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PCA9512A interface to a 2.5V I2C master

Question asked by Matt Fienberg on Jul 6, 2020
Latest reply on Jul 15, 2020 by Matt Fienberg

Hello,

 

The PCA9512A datasheet includes the following note: 

 

PCA9512A datasheet snip

(1)  Can someone confirm that the pull-up resistor voltage need not match the supply voltage without enabling the acceleration function?  Specifically, is there a hazard in using 2.5V pull-ups with a PCA9512A device powered by 3.3V?

 

My application has an 2.5V I2C master (whose input may not exceed 3.05V (VDDIO + 0.550V).  The PCA9512 has a VCC spec of 2.7V minimum.  I experimented with a PCA9515 legally powered at 2.5V, but there's an fixed-offset component (a PCA9615B) downstream that can't propagate the bus.  I could create a tiny 2.7V or 3.0V supply; but would prefer not, unless absolutely necessary.  Assuming the scenario works as I'd like--  I'd have a pair of pull-up resistors to 2.5V on the primary side of the PCA9512A with VCC = 3.3V; while the secondary side has, in two instances 3.3V pullups with VCC2=3.3V, and in a third, 5V pull-ups with VCC2 = 5V.

 

(2)  Of lesser importance, I'd like to understand what the hazard is in enabling the accelerator in this scenario.  Has no bearing on my application; just intellectual curiosity.

 

Thanks very much in advance!

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