The ISOW14x2 family of devices has built-in under-voltage lockout (UVLO) on all supplies (V_DD, V_IO and V_ISOOUT) with positive-going and negative-going thresholds and hysteresis. Both the power converter supply (V_DD) and Logic supply (V_IO) need to be present for the device to work. If either of them is below its UVLO, both the signal path and the power converter are disabled.

Assuming V_IO is above its UVLO+, when the V_DD voltage crosses the positive-going UVLO threshold during power-up, the DC-DC converter initializes and the power converter duty cycle is increased in a controlled manner. This soft-start scheme limits primary peak currents drawn from the V_DD supply and charges the V_ISOOUT output in a controlled manner, avoiding overshoots. RS-485 driver output is in high impedance state in this duration. When the UVLO positive-going threshold is crossed on the secondary side V_ISOOUT pin, the feedback channel starts providing feedback to the primary controller. The regulation loop takes over and RS-485 drive output, Received data output R and general purpose logic output OUT take their respective states defined by the inputs to the device i.e. Driver enable(DE), Driver data to be transmitted D, Receiver enable RE and general purpose logic input IN respectively. Designers should consider a sufficient time margin (typically 5 ms with 10-µF load capacitance) to allow this power up sequence before any usable system functionality.

When either of V_DD or V_IO is lost, the primary side DC-DC controller turns off when the UVLO lower threshold is reached. The V_ISOOUT capacitor then discharges depending on the isolation channels and RS-485 load.