AD1852
Table III. SPI Digital Timing
Min
Unit
0
VOLUME REQUEST REGISTER
tCCH
tCCL
tCSU
tCHD
tCLL
tCLH
tCLSU
CCLK HI Pulsewidth
CCLK LOW Pulsewidth
CDATA Setup Time
40
40
10
ns
ns
ns
ns
ns
ns
ns
–60
0
CDATA Hold Time
10
10
10
4 × tMCLK
CLATCH LOW Pulsewidth
CLATCH HI Pulsewidth
CLATCH Setup Time
ACTUAL VOLUME REGISTER
–60
Register Addresses
The lowest two bits of the 16-bit input word are decoded as fol-
lows to set the register that the upper 14 bits will written into.
TIME
20ms
Figure 8. Smooth Volume Control
SPI Timing
VOLUME LEFT AND VOLUME RIGHT REGISTERS
A write operation to the left or right volume registers will acti-
vate the “autoramp” clickless volume control feature of the
AD1852. 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 four bits are
not fed into the autoramp circuit and thus take effect immediately.
This arrangement gives a worst-case ramp time of about 20 ms
for step changes of more than 60 dB, which has been deter-
mined by listening tests to be optimal in terms of preventing the
perception of a “click” sound on large volume changes. See Fig-
ure 8 for a graphical description of how the volume changes
as a function of time.
The SPI port is a 3-wire interface with serial data (CDATA),
serial bit clock (CCLK), and data latch (CLATCH). The
data is clocked into an internal shift register on the rising
edge of CCLK. The serial data should change on the falling
edge of CCLK and be stable on the rising edge of CCLK.
The rising edge of CLATCH is used internally to latch the par-
allel data from the serial-to-parallel converter. This rising edge
should be aligned with the falling edge of the last CCLK pulse
in the 16-bit frame. The CCLK can run continuously between
transactions.
Note that the serial control port timing is asynchronous to the
serial data port timing. Changes made to the attenuator level
will be updated on the next edge of the L/RCLK after the
CLATCH write pulse as shown in Figure 7.
The 14-bit volume control word is used to multiply the signal,
and therefore the control characteristic is linear, not dB. A constant
dB/step characteristic can be obtained by using a lookup table
in the microprocessor that is writing to the SPI port. The volume
word is unsigned (i.e., 0 dB is 11 1111 1111 1111).
Mute
The AD1852 offers two methods of muting the analog output.
By asserting the MUTE (Pin 23) signal HI, both the left and
right channel are muted. As an alternative, the user can assert
the mute bit in the serial control register (data11) HI. The
AD1852 has been designed to minimize pops and clicks when
muting and unmuting the device by automatically “ramping”
the gain up or down. When the device is unmuted, the volume
returns to the value set in the volume register.
Table IV.
Bit 1
Bit 0
Register
0
1
0
0
0
1
Volume Left
Volume Right
Control Register
REV. 0
–9–
ADI [ ADI ]
