AD5781ARUZ-REEL7 Analog Devices Inc, AD5781ARUZ-REEL7 Datasheet - Page 24

• Manufacturer Part Number: AD5781ARUZ-REEL7
• Description: 18bit, 4LSB, Unbuffered Ref
• Manufacturer: Analog Devices Inc

Specifications of AD5781ARUZ-REEL7

• Design Resources: 18-Bit Accurate, low noise, precision bipolar DC voltage source (CN0177)
• Settling Time: 1µs
• Number Of Bits: 18
• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital, Dual ±
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power Dissipation (max): -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD5781
AD5781 FEATURES
POWER-ON TO 0 V
The AD5781 contains a power-on reset circuit that, as well as
resetting all registers to their default values, controls the output
voltage during power-up. Upon power-on, the DAC is placed in
tristate (its reference inputs are disconnected), and its output is
clamped to AGND through a ~6 kΩ resistor. The DAC remains
in this state until programmed otherwise via the control
register. This is a useful feature in applications where it is
important to know the state of the DAC output while it is in the
process of powering up.
CONFIGURING THE AD5781
After power-on, the AD5781 must be configured to put it into
normal operating mode before programming the output. To do
this, the control register must be programmed. The DAC is
removed from tristate by clearing the DACTRI bit, and the
output clamp is removed by clearing the OPGND bit. At this
point, the output goes to V
programmed to the DAC register.
DAC OUTPUT STATE
The DAC output can be placed in one of three states, controlled
by the DACTRI and OPGND bits of the control register, as
shown in Table 16.
Table 16. AD5781 Output State Truth Table
DACTRI
0
0
1
1
LINEARITY COMPENSATION
The integral nonlinearity (INL) of the AD5781 can vary
according to the applied reference voltage span; the LIN COMP
bits of the control register can be programmed to compensate
for this variation in INL. The specifications in this data sheet
are obtained with LIN COMP = 0000 for reference spans up to
and including 10 V and with LIN COMP = 1100 for a reference
span of 20 V. The default value of the LIN COMP bits is 0000.
OUTPUT AMPLIFIER CONFIGURATION
There are a number of different ways that an output amplifier
can be connected to the AD5781, depending on the voltage
references applied and the desired output voltage span.
Unity Gain Configuration
Figure 48 shows an output amplifier configured for unity gain,
in this configuration the output spans from V
OPGND
0
1
0
1
Output State
Normal operating mode.
Output is clamped via ~6 kΩ to AGND.
Output is in tristate.
Output is clamped via ~6 kΩ to AGND.
REFN
unless an alternative value is first
REFN
to V
REFP.
Rev. 0 | Page 24 of 28
A second unity gain configuration for the output amplifier is
one that removes an offset from the input bias currents of the
amplifier. It does this by inserting a resistance in the feedback
path of the amplifier that is equal to the output resistance of the
DAC. The DAC output resistance is 3.4 kΩ. By connecting R1
and R
available on-chip. Because the resistors are all on one piece of
silicon, they are temperature coefficient matched. To enable this
mode of operation, the RBUF bit of the control register must be
set to Logic 1. Figure 49 shows how the output amplifier is
connected to the AD5781. In this configuration, the output
amplifier is in unity gain and the output spans from V
V
placed in the amplifier feedback path to improve dynamic
performance.
REFP
1/2 AD8676
1/2 AD8676
1/2 AD8676
1/2 AD8676
Figure 49. Output Amplifier in Unity Gain with Amplifier Input Bias Current
. This unity gain configuration allows a capacitor to be
FB
V
V
in parallel, a resistance equal to the DAC resistance is
V
V
REFPF
REFNF
Figure 48. Output Amplifier in Unity Gain Configuration
REFPF
REFNF
V
V
V
V
REFP
REFN
REFP
REFN
18-BIT
DAC
18-BIT
DAC
V
V
V
V
REFPS
REFNS
REFNS
REFPS
R1
A1
6.8kΩ
Compensation
6.8kΩ 6.8kΩ
R1
AD5781
R
AD5781
FB
R
FB
6.8kΩ
V
V
R
OUT
INV
R
OUT
INV
FB
FB
10pF
AD8675,
ADA4898-1,
ADA4004-1
AD8675,
ADA4898-1,
ADA4004-1
REFN
V
V
OUT
OUT
to