To disable the +1.2V internal regulator, a pull-up strapping resistor should be connected from the REGOFF configuration strap to VDD2A.
At power-on, after both VDDIO and VDD2A are within specification, the transceiver will sample REGOFF to determine whether the internal regulator should turn on.
If the pin is sampled at a voltage greater than V IH , then the internal regulator is disabled and the system must supply +1.2V to the VDDCR pin. The VDDIO voltage must be at least 80% of the operating voltage level (1.44V when operating at 1.8V, 2.0V when operating at 2.5V, 2.64V when operating at 3.3V) before voltage is applied to VDDCR.
As described in Section 3.7.3.2, when REGOFF is left floating or connected to VSS, the internal regulator is enabled and the system is not required to supply +1.2V to the VDDCR pin.