The automatic powerdown is a feature of the ICL3227. It is hardwired, the only way to suppress it by software is to "talk" to the transceiver in intervals under the time-out for this feature. But you can modify the hardware to permanently disable the powerdeown or make it switchable: Pin 12 of U7 has to be lifted from GND and tied to 3.3V (Pin 15 or 16) for permanent active, or wired to an unused processor pin to switch between active and auto-powerdown.
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