PCA9555: Bits in register 0 and 1 are inverted after power up.

Han Wang

Part Number: PCA9555
Other Parts Discussed in Thread: TCA9555

Hi team,

My customer has a abnormal issue for PCA9555. They found that after power on, the input register 0 and 1 are all inverted. And after they write 0 to register 4 and 5. The input register 0 and 1 become normal. Do you have any insight for it? I attached the SCH and the start up waveform: red is the 3.3V power; Yellow is SDA and Blue is SCL. also, the waveform looks strange too. The schematic shows it's NXP's part, but confirmed that they are using TI's part for this test, and NXP's part do not have this issue.

THanks

Han

riser2-1_x16 x16 PCIe RiserBF_SCH_SDV_PASS2_20240129-BOMCHANGE.pdf

over 1 year ago

0 Adam Arnold over 1 year ago

TI__Prodigy 190 points

Hi Han,

PCA9555 suffers from PoR issues often when the device is powered from a none GND state. This can cause the internal registers to differ from their default state. It is recommended to use TCA9555 which has the same functionality but resolves this issue.

Regards,

Adam

0 Han Wang over 1 year ago in reply to Adam Arnold

TI__Intellectual 1245 points

Hi Adam,

THanks for your reply! Customer does not have time to change to TCA in their project. Can they use I2C to clear the register 4 and 5 right after power on to workaround this ?

THanks,

Han

0 Han Wang over 1 year ago in reply to Adam Arnold

TI__Intellectual 1245 points

Hi Adam,

Another question, do we know the device is powered from what voltage that will have this problem?

Thanks,

Han

0 Adam Arnold over 1 year ago in reply to Han Wang

TI__Prodigy 190 points

Hi Han,

Yes to work around this issue, they can rewrite to all registers after power up.

This may occur anytime the device is powered from non-GND.

Regards,

Adam

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PCA9555: Bits in register 0 and 1 are inverted after power up.