The TCAN28xx line of devices includes 3 WAKE pins that can be used as local wake-up signals to the device that are called WAKE1, WAKE2, and WAKE3/DIR. Local wake-up pins can be configured to send a wake-up signal on a falling edge, rising edge, or pulse input on these pins. Local wake ups can transition the SBC out of sleep mode when the signals are received. A potential use case of this feature is to initialize a device wake-up on the closing of a car door – assume that there is a hall-effect sensor on the door to the vehicle that is wired to push the WAKE pin high when the door closes – this can be used to wake-up the SBC upon vehicle door closing as this can indicate that the vehicle can have passengers inside and IC functionality can be needed at that point.

The LWU pins do have alternative functions beyond standard wake pins. WAKE1 and WAKE2 can be used in battery monitoring applications.

Figure 7-1 WAKE1/WAKE2 Alternative Function: Battery Monitoring with External ADC

In a battery monitoring application WAKE1 and WAKE2 are no longer LWU pins but instead act as the input and output of an analog switch. Before WAKE1 is a resistance that helps to limit current through the switch path as well as decoupling capacitor to GND. The battery signal is then transmitted through the switch and goes to a resistor divider to attenuate the voltage before this is moved to an external ADC (which can be integrated into the companion controller). The WAKE pins are capable of working up to 40V, so with a few additional resistors a battery monitoring circuit that attenuates the voltage before the ADC to prevent damage can easily be constructed if 3 local wake sources are unneeded in application.

WAKE3 also has an alternate function – as a direct drive input for the HSS module. Essentially WAKE3/DIR can be used to close/open any switch of combination of switches in the HSS module from an external source. If the HSS configuration options do not meet the systems needs WAKE3/DIR used as a direct drive pin can open up the control of the HSS module to a much larger pool of inputs.

Figure 7-2 WAKE3 Alternative Function: Direct Drive for HSSx Module

While not directly an “alt function” of the wake pins – a common use case is to actually use HSS4 as a cyclic sensing wake source. During cyclic sensing wake the HSS4 module is tied to a timer (either timer1 or timer2) and the HSS4 output is directly connected to the WAKE pin – so during sleep mode HSS4 will put a signal onto the WAKE pin line to wake up the device periodically during sleep – and this can also be used in fail-safe mode as well.

Figure 7-3 Application Showing HSS4 and WAKE1 Connected for Cyclic Sensing Wake