PCA9519PW output rise time

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PCA9519PW output rise time

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Qbert
Contributor I

Using PCA9519PW as an I2C repeater/buffer on a 3.3V bus (A side and B side are both 3.3V).  Even before the bus leaves the board we see slow rise times on SCL and SDA.  Maybe 5-10% of the signal reaches 3.3V when transitioning high (Fast I2C). Going from 10k to 5k pullup has very limited improvement. Is this normal with this part, does anyone else have experience with this IC?

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Qbert
Contributor I

I can't upload a portion of the schematic, but the wave form we're seeing is very similar to this 

Qbert_0-1686237223931.png

There is some ringing on the falling edge.  We have .1uF caps on the VccA and VccB.  A side connects directly to the I2C pins on the MCU with no pullups.  A side signals are nice and square.  B side has 10k pullups and routes through a ferrite bead (1kohm at 100Mhz) then to a connector.  10K pullups are between the ferrite and the PCA9519PW.  With nothing connected to the connector we see slightly better wave form than the picture above.  In system we get valid data occasionally.  Adding just the 10-20pF of the oscilloscope probe is enough to stop any data from coming through.

I noticed the datasheet says VccA Max is VccB-1.5.  I'm wondering if the higher voltage we have at VccA could be our problem.

 

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guoweisun
NXP TechSupport
NXP TechSupport

Can you show schematic and test waveforms?

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