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Design Guideline: Selecting Proper Inductors for the BLE and SIMO Bucks on Apollo3 MCUs

Grant Whitacre
  • Updated

Overview

This design guideline describes the recommended BLE and SIMO buck inductors for Apollo3 MCUs.

 

Applicable Silicon Revisions and Packages

This design guideline applies to all versions and packages of Apollo3 MCUs.

 

Application Impact

Following these recommendations ensures that the Apollo3's internal rails are properly maintained throughout all modes of operation of the MCU, and that brownouts are less likely to occur.

 

Guidelines

Requirements for Inductor Characteristics

BLE Buck

For operation across Apollo3's full voltage range of 1.755 V - 3.63 V, it is recommended to use an inductor with the following characteristics:

  • 1 uH
  • Saturation current > 800 mA, e.g., < 20% loss at 1 A current
  • Maximum DC resistance < 0.55 ohms
  • Operating frequency range > 20 MHz

Proposed part:  Murata DFE18SAN1R0ME0 (0603)

SIMO Buck

For operation across the full voltage range, it is recommended to use an inductor with the following characteristics:

  • 2.2 uH
  • Saturation current > 400 mA (> 500 mA preferred)
  • Maximum DC resistance < 0.55 ohms
  • Operating frequency range > 20 MHz

Proposed part: Murata DFE201610E-2R2M=P2 (0806) or Taiyo Yuden MBKK1608T2R2M (0603)

The  above saturation current requirements can be relaxed to 120 mA – 400 mA when operating within a limited voltage range of 1.755 V - 1.90 V, and limited temperature range of -20 C to 60 C.

 

Required SIMO Buck Software Settings for Revision B0

To configure for the above relaxed inductor requirements with < 400 mA saturation current,  the simobuck ton, toff, and zero crossing trim settings need to be changed for Apollo3 B0 silicon. Those trim settings can be changed by adding the following code at the very beginning of 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.

 

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