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 bi-directional input thresholds. This terminal may be used with a switch to V_SUP or ground. If the terminal is not used it should be pulled to ground to avoid unwanted parasitic wake up events.

The WAKE terminal defaults to bi-directional input but can be 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 needs to be at either a low state or high state for t_WAKE before a state transition for a WAKE input can be determined.

There are two other wake methods that can be 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 will wake or not wake. 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 can be configured as a filtered wake input. Writing a 1b to this bit will disable 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 will turn on and device will enter 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 can be determined from register 11h[5:4]. When a WAKE pin change takes place, the device will register 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 may look like a LWU event and could be 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