Headphones Outputs; Limitations In Using Audio Features; Usb Otg Fs Port; Stm32L4R9I-Eval Used As Usb Device - ST STM32L4R9I-EVAL User Manual

Hardware layout and configuration
9.9.2

Headphones outputs

The STM32L4R9I-EVAL board potentially drives two sets of stereo headphones. Identical or
different stereo audio content are played back in each set of headphones. STM32L4R9AII6
sends up to two independent stereo audio channels, via its SAI1 TDM port, to the WM8994
codec device. The codec device converts the digital audio stream to stereo analog signals. It
then boosts them for direct drive of headphones connecting to 3.5 mm stereo jack receptacles
on the board, CN24 for Audio-output1 and CN23 for Audio_output2.
The CN23 jack takes its signal from the output of the WM8994 codec device intended for
driving an amplifier for loudspeakers. A hardware adaptation is incorporated on the board to
make it compatible with a direct headphone drive. The adaptation consists of coupling
capacitors blocking the DC component of the signal, attenuator and anti-pop resistors. The
loudspeaker output of the WM8994 codec device must be configured by software in linear
mode called "class AB" and not in switching mode called "class D".
The I²C-bus address of WM8994 is 0b0011 010x.
9.9.3

Limitations in using audio features

Due to the share of some terminals of STM32L4R9AII6 by multiple peripherals, the following
limitations apply in using the audio features:
•
If the SAI1_MCLKA and SAI1_FSA are used as part of SAI1 port, it cannot be used as
CAN peripheral.
• If the SAI1_SDB is used as part of SAI1 port, it cannot be used as Comp2_OUT signal.
•
If the SAI1 port of STM32L4R9AII6 is used for streaming audio to the WM8994 codec
IC, STM32L4R9AII6 cannot control the motor.
•
If the digital microphones are attached to STM32L4R9AII6, control the motor cannot be
driven.
9.10

USB OTG FS port

The STM32L4R9I-EVAL board supports USB OTG full-speed (FS) communication. The
USB OTG connector CN3 is Micro-AB type.
9.10.1

STM32L4R9I-EVAL used as USB device

When a "USB host" connection to the CN3 Micro-AB USB connector of STM32L4R9I-EVAL
is detected, the board starts behaving as "USB device". Depending on the powering
capability of the USB host, the board potentially takes power from VBUS terminal of CN3. In
the board schematic diagrams, the corresponding power voltage line is called U5V.
Section 9.5
The resistor R23 must be left open to prevent STM32L4R9I-EVAL from sourcing 5 V to VBUS
terminal, which would cause conflict with the 5 V sourced by the USB host. This may happen
if the MFX_GPIO6 is controlled by the software of the MFX MCU such that, it enables the
output of U2 power switch.
9.10.2

STM32L4R9I-EVAL used as USB host

When a "USB device" connection to the CN3 Micro-AB USB connector is detected, the
STM32L4R9I-EVAL board starts behaving as "USB host". It sources 5 V on the VBUS
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provides information on how to set associated jumpers for this powering option.
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