Other Parts Discussed in Thread: BQ76942, TCA9800
Tool/software:
Hello,
I'm trying to use an ISO1640 isolator in my application, in combination with BQ76942 on slave side and mCU on host side.
I know that normal connection would be: mCU ---- (side 1) ISO1640 (side 2) ---- BQ76942. But I'm thinking about connecting mCU to the side 2 of ISO1640 and BQ76942 to the side 1, because ISO1640 supports more capacitance on the bus on the side 2 than on the side 1.
My idea is to make something like this:
Idea is to "reverse" sides of ISO1640, because cable length or distance (and consequently capacitance) will be larger between ISO and mCU than between ISO and BQ.
The problem I have here is next:
- BQ76942 has Vil(max) = 0.33 x REG18 = 0.6 V (if REG18 is 1.8 V) and Vil(max) = 0.53 V (if REG18 = 1.6 V which is minimum per datasheet)
- ISO1640 has Vol(min) = 570 mV and Vol(max) = 710 mV
The problem is that logical zero provided by ISO1640 could be higher than maximal logical zero recognized by BQ7642 (Vol (min) of ISO1640 is higher than Vil (max) of BQ76942). I'm not sure if BQ76942 would recognize signal as logical zero really only up to Vil(max) point or also higher - for example 0.71 V would BQ76942 recognize as logical zero or one?
Do you suggest to put I2C buffer between ISO1640 and BQ7642 or do you think that it will work without problems without buffer? Situation is marginal...
Many thanks,
Dejan.
