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AD5024 Fiches technique(PDF) 21 Page - Analog Devices
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AD5024 Fiches technique(HTML) 21 Page - Analog Devices
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Rev. F | Page 21 of 28
MODES OF OPERATION
There are three main modes of operation: standalone mode
where a single device is used, daisy-chain mode for a system
that contains several DACs, and power-down mode when the
supply current falls to 0.4 µA at 5 V.
The write sequence begins by bringing the SYNC line low. Data
from the DIN line is clocked into the 32-bit shift register on the
falling edge of SCLK. The serial clock frequency can be as high
as 50 MHz, making the AD5024/AD5044/AD5064/AD5064-1
compatible with high speed DSPs. On the 32
falling clock edge,
the last data bit is clocked in and the programmed function is
executed, that is, an LDAC-dependent change in DAC register
contents and/or a change in the mode of operation. At this
stage, the SYNC line can be kept low or be brought high. In
either case, it must be brought high for a minimum of 3 µs
(single channel, see Table 4, t
parameter) before the next write
sequence so that a falling edge of SYNC can initiate the next
write sequence. SYNC should be idled at rails between write
sequences for even lower power operation of the part.
In a normal write sequence, the SYNC line is kept low for at
least 32 falling edges of SCLK, and the DAC is updated on the
falling edge. However, if SYNC is brought high before the
falling edge, this acts as an interrupt to the write sequence.
The write sequence is seen as invalid. Neither an update of the
DAC register contents nor a change in the operating mode
occurs (see Figure 50).
For systems that contain several DACs the SDO pin can be
used to daisy-chain several devices together and provide serial
The daisy-chain mode is enabled through a software executable
daisy-chain enable (DCEN) command. Command 1000 is
reserved for this DCEN function (see Table 8). The daisy-chain
mode is enabled by setting Bit DB1 in the DCEN register. The
default setting is standalone mode, where DB1 = 0.
Table 10 shows how the state of the bit corresponds to the mode
of operation of the device.
Table 10. DCEN (Daisy-Chain Enable) Register
Standalone mode (default)
The SCLK is continuously applied to the shift register when
SYNC is low. If more than 32 clock pulses are applied, the data
ripples out of the shift register and appears on the SDO line.
This data is clocked out on the rising edge of SCLK and is valid
on the falling edge. By connecting this line to the DIN input on
the next DAC in the chain, a daisy-chain interface is constructed.
Each DAC in the system requires 32 clock pulses; therefore, the
total number of clock cycles must equal 32N, where N is the
total number of devices that are updated. If SYNC is taken high
at a clock that is not a multiple of 32, it is considered an invalid
frame and the data is discarded.
When the serial transfer to all devices is complete, SYNC is
taken high. This prevents any further data from being clocked
into the shift register.
In daisy-chain mode, the LDAC pin cannot be tied permanently
low. The LDAC pin must be used in asynchronous LDAC update
mode, as shown in Figure 5. The LDAC pin must be brought
high after pulsing. This allows all DAC outputs to simulta-
The serial clock can be continuous or a gated clock. A continuous
SCLK source can be used only if SYNC can be held low for the
correct number of clock cycles. In gated clock mode, a burst
clock containing the exact number of clock cycles must be used,
and SYNC must be taken high after the final clock to latch the data.
Table 11. 32-Bit Shift Register Contents for Daisy-Chain Enable
DB31 to DB28
DB19 to DB2
Command bits (C3 to C0)
Address bits (A3 to A0)
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