TCAL9538: CLock Stretching

Youhei Miyaoka

Part Number: TCAL9538

Tool/software:

Hi team,

My customer are using USB to I2C Converter with Clock stretching option in order to communicate with TI Serializer . The same I2C Bus is connected with the IO expander TCAL9538PWR. Does IO expander also be Clock stretching option support required ? is the above-mentioned part number support clock stretching?.

Regards,

Youhei MIYAOKA

4 months ago

+1 Tyler Townsend 4 months ago

TI__Mastermind 47998 points

Hi Youhei,

TCAL9538PWR does not have a pull-down driver on SCL and cannot clock stretch.

None of our I/O expanders currently have clock stretching capability. Why does the customer need clock stretching on an I2C I/O expander?

Regards,

Tyler

0 Youhei Miyaoka 4 months ago in reply to Tyler Townsend

TI__Expert 4065 points

Hi Tyler,

Thank you. They are seeing one Issue , explained below

Refer below Picture, they are using the below configuration for one of the applications. In order to meet the Clock stretching requirements , the USB to I2C Converter chosen with Clock stretching capability. In the same Bus, IO expander -1 and 2 is connected .

Issue : they are facing I2C Bus Hang Issue when we try to use IO expander -1 and 2 and it is randomly . So suspecting IO Expander having any need of Clock stretching features.

Regards,

Youhei

0 Clemens Ladisch 4 months ago in reply to Youhei Miyaoka

Guru 317280 points

The I/O expanders never pull SCL low.

Why is the bus hanging? Is SCL or SDA stuck low? Can you check which device pulls the line low (this requires measuring the voltage drop over a series resistor in front of the device)?

0 Tyler Townsend 4 months ago in reply to Youhei Miyaoka

TI__Mastermind 47998 points

Hi Youhei,

Like Clemens asked, is SDA or SCL being pulled LOW?

How is the customer determining that the pull LOW is occurring from the I/O expanders and not the serializer?

Regards,

Tyler

0 Youhei Miyaoka 3 months ago in reply to Tyler Townsend

TI__Expert 4065 points

Hi Tyler, Clemens,

Thank you. I will move to internal discussion.

Regards,

Youhei

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TCAL9538: CLock Stretching