TCA6424A: TCA6424A I2C NACK

?? ?

Part Number: TCA6424A

Tool/software:

Dear support team,

I'm trying to get a TCA6424A to work. Sadly, it doesn't reply at all to I2C commands. Another slave on the same bus works without any problems. I would appreciate if you could point me at the thing I'm missing here...

This is a pic of the scope screen:

As you can see, the address byte doesn't get ACK'd.

This is the schematic:

I noticed that there was a similar issue six years ago.It was caused by layout error. I have confirmed mine is correct.

I tryed to remove the another slave on the same bus but it still doesn't work。

As I'm running out of ideas, I'd really appreciate some help here!

Thank you!

Best regards

6 months ago

0 Clemens Ladisch 6 months ago

Guru 316470 points

The waveform looks OK.

Check the voltages at the supply and control pins.

0 Tyler Townsend 6 months ago

TI__Mastermind 46988 points

Hi ?? ?,

Are you able to take oscilloscope captures of the SDA/SCL lines?

What are the PU resistor values of the SDA/SCL lines?

Regards,

Tyler

0 ?? ? 6 months ago in reply to Clemens Ladisch

Prodigy 10 points

Thank you for your reply，

The voltages at the supply pin is 1.8V seems normal，RESET pin is 1.8V, and INT pin is 1.67V.

0 ?? ? 6 months ago in reply to Tyler Townsend

Prodigy 10 points

Thank you for your reply，

The PU resistor values of the SDA/SCL lines is 4.7K and it connected VCCI/VCCP.

The waveform seems normal.

0 Tyler Townsend 6 months ago in reply to ?? ?

TI__Mastermind 46988 points

Hi,

With ADDR = 1, the target address is correct.

This is a read command since 8th bit = 1.

Is this read command being issued at power up? If there is not command byte written to the device, issuing a read command will NACK since the pointer byte has not been set (the TCA6424A does not know which register to read from upon power up).

First write the command byte to set the pointer byte, then issue a read command. This should ACK.

Example in figure 8-9.

Regards,

Tyler

0 ?? ? 6 months ago in reply to Tyler Townsend

Prodigy 10 points

Hi,Tyler

We've tried to write to the device,but it is still nack.

0 Tyler Townsend 6 months ago in reply to ?? ?

TI__Mastermind 46988 points

Where is this scope being measured from? Can we scope the SDA/SCL directly at the IC?

Have we checked that VCC is reaching the IC?

GND'ing connection good?

Same with Address pins, are the voltages measured on a DMM as expected?

Regards,

Tyler

0 ?? ? 6 months ago in reply to Tyler Townsend

Prodigy 10 points

HI Tyler

I have checked all the points you mentioned, and everything seems to be in order.

And I noticed a detail in the datasheet as shown in the figure below. Do we need to control VCCP for a power reset cycle?

0 Tyler Townsend 6 months ago in reply to ?? ?

TI__Mastermind 46988 points

VCCP does control the power reset cycle yes. What is happening to VCCP when you are writing I2C commands?

Both VCCI and VCCP should be powered up for this device to work properly. VCCI is the I2C supply, VCCP is the p-port side voltage, VCCP is also connected to the PoR.

0 ?? ? 6 months ago in reply to Tyler Townsend

Prodigy 10 points

VCCP and VCCI are connected together and are powered by a constant 1.8V supply. When writing to the I2C, the VCCP remains unchanged, as it is provided by the internal PMIC of the SoC. If the voltage drops below 0.2V, the system will fail to operate.

0 Tyler Townsend 6 months ago in reply to ?? ?

TI__Mastermind 46988 points

This sounds like correct operation of the device.

If VCCP falls below the operation voltage of 1.65V, then behavior is not characterized for the device.

Has this issue been repeated on multiple TCA6424A's?

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TCA6424A: TCA6424A I2C NACK