Datasheet

PCA9306

SCPS113J –OCTOBER 2004–REVISED OCTOBER 2010

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The 3-dB point of the PCA9306 is ≈600 MHz. However, this measurement is an analog type of measurement.

For digital applications the signal should not degrade up to the fifth harmonic of the digital signal. As a rule of

thumb, the frequency bandwidth should be at least five times the maximum digital clock rate. This component of

the signal is very important in determining the overall shape of the digital signal. In the case of the PCA9306,

digital clock frequency of >100 MHz can be achieved.

The PCA9306 does not provide any drive capability like the PCA9515 or PCA9517 series of devices. Therefore

higher frequency applications will require higher drive strength from the host side. No pullup resistor is needed on

the host side (3.3 V) if the PCA9306 is being driven by standard CMOS totem pole output driver. Ideally, it is best

to minimize the trace length from the PCA9306 on the sink side (1.8 V) to minimize signal degradation.

You can then use a simple formula to compute the maximum "practical" frequency component. Or the "knee"

frequency (f

knee

). All fast edges have an infinite spectrum of frequency components. However, there is an

inflection (or "knee") in the frequency spectrum of fast edges where frequency components higher than f

knee

are

insignificant in determining the shape of the signal.

To calculate f

knee

= 0.5/RT (10–80%)

knee

= 0.4/RT (20–80%)

For signals with rise time characteristics based on 10- to 90-percent thresholds, f

knee

is equal to 0.5 divided by

the rise time of the signal. For signals with rise time characteristics based on 20- to 80-percent thresholds, which

is very common in many of today's device specifications, f

knee

is equal to 0.4 divided by the rise time of the

signal.

Some guidelines to follow that will help maximize the performance of the device:

• Keep trace length to a minimum by placing the PCA9306 close to the I

C output of the processor

• The trace length should be less than half the time of flight to reduce ringing and line reflections or non

monotonic behavior in the switching region

• To reduce overshoots, a pullup resistor can be added on the 1.8 V side; be aware that a slower fall time is to

be expected

Product Folder Link(s): PCA9306