Microphone Functionality; Figure 17. Ts4657 Stereo Dac Output Audio Rca Connectors J1, J3 - ST STM32 User Manual

Connectors and functionality of the TS4657 audio card

Figure 17. TS4657 stereo DAC output audio RCA connectors J1, J3

LRCLK
3
SDAT
4
Digital
audio
5 BCLK
interface
MCLK
6
FMT2
7
Control interface
FMT1
8
9.5

Microphone functionality

An onboard microphone is available on the TS4657 audio card. The microphone is
connected to the microphone preamplifier TS472, which operates in single-ended output
configuration. The preamplifier output is available on the I
connected also to the ADC input pin of the STM32 MCU on the controller board.
The microphone unit U5 is supplied from the TS472 preamplifier 2.0 V bias pin. R11, R12
(1 KΩ) resistors are polarizing resistors for biasing of the microphone. C19 and C20 are
input coupling capacitors that block the DC voltage at the amplifier input pins and their value
determines also the cut-off of the low input frequencies. C18 and C23 are low pass filter
capacitors which allow to cut-off the high frequencies (100 pF ~ 20 kHz). C28 is assembled
with 0Ω resistor in order to have DC coupling between the preamplifier and the STM32
microcontroller. For AC coupling the C28 value determines also the cut-off of the low output
frequencies. The preamplifier gain can be changed by different values of the R17 resistor
(see TS472 datasheet on www.st.com). In this configuration the gain is fixed to 40 dB. R3
represents the input impedance of the following stage and is also used to charge the output
capacitor C28. R3 is assembled in the default configuration but can be safely removed. R15
is not necessary in case the standby pin connection is correctly handled on the side of the
microcontroller. TS472 has a weak pull-down resistor already embedded. If there is no
connection on the standby pin to the microcontroller, the preamplifier is in the standby mode.
The amplifier is powered from +3.3 V coming from the controller board.
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13 19
V CCA V CCD
NCP
PCP LDO
DAC
Digital
filters
DAC
GNDA
GNDD
STDBY
9
2 1
20 10
Doc ID 15867 Rev 1
18 14
U1
V REGD
LDO
V REGA
L OUT
12
820 Ω
R OUT
11
GNDD
GNDA GNDA E-PAD
15 16 17 21
2
RCA WBTOR 1
J1
GND
C10
GND
2.2 nF
R4
R5
820 Ω
C14
GND
2.2 nF
GND
J3
RCA WBTOR 1
S audio connector P1 and is
UM0722
AM00486