ADR293GR Analog Devices Inc, ADR293GR Datasheet - Page 11

• Manufacturer Part Number: ADR293GR
• Description: IC VREF PREC 5V 5MA OUT 8-SOIC
• Manufacturer: Analog Devices Inc
• Series: XFET®r

Specifications of ADR293GR

• Rohs Status: RoHS non-compliant
• Reference Type: Series
• Voltage - Output: 5V
• Tolerance: ±0.2%
• Temperature Coefficient: 30ppm/°C
• Voltage - Input: 6 ~ 15 V
• Number Of Channels: 1
• Current - Quiescent: 15µA
• Current - Output: 5mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Current - Cathode: -

APPLICATIONS
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, it is often required to reconfigure a current-
switching DAC into a voltage-switching DAC by using a 1.25 V
reference, an op amp, and a pair of resistors. Using a current-
switching DAC directly requires the need for an additional
operational amplifier at the output to reinvert the signal.
Therefore, a negative voltage reference is desirable from the
point that 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 by using an operational amplifier and
a pair of matched resistors in an inverting configuration. The
disadvantage to that approach is that the largest single source of
error in the circuit is the relative matching of the resistors used.
The circuit illustrated in Figure 23 avoids the need for tightly
matched resistors with the use of an active integrator circuit. In
this circuit, the output of the voltage reference provides the
input drive for the integrator. To maintain circuit equilibrium,
the integrator adjusts its output to establish the proper
relationship between the reference’s V
with this approach should be mentioned. Although rail-to-rail
output amplifiers work best in the application, these operational
amplifiers require a finite amount (mV) of headroom when
required to provide any load current. The choice for the circuit’s
negative supply should take this issue into account.
Figure 23. A Negative Precision Voltage Reference Uses No Precision Resistors
A PRECISION CURRENT SOURCE
Many times in low power applications, the need arises for a
precision current source that can operate on low supply
voltages. As shown in Figure 24, the ADR293 is configured as a
precision current source. The circuit configuration illustrated is
a floating current source with a grounded load. The output
ADR293
GND
V
2
4
IN
V
OUT
6
100kΩ
1kΩ
1µF
A1 = 1/2 OP291, 1/2 OP295
1µF
A1
+5V
–5V
OUT
and GND. One caveat
100Ω
–V
REF
Rev. C | Page 11 of 16
voltage of the reference is bootstrapped across R
the output current into the load. With this configuration, circuit
precision is maintained for load currents in the range from the
reference’s supply current, typically 15 μA to approximately 5 mA.
KELVIN CONNECTIONS
In many portable instrumentation applications where PC board
cost and area go hand-in-hand, circuit interconnects are very
often of dimensionally minimum width. These narrow lines
can cause large voltage drops if the voltage reference is required
to provide load currents to various functions. In fact, a circuit’s
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
connection in Figure 25 overcomes the problem by including
the wiring resistance within the forcing loop of the op amp.
Because the op amp senses the load voltage, op amp loop
control forces the output to compensate for the wiring error and
to produce the correct voltage at the load.
ADR293
ERROR
GND
ADR293
V
2
4
Figure 25. Advantage of Kelvin Connection
IN
V
GND
OUT
V
= R × I
Figure 24. A Precision Current Source
2
4
IN
V
OUT
6
1µF
6
L
) at the load. However, the Kelvin
1µF
100kΩ
ADJUST
I
SY
A1
V
IN
R
R
L
I
LW
OUT
R1
P1
R
LW
R
SET
SET
+V
SENSE
+V
FORCE
R
L
, which sets
OUT
OUT
ADR293