ADR423 Analog Devices, ADR423 Datasheet - Page 15

• Manufacturer Part Number: ADR423
• Description: Ultraprecision Low Noise/ 2.048 V/2.500 V/ 3.00 V/5.00 V XFET Voltage References
• Manufacturer: Analog Devices

Precision Voltage Reference for Data Converters
The ADR42x family has a number of features that make it ideal
for use with A/D and D/A converters. The exceptional low noise,
tight temperature coefficient, and high accuracy characteristics
make the ADR42x ideal for low noise applications such as cellular
base station applications.
Another example of ADC for which the ADR421 is also well-suited
is the AD7701. Figure 12 shows the ADR421 used as the precision
reference for this converter. The AD7701 is a 16-bit A/D converter
with on-chip digital filtering intended for the measurement of wide
dynamic range and low frequency signals such as those representing
chemical, physical, or biological processes. It contains a charge-
balancing (sigma-delta) ADC, calibration microcontroller with on-chip
static RAM, a clock oscillator, and a serial communications port.
R1, R2
R1 = R2
R1 = R2
R1 = R2
R1 = 3R2
R1 = 3R2
R1 = 3R2
DACA
DACB
DACC
DACD
V
V
V
V
REFA
REFB
REFC
REFD
Table III. V
AD7398
0000 0000 0000
1000 0000 0000
1111 1111 1111
0000 0000 0000
1000 0000 0000
1111 1111 1111
Digital Code
REFX
V
V
V
V
OUTA
OUTB
OUTC
OUTD
vs. R1 and R2
V
IN
0.1%
R1
V
V
V
ADR425
OC
OD
OB
= V
= V
= V
V
2 V
1.3 V
V
4 V
1.6 V
V
R2
REF
REF
REF
REFX
REFX
V
REFX
0.1%
REF
REF
REF
REF
REF
(D
(D
(D
C
D
B
)
)
)
Precision Boosted Output Regulator
A precision voltage output with boosted current capability can
be realized with the circuit shown in Figure 13. In this circuit,
U
N
configuration, a 50 mA load is achievable at V
ate heat will be generated on the MOSFET and higher current
can be achieved with a replacement of the larger device. In
addition, for heavy capacitive load with step input, a buffer may
be added at the output to enhance the transient response.
ANALOG
SUPPLY
CALIBRATE
V
2
1
IN
, therefore, the load current will be furnished by V
ANALOG
GROUND
ANALOG
forces V
RANGES
ANALOG
+5V
SELECT
SUPPLY
INPUT
ADR420/ADR421/ADR423/ADR425
–5V
0.1 F
0.1 F
GND
4
2 U1
V
O
IN
0.1 F
V
TRIM
to be equal to V
ADR421
OUT
10 F
6
5
ADR42x
10 F
GND
0.1 F
V
IN
V
OUT
AD8601
REF
V+
5V
V–
BP/UP
AGND
AV
CAL
A
AV
V
IN
REF
SS
by regulating the turn on of
DD
2N7002
U2
N1
AD7701
CLKOUT
SLEEP
SDATA
MODE
CLKIN
DRDV
DGND
SCLK
DV
DV
SC2
SC1
CS
DD
SS
IN
of 5 V. Moder-
0.1 F
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
R
IN
L
. In this
25
0.1 F
V
O