A small, ready-to-use TLV320ADC6140 board

This is a four-channel line-level audio ADC on a small 4-layer board. It is built around the TI TLV320ADC6140.

I needed a real ADC to test audio capture on a Raspberry Pi Pico 2 (RP2350). TI's evaluation kit costs about $200 and comes with a large USB motherboard I didn't need. I wanted something small that just works. You plug in power, I2C and the audio bus, and it runs.

What's on the board

• TLV320ADC6140 four-channel ADC, up to 768 kHz and 32-bit
• 24.576 MHz TCXO (Abracon ASTX-H11, ±2.5 ppm) as the audio master clock
• Low-noise 3.3 V LDO (TPS7A2033) for the analog supply, powered from 5 V
• Four balanced line inputs on 3-pin headers: tip, ring and sleeve
• I2C pull-ups and a shutdown pull-down already fitted
• Two solder jumpers that set the I2C address. The default is 0x4C.
• Test points for MCLK, AVDD and GND

How it works

The Pico sends 5 V, 3.3 V and I2C through an 8-pin header (J1). It configures the ADC over I2C and then drives SHDNZ high to wake it. The ADC streams TDM audio out a 6-pin header (J2): FSYNC, BCLK and SDOUT, each with a ground pin beside it. Each signal line has a 33 Ω series resistor, so jumper wires to the Pico work cleanly.

Each input is balanced line level. It is AC-coupled straight into the ADC. The ADC clips at about 2 Vrms differential (about +8 dBu). There is no phantom power.

Firmware notes

• The input coupling caps are 4.7 µF. Set a longer quick-charge time than the default.
• Set the input impedance to 10 kΩ. This gives a 3.4 Hz high-pass corner.

Assembly

All the SMD parts are on the top side. The BOM and centroid files are included. The pin headers are through-hole and soldered by hand.

Ordering:

If using the PCBA service, these are the four layers to enter if prompted.

• L1: adc-breakout-F_Cu.gbr
• L2: adc-breakout-In1_Cu.gbr
• L3: adc-breakout-In2_Cu.gbr
• L4: adc-breakout-B_Cu.gbr

Licence:

The design is licensed under CERN-OHL-W-2.0 (similar to LGPL). See LICENSE in the GitHub repo.