I would appreciate it very much if someone could answer a few questions regarding the use of the ISO7141CC in a partial power-down mode of operation.
My application includes several modules on a same bus (power rails, SPI and a set of other digital signals). Each module has an isolation barrier with the ISO7141CC for the SPI signals (3.3 V) and a transformer driven by the SN6501 for powering the circuitry on the isolated side. On the bus side of the module is an MSP430 controller which is always on. It powers up the rest of the module circuitry when needed, via power distribution switches. In this way the bus side of the ISO7141CC can be left without power, but with active digital signals on its pins INA, INB, and INC, driven by the bus (it is always on). A module would be powered up or down individually, while other modules may remain active and normally use the same SPI signals on the bus.
The questions:
1. Are the inputs (INA, INB, INC and EN1) of the ISO7141CC actually tolerant to voltages within the range [2.7 V, 5.5 V] when the VCC1 pin is connected to GND1? The input schematics given in the datasheet (page 20), as well as the Table 3 (page 19), imply that they are. However, the Absolute maximum ratings (page 5) do not. On the page 1 there is the following sentence: "All inputs are 5-V tolerant when supplied from a 2.7-V or 3.3-V supply." I am confused what that actually means for my application. If the inputs are tolerant, how high would be their high-level input current when the VCC1 pin is connected to GND1?
2. Is the output OUTD of the ISO7141CC tolerant to voltages within the range [2.7 V, 5.5 V] when the VCC1 pin is connected to GND1? The output schematic given in the datasheet (page 20) implies that it is not, because of the diode between the OUTD pin and the VCC1 pin. Therefore, I intend to buffer the OUTD signal with the SN74LVC1G125 or a similar IC. Do you have a better suggestion?
3. Is there a different digital isolator that is more suitable for the described application (basic isolation, very limited board area)?
Best regards,
Frant
