AD5755 Analog Devices, AD5755 Datasheet - Page 40

• Manufacturer Part Number: AD5755
• Description: Quad Channel, 16-Bit, Serial Input,
• Manufacturer: Analog Devices

Specifications of AD5755

• Resolution (bits): 16bit
• Dac Update Rate: 91kSPS
• Dac Settling Time: 11µs
• Max Pos Supply (v): +33V
• Single-supply: No
• Dac Type: I or V Out
• Dac Input Format: SPI

AD5755
DEVICE FEATURES
OUTPUT FAULT
The AD5755 is equipped with a FAULT pin, an active low open-
drain output allowing several AD5755 devices to be connected
together to one pull-up resistor for global fault detection. The
FAULT pin is forced active by any one of the following fault
scenarios:
•
•
•
•
The V
of the status register (see Table 30) are used in conjunction with
the FAULT output to inform the user which one of the fault
conditions caused the FAULT output to be activated.
VOLTAGE OUTPUT SHORT-CIRCUIT PROTECTION
Under normal operation, the voltage output sinks/sources up
to 12 mA and maintains specified operation. The maximum
output current or short-circuit current is programmable by
the user and can be set to 16 mA or 8 mA. If a short circuit is
detected, the FAULT goes low, and the relevant V
in the status register is set.
DIGITAL OFFSET AND GAIN CONTROL
Each DAC channel has a gain (M) and offset (C) register, which
allow trimming out of the gain and offset errors of the entire
signal chain. Data from the DAC data register is operated on by
a digital multiplier and adder controlled by the contents of the
M and C registers. The calibrated DAC data is then stored in the
DAC input register.
The voltage at I
range due to an open-loop circuit or insufficient power
supply voltage. The internal circuitry that develops the
fault output avoids using a comparator with windowed
limits because this requires an actual output error before
the FAULT output becomes active. Instead, the signal is
generated when the internal amplifier in the output stage
has less than approximately 1 V of remaining drive
capability. Thus, the FAULT output activates slightly before
the compliance limit is reached.
A short is detected on a voltage output pin. The short-
circuit current is limited to 16 mA or 8 mA, which is
programmable by the user. If using the AD5755 in unipolar
supply mode, a short-circuit fault may be generated if the
output voltage is below 50 mV.
An interface error is detected due to a PEC failure. See the
Packet Error Checking section.
If the core temperature of the AD5755 exceeds
approximately 150°C.
OUT_x
fault, I
OUT_x
OUT_x
fault, PEC error, and over TEMP bits
attempts to rise above the compliance
OUT_x
fault bit
Rev. A | Page 40 of 52
Although Figure 76 indicates a multiplier and adder for each
channel, there is only one multiplier and one adder in the device,
and they are shared among all four channels. This has
implications for the update speed when several channels are
updated at once (see Table 3).
Each time data is written to the M or C register, the output is
not automatically updated. Instead, the next write to the DAC
channel uses these M and C values to perform a new calibration
and automatically updates the channel.
The output data from the calibration is routed to the DAC input
register. This is then loaded to the DAC as described in the
Theory of Operation section. Both the gain register and the
offset register have 16 bits of resolution. The correct method to
calibrate the gain/offset is to first calibrate out the gain and then
calibrate the offset.
The value (in decimal) that is written to the DAC input register
can be calculated by
where:
D is the code loaded to the input register of the DAC channel.
M is the code in the gain register (default code = 2
C is the code in the offset register (default code = 2
STATUS READBACK DURING A WRITE
The AD5755 has the ability to read back the status register
contents during every write sequence. This feature is enabled
via the STATREAD bit in the main control register. This allows
the user to continuously monitor the status register and act
quickly in the case of a fault.
When status readback during a write is enabled, the contents of
the 16-bit status register (see Table 30) are output on the SDO
pin, as shown in Figure 5.
The AD5755 powers up with this feature disabled. When this is
enabled, the normal readback feature is not available, except for
the status register. To read back any other register, clear the
STATREAD bit first before following the readback sequence.
STATREAD can be set high again after the register read.
Code
REGISTER
REGISTER
REGISTER
DACRegiste
INPUT
M
C
Figure 76. Digital Offset and Gain control
r
=
D
×
(
M
2
16
+
) 1
+
C
REGISTER
−
DAC
2
15
Data Sheet
16
15
DAC
– 1).
).
(1)