VDD_GPIO = 1V8, external LDO needed?

Question

Hello Nordic team and fellow developers, 
 We are now making our custom board, and have a few questions: 
 1. MAGPIO gets 1V8 internally, but COEX needs it from VDD_GPIO. There are no 1V8 pins available to supply the VDD_GPIO pin, so this needs to come externally. In our design, this is the only need for VDD_GPIO. Are there any way we can make a design which uses the internal 1V8 for COEX/VDD_GPIO, so we won't have to implement a LDO/PMIC only for this? I've read that the SIM_1V8 can not be used for anything other than the SIM-card. 
 2. Marketing materials for the nRF9160 shows PMIC included in the SiP, but the designs I've seen still use an external PMIC. I suspected this is mainly for battery charging. Are we missing something obvious here? Can we somehow skip the external PMIC all together? (Somewhat related to question 1). 
 Thank you all for all and any help! 
 Kind regards, 
 Torje

helsing · Accepted Answer

Hi Torje, 
 
 Are there any way we can make a design which uses the internal 1V8 for COEX/VDD_GPIO I am not aware of any way to supply VDD_GPIO with 1V8 from an internal voltage. , so we won't have to implement a LDO/PMIC only for this? One option is to supply both VDD and VDD_GPIO from the same voltage source. The operating voltage range of your device will then be restricted by the operating range for both VDD and VDD_GPIO which now becomes 3.3V(3.0V) to 3.6V. Numbers are taken from PS, Table 1 . In our design, this is the only need for VDD_GPIO Here is an idea: If the only 1V8 communication with other devices is via COEX, then perhaps you could power VDD_GPIO with the same voltage as VDD, and then use a voltage divider on COEX in order to lower the voltage down to the desired range? After all, COEX could be configured to only be high for a limited amount of time. Let me know if this is something you would want us to look into. You would have to consider the input impedance of the device you are communicating with and test that this works as expected. 
 Can we somehow skip the external PMIC all together? Yes, you may supply VDD directly from the battery. However, regulating the voltage could potentially give you a longer battery life, depending on various conditions like battery voltage, battery type, ambient temperature and your application. Regulation VDD becomes even more important if your operating voltage range is limited by the choice of supplying VDD and VDD_GPIO with the same voltage(as mentioned above).

VDD_GPIO = 1V8, external LDO needed?

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