My customers are considering the LTC 4314.
Using a 1.8 V master, the level shifts to 1.8 V on the primary side and 3.3 V on the secondary side.
# 1 When setting the bus on the primary side to 1.8 V, are there any problems with the following conditions? (Can the primary bus power supply voltage be lower than VCC?)
VCC = 3.3 V
Primary side bus power supply voltage (SCL IN, SDA IN Pull up) = 1.8 V VCC2 = GND Secondary side bus power supply voltage (SCL IN, SDA IN Pull up) = 3.3 V
# 2 I would like to control the ENABLE pin with the 1.8 V system, but the electric characteristics are VEN (TH) = 0.8 V
(min), 1.4 V (typ), 2.0 V (max).
In the case of VEN (TH) = 2 V, there is a possibility that it can not recognize High at 1.8 V input, right? Is the 0.8
to 2.0 V variation with the device?
Equation 5 in the "Level Translating to Bus Voltages < 2.25V" Section should help with the first question.
Since this application has VCC2 tied to GND, VMIN is going to be the VCC voltage (3.3V here). 1.8V should be fine for the buses here.
The second question, I will need to research. I'll be back to you shortly on that one.
The VEN (TH) spec means the enables pins will need to interface with a device that has a VOL<0.8V and VOH>2V. In this application there needs to be an external level shift for the 1.8V input high to get over 2V to reliably control the ENABLE pins.