained. The

traces are 1 or 2 inches long with trace capacitance of about 2 pF per inch.

Answer — The frequency of the PCA9306 is limited by the capacitance of the part, the

capacitance of the traces and the pull-up resistors used. The limiting case is probably the

LOW-to-HIGH transition in the GTL to LVTTL direction, and there the use of the lowest

acceptable resistor values will minimize the rise time delay. Assuming 50 pF capacitance

and 220

Ω resistance, the RC time constant is 11 ns (50 pF × 220 Ω). With 19 MHz

corresponding to 50 ns period the PCA9306 will support this application.