ADR421BRZ Analog Devices Inc, ADR421BRZ Datasheet - Page 19

• Manufacturer Part Number: ADR421BRZ
• Description: IC REF PREC LONOISE 2.50V 8-SOIC
• Manufacturer: Analog Devices Inc
• Series: XFET®r

Specifications of ADR421BRZ

• Temperature Coefficient: 3ppm/°C
• Design Resources: 40 Channels of Programmable Voltage with Excellent Temperature Drift Performance Using AD5380 (CN0007) 40 Channels of Programmable Voltage with Excellent Temperature Drift Performance Using AD5381 (CN0010) 32 Channels of Programmable Voltage with Excellent Temperature Drift Performance Using AD5382 (CN0011) 32 Channels of Programmable Voltage with Excellent Temperature Drift Performance Using AD5383 (CN0014) 8 to 16 Channels of Programmable Voltage with Excellent Temperature Drift Performance Using AD5390/1/2 (CN0029) High Precision Digital-to-Analog Conversion Using the 16-Bit AD5542/1, ADR421, and AD8628 (CN0079) 16 Channels of Programmable Output Span Using AD5360 (CN0131) Layout Considerations for an Expandable Multichannel Simultaneous Sampling Data Acquisition System Based on AD7606 (CN0148) 40 Channels of Programmable Output Span Using AD5371 (CN0149) Software Calibrated, 1 MHz to 8 GHz, 70 dB RF Power Measurement System Using AD8318 (CN0150) How to Achieve High Precision Voltage Level Setting Using AD5541A/42A (CN0169)
• Reference Type: Series
• Voltage - Output: 2.5V
• Tolerance: ±0.04%
• Voltage - Input: 4.5 ~ 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: 4.5V To 18V
• Reference Voltage: 2.5V
• Reference Voltage Tolerance: 1mV
• 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

PROGRAMMABLE CURRENT SOURCE
Together with a digital potentiometer and a Howland current
pump, the ADR425 forms the reference source for a program-
mable current as
and
where:
D is the decimal equivalent of the input code.
N is the number of bits.
R1' and R2' must be equal to R1 and R2
Theoretically, R2
the current needed within A2 output current driving capability.
In the example shown in Figure 47,
a maximum of 10 mA. Because the current pump uses both
positive and negative feedback, capacitors C1 and C2 are needed
to ensure that negative feedback prevails and, therefore, avoiding
oscillation. This circuit also allows bidirectional current flow if
the inputs V
with the dual-polarity references as previously shown.
V
GND
V
DD
2
ADR425
IN
4
U1
VW
I
TRIM
V
L
OUT
=
=
⎛
⎜
⎝
5
6
A
R2
2
DIGITAL POT
D
and V
N
Figure 47. Programmable Current Source
U2
A
AD5232
R2
×
A
R1
B
U2
+
B
B
can be made as small as needed to achieve
V
B
R2
W
B
REF
B
of the digital potentiometer are supplied
B
⎞
⎟
⎠
OP2177
V
V
V+
V–
×
DD
SS
A1
V
W
OP2177
10pF
