ADR292FR Analog Devices Inc, ADR292FR Datasheet - Page 15

• Manufacturer Part Number: ADR292FR
• Manufacturer: Analog Devices Inc

Specifications of ADR292FR

• Fixed / Adjust / Prog: Precision
• Output Voltage (max): 4.096V
• Temperature Coefficient: 20ppm/°C
• Reference Voltage Accuracy (max): 0.1
• Line Regulation: 100ppm/V
• Load Regulation: 100ppm/mA
• Input Voltage (max): 18V
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• Mounting: Surface Mount
• Pin Count: 8
• Package Type: SOIC N
• Lead Free Status / Rohs Status: Not Compliant

KELVIN CONNECTIONS
In many portable instrumentation applications, the PC board
area is directly related to cost; therefore, circuit interconnects
are reduced to a minimal width. These narrow lines can cause
large voltage drops if the voltage reference is required to provide
load currents to various functions. In fact, circuit interconnects
can exhibit a typical line resistance of 0.45 mΩ/square (1 oz. Cu,
for example). Force and sense connections, also referred to as
Kelvin connections, offer a convenient method of eliminating
the effects of voltage drops in circuit wires. Load currents flowing
through wiring resistance produce an error (V
the load. However, the Kelvin connection shown in Figure 36
overcomes the problem by including the wiring resistance
within the forcing loop of the op amp. Since the op amp senses
the load voltage, the op amp loop control forces the output to
compensate for the wiring error producing the correct voltage
at the load.
LOW POWER, LOW VOLTAGE REFERENCE FOR
DATA CONVERTERS
The ADR291/ADR292 family has a number of features that
makes it ideally suited for use with analog-to-digital and digital-
to-analog converters. Because of its low supply voltage, the
ADR291 can be used with converters that run on 3 V supplies
without having to add a higher supply voltage for the reference.
The low quiescent current (12 μA maximum) and low noise,
tight temperature coefficient, combined with the high accuracy
of the ADR291/ADR292, make it ideal for low power applica-
tions such as handheld, battery-operated equipment.
One such ADC for which the ADR291 is well suited is the
AD7701. Figure 37 shows the ADR291 used as the reference
for this converter. The AD7701 is a 16-bit ADC with on-chip
digital filtering intended for the measurement of wide dynamic
range, low frequency signals such as those representing chemical,
physical, or biological processes. It contains a charge balancing
(Σ-Δ) ADC, calibration microcontroller with on-chip static
RAM, a clock oscillator, and a serial communications port.
This entire circuit runs on ±5 V supplies. The power dissipation
of the AD7701 is typically 25 mW and, when
ADR291/
ADR292
GND
V
Figure 36. Advantage of Kelvin Connection
2
4
IN
V
OUT
6
1µF
100kΩ
A1 = 1/2 OP295
A1
V
IN
R
LW
R
LW
ERROR
R
+V
SENSE
+V
FORCE
L
= R × I
OUT
OUT
L
) at
Rev. E | Page 15 of 20
combined with the power dissipation of the ADR291 (60 μW),
the entire circuit still consumes about 25 mW.
VOLTAGE REGULATOR FOR PORTABLE
EQUIPMENT
The ADR291/ADR292 family of references is ideal for provid-
ing a stable, low cost, and low power reference voltage in
portable equipment power supplies. Figure 38 shows how the
ADR291 and ADR292 can be used in a voltage regulator that
not only has low output noise (as compared to switch mode
design) and low power, but also a very fast recovery after
current surges. Some precautions should be taken in the
selection of the output capacitors. Too high an ESR (effective
series resistance) could endanger the stability of the circuit. A
solid tantalum capacitor, 16 V or higher, and an aluminum
electrolytic capacitor, 10 V or higher, are recommended for C1
and C2, respectively. Also, the path from the ground side of C1
and C2 to the ground side of R1 should be kept as short as
possible.
ANALOG
SUPPLY
LEAD-ACID
CHARGER
CALIBRATE
BATTERY
INPUT
Figure 37. Low Power, Low Voltage Supply Reference for the AD7701
+5V
GROUND
ANALOG
ANALOG
RANGES
ANALOG
SELECT
SUPPLY
INPUT
0.1µF
–5V
6V
Figure 38. Voltage Regulator for Portable Equipment
0.1µF
+
0.1µF
0.1µF
ADR291/
ADR292
ADR291
GND
GND
10µF
V
V
0.1µF
4
2
IN
OUT
NC
402kΩ
V
V
OUT
IN
1%
R1
10µF
6
3
AV
V
BP/UP
CAL
A
AGND
AV
2
3
REF
IN
DD
SS
OP20
AD7701
402kΩ
7
4
1%
R2
CLKOUT
ADR291/ADR292
SLEEP
SDATA
MODE
CLKIN
6
DGND
DRDY
SCLK
DV
DV
SC1
SC2
510kΩ
CS
DD
SS
R3
TANT
68µF
C1
IRF9530
0.1µF
+
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
+ C2
0.1µF
5V, 100mA
1000µF
ELECT