Data Sheet AD5304/AD5314/AD5324
Rev. H | Page 15 of 24
BIT15
(MSB)
A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 0 0 X X
BIT0
(LSB)
PD
LDAC
DATA BITS
0929-032
Figure 32. AD5304 Input Shift Register Contents
BIT15
(MSB)
BIT0
(LSB)
A1 A0 D7D8D9 D6 D5 D4 D3 D2 D1 D0 X XPD
LDAC
DATA BITS
00929-033
Figure 33. AD5314 Input Shift Register Contents
BIT15
(MSB)
BIT0
(LSB)
A1 A0 D7D8D9D10D11 D6 D5 D4 D3 D2 D1 D0PD
LDAC
DATA BITS
00929-034
Figure 34. AD5324 Input Shift Register Contents
Input Shift Register
The input shift register is 16 bits wide. Data is loaded into the
device as a 16-bit word under the control of a serial clock input,
SCLK. See Figure 2 for the timing diagram of this operation. The
16-bit word consists of four control bits followed by 8, 10, or 12
bits of DAC data, depending on the device type. Data is loaded
MSB first (Bit 15) and the first two bits determine whether the
data is for DAC A, DAC B, DAC C, or DAC D. Bit 13 and Bit 12
control the operating mode of the DAC. Bit 13 is
PD
, and deter-
mines whether the part is in normal or power-down mode. Bit 12 is
LDAC
, and controls when DAC registers and outputs are updated.
Table 6. Address Bits
A1 A0 DAC Addressed
0 0 DAC A
0 1 DAC B
1 0 DAC C
1 1 DAC D
Address and Control Bits
PD
0: All four DACs go into power-down mode, consuming
only 200 nA @ 5 V. The DAC outputs enter a high
impedance state.
1: Normal operation.
LDAC
0: All four DAC registers and, therefore, all DAC outputs
updated simultaneously on completion of the write
sequence.
1: Only addressed input register is updated. There is
no change in the content of the DAC registers.
The AD5324 uses all 12 bits of DAC data; the AD5314 uses 10 bits
and ignores the 2 LSB Bits. The AD5304 uses eight bits and ignores
the last four bits. The data format is straight binary, with all 0s
corresponding to 0 V output and all 1s corresponding to full-scale
output (V
REF
− 1 LSB).
The
SYNC
input is a level-triggered input that acts as a frame
synchronization signal and chip enable. Data can be transferred
into the device only while
SYNC
is low. To start the serial data
transfer, take
SYNC
low, observing the minimum
SYNC
to SCLK
falling edge setup time, t
4
. After
SYNC
goes low, serial data shifts
into the device’s input shift register on the falling edges of SCLK
for 16 clock pulses. Any data and clock pulses after the 16
th
falling
edge of SCLK are ignored because the SCLK and DIN input buffers
are powered down. No further serial data transfer occurs until
SYNC
is taken high and low again.
SYNC
can be taken high after the falling edge of the 16
th
SCLK
pulse, observing the minimum SCLK falling edge to
SYNC
rising edge time, t
7
.
After the end of the serial data transfer, data automatically transfers
from the input shift register to the input register of the selected
DAC. If
SYNC
is taken high before the 16
th
falling edge of SCLK,
the data transfer is aborted and the DAC input registers are not
updated.
When data has been transferred into three of the DAC input
registers, all DAC registers and all DAC outputs are simultaneously
updated by setting
LDAC
low when writing to the remaining
DAC input register.
Low Power Serial Interface
To reduce the power consumption of the device even further, the
interface fully powers up only when the device is being written
to, that is, on the falling edge of
SYNC
. As soon as the 16-bit
control word has been written to the part, the SCLK and DIN
input buffers are powered down. They power up again only
following a falling edge of
SYNC
.
