7.3.1 Analog Outputs

The PCM1690 includes eight DACs, each with individual pairs of differential voltage outputs pins. The full-scale output voltage is (1.6 × VCC1) V_PP at the differential output mode. A DC-coupled load is allowed in addition to an AC-coupled load if the load resistance conforms to the specification. These balanced outputs are each capable of driving 0.8 VCC1 (4 V_PP) typical into a 5-kΩ, AC-coupled or 15-kΩ, DC-coupled load with VCC1 = +5 V. The internal output amplifiers for VOUT1 through VOUT8 are biased to the DC common voltage, equal to (0.5 × VCC1).

The output amplifiers include an RC continuous-time filter that helps to reduce the out-of-band noise energy present at the DAC outputs as a result of the noise shaping characteristics of the PCM1690 delta-sigma (ΔΣ) DACs. The frequency response of this filter is shown in the Analog Filter Characteristic (Figure 14). By itself, this filter is not enough to attenuate the out-of-band noise to an acceptable level for most applications. An external lowpass filter is required to provide sufficient out-of-band noise rejection. Further discussion of DAC post-filter circuits is provided in the Application Information section.

7.3.2 Voltage Reference VCOM

The PCM1690 includes a pin for the common-mode voltage output, VCOM. This pin must be connected to the analog ground through a decoupling capacitor. This pin can also be used to bias external high-impedance circuits, if they are required.

7.3.3 System Clock Input

The PCM1690 requires an external system clock input applied at the SCKI input for DAC operation. The system clock operates at an integer multiple of the sampling frequency, or f_S. The multiples supported in DAC operation include 128 f_S, 192 f_S, 256 f_S, 384 f_S, 512 f_S, 768 f_S, and 1152 f_S. Details for these system clock multiples are shown in Table 2. Figure 1 and System Clock Timing Requirements show the SCKI timing requirements.

7.3.4 Sampling Mode

The PCM1690 supports three sampling modes (single rate, dual rate, and quad rate) in DAC operation. In single rate mode, the DAC operates at an oversampling frequency of x128 (except when SCKI = 128 f_S and 192 f_S). This mode is supported for sampling frequencies less than 50 kHz. In dual rate mode, the DAC operates at an oversampling frequency of x64; this mode is supported for sampling frequencies less than 100 kHz. In quad rate mode, the DAC operates at an oversampling frequency of x32. The sampling mode is automatically selected according to the ratio of system clock frequency and sampling frequency by default (that is, single rate for 512 f_S, 768 f_S, and 1152 f_S; dual rate for 256 f_S and 384 f_S; and quad rate for 128 f_S and 192 f_S), but manual selection is also possible for specified combinations through the serial mode control register.

Table 3 and Figure 22 show the relation among the oversampling rate (OSR) of the digital filter and ΔΣ modulator, the noise-free shaped bandwidth, and each sampling mode setting.

Figure 22. ΔΣ Modulator and Digital Filter Characteristic

7.3.5 Reset Operation

The PCM1690 has both an internal power-on reset circuit and an external reset circuit. The sequences for both reset circuits are shown in Figure 23 and Figure 24. Figure 23 describes the timing at the internal power-on reset. Initialization is triggered automatically at the point where VDD exceeds 2.2 V typical, and the internal reset is released after 3846 SCKI clock cycles from power-on if RST is held high and SCKI is provided. VOUT from the DACs are forced to the VCOM level initially (that is, 0.5 × VCC1) and settle at a specified level according to the rising VCC. If synchronization among SCKI, BCK, and LRCK is maintained, VOUT provides an output that corresponds to DIN after 3846 SCKI clocks from power-on. If the synchronization is not held, the internal reset is not released, and both operating modes are maintained at reset and power-down states; after synchronization forms again, the DAC returns to normal operation with the previous sequences.

