The device enters a brownout condition when the input voltage drops below Vbrownout (see Figure 8-4 and Figure 8-5). This condition must be considered during design of the power supply routing, especially when operating from a battery. High-current operations, such as a TX packet or any external activity (not necessarily related directly to networking) can cause a drop in the supply voltage, potentially triggering a brownout condition. The resistance includes the internal resistance of the battery, the contact resistance of the battery holder (four contacts for 2× AA batteries), and the wiring and PCB routing resistance.
When the device is in HIBERNATE state, brownout is not detected. Only blackout is in effect during HIBERNATE state.
In the brownout condition, all sections of the device (including the 32-kHz RTC) shut down except for the Hibernate module, which remains on. The current in this state can reach approximately 400 µA. The blackout condition is equivalent to a hardware reset event in which all states within the device are lost.
Table 8-1 lists the brownout and blackout voltage levels.