The WAKE terminal is a ground biased input terminal that can support high voltage wake inputs used for local wake up (LWU) request via a voltage transition. The terminal triggers a LWU event on either a low to high or high to low transition as it has bidirectional input thresholds. This terminal may be used with a switch to V_SUP or ground. If the terminal is not used, pull the terminal to ground to avoid unwanted parasitic wake up events.

The WAKE terminal defaults to bidirectional input, but is configured for rising edge and falling edge transitions (see Figure 8-15 and Figure 8-16), by using WAKE_CONFIG register 11h[7:6]. Once the device enters sleep mode, the WAKE terminal voltage level must be at either a low state or high state for t_WAKE before a state transition for a WAKE input is determined.

There are two other wake methods that are used with the WAKE pin, a pulse wake and a filtered wake. For the pulsed wake input, a pulse on the WAKE pin must be within a specified time to be considered valid. A pulse width less than t_{WAKE_INVALID} is filtered out for both the pulse and filtered wake configurations. For the pulse configuration, the pulse must be between t_{WK_WIDTH_MIN} and t_{WK_WIDTH_MAX}, see Figure 8-17. This figure provides three examples of pulses, and whether the device wakes or not. t_{WK_WIDTH_MIN} is determined by the value for t_{WK_WIDTH_INVALID} which is set by register 11h[3:2]. There are two regions where a pulse may or may not be detected. By using register 1Bh[1], WAKE_WIDTH_MAX_DIS, the pulse mode is configured as a filtered wake input. Writing a 1b to this bit disables t_{WK_WIDTH_MAX}, and the WAKE input is based upon the configuration of register 11h[3:2] which selects a t_{WK_WIDTH_INVALID} and t_{WK_WIDTH_MIN} value. A WAKE input of less than t_{WK_WIDTH_INVALID} is filtered out, and if longer than t_{WK_WIDTH_MIN}, INH turns on, and the device enters standby mode. The region between the two may or may not be recognized, see Figure 8-18. Register 12h[7] determines the direction of the pulse or filter edge that is recognized. The status of the WAKE pin is determined from register 11h[5:4]. When a WAKE pin change takes place, the device registers this as a rising edge or falling edge. This is latched until a 00b is written to the bits.

The LWU circuitry is active in sleep mode, standby mode and transition state of going to sleep. If a valid LWU event occurs the device transitions to standby mode. The LWU circuitry is not active in normal mode. A constant high level on WAKE has an internal pull up to V_SUP, and a constant low level on WAKE has an internal pull down to GND. On power up, this looks like a LWU event, and is flagged as such.

Figure 8-15 Local Wake Up – Rising Edge

Figure 8-16 Local Wake Up – Falling Edge

Figure 8-17 WAKE Pin Pulse Behavior

Figure 8-18 WAKE Pin Filtered Behavior