ADR420ARZ Analog Devices Inc, ADR420ARZ Datasheet - Page 17

• Manufacturer Part Number: ADR420ARZ
• Description: IC VREF PREC 10MA 2.048V 8SOIC
• Manufacturer: Analog Devices Inc
• Series: XFET®r

Specifications of ADR420ARZ

• Temperature Coefficient: 10ppm/°C
• Design Resources: High Accuracy, Bipolar Voltage Output Digital-to-Analog Conversion Using AD5765 (CN0073) High Accuracy, Bipolar Voltage Output Digital-to-Analog Conversion Using AD5763 (CN0074)
• Reference Type: Series
• Voltage - Output: 2.048V
• Tolerance: ±0.15%
• Voltage - Input: 4 ~ 18 V
• Number Of Channels: 1
• Current - Quiescent: 500µA
• Current - Output: 10mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Topology: Series
• Input Voltage: 4V To 18V
• Reference Voltage: 2.048V
• Reference Voltage Tolerance: 3mV
• Voltage Reference Case Style: SOIC
• No. Of Pins: 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Cathode: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

APPLICATIONS
OUTPUT ADJUSTMENT
The ADR42x trim terminal can be used to adjust the output
voltage over a ±0.5% range. This feature allows the system
designer to trim system errors out by setting the reference to
a voltage other than the nominal. This is also helpful if the
part is used in a system at temperature to trim out any error.
Adjustment of the output has a negligible effect on the
temperature performance of the device. To avoid degrading
temperature coefficients, both the trimming potentiometer
and the two resistors need to be low temperature coefficient
types, preferably <100 ppm/°C.
REFERENCE FOR CONVERTERS IN OPTICAL
NETWORK CONTROL CIRCUITS
In the high capacity, all optical router network of Figure 41,
arrays of micromirrors direct and route optical signals from
fiber to fiber, without first converting them to electrical form,
which reduces the communication speed. The tiny micro-
mechanical mirrors are positioned so that each is illuminated
by a single wavelength that carries unique information and
can be passed to any desired input and output fiber. The mirrors
are tilted by the dual-axis actuators controlled by precision
analog-to-digital converters (ADCs) and digital-to-analog
converters (DACs) within the system. Due to the microscopic
movement of the mirrors, not only is the precision of the
converters important, but the noise associated with these
controlling converters is extremely critical, because total noise
within the system can be multiplied by the numbers of
converters used. Consequently, the exceptional low noise of the
ADR42x is necessary to maintain the stability of the control
loop for this application.
INPUT
ADR420/
ADR421/
ADR423/
GND
ADR425
V
2
4
IN
V
TRIM
Figure 40. Output Trim Adjustment
OUT
6
5
470kΩ
R1
R2
R
10kΩ
10kΩ (ADR420)
15kΩ (ADR421)
P
OUTPUT
V
OUT
= ±0.5%
Rev. H | Page 17 of 24
A NEGATIVE PRECISION REFERENCE
WITHOUT PRECISION RESISTORS
In many current-output CMOS DAC applications where
the output signal voltage must be of the same polarity as the
reference voltage, a current-switching DAC is often recon-
figured into a voltage-switching DAC with a 1.25 V reference,
an op amp, a pair of resistors, and an additional operational
amplifier at the output to reinvert the signal. A negative voltage
reference should be used because an additional operational
amplifier is not required for either reinversion (current-switching
mode) or amplification (voltage-switching mode) of the DAC
output voltage. In general, any positive voltage reference can be
converted into a negative voltage reference using an operational
amplifier and a pair of matched resistors in an inverting
configuration. The disadvantage to this approach is that the
largest single source of error in the circuit is the relative
matching of the resistors used.
A negative reference can easily be generated by adding a
precision op amp and configuring as shown in Figure 42. V
is at virtual ground and, therefore, the negative reference can be
taken directly from the output of the op amp. The op amp must
be dual-supply, low offset and have rail-to-rail capability if
negative supply voltage is close to the reference output.
ELECTRONICS
CONTROL
LASER BEAM
ACTIVATOR
ADR420/ADR421/ADR423/ADR425
LEFT
SOURCE FIBER
Figure 41. All Optical Router Network
AMPL
DAC
GIMBAL + SENSOR
Figure 42. Negative Reference
–V
A1
DD
MEMS MIRROR
A1 = OP777, OP193
6
PREAMP
DSP
ADC
V
OUT
ADR420/
ADR421/
ADR423/
ADR425
+V
GND
V
2
4
IN
DD
AMPL
DAC
ACTIVATOR
RIGHT
–V
DESTINATION
FIBER
REF
ADR421
ADR421
ADR421
OUT