PCA9515A: Clarification on MCU Driving Multiple I2C Buffers

SIVAPOORANI M

Part Number: PCA9515A
Other Parts Discussed in Thread: TCA9517A, ISO1540, TCA9517, PCA9517, PCA9515B

Tool/software:

I am working on the I2C interface where the MCU (MIMRT1024CAG4B) drives the two I2C buffer (PAC9515A) that are placed on the same board. One Buffer output drives the on-board devices, while the other I2C buffer is routed through a ribbon cable to the devices on a second board. I need clarification on whether this setup will work reliably and Considerations regarding the Pull-up resistor, bus loading and signal integrity.

The attached image shows the MCU interfacing two buffers through I2C interface.

24 days ago

0 Tyler Townsend 24 days ago

TI__Mastermind 48128 points

Hi Sivapoorani,

Just to confirm, side 0 is shared amongst both PCA9515A devices correct? The schematic net name is a little difficult for me to read.

Regards,

Tyler

0 SIVAPOORANI M 24 days ago in reply to Tyler Townsend

Prodigy 10 points

Hi Tyler,

Yes, Both PCA9515A has shared I2C3 SCL & SDA signals. U89 (Placed Below MCU) Buffer output is driving on-board I2C devices whereas U161 Buffer output is driving daughter board through Ribbon cable.

Regards,

Sivapoorani

0 Tyler Townsend 24 days ago in reply to SIVAPOORANI M

TI__Mastermind 48128 points

Hi Sivapoorani,

Let me get back to you by end of today.

Regards,

Tyler

0 Tyler Townsend 24 days ago in reply to SIVAPOORANI M

TI__Mastermind 48128 points

Hi Sivapoorani,

PCA9515A cannot be connected in parallel due to VILC spec. The output of one PCA9515A cannot be recognized by the other buffer in parallel as a logic LOW.

VILC = 0.4V

VOL = 0.52 V typical.

For TCA9517A, A-A, A-B, B-A connections are allowed, but never B-B connections.

See this application note for more information.

https://www.ti.com/lit/an/scpa054/scpa054.pdf?ts=1719932118796&ref_url=https%253A%252F%252Fwww.google.com%252F

Regards,

Tyler

0 SIVAPOORANI M 19 days ago in reply to Tyler Townsend

Prodigy 10 points

Hi Tyler,

Thank you for the reply.

Kindly confirm the below two queries.

1. As per your recommendation we have changed the I2C buffer from PCA9515A to PCA9517A. MCU is connected to I2C buffers as A-B combination. Please confirm the below schematics combination.

2. I2C Buffer has been connected to slaves (IO expander, Isolator). Let me know if there is any concern in this design.

Regards,

Sivapoorani M

0 Tyler Townsend 19 days ago in reply to SIVAPOORANI M

TI__Mastermind 48128 points

Hi Sivapoorani,

The schematic now shows an ISO1540 device which also has VIL/VOL restrictions. However, side 2 is connected to B-side of TCA9517, this is okay since ISO1540 VIL2 = 0.3 x VCC2 which is enough VIL margin. VOL2 from ISO1540 is good at 0.4V which meets a VILC of the TCA9517.

Also, I recommend TCA9517A, not PCA9517.

Where does this segment go to? Does it go to another buffer?

Once we understand where the red arrow leads and confirm that no issues exist on that segment, this schematic looks good.

Regards,

Tyler

0 SIVAPOORANI M 18 days ago in reply to Tyler Townsend

Prodigy 10 points

Hi Tyler,

Thank you for your valuable time and response.

We will change the I2C Buffer from PCA9517 to TCA9517.

The I2C Buffer has been connected to Side 2 of another ISO1540 Isolator. Please validate the design and let me know any concerns.

+1 Tyler Townsend 18 days ago in reply to SIVAPOORANI M

TI__Mastermind 48128 points

Hi Sivapoorani,

PCA9515B side B connected to side 2 of two parallel ISO1540's seems to check out from a VIL/VOL electrical spec when comparing each datasheet.

It might be more beneficial to use TCA9517A in place of the PCA9515A. This is because TCA9517A has a higher VILC = 0.45V. The VOL coming from the ISO1540 is at max 0.4V. You would be just within the VILC spec of the PCA9515A

TCA9517A would give a little more margin on VIL than the PCA9515A.

Regards,

Tyler

0 SIVAPOORANI M 3 hours ago in reply to Tyler Townsend

Prodigy 10 points

Hi Tyler,

Thank you for your valuable support and guidance on the design. It has been very helpful in moving the implementation forward.

Thanks & Regards,

Sivapoorani

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PCA9515A: Clarification on MCU Driving Multiple I2C Buffers