SLES102B December   2003  – March 2015 PCM1798


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics for Digital Filter
      1. 6.7.1 Analog Dynamic Performance
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 System Clock and Reset Functions
        1. System Clock Input
      2. 7.3.2 Power-On and External Reset Functions
      3. 7.3.3 Audio Data Interface
        1. Audio Serial Interface
        2. PCM Audio Data Formats and Timing
      4. 7.3.4 Function Descriptions
        1. Audio Data Format
        2. Soft Mute
        3. De-Emphasis
        4. Zero Detection
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Application for External Digital Filter Interface
        1. Design Requirements
        2. Detailed Design Procedure
          1. Application for Interfacing With an External Digital Filter
          2. Audio Format
          3. Analog Output
        3. Application Curves
      2. 8.2.2 PCM1798 Typical Application
        1. Design Requirements
        2. Detailed Design Procedure
          1. I/V Section
          2. Differential Section
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Trademarks
    2. 11.2 Electrostatic Discharge Caution
    3. 11.3 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DB|28
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8 Application and Implementation


Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

8.1 Application Information

The PCM1798 device is a hardware-controlled, differential current output DAC that can accept multiple formats of 16- or 24-bit PCM audio data. Because the PCM1798 is a current output part, in most cases a current to voltage stage is required before the signal is passed to the amplifier stage. A microcontroller or DSP can use GPIO to manipulate the control pins CHSL, DEM, FMT0, FMT1, MONO, and MUTE. The PCM1798 requires a 5-V analog supply, as well as a 3.3-V digital supply.

8.2 Typical Applications

8.2.1 Application for External Digital Filter Interface

PCM1798 connection_diagram_for_external_digital_filter_sles102.gifFigure 26. Connection Diagram for External Digital Filter (Internal DF Bypass Mode) Application Design Requirements

  • Control: Host controller with SPI communication
  • Audio Output: I/V output circuitry
  • Audio Input: Digital Audio Filter with I2S or DSD output Detailed Design Procedure Application for Interfacing With an External Digital Filter

For some applications, it may be desirable to use a programmable digital signal processor as an external digital filter to perform the interpolation function. The following pin settings enable the external digital filter application mode.

  • MONO (pin 1) = LOW
  • CHSL (pin 2) = HIGH
  • FMT0 (pin 11) = HIGH
  • FMT1 (pin 12) = HIGH

The pins used to provide the serial interface for the external digital filter are shown in the connection diagram of Figure 26. The word clock (WDCK) must be operated at 8× or 4× the desired sampling frequency, fS.

Pin assignment when using the external digital filter interface:

  • LRCK (pin 4): WDCK as word clock input
  • DATA (pin 5): Monaural audio data input
  • BCK (pin 6): Bit clock input Audio Format

The PCM1798 in the external digital filter interface mode supports the 24-bit right-justified audio format as shown in Figure 27.

PCM1798 audio_data_input_format_for_external_digital_sles102.gifFigure 27. Audio Data Input Format for External Digital Filter (Internal DF Bypass Mode) Application Analog Output

Table 3 and Figure 28 show the relationship between the digital input code and analog output.

Table 3. Analog Output Current and Voltage(1)

800000 (–FS) 000000 (BPZ) 7FFFFF (+FS)
IOUTN [mA] –1.5 –3.5 –5.5
IOUTP [mA] –5.5 –3.5 –1.5
VOUTN [V] –1.23 –2.87 –4.51
VOUTP [V] –4.51 –2.87 –1.23
VOUT [V] –2.98 0 2.98
(1) VOUTN is the output of U1, VOUTP is the output of U2, and VOUT is the output of U3 in the measurement circuit of Figure 23.
PCM1798 the_relationship_between_digital_input_sles102.gifFigure 28. Relationship Between Digital Input and Analog Output Application Curves

PCM1798 graph_02_sles102.gif
Pass-Band Ripple, Sharp Rolloff
Figure 29. Amplitude vs Frequency
PCM1798 graph_04_sles102.gif
Transition Characteristics, Slow Rolloff
Figure 30. Amplitude vs Frequency

8.2.2 PCM1798 Typical Application

PCM1798 typical_application_circuit_sles102.gifFigure 31. Typical Application Circuit Design Requirements

The design of the application circuit is very important in order to actually realize the high S/N ratio of which the PCM1798 is capable. This is because noise and distortion that are generated in an application circuit are not negligible.

In the third-order LPF circuit of Figure 32, the output level is 2.1 V RMS, and 123 dB S/N is achieved. Detailed Design Procedure I/V Section

The current of the PCM1798 on each of the output pins (IOUTL+, IOUTL–, IOUTR+, IOUTR–) is 4 mA p-p at 0 dB (full scale). The voltage output level of the I/V converter (Vi) is given by following equation:

Equation 1. VI = 4 mAp–p × Rf (Rf : feedback resistance of I/V converter)

TI recommends an NE5534 operational amplifier for the I/V circuit to obtain the specified performance. Dynamic performance such as the gain bandwidth, settling time, and slew rate of the operational amplifier affects the audio dynamic performance of the I/V section. Differential Section

The PCM1798 voltage outputs are followed by differential amplifier stages, which sum the differential signals for each channel, creating a single-ended I/V op-amp output. In addition, the differential amplifiers provide a low-pass filter function.

The operational amplifier recommended for the differential circuit is the low-noise type.

PCM1798 measurement_circuit_sles102.gifFigure 32. Measurement Circuit
PCM1798 measurement_circuit_for_monaural_mode_sles102.gifFigure 33. Measurement Circuit for Monaural Mode