Apollo3 SIMOBUCK Q&A

Full question(s):

I am using Apollo3 deep sleep example code to test current on my board and Apollo3 EVB. The current on my board is much higher (200uA @ 1.8V) than the current on EVB. After swapping the simobuck inductors for my board and EVB，the big current follows with the inductor from my board. The inductor on my board has much lower saturation current comparing with the inductor on EVB. What is the recommendation of Apollo3 SIMOBUCK inductor?

Answer(s):

1. For operation across full voltage range (1.755V - 3.63V), recommend to use 2.2uH high saturation current (>400mA) inductor. Inductor with saturation current > 500mA is preferred for best efficiency. Inductor's max DC resistance should be less than 0.55 ohm and inductor's operating frequency should be more than 20MHz.

2. Inductors with a saturation current 120mA – 400mA can be used within limited voltage range(1.755V -  1.90V) at limited temperature range (-20C to 60C). To implement this,  simobuck ton, toff, and zero crossing trim settings need to be changed for Apollo3 B0 silicon. Those trim settings can be changed by adding following code at the very beginning of the user code when apollo3 first powers up.

*(uint32_t *)(0x40020354) = ((*(volatile uint32_t *)(0x40020354)) & 0xFF000FFF) | (0x0032A000);
*(uint32_t *)(0x40020358) = ((*(volatile uint32_t *)(0x40020358)) & 0x807F0000) | (0x1D001625);
*(uint32_t *)(0x4002035C) = ((*(volatile uint32_t *)(0x4002035C)) & 0xFFFFC3F0) | (0x00002803);

(Note: These trim changes only apply to Apollo3 B0 silicon. They are not needed for Apollo3 A1 silicon)

For more details, please refer to following Low Saturation Current Inductor PVT Validation Report.