Q: We're using your MAX3491CSD component and need to verify that it is cold sparing. This condition is also referred to as "partial power" sometimes and describes an operational state where your MAX3491CSD receiver is powered down, but the driver (in a different box) is still powered up and driving your un-powered device's input. Even though the 422 spec says the receiver shall only draw 3.6mA powered or not, vendors often place ESD protection diodes at their inputs which present a "sneak path" for current to flow from the I/O pin to the Vcc rail and an attempt to power up the device and sometimes the board through the powered I/O.
We are using this partial power scenario, so I need to confirm that this part does not have this current path from I/O to rail and present unintended behavior.
A: The IC designer has confirmed: the ESD circuit would not cause leakage through any "sneak path" from the I/O pins (A, B for MAX3491) to the VCC rail.
In general you can examine the Absolute Maximum Ratings pin voltages to determine the "sneak path" or ESD diode forward path relationships. For MAX3491 the bus-side I/O voltages are independent of VCC. Similarly the logic side control and driver input voltages are independent of VCC. Only the logic side receiver output, RO, has an ESD protection diode to VCC as indicated by the abs max voltage of (VCC + 0.3V).
Supply Voltage (VCC) .............................................................7V
Control Input Voltage (RE, DE).................................-0.3V to 7V
Driver Input Voltage (DI)............................................-0.3V to 7V
Driver Output Voltage (A, B, Y, Z) ........................-7.5V to 12.5V
Receiver Input Voltage (A, B)...............................-7.5V to 12.5V
Receiver Output Voltage (RO) ................. -0.3V to (VCC + 0.3V)