Power supply design is one of the main factors in achieving good RF performance, low current consumption, and reliable behavior of a product over its life time in various conditions. VDD1 (pin 102) and VDD2 (pin 22) are the main power supply inputs for nRF9160 and form the combined VDD.
VDD1 is connected to the DC converter input of the nRF9160-internal PMU that supplies the System on Chip (SoC). VDD2 is connected to the DC converter input of the nRF9160-internal PMU that supplies the RF Power Amplifier (PA). The operational voltage of VDD1 and VDD2 ranges from 3.0 V to 5.5 V. To comply with the RF performance specifications in Electrical specification in nRF9160 Product Specification, the inbuilt LTE modem transceiver is not recommended to be used below 3.3 V, even though nRF9160 can operate down to 3.0 V.
To ensure the operation described in nRF9160 Product Specification it is important to prevent voltage drops and ripple below 3.3 V in VDD. Voltage drop is most likely to occur during LTE transmit. This is due to peaks of up to 500 mA/3.3 V happening during VDD2 current consumption. VDD must not drop below 3.0 V during any nRF9160 operation. To minimize supply voltage ripple and suppress EMI coupling to/from nRF9160, it is recommended to place low ESR capacitors close to the VDD1 and VDD2 pins. Supply capacitors of low ESR (<0.1 Ω) are recommended.
To improve power delivery, voltage ripple, and EMI performance, it is recommended to have at least one low ESR supply capacitor C3 in VDD1 and C10 in VDD2. Placing ferrite bead FB1 at VDD1 is highly recommended. To further improve filtering for high-frequency components, you can optionally add C1 and C2 to VDD1, and C8 and C9 to VDD2. The components' electrical values may vary depending on the application, but for C1 and C8 the recommended range is from 10 pF to 100 pF, whereas for C2 and C9 the recommended range is from 1 nF to 470 nF.
For VDD_GPIO, the minimum recommendation is low ESR supply capacitor C6. Filtering for high-frequency components can be improved by adding C5 in the range of 1 nF to 470 nF.
To improve the supply network's EMI performance, a series three terminal filter capacitor can be added close to the battery. For example, Murata NFM15PC can be used. The filter capacitor attenuates unwanted noise generated at wide frequency range approximately from 10 MHz to 3 GHz.