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PCA9515B: PCA9515B

Shlomi Yehezkia
Mastermind 6150 points
Part Number: PCA9515B
Other Parts Discussed in Thread: TCA9802, TCA9509

Hi Team,

 

I am working on a new design of a 4K video RF module.

 

I am looking for an I2C buffer, mainly for electrical and capacitive I2C isolation.

 

I've found PCA9515B online. PCA9515B have a relatively high VOL (0.52V typically).

 

In addition, there is the requirement for VILC which, if I understand correctly, requires buffer input voltage to be at least 70mV less than VOL.

 

Since this is a generic I2C bus exposed to an OEM customers of my I find those limiting.

 

Do you have some other solution to offer?

 

Thanks,

Shlomi

  • 0
    TI__Mastermind 49270 points
    Hey Shlomi,

    "In addition, there is the requirement for VILC which, if I understand correctly, requires buffer input voltage to be at least 70mV less than VOL."
    -The PCA9515B actually requires 120mV less....unfortunately...

    "PCA9515B have a relatively high VOL (0.52V typically)."
    I understand the concern here, with a higher Vol there may be concerns with devices which may have low Vil requirements below 0.52V. Particularly with lower voltage devices.

    TI does offer the TCA980x family which breaks away from the use of a static voltage offset and uses a current source to monitor whether it is sourcing or sinking current. This gets rid of the large Vol seen by the static voltage offset architectures seen in most buffers. For example, TCA9802 has a Vol of about 0.2V. We also get rid of the Vilc parameter however there is a minimum amount of current that must be sunk by the transceivers to propagate lows which is denoted as I(iLC). This basically means if the FET has a resistance of 150 ohms or less when pulling down, the device will work. More than that and this device will not. This impedance value is typically lower than 150 ohms for transceivers anyways and is lower with higher Vcc of the transceiver.


    The device will also allow for us to get rid of pull up resistors on B side as the B side will internally pull up to VccB and can be effective in reducing space (2 less resistors). [This is not an option, pull up resistors may cause the device to malfunction]

    The only limitation I really see with this device is it has a max operating voltage of 3.6V. If you want to interface it with a 5V transceiver, you will need to use a level translator.

    If the Vcc range is an issue, TCA9509 is a second option as it can go up to 5.5V. It has a lower Vol of about 0.2V as well and Vilc of 0.15mV. The Vol devices into the TCA9509 can be reduce to be below Vilc by simply increasing the pull up resistor. (This assumes the bus capacitance is not too large).

    Thanks,
    -Bobby