nRF9151 sch design problem

[sean]

Hello,

   We have a water meter project that involves cellular and GPS functionalities, and we need to design the schematic. After reviewing the hardware design guidelines, I still have some questions and would appreciate your help in answering them.

1.What are the main functions of the chip's COEX0, COEX1, and COEX2 pins? If they are used to enable/disable the GPS and cellular modules, which has higher priority: internal software control or COEX control?

2.Due to the small size of the PCB, we plan to design the GPS with a passive antenna. Can we remove the SKY15943-11 chip? If SKY15943-11 chip is not used, what other impacts might arise?

3.We need to understand the power-up sequence requirements for the chip and the timing requirements for nRESET;  How soon after power-up can the chip start running to the main function?

4.Could you provide a brief description of what the AUX pin is used for? During product design, should we pay attention to it or reserve space for it?

[ketiljo]

1.What are the main functions of the chip's COEX0, COEX1, and COEX2 pins? If they are used to enable/disable the GPS and cellular modules, which has higher priority: internal software control or COEX control?

See https://docs.nordicsemi.com/bundle/nwp_056/page/WP/nwp_054/coex_if.html

The COEX pins are controlled directly by the modem.

2.Due to the small size of the PCB, we plan to design the GPS with a passive antenna. Can we remove the SKY15943-11 chip? If SKY15943-11 chip is not used, what other impacts might arise?

You need ether an active GPS antenna, or a passive antenna with a LNA. Using only a passive GPS antenna is not recommended. https://docs.nordicsemi.com/bundle/nwp_056/page/WP/nwp_054/antenna.html

3.We need to understand the power-up sequence requirements for the chip and the timing requirements for nRESET;  How soon after power-up can the chip start running to the main function?

It highly depends on what firmware is running on your device, but in most cases it is in the hundreds of milliseconds range, depending on logging etc. in the secure-side image(s) running.

4.Could you provide a brief description of what the AUX pin is used for? During product design, should we pay attention to it or reserve space for it?

https://docs.nordicsemi.com/bundle/nwp_056/page/WP/nwp_054/aux_if.html. If you don't need it, you can leave it floating. 

[sean]

Hi，  

Thank you for your response. Regarding the third question, what we need here is a power-up sequence diagram for the power supply and nRESET. Is it possible to provide this?

Since we are turning off the power supply to the nRF9151 to save power, we need to quickly power up the chip and run the program. Could you recommend the minimum RC reset circuit parameters for the nRESET pin? Additionally, what is the minimum duration that nRESET needs to be held to ensure a hardware reset of the chip?