LC79D standby mode

We want to implement standby mode for board with LC79D.
According to the datasheet, power off should looks like this:

  • Host processor detect, that main power is switched off
  • External active antenna power switched off by hardware, LC79D continue to work on backup battery/capacitor
  • Host processor issue $PQSTOPGNSS command to LC79D
    (GNSS module write to NVM and continue to draw full current, 40+ mA)
  • Host processor need to wait until the command above will be executed
    (what is timing here ? 100us, 1ms, 10ms, 100ms ? )
  • Host processor driving NSTANDBY low with open collector
    circuit, GNSS module switched off (what is timing here ?
    100us, 1ms, 10ms ?) and draw 15 uA standby current from backup battery.

Power on procedure looks simple:
Do not drive NSTANDBY

So, we have few questions.

  • What is minimal timing between end of the $PQSTOPGNSS command and
    driving NSTANDBY low ? What happens, if host processor put NSTANDBY low
    immediately after end of $PQSTOPGNSS command ?
  • What is timing between driving NSTANDBY low and GNSS module
    switching off to the standby mode ?

Dear Avlad,
I’m sorry for the delay.
1, When the ACK of $PQSTOPGNSS is received, you could drive the NSTANDBY low. If host processor put NSTANDBY low immediately, the module will enter standby mode immediately but some parameters may not be saved.

2, The standby mode is controlled by NSTANDBY pin. When drive NSTANDBY low, the GNSS module enter standby mode immediately.

Please note that the TTFF of Standby mode without LTO is a bit longer. Please refer to LC79D_Low power consumption TTFF time verification_20200824 for TTFF & Quectel_LC79D_Hardware_Design_V1.0 for power consumption.

Best Regards

Hello Berton.Peng,
looking at the data in the Excel sheet it seems that without LTO the Standby mode is equivalent to cold start. Isn’t it strange comparing to modules like L86 or L96? I’ve created separate thread for this discussion, so please answer it there if you have any ideas.
Thank you