SCHS463 May   2025 CD3268A , CD3269A

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements
  7. 6 Parameter Measurement Information
    1. 6.1 eN-MIC Microphone Integrated Noise Measurement
    2. 6.2 Current Measurements
    3. 6.3 MICPWR Output Voltage Measurement
    4. 6.4 Tone Mode Threshold Measurements
    5. 6.5 Impedance Measurements
    6. 6.6 Tone Mode Output Measurements
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Tone Mode Start-up Timing
      2. 7.3.2 Authentication
      3. 7.3.3 Shunt Regulator
      4. 7.3.4 Power-on-reset
    4. 7.4 Device Functional Modes
      1. 7.4.1 Button Mode
      2. 7.4.2 Tone Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
      2. 9.1.2 Development Support
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.4.2 Tone Mode

When the CD326x detects a value higher than the rising tone mode threshold voltage (2.35V typical) on the MIC pin, the CD326x enters tone mode. When the device transitions to tone mode while supplying voltages below the tone mode threshold voltage, the overshoot voltage from the supply temporarily pushes the MIC pin voltage above the threshold. Decreasing the ramp of the supply or reducing the supply voltage are both options to reduce the inrush current leading to this functionality.

Figure 7-5 shows the start-up sequence for when the CD326x enters tone mode. Upon entering tone more, the device opens the switch that connects the MIC and REM pins (Switch B). After a predetermined delay, the device shorts the VSHUNT pin and the MICPWR pin (Switch A). This functionality aids in preventing unwanted noise from the internal circuitry being mixed onto the microphone bias line. Following another predetermined delay, the CD326x sends an acknowledge tone sequence as described in Section 7.3.2.

When a microphone is biased and in use, the switch-resistor network used for button mode causes large DC level shifts in the bias voltage. This level shift can result in unwanted, audible clicks, pops, or de-biasing of the microphone. To prevent these results, when the CD326x enters tone mode, the CD326x disconnects the switch-resistor network from the microphone bias line, provides power to an external microphone through a shunt regulator, and engages a tone generation circuit. The TONE pin AC couples the tones onto the microphone bias line for a specially enabled audio interface to interpret. Using the output from the MICPWR pin, the external microphone can be biased directly or through an external circuit as shown in Figure 8-1.

During a typical application where IMICPWR falls between 120µA and 150µA, the MICPWR pin provides a voltage from 1.51V to 1.61V (1.56V typical, see VMICPWR). Leaving the MICPWR pin floating or drawing current outside of these limits results in voltage exceeding the MICPWR output voltage specifications. Additionally, increasing the voltage on the MIC pin above 2.5V drives the MICPWR output voltage above 1.61V.

CD3268A CD3269A Tone Mode Power-up Sequence Figure 7-5 Tone Mode Power-up Sequence

For accuracy, the CD326x transmits two tones for each button press as shown in Figure 7-6. The first tone is enabled for a period of 0.9ms and is a calibration frequency. The second tone is enabled for a period of 1.8ms and is the unique frequency for the selected button. The specially enabled audio interface calculates the ratio of these two frequencies and translates the ratio into button press information. This functionality provides accurate results independent of clock frequency variation.

CD3268A CD3269A Tone Transmit and Decode Method Figure 7-6 Tone Transmit and Decode Method
A. Count 63 tone pulses to set tCAL.
B. Count n tone pulses over tCAL.
C. Tone frequency decoded from n value.
D. Tone activity sampled. If active, ACK tone received. If not active, button tone received.

The CD326x remains in tone mode until the MIC pin voltage falls below 0.8V. When power recovers, the CD326x enters button mode or tone mode depending on the voltage detected at the MIC pin. See Section 7.3.4 for more details about this process.

CD3268A CD3269A Tone Mode Acknowledge Timing
Calibration tone tCAL = 0.9ms (typ)ACK tone tACK = 5.5ms (typ)
Figure 7-7 Tone Mode Acknowledge Timing