The CM6646 from C-Media Electronics is a highly integrated USB 2.0 high-speed audio codec designed for headphone, microphone, and headset applications. It combines USB audio control, analog audio conversion, headphone drive, an embedded MCU, and multiple external control interfaces in a single device.
The device is compliant with USB 2.0 Full-Speed and High-Speed, USB Audio Class 2.0, and USB HID Class 1.1. It supports USB suspend, resume, and reset functions together with control, interrupt, and isochronous transfers.
The integrated audio codec provides 2-channel DAC outputs and 2-channel ADC inputs. Both playback and recording support 16-, 24-, and 32-bit audio data with sampling rates of 44.1, 48, 88.2, 96, 176.4, and 192kHz, providing up to 192kHz/32-bit audio capability.
An integrated true cap-less/zero-ground headphone driver with anti-pop technology reduces the need for external output coupling capacitors and simplifies compact USB headset designs.
The CM6646 provides an analog-input-to-analog-output mixer path with independent volume control and supports two output-endpoint audio-stream mixing. It also integrates 5-band EQ for both playback and recording paths.
A standard S/PDIF digital audio output supports up to 192kHz/24-bit audio and is compatible with the AES/EBU IEC-60958 specification.
The device embeds an 8051 microcontroller with 512KB Flash. MCU clock speed is programmable from 3.072MHz to 65.536MHz, while firmware can be used to modify USB topology, communicate with external peripherals, and customize VID, PID, product strings, and other USB configuration parameters.
External control resources include one master I²C interface and one slave I²C interface, both supporting 100kHz and 400kHz operation, plus a master SPI interface supporting up to 24.576Mb/s depending on MCU clock speed. Seven programmable GPIOs and six PWM LED-driver outputs are also provided.
An integrated 7-bit SAR ADC supports combo-jack and Google-button detection. The device also includes an embedded oscillator for crystal-less operation, an integrated USB 2.0 transceiver, and a power-on-reset circuit.
The CM6646 operates from a single 5V supply and includes an internal 5V-to-3.3V regulator. Its 3.3V digital I/O pads are 5V tolerant, and both USB bus-powered and self-powered system configurations are supported.
The device is supplied in a compact 48-pin QFN package measuring 5 × 5mm. C-Media’s current official website still lists the CM6646 in its USB Audio Codec portfolio and provides an order option, but does not publish a separate Active, NRND, or Obsolete lifecycle field for the device.
Key Specifications
- Manufacturer: C-Media Electronics
- Manufacturer Part Number: CM6646
- Device Type: USB Audio Codec
- USB: USB 2.0
- USB Speed: Full-Speed / High-Speed
- USB Audio Class: UAC 2.0
- USB HID: Class 1.1
- DAC Channels: 2
- ADC Channels: 2
- Maximum Sample Rate: 192kHz
- Maximum Resolution: 32-bit
- Supported Sample Rates: 44.1 / 48 / 88.2 / 96 / 176.4 / 192kHz
- Supported Audio Width: 16 / 24 / 32-bit
- Headphone Amplifier: Integrated
- Headphone Architecture: True Cap-Less / Zero-Ground
- Anti-Pop: Supported
- Playback EQ: 5-Band
- Recording EQ: 5-Band
- Two Output Endpoint Mixing: Supported
- S/PDIF Output: Supported
- Maximum S/PDIF Format: 192kHz / 24-bit
- Embedded MCU: 8051
- MCU Clock: 3.072MHz to 65.536MHz
- Embedded Flash: 512KB
- Master I²C: 1
- Slave I²C: 1
- I²C Speed: 100kHz / 400kHz
- SPI Master: 1
- Maximum SPI Speed: 24.576Mb/s
- GPIO: 7
- PWM LED Outputs: 6
- Integrated SAR ADC: 7-bit
- Combo-Jack Detection: Supported
- Google-Button Detection: Supported
- Crystal-Less Design: Supported
- Supply: Single 5V
- Internal Regulator: 5V to 3.3V
- Digital I/O: 3.3V with 5V Tolerance
- Bus-Powered Mode: Supported
- Self-Powered Mode: Supported
- Package: QFN-48
- Package Size: 5 × 5mm
- Lifecycle: No explicit lifecycle field published on the current C-Media product page
Typical Applications
Suitable for USB headsets, USB headphones, USB microphones, gaming headsets, conferencing audio devices, USB sound cards, USB audio adapters, and other high-definition USB playback and recording products.
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