Datasheet

Data Sheet AD5424/AD5433/AD5445
Rev. D | Page 23 of 28
Provided the DAC switches are driven from true wideband
low impedance sources (V
IN
and AGND), they settle quickly.
Consequently, the slew rate and settling time of a voltage
switching DAC circuit is determined largely by the output op
amp. To obtain minimum settling time in this configuration, it
is important to minimize capacitance at the V
REF
node (voltage
output node in this application) of the DAC. This is done by using
low inputs capacitance buffer amplifiers and careful board design.
Most single-supply circuits include ground as part of the analog
signal range, which in turns requires an amplifier that can handle
rail-to-rail signals. There is a large range of single-supply
amplifiers available from Analog Devices.
PARALLEL INTERFACE
Data is loaded to the AD5424/AD5433/AD5445 in the format
of an 8-, 10-, or 12-bit parallel word. Control lines
CS
and R/
W
allow data to be written to or read from the DAC register. A
write event takes place when
CS
and R/
W
are brought low, data
available on the data lines fills the shift register, and the rising
edge of
CS
latches the data and transfers the latched data-word
to the DAC register. The DAC latches are not transparent, thus
a write sequence must consist of a falling and rising edge on
CS
to ensure that data is loaded to the DAC register and its analog
equivalent is reflected on the DAC output.
A read event takes place when R/
W
is held high and
CS
is
brought low. New data is loaded from the DAC register back to
the input register and out onto the data line where it can be read
back to the controller for verification or diagnostic purposes.
MICROPROCESSOR INTERFACING
ADSP-21xx-to-AD5424/AD5433/AD5445 Interface
Figure 56 shows the AD5424/AD5433/AD5445 interfaced to
the ADSP-21xx series of DSPs as a memory-mapped device. A
single wait state may be necessary to interface the AD5424/
AD5433/AD5445 to the ADSP-21xx, depending on the clock
speed of the DSP. The wait state can be programmed via the
data memory wait state control register of the ADSP-21xx
(see the ADSP-21xx family user’s manual for details).
03160-056
R/W
DB0 TO DB11
AD5424/
AD5433/
AD5445*
ADDRESS
DECODER
CS
DATA 0 TO
DATA 23
ADDRESS BUS
ADDR
0
TO
ADRR
13
ADSP-21xx*
DATA BUS
DMS
WR
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 56. ADSP21xx-to-AD5424/AD5433/AD5445 Interface
8xC51-to-AD5424/AD5433/AD5445 Interface
Figure 57 shows the interface between the AD5424/AD5433/
AD5445 and the 8xC51 family of DSPs. To facilitate external
data memory access, the address latch enable (ALE) mode is
enabled. The low byte of the address is latched with this output
pulse during access to external memory. AD0 to AD7 are the
multiplexed low order addresses and data bus and require
strong internal pull-ups when emitting 1s. During access to
external memory, A8 to A15 are the high order address bytes.
Since these ports are open drained, they also require strong
internal pull-ups when emitting 1s.
03160-063
R/W
DB0 TO DB11
AD5424/
AD5433/
AD5445*
ADDRESS
DECODER
CS
AD0 TO AD7
ADDRESS BUS
A8 TO A15
8051*
DATA BUS
WR
*ADDITIONAL PINS OMITTED FOR CLARITY
8-BIT
LATCH
ALE
Figure 57. 8xC51-to-AD5424/AD5433/AD5445 Interface
ADSP-BF5xx-to-AD5424/AD5433/AD5445 Interface
Figure 58 shows a typical interface between the AD5424/
AD5433/AD5445 and the ADSP-BF5xx family of DSPs. The
asynchronous memory write cycle of the processor drives the
digital inputs of the DAC. The
AMS
x line is actually four memory
select lines. Internal ADDR lines are decoded into
AMS
3-0
, these
lines are then inserted as chip selects. The rest of the interface is
a standard handshaking operation.
03160-057
R/W
DB0 TO DB11
AD5424/
AD5433/
AD5445*
ADDRESS
DECODER
CS
DATA 0 TO
DATA 23
ADDRESS BUS
ADDR
1
TO
ADRR
19
ADSP-BF5xx
DATA BUS
AMSx
AWE
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 58. ADSP-BF5xx-to-AD5424/AD5433/AD5445 Interface