Figure 24 shows a timing diagram at the external reset. RST accepts an externally-forced reset with RST low, and provides a device reset and power-down state that achieves the lowest power dissipation state available in the PCM1690. If RST goes from high to low under synchronization among SCKI, BCK, and LRCK, the internal reset is asserted, all registers and memory are reset, and finally the PCM1690 enters into all power-down states. At the same time, VOUT is immediately forced into the AGND1 level. To begin normal operation again, toggle RST high; the same power-up sequence is performed as the power-on reset shown in Figure 23.

The PCM1690 does not require particular power-on sequences for VCC and VDD; it allows VDD on and then VCC on, or VCC on and then VDD on. From the viewpoint of the Absolute Maximum Ratings, however, simultaneous power-on is recommended for avoiding unexpected responses on VOUTx. Figure 23 shows the response for VCC on with VDD on.

Figure 23. Power-On-Reset Timing Requirements

Figure 24. External Reset Timing Requirements

7.3.6 Zero Flag

The PCM1690 has two ZERO flag pins (ZERO1 and ZERO2) that can be assigned to the combinations shown in Table 4. Zero flag combinations are selected through control register settings. If the input data of the left and right channel of all assigned channels remain at '0' for 1024 sampling periods (LRCK clock periods), the ZERO1/2 bits are set to a high level, logic '1' state. Furthermore, if the input data of any channels of assigned channels read '1', the ZERO1/2 are set to a low level, logic '0' state, immediately. Zero data detection is supported for 16-/20-/24-bit data width, but is not supported for 32-bit data width.

The active polarity of the zero flag output can be inverted through control register settings. The reset default is active high for zero detection. In parallel hardware control mode, ZERO1 and ZERO2 are fixed with combination A shown in Table 4.

7.3.7 AMUTE Control

The PCM1690 has an AMUTE control input, status output pins, and functionality. AMUTEI is the input control pin of the internal analog mute circuit. An AMUTEI low input causes the DAC output to cut-off from the digital input and forces it to the center level (0.5 VCC1). AMUTEO is the status output pin of the internal analog mute circuit. AMUTEO low indicates the analog mute control circuit is active because of a programmed condition (such as an SCKI halt, asynchronous detect, zero detect, or issue with the DAC disable command) that forces the DAC outputs to a center level. Because AMUTEI is not terminated internally and AMUTEO is an open-drain output, pull-ups by the appropriate resistors are required for proper operation.

Additionally, because the AMUTEI pin control and power-down control in register (OPEDA when high, PSMDA when low) do not function together, AMUTEI takes priority over power-down control. Therefore, power-down control is ignored during AMUTEI low, and AMUTEI low forces the DAC output to a center level (0.5 VCC1) even if the power-down control is asserted.

7.3.8 Three-Wire (SPI) Serial Control

The PCM1690 includes an SPI-compatible serial port that operates asynchronously with the audio serial interface. The control interface consists of MD/SDA/DEMP, MC/SCL/FMT, and MS/ADR0/RSV. MD is the serial data input to program the mode control registers. MC is the serial bit clock that shifts the data into the control port. MS is the select input to enable the mode control port.

7.3.9 Control Data Word Format

All single write operations via the serial control port use 16-bit data words. Figure 25 shows the control data word format. The first bit (fixed at '0') is for write controls; after the first bit are seven other bits, labeled ADR[6:0] that set the register address for the write operation. The eight least significant bits (LSBs), D[7:0] on MD, contain the data to be written to the register specified by ADR[6:0].

Figure 25. Control Data Word Format for MD

7.3.10 Register Write Operation

Figure 26 shows the functional timing diagram for single write operations on the serial control port. MS is held at a high state until a register is to be written. To start the register write cycle, MS is set to a low state. 16 clocks are then provided on MC, corresponding to the 16 bits of the control data word on MD. After the 16th clock cycle has been completed, MS is set high to latch the data into the indexed mode control register.

Also, the PCM1690 supports multiple write operations in addition to single write operations, which can be performed by sending the following N-times of the 8-bit register data after the first 16-bit register address and register data while keeping the MC clocks and MS at a low state. Closing a multiple write operation can be accomplished by setting MS to a high state.

