STM32WB55CCU6TR datasheet(22/193 Pages) STMICROELECTRONICS

22 / 193 page

Functional overview

STM32WB55xx STM32WB35xx

22/193

DS11929 Rev 10

3.5

Boot modes and FW update

At startup, BOOT0 pin and BOOT1 option bit are used to select one of three boot options:



Boot from user Flash



Boot from system memory



Boot from embedded SRAM

The devices always boot on CPU1 core. The embedded bootloader code makes it possible

to boot from various peripherals:



USB



UART



I2C



SPI

Secure Firmware update (especially BLE and 802.15.4) from system boot and over the air is

provided.

3.6

RF subsystem

The STM32WB55xx and STM32WB35xx embed an ultra-low power multi-standard radio

Bluetooth® Low Energy (BLE) and 802.15.4 network processor, compliant with Bluetooth®

specification v5.0 and IEEE® 802.15.4-2011. The BLE features 1 Mbps and 2 Mbps transfer

rates, supports multiple roles simultaneously acting at the same time as Bluetooth® Low

Energy sensor and hub device, embeds Elliptic Curve Diffie-Hellman (ECDH) key

agreement protocol, thus ensuring a secure connection.

The Bluetooth® Low Energy stack and 802.15.4 Low Level layer run on an embedded Arm®

Cortex®-M0+ core (CPU2). The stack is stored on the embedded Flash memory, which is

also shared with the Arm® Cortex®-M4 (CPU1) application, making it possible in-field stack

update.

3.6.1

RF front-end block diagram

The RF front-end is based on a direct modulation of the carrier in Tx, and uses a low IF

architecture in Rx mode.

Thanks to an internal transformer at RF pins, the circuit directly interfaces the antenna

(single ended connection, impedance close to 50 Ω). The natural bandpass behavior of the

internal transformer, simplifies outside circuitry aimed for harmonic filtering and out of band

interferer rejection.

In Transmit mode, the maximum output power is user selectable through the programmable

LDO voltage of the power amplifier. A linearized, smoothed analog control offers clean

power ramp-up.

In receive mode the circuit can be used in standard high performance or in reduced power

consumption (user programmable). The Automatic gain control (AGC) is able to reduce the

chain gain at both RF and IF locations, for optimized interference rejection. Thanks to the

use of complex filtering and highly accurate I/Q architecture, high sensitivity and excellent

linearity can be achieved.

The bill of material is reduced thanks to the high degree of integration. The radio frequency

source is synthesized form an external 32 MHz crystal that does not need any external

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