TCA9517: Spec questions

Shinya Sawamoto said:

Part Number: TCA9517

Hello team,

I have several questions about TCA9517 spec items as follows.
1) Regarding the power up sequence, is the device can be ready to enable when both VCCB>2.5V and VCCA>0.8V are satisfied?

[Bobby] Yes, though typically you can just tie enable to VCCB.

2) When we think about minimum case of the B-side low level input, it looks we can calculate it by 0.38V=0.45V-0.07V, is it correct? I'd like to know the noise margin correctly.

[Bobby] Based on my memory, I've looked through the ViLc validation files for the device about a year ago and found that the ViLc min is actually ~0.4V with very little variation.

3) Regarding the Figure-6 on the datasheet, how come the step wise input waveform in the device timing flow. Could you kindly tell the mechanism?

[Bobby] The step is the static voltage offset which prevents the device from locking itself low. You need to remember this devices SDA/SCL pins are both inputs and outputs, so if you output a low and your input sees a low, it wants to output a low on the other side. This generates a loop of lows, the static offset resolves this problem by making sure the VoL on B side is larger than the ViLc on B side so the device doesn't get stuck low. B side will not go high until A side goes above a certain threshold (figure 6 states it is 50% of VccA when above 2V.

Thanks in advance.
S.Sawamoto

Thanks a lot for your kind answers, Bobby!