Other Parts Discussed in Thread: TCA9536
Hi team,
my customer is find the following issue with PCA9536:
I am writing to you for clarification on the integrated PCA9536, referring in particular to the errata reference made in paragraph 10 of the datasheet (Power Supply recommendations).
To complete a reset cycle, the VCC of the IC shall fall below 0.2V as per paragraph 8.4.1.
We have actually measured that by completing a cycle from 3.3V (our VCC) to 0.5V and then again at 3.3V, the PCA restarts with random values of its internal registers.
In certain situations, the power node of the PCA remains at 0.5V when the board is turned off, so we are looking for a solution that will allow us not to redesign the board.
As a software work-around, we assumed to rewrite its registers via i2c every time it was started, thus returning it to a “known” state.
For completeness, we use the PCA’s gpios as inputs to recognize which board it is mounted on (1 pull configuration for each board). The strategy is to rewrite the configuration and reverse polarity registry at every boot, then read the input levels to the device correctly.
In the errata I referred to, there is mention of a “lock up” condition if the POR cycle is not respected. Is it guaranteed that rewriting the registers will always return the device to a known state or is there a risk of i2c bus blocking or other causes that make the PCA unreachable? What do you also think of the strategy of rewriting those two registers? Are there any alternatives?
Could you please help support?
Best regads, Riccardo