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AD1959 Fiches technique(PDF) 6 Page - Analog Devices

No de pièce AD1959
Description  PLL/Multibit DAC
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Fabricant  AD [Analog Devices]
Site Internet  http://www.analog.com
Logo AD - Analog Devices

AD1959 Fiches technique(HTML) 6 Page - Analog Devices

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REV. 0
AD1959
–6–
FUNCTIONAL DESCRIPTION
DAC
The AD1959 has two DAC channels arranged as a stereo pair
with single-ended analog outputs. Each channel has its own
independently programmable attenuator, adjustable in 16384
linear steps. Digital inputs are supplied through a serial data input
pin, SDATA, a frame clock, LRCLK and a bit clock, BLCK.
Each analog output pin sits at a dc level of VREF, and swings
± 1.585 V for a 0 dB digital input signal. A single op amp
third-order external low-pass filter is recommended to remove
high-frequency noise present on the output pins. The output
phase can be changed in an SPI control register to accommo-
date inverting and noninverting filters. Note that the use of op
amps with low slew rate or low bandwidth may cause high fre-
quency noise and tones to fold down into the audio band; care
should be exercised in selecting these components.
The FILTD and FILTR pins should be bypassed by external
capacitors to ground. The FILTD pin is used to reduce the noise
of the internal DAC bias circuitry, thereby reducing the DAC
output noise. The voltage at the VREF pin, FILTR (~2.39 V) can
be used to bias external op amps used to filter the output signals.
The DAC master clock frequency is 256 fS for the 32 kHz–48 kHz
range. For the 96 kHz range this is 128 fS. It is supplied inter-
nally from the PLL clock system when MCLK mode is set to
Output in the PLL Control Register. When the MCLK mode is
changed to Input, it must be supplied from an external source
connected to MCLK. The output from the 27 MHz PLL clock
is disabled in this case.
PLL Clock System
The PLL clock system operates from a 27 MHz master clock
supplied by the on-board crystal oscillator or an external source
connected to XIN. With the MCLK mode set to Output, the
27 MHz clock is buffered out to the MCLK pin. When set to
Input, the MCLK is the 256 fS master clock input for the DAC.
SCLK0 produces a 33.8688 MHz output, SCLK1 is intended
to be used as a master audio clock and will be a multiple of the
sample rate set in the PLL control register. It can be set to
256 fS or 384 fS using Bit 5 and to 512 fS or 768 fS, with Bit 4.
SCLK2 can be set to a constant 22.5792 MHz (512
× 44.1 kHz)
or 512 fS by Bit 3 of the PLL Control Register. Please note that
SCLK2 is intended to operate a DSP and does not meet the
jitter specifications stated under Analog Performance. All the
generated clocks can be set to 1/2 their nominal rate by setting
REF_Div2, Bit 8 in the PLL Control Register.
Reset
RESET will set the control registers to their default settings. The
chip should be reset on power-up. After reset is deasserted, the
part will come out of reset on the next rising LRCLK.
Serial Control Port
The AD1959 has an SPI-compatible control port to permit
programming the internal control registers for the PLL and DAC.
The DAC output levels may be independently programmed
by means of an internal digital attenuator adjustable in 16384
linear steps.
The SPI control port is a 3-wire serial control port. The format
is similar to the Motorola SPI format except the input data word
is 16 bits wide. Max serial bit clock frequency is 8 MHz and
may be completely asynchronous to the PLL system or the
DAC. Figure 1 shows the format of the SPI signal. Note that the
CCLK can be gated or continuous, CLATCH should be low
during the 16 active clocks.
CLATCH
CCLK
CDATA
D0
D15
D14
Figure 1. Format of SPI Signal


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