1. X = don't care.

Figure 26. Register Write Operation

7.3.11 Two-Wire (I²C) Serial Control

The PCM1690 supports an I²C-compatible serial bus and data transmission protocol for fast mode configured as a slave device. This protocol is explained in the I²C specification 2.0.

The PCM1690 has a 7-bit slave address, as shown in Figure 27. The first five bits are the most significant bits (MSB) of the slave address and are factory-preset to 10011. The next two bits of the address byte are selectable bits that can be set by MS/ADR0/RSV and TEST/ADR1/RSV. A maximum of four PCM1690s can be connected on the same bus at any one time. Each PCM1690 responds when it receives its own slave address.

Figure 27. Slave Address

7.3.12 Packet Protocol

A master device must control the packet protocol, which consists of a start condition, slave address with the read/write bit, data if a write operation is required, acknowledgment if a read operation is required, and stop condition. The PCM1690 supports both slave receiver and transmitter functions. Details about DATA for both write and read operations are described in Figure 28.

1. R/W: Read operation if '1'; write operation otherwise.

2. ACK: Acknowledgment of a byte if '0', not Acknowledgment of a byte if '1'.

3. DATA: Eight bits (byte); details are described in the Write Operation and Read Operation sections.

Figure 28. I²C Packet Control Protocol

7.3.13 Write Operation

The PCM1690 supports a receiver function. A master device can write to any PCM1690 register using single or multiple accesses. The master sends a PCM1690 slave address with a write bit, a register address, and the data. If multiple access is required, the address is that of the starting register, followed by the data to be transferred. When valid data are received, the index register automatically increments by one. When the register address reaches &h4F, the next value is &h40. When undefined registers are accessed, the PCM1690 does not send an acknowledgment. Figure 29 shows a diagram of the write operation. The register address and write data are in 8-bit, MSB-first format.

NOTE: M = Master device, S = Slave device, St = Start condition, W = Write, ACK = Acknowledge, and Sp = Stop condition.

Figure 29. Framework for Write Operation

7.3.14 Read Operation

A master device can read the registers of the PCM1690. The value of the register address is stored in an indirect index register in advance. The master sends the PCM1690 slave address with a read bit after storing the register address. Then the PCM1690 transfers the data that the index register points to. Figure 30 shows a diagram of the read operation.

NOTE: M = Master device, S = Slave device, St = Start condition, Sr = Repeated start condition, W = Write, R = Read, ACK = Acknowledge, NACK = Not acknowledge, and Sp = Stop condition.

NOTE: The slave address after the repeated start condition must be the same as the previous slave address.

Figure 30. Framework for Read Operation

7.3.15 Timing Requirements: SCL and SDA

A detailed timing diagram for SCL and SDA is shown in Figure 5.

7.4.1 Audio Serial Port Operation

The PCM1690 audio serial port consists of six signals: BCK, LRCK, DIN1, DIN2, DIN3, and DIN4. BCK is a bit clock input. LRCK is a left/right word clock input or frame synchronization clock input. DIN1/2/3/4 are the audio data inputs for VOUT1–8.

7.4.2 Audio Data Interface Formats and Timing

The PCM1690 supports 10 audio data interface formats: 16-/20-/24-/32-bit I²S, 16-/20-/24-/32-bit left-justified, 24-bit right-justified, 16-bit right-justified, 24-bit left-justified mode DSP, 24-bit I²S mode DSP, 24-bit left-justified mode TDM, 24-bit I²S mode TDM, 24-bit left-justified mode high-speed TDM, and 24-bit I²S mode high-speed TDM. In the case of I²S, left-justified, and right-justified data formats, 64 BCKs, 48 BCKs, and 32 BCKs per LRCK period are supported; but 48 BCKs are limited in 192/384/768 f_S SCKI, and 32 BCKs are limited in 16-bit right-justified only. In the case of TDM data format in single rate, BCK, LRCK, and DIN1 are used. In the case of TDM data format in dual rate, BCK, LRCK, and DIN1/2 are used. In the case of high-speed TDM format in dual rate, BCK, LRCK, and DIN1 are used. In the case of high-speed TDM format in quad rate, BCK, LRCK, and DIN1/2 are used. TDM format and high-speed TDM format are supported only at SCKI = 512 f_S, 256 f_S, 128 f_S, and f_BCK ≤ f_SCKI. The audio data formats are selected by MC/SCL/FMT in hardware control mode and by control register settings in software control mode. All data must be in binary twos complement and MSB first.

