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 VSUP 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 10-14 and Figure 10-15, 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 tWAKE before a state transition for a WAKE input can be determined.
There are two other wake methods that can be utilized 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 tWAKE_INVALID will be filtered out for both the pulse and filtered wake configurations. For the pulse configuration, the pulse must be between tWK_WIDTH_MIN and tWK_WIDTH_MAX, see Figure 10-16. This figure provides three examples of pulses and whether the device will wake or not wake. tWK_WIDTH_MIN is determined by the value for tWK_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, WAKE_WIDTH_MAX_DIS, the pulse mode can be configured as a filtered wake input. Writing a 1 to this bit will disable tWK_WIDTH_MAX and the WAKE input will be based upon the configuration of register 11h[3:2] which selects a tWK_WIDTH_INVALID and tWK_WIDTH_MIN value. A WAKE input of less than tWK_WIDTH_INVALID will be filtered out and if longer than tWK_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 10-17. Register 12h 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 will be latched until a 00 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 VSUP, 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.
When either a rising or falling edge is selected for the WAKE pin the state prior to the edge requires a tWAKE period of time.