BelaSigna 200
Table 2: Non-Critical Signal
Pin Name
Description
Routing Guideline
CAP0, CAP1
Internal charge pump - capacitor connection
Place 100nF capacitor close to pins
Not critical
Connect to test points
DEBUG_TX, DEBUG_RX
Debug port
TWSS_SDA, TWSS_CLK
GPIO[14..0]
TWSS port
Not critical
Not critical
General-purpose I/O
General-purpose I/O
GPIO[15]
Determines voltage mode during boot. For 1.8V operation,
should be connected to DGND
Not critical
UART_RX, UART_TX
General-purpose UART
Not critical
Not critical
PCM_FRAME, PCM_CLK, PCM_OUT,
PCM_IN
Pulse code modulation port
I2S_INA, I2S_IND, I2S_FA, I2S_FD,
I2S_OUTA, I2S_OUTD
Philips I²S compatible port
Not critical
Not critical
DCLK
Programmable clock output
Low-speed A/D converters
If used, keep away from analog
inputs/outputs
LSAD[5..0]
Not critical
SPI_CLK, SPI_CS, SPI_SERI,
SPI_SERO
Serial peripheral interface port
Connect to EEPROM
Not critical
3.3 Audio Inputs
The audio input traces should be as short as possible. The input impedance of each audio input pad (e.g., AI0, AI1, etc.,) is high
(approximately 500kΩ); therefore a 10nF capacitor is sufficient to decouple the DC bias1. Keep audio input traces strictly away from
output traces. Microphone ground terminals should be connected to the AGND plane (if present) or share a trace with the input ground
reference voltage pin (AIR) to the star point.
Analog and digital outputs MUST be kept away from microphone inputs.
3.4 Audio Outputs
The audio output traces should be as short as possible. If the direct digital output is used, the trace length of RCVRx+ and RCVRx-
should be approximately the same to provide matched impedances. If the analog audio output is used, the ground return for the
external power amplifier should share a trace with the output ground reference voltage pin (AOR) to the star point.
1 The capacitor and the internal resistance form a first-order analog high pass filter whose cutoff frequency can be calculated by f3dB (Hz) = 1/(RC2π), which results with
~30Hz for 10nF capacitor.
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