AD1853 Analog Devices, AD1853 Datasheet - Page 9

• Manufacturer Part Number: AD1853
• Description: Stereo/ 24-Bit/ 192 kHz/ Multibit DAC
• Manufacturer: Analog Devices

REV. A
SPI REGISTER DEFINITIONS
The SPI port allows flexible control of many chip parameters.
It is organized around three registers; a LEFT-CHANNEL
VOLUME register, a RIGHT-CHANNEL VOLUME register
and a CONTROL register. Each WRITE operation to the
AD1853 SPI control port requires 16 bits of serial data in
MSB-first format. The bottom two bits are used to select one
of three registers, and the top 14 bits are then written to that
register. This allows a write to one of the three registers in a
single 16-bit transaction.
The SPI CCLK signal is used to clock in the data. The incom-
ing data should change on the falling edge of this signal. At the
end of the 16 CCLK periods, the CLATCH signal should rise
to latch the data internally into the AD1853.
Register Addresses
The lowest two bits of the 16-bit input word are decoded as
follows to set the register into which the upper 14 bits will be
written.
Bit 1
0
1
0
Bit 0
0
0
1
t
t
t
t
t
t
CCH
CCL
CSU
CHD
CLL
CLH
Register
Volume Left
Volume Right
Control Register
CCLK HI Pulsewidth
CCLK LOW Pulsewidth
CDATA Setup Time
CDATA Hold Time
CLATCH LOW Pulsewidth
CLATCH HI Pulsewidth
Table III. Digital Timing
–9–
VOLUME LEFT and VOLUME RIGHT Registers
A write operation to the left or right volume registers will acti-
vate the “auto-ramp” clickless volume control feature of the
AD1853. This feature works as follows. The upper 10 bits of
the volume control word will be incremented or decremented by
1 at a rate equal to the input sample rate. The bottom 4 bits are
not fed into the auto-ramp circuit and thus take effect immedi-
ately. This arrangement gives a worst-case ramp time of about
1024/F
determined by listening tests to be optimal in terms of pre-
venting the perception of a “click” sound on large volume
changes. See Figure 8 for a graphical description of how the
volume changes as a function of time.
The 14-bit volume control word is used to multiply the signal,
and therefore the control characteristic is linear, not dB. A con-
stant dB/step characteristic can be obtained by using a lookup
table in the microprocessor that is writing to the SPI port.
–60
–60
0
0
S
for step changes of more than 60 dB, which has been
Min
40
40
10
10
10
10
Figure 8. Smooth Volume Control
20ms
Units
ns
ns
ns
ns
ns
ns
VOLUME REQUEST REGISTER
ACTUAL VOLUME REGISTER
AD1853
TIME