The guidelines to design a system with the lowest suspend mode current are listed below.
1. VUSB pin of CX3 to be connected to 3.3V instead of 5V (The firmware will need relevant modifications accordingly).
2. Provision to switch off all other elements in the system should be available. Only CX3 should be active/powered in the entire system. It should also be ensured that the standby current drawn by the other power regulators in the system should be negligible (when the regulators are disabled/shut off)
3. Very high efficiency switching regulators must be used to power the CX3 chip (1.2V, 1.8V and 3.3V). As per the above calculation the efficiency needs to be at least 85% at low currents. The below part numbers can be considered (owing to their high efficiency at low currents).
4. A low power 19.2 MHz clock oscillator chip must be used. The above estimate considers a current of 1 mA at 1.8V.
5. It must be ensured in the system design that the standby currents of the turned off regulators are negligible and do not add up to a significant value (choose regulators suitably).
6. There must be provision in the design to disconnect the below circuits while entering suspend mode. The same has to resumed once out of suspend. VDDIO2, VDDIO3,VDD_MIPI, REFCLK