The PCM514x devices are powered through the pins shown in Figure 79.
|NAME||USAGE / DESCRIPTION|
|AVDD||Analog voltage supply; must be 3.3 V. This powers all analog circuitry that the DAC runs on.|
|DVDD||Digital voltage supply. This is used as the I/O voltage control and the input to the onchip LDO.|
|CPVDD||Charge Pump Voltage Supply - must be 3.3 V|
|LDOO||Output from the onchip LDO. Should be used with a 0.1-µF decoupling cap. Can be driven (used as power input) with a 1.8-V supply to bypass the onchip LDO for lower power consumption.|
Under certain conditions, the PCM514x devices can exhibit some pops on power down. Pops are caused by a device not having enough time to detect power loss and start the muting process.
The PCM514x devices have two auto-mute functions to mute the device upon power loss (intentional or unintentional).
When the XSMT pin is pulled low, the incoming PCM data is attenuated to 0, closely followed by a hard analog mute. This process takes 150 sample times (ts) + 0.2 ms.
Because this mute time is mainly dominated by the sampling frequency, systems sampling at 192 kHz will mute much faster than a 48-kHz system.
When clock error is detected on the incoming data clock, the PCM514x devices switch to an internal oscillator, and continue to the drive the output, while attenuating the data from the last known value. Once this process is complete, the PCM514x outputs are hard muted to ground.
These auto-muting processes can be manipulated by system designs to mute before power loss in the following ways:
Many systems use a low-noise regulator to provide an AVDD 3.3-V supply for the DAC. The XSMT Pin can take advantage of such a feature to measure the pre-regulated output from the system SMPS to mute the output before the entire SMPS discharges. Figure 82 shows how to configure such a system to use the XSMT pin. The XSMT pin can also be used in parallel with a GPIO pin from the system microcontroller/DSP or power supply.
External Power Sense Undervoltage Protection Mode is supported only when
DVDD = 3.3 V.
The XSMT pin can also be used to monitor a system voltage, such as the 24-VDC LCD TV backlight, or 12-VDC system supply using a voltage divider created with two resistors. (See Figure 83.)
If XSMT is moved from 1 to 0 in 20 ns or less, then the device will interpret it as a digital controlled request to mute. It will perform a soft mute, then move to standby.
A timing diagram to show this is shown in Figure 84.
The XSMT input pin voltage range is from –0.3 V to DVDD + 0.3 V. The ratio of external resistors must produce a voltage within this input range. Any increase in power supply (such as power supply positive noise or ripple) can pull the XSMT pin higher than DVDD + 0.3 V.
For example, if the PCM514x is monitoring a 12-V input, and dividing the voltage by 4, then the voltage at XSMT during ideal power supply conditions is 3.3 V. A voltage spike higher than 14.4 V causes a voltage greater than 3.6 V (DVDD + 0.3) on the XSMT pin, potentially damaging the device.
Providing the divider is set appropriately, any DC voltage can be monitored.
The trigger voltage values for the soft mute and hard mute are shown in Table 47. The range of values will vary from device to device, but typical thresholds are shown. XSMT should be set up to nominally be 3.3 V along with DVDD, but derived from a higher system power supply rail.
|Soft Mute Threshold Voltage||2||2.2||0.9 × DVDD||V|
|Hard Mute Threshold Voltage||0.1 × DVDD||0.9||1.2||V|
The PCM514x includes a power-on reset function, as shown in Figure 85. With VDD > 2.8 V, the power-on reset function is enabled. After the initialization period, the PCM514x is set to its default reset state. Analog output will begin ramping after valid data has been passing through the device for the given group delay given by the digital interpolation filter selected.
The PCM514x includes a power-on reset function, as shown in Figure 86. With AVDD greater than approximately 2.8 V, CPVDD greater than approximately 2.8 V, and DVDD greater than approximately 1.5 V, the power-on reset function is enabled. After the initialization period, the PCM514x is set to its default reset state.
The internal digital core of the PCM514x devices run from a 1.8-V supply. This can be generated by the internal LDO, or by an external 1.8-V supply.
DVDD is used to set the I/O voltage, and to be used as the input to the onchip LDO that creates the 1.8 V required by the digital core.
For systems that require 3.3-V I/O support, but lower power consumption, DVDD should be connected to 3.3 V and LDOO can be connected to an external 1.8-V source. Doing so will disable the onchip LDO.
When setting I/O voltage to be 1.8 V, both DVDD and LDOO must be provided with an external 1.8-V supply.
The PCM514x devices offer two power-save modes: standby and power-down.
When a clock error (SCK, BCK, and LRCK) or clock halt is detected, the PCM514x device automatically enters standby mode. The DAC and line driver are also powered down.
When BCK and LRCK remain at a low level for more than 1 second, the PCM514x device automatically enters powerdown mode. Power-down mode disables the negative charge pump and bias/reference circuit, in addition to those disabled in standby mode.
When expected audio clocks (SCK, BCK, LRCK) are applied to the PCM514x device, or if BCK and LRCK start correctly while SCK remains at ground level for 16 successive LRCK periods, the device starts its powerup sequence automatically.
|Page 0, Register 2, D(4)||Software standby mode command|
|Page 0, Register 2, D(0)||Software power-down command|
|Page 0, Register 2, D(4) and D(0)||Software power-up sequence command (required after software standby or power-down)|
|Page 0, Register 44, D(2:0)||Detection time of BCK and LRCK halt|