Datasheet

AD5755-1 Data Sheet
Rev. E | Page 30 of 52
with all zeros. This means that if the user clears the part after
power-up, the output is actively driven to 0 V (if the channel
has been enabled for clear).
After a device power on, or a device reset, it is recommended to
wait 100 μs or more before writing to the device to allow time
for internal calibrations to take place.
SERIAL INTERFACE
The AD5755-1 is controlled over a versatile 3-wire serial
interface that operates at clock rates of up to 30 MHz and is
compatible with SPI, QSPI, MICROWIRE, and DSP standards.
Data coding is always straight binary.
Input Shift Register
The input shift register is 24 bits wide. Data is loaded into the
device MSB first as a 24-bit word under the control of a serial
clock input, SCLK. Data is clocked in on the falling edge of SCLK.
If packet error checking, or PEC (see the Device Features
section), is enabled, an additional eight bits must be written to
the AD5755-1, creating a 32-bit serial interface.
There are two ways in which the DAC outputs can be updated:
individual updating or simultaneous updating of all DACs.
Individual DAC Updating
In this mode,
LDAC
is held low while data is being clocked into
the DAC data register. The addressed DAC output is updated on
the rising edge of
SYNC
. See Table 3 and Figure 3 for timing
information.
Simultaneous Updating of All DACs
In this mode,
LDAC
is held high while data is being clocked
into the DAC data register. Only the first write to each channel’s
DAC data register is valid after
LDAC
is brought high. Any subse-
quent writes while
LDAC
is still held high are ignored, though
they are loaded into the DAC data register. All the DAC outputs
are updated by taking
LDAC
low after
SYNC
is taken high.
V
OUT_x
DAC
REGISTER
INTERFACE
LOGIC
OUTPUT
I/V AMPLIFIER
LDAC
SDO
SDIN
16-BIT
DAC
V
REFIN
SYNC
DAC DATA
REGISTER
OFFSET
AND GAIN
CALIBRATION
DAC INPUT
REGISTER
SCLK
09226-072
Figure 74. Simplified Serial Interface of Input Loading Circuitry
for One DAC Channel
TRANSFER FUNCTION
Table 6 shows the input code to ideal output voltage relationship
for the AD5755-1 for straight binary data coding of the ±10 V
output range.
Table 6. Ideal Output Voltage to Input Code Relationship
Digital Input
Straight Binary Data Coding Analog Output
MSB LSB V
OUT
1111 1111 1111 1111 +2 V
REF
× (32,767/32,768)
1111 1111 1111 1110 +2 V
REF
× (32,766/32,768)
1000 0000 0000 0000 0 V
0000
0000
0000
0001
−2 V
REF
× (32,767/32,768)
0000 0000 0000 0000 −2 V
REF