PCA9745B SDO stays low

[bmerrill]

PCA9745B SDO stays in a low impedance state. It does not matter if CS is high or low.

setup:

Reset tied high, OE tied low, VDD supplied with 3.3v. 3.3v logic on SPI

The PCA9745 has been verified to pull the SDO low. when disconnecting the 50ohm resistor to it, the line is no longer held low

[kounotetsu]

Hi, do you have any resolution on this issue?
I have the same symptom with all of the products.
Although the product functionality is fine, I have never read registers inside, since SDO signal must be disconnected.
I have found same topic in this forum "PCA9745B SDO high-impedance state" which is not solved, too.
https://community.nxp.com/t5/Other-NXP-Products/PCA9745B-SDO-high-impedance-state/m-p/994889

[guoweisun]

what's the result if disconnect the SDO pin of PCA9745 with MCU side?you can test it!

[guoweisun]

If you disconnect SDO pin to MCU then test it, what's the result?

[bmerrill]

The PCA9745B has been isolated from other components on a separate proto-board.

With no connection to the MCU (or anything but a scope), the SDO line still stays low, with Chip select low or high.

Only when in the reset state does the SDO line go high.

3 separate PCA9745B's have been tested and exhibit the same failure type

[guoweisun]

Do you mean your PCA9745B no work normally because of SDO always LOW?

[bmerrill]

Yes, the PCA9745B is not working normally, as it should go into tristate, or high impedance when Chipselect goes high. Instead, SDO is always low.

[guoweisun]

Please according and setting your SPI communication timing as datasheet page39-Fig 19. Definition of timing then to try again.