We are using MC60 module and using External watchdog circuit, I am referring to Quectel_OpenCPU_Watchdog_Application_Note_V1.0.pdf.
But it’s not clear how does Startup Circuit mentioned in this document works. The startup Circuit is supposed to automatically pulldown the PWRKEY momentarily as soon as VBAT is supplied by the watchdog. But it is not clean how does this Startup Circuit works. Can anyone please explain?
When the PWRKEY pin is connected to a 100uF large capacitor, the PWRKEY pin will be pulled down and the module will be turned on. The watchdog circuit can power on and off the module again when encountering abnormal conditions.
@Jouni.yang-Q
What is the purpose of R5 (NM_0R) resistor in the startup circuit? Is this an 0ohm resistor?
NM means that the device is not attached to the actual circuit. The main purpose is to be compatible with the design. If a 0 ohm resistor is attached, the PWRKEY pin will be pulled low all the time, and it will automatically turn on when it is powered on.
Q1. >>>When the PWRKEY pin is connected to a 100uF large capacitor, the PWRKEY pin will be pulled down and the module will be turned on.
Does the PWRKEY is pulled down momentarily (to send 1 second low pulse on PWRKEY) OR it remains pulled down all the time?
Q2. In the Startup circuit design C1(100uF large capacitor) is connected to VBAT with Schottky Diode D2, what is the purpose of this diode?
A1: PWRKEY is temporarily pulled down, and PWRKWY will become high after the capacitor is charged.
A2: This diode is mainly used for discharging the 100UF capacitor after the module is turned off, and for the next time it is powered on.