Table 5 summarizes the applicable formats and describes the relationships among them and the respective restrictions with mode control. Figure 31 through Figure 37 show 10 audio interface data formats.

N = 15/19/23/31, M = 14/18/22/30, and L = 13/17/21/29

Figure 31. Audio Data Format: 16-/20-/24-/32-Bit I²S

N = 15/19/23/31, M = 14/18/22/30, and L = 13/17/21/29

Figure 32. Audio Data Format: 16-/20-/24-/32-Bit Left-Justified

Figure 33. Audio Data Format: 24-Bit Right-Justified

Figure 34. Audio Data Format: 16-Bit Right-Justified

Figure 35. Audio Data Format: 24-Bit DSP Format

SCKI = 128 f_S, 256 f_S, and 512 f_S Only

Figure 36. Audio Data Format: 24-Bit TDM Format

SCKI = 128 f_S and 256 f_S Only

Figure 37. Audio Data Format: 24-Bit High-Speed TDM Format

7.4.3 Synchronization With the Digital Audio System

The PCM1690 operates under the system clock (SCKI) and the audio sampling rate (LRCK). Therefore, SCKI and LRCK must have a specific relationship. The PCM1690 does not need a specific phase relationship between the audio interface clocks (LRCK, BCK) and the system clock (SCKI), but does require a specific frequency relationship (ratiometric) between LRCK, BCK, and SCKI.

If the relationship between SCKI and LRCK changes more than ±2 BCK clocks because of jitter, sampling frequency change, etc., the DAC internal operation stops within 1/f_S, and the analog output is forced into VCOM (0.5 VCC1) until re-synchronization between SCKI, LRCK, and BCK completes and then 38/f_S (single, dual rate) or 29/f_S (quad rate) passes. In the event the change is less than ±2 BCKs, re-synchronization does not occur, and this analog output control and discontinuity does not occur.

Figure 38 shows the DAC analog output during loss of synchronization. During undefined data periods, some noise may be generated in the audio signal. Also, the transition of normal to undefined data and undefined (or zero) data to normal data creates a discontinuity of data on the analog outputs, which then may generate some noise in the audio signal.

DAC outputs (VOUTx) hold the previous state if the system clock halts, but the asynchronous and re-synchronization processes will occur after the system clock resumes.

Figure 38. DAC Outputs During Loss of Synchronization

7.4.4 Mode Control

The PCM1690 includes three mode control interfaces with two oversampling configurations, depending on the input state of the MODE pin, as shown in Table 6. The pull-up and pull-down resistors must each be less than 10 kΩ.

The input state of the MODE pin is sampled at the moment of power-on, or during a low-to-high transition of the RST pin, with the system clock input. Therefore, input changes after reset are ignored until the next power-on or reset. From the mode control selection described in Table 6, the functions of four pins are changed, as shown in Table 7.

In serial mode control, the actual mode control is performed by register writes (and reads) through the SPI- or I²C-compatible serial control port. In parallel mode control, two specific functions are controlled directly through the high/low control of two specific pins, as described in the following section.

7.4.5 Parallel Hardware Control

The functions shown in Table 8 and Table 9 are controlled by two pins, DEMP and FMT, in parallel hardware control mode. The DEMP pin controls the 44.1-kHz digital de-emphasis function of all eight channels. The FMT pin controls the audio interface format for all eight channels.

7.5.1 Control Register Definitions (Software Mode Only)

The PCM1690 has many user-programmable functions that are accessed via control registers, and are programmed through the SPI or I²C serial control port. Table 10 shows the available mode control functions along with reset default conditions and associated register address. Table 11 lists the register map.

7.5.2 Register Definitions