BelaSigna R262
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Table 5. NON−CRITICAL SIGNALS
Pin Name Description Connection Guidelines
CAP0, CAP1 Internal charge pump −
capacitor connection
Place 100 nF capacitor very close to pins
I2C_SDA, I2C_SCL I
2
C port
Keep as short as possible. Place pull−up resistors (10 kW) to VDDO
SWAP_CHAN Control GPIO Not critical when used as GPIO
CLOCK_SEL,
BOOT_SEL,
CHAN_SEL and
ALPHA_SEL
Low−speed A/D converters
(Multiplexed with SPI port)
Not critical when used as LSAD
Place resistive divider for hardware configuration of BelaSigna R262
SPI_CLK, SPI_CS,
SPI_SERO,
SPI_SERI
Serial peripheral interface port
(Multiplexed with LSAD and
GPIOs)
Keep away from analog input lines when used as SPI signals
NRESET Reset Not critical
Leave unconnected if unused
DEBUG_RX,
DEBUG_TX
Debug Port Not critical
If possible, connect to test points, otherwise connect DEBUG_RX to VDDO
and leave DEBUG_TX floating
RESERVED Reserved pin Leave unconnected or connect to VSSA if PCB routing constraints force it
VBATRCVR Output driver power supply If the output driver is being used:
− Place a separate 4.7 mF (min. 2.2 mF) decoupling capacitor close to pin
− Connect positive terminal of capacitor to VBAT & VBATRCVR
− Connect negative terminal of capacitor to VSSRCVR
If the analog outputs or the DMIC output are being used:
− Separate decoupling capacitor on VBATRCVR is not required
− Connect VBATRCVR to VDDA (which has its own decoupling capacitor)
Audio Inputs
The audio input traces should be as short as possible. The
input impedance of each audio input pad (e.g., MIC0, AI1,
MIC2, AI3) is high (approximately 500 kW with
preamplifiers enabled); therefore a 10 nF capacitor is
sufficient to decouple the DC bias. This capacitor and the
internal resistance form a first−order analog high pass filter
whose cut−off frequency can be calculated by
f
3dB
(Hz) = 1/(R x C x 2π), which results in ~30 Hz for a
10 nF capacitor. This 10 nF capacitor value applies when the
preamplifier is being used, in other words, when a non−unity
gain is applied to the signals; for MIC0 and MIC2, the
preamplifier is enabled by the ROM−based application.
When the preamplifier is bypassed, the impedance is
reduced; hence, the cut−off frequency of the resulting
high−pass filter could be too high. In such a case, the use of
a 30−40 nF serial capacitor is recommended. In cases where
line−level analog inputs without DC bias are used, the
capacitor may be omitted for transparent bass response.
ON Semiconductor recommends the use of NPO/COG
dielectric for SMT capacitors, as they have demonstrated
better performance compared to other capacitors with X7R
dielectric.
Microphone Power Supply
BelaSigna R262 provides a microphone power supply
(VMIC) and ground (VSSA). In case VMIC cannot be used
because of PCB routing constraints, the power supplies
VREG (1.0 V) or VDDA (2.0 V) can alternatively be used.
Keep audio input traces strictly away from output traces.
Audio outputs must be kept away from microphone inputs
to avoid cross−coupling.
Audio Outputs
The audio output traces should be as short as possible. The
trace length of the two signals should be approximately the
same to provide matched impedances.
Recommendation for Unused Pins
Table 6 shows the connection details for each pin when
they are not used.
Table 6. UNUSED PIN RECOMMENDATIONS
Signal Name Connection Guidelines
A_OUT0 Do not connect
A_OUT1 Do not connect
AI3/VMIC/LOUT0 Do not connect
AI1/LOUT1 Connect to VSSA
DMIC_OUT Do not connect
SWAP_CHAN Do not connect
NRESET Do not connect
