Bluetooth LE Output Power configuration is required to manage the application's RF range and power consumption depending on the customer's needs.
This wiki page describes how to properly configure output power in a Bluetooth LE application from HW and SW point of view.
- Chapter 1 provides details about Hardware configuration.
- Chapter 2 provides details about Software configuration.
- Chapter 3 provides summary about Hardware & Software configuration depending on customer's needs.
1. STM32WBA Bluetooth® LE hardware configuration for maximum Output Power
On an STM32WBA device, RF output power level depends on:
- PA output power table
- VDDRFPA input voltage.
For LDO variant of STM32WBA, VDDRFPA pin must be connected to VDD.
For SMPS variant of STM32WBA, VDDRFPA can be connected either to VDD11 or directly to VDD.
- If connected to VDD11, you’ll have optimized current consumption, but output power is maximum limited to 3 dBm.
- If connected to VDD, output power can be up to 10 dBm.
| Hardware Output power configuration |
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If targeting more than 10 dBm output power, an external PA should be used.
| Transmit path and output power control |
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1.1. STM32WBA VDDRFPA voltage level vs output power
The following table resumes the minimum VDDRFPA value required to reach the maximum transmit output power through internal PA
2.4 GHz RADIO Supply Configuration
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1.2. STM32WBA ST evaluation boards hardware configuration vs output power
The STM32WBA boards offer different possible Output Power configuration by simple PCB board modifications summarized in the following table:
STM32WBA Transmit output power PCB configuration
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- *For STM32WBA5M module, VDDRFPA is connected internally to VDD for maximum RF power. For more detail, refer to the STM32WBA5MMG Datasheet DS14801 [1]
2. STM32WBA Bluetooth® LE Output Power Software configuration
2.1. STM32WBA Power Table Selection
A power table defines the possible values of PA_Level that can be selected in application. Only one power table can be selected, and it must be aligned with hardware configuration presented in previous chapter.
The following table summarizes the four given power tables:
STM32WBA Power Tables
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*For more details about power tables and PA_Level values you can refer to the STM32WBA BLE Wireless Interface Documentation.[2]
Power tables can be configured through STM32CubeMx as follow:
| STM32CubeMX Power Tables configuration |
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After code generation, power table ID can be found with CFG_RF_TX_POWER_TABLE_ID under app_conf.h.
2.2. In application TX Power configuration commands
After system reset, by default, the application select the maximum supported TX power value (PA_Level). This value can be modified with:
•aci_hal_set_tx_power_level() command: Once this command is given, the output power changes instantly, regardless if there is a BLE communication going on or not.
•aci_gap_adv_set_configuration_v2() command: Used to set the extended advertising configuration for one advertising set.
TX power value is kept until next reset or until overwritten by one of the latest two commands. To properly configure the TX power value, The CFG_TX_POWER (PA_Level) value must be aligned with the selected power table. Refer to the TX Power Level table in the STM32WBA BLE Wireless Interface Documentation.[2]
| TX Power Level |
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2.3. LE Power Control feature
The LE Power Control feature allows a Bluetooth LE device to dynamically adjust its RF transmit power based on link quality (e.g. RSSI). The goal is to maintain a reliable connection while reducing power consumption by avoiding sending at maximum TX power when it is not needed. The Bluetooth LE power control is only available on some libraries and on connected state:
LE Power Control
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The LE Power control variation is not impacted by TX Power configuration commands; the variation will follow the power table range.
Example: The application uses a power Table ID 0 “Up to +10 dBm” and set the legacy advertising TX power to +7 dbm with aci_hal_set_tx_power_level().
Advertising: TX power will be +7 dbm.
Connected state: if LE power Control Not supported: TX power will be +7 dbm.
Connected state: if LE power Control supported: TX power will vary from -20 dbm to +10 dbm.
2.3.1. LE Power Control Customization
Customer can cap LE Power Control range by removing extra values in used table in power_table.c file:
| LE Power Control Customization |
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3. STM32WBA Bluetooth® LE Output Power Configuration summary
The following figure summarizes the STM32WBA RF output power HW and SW configuration.
| STM32CubeMX Power Tables configuration |
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- Power consumption recommendation: for an application requiring no more than 3dBm RF output power, it is recommended to connect VDDRFPA to VDD11.
4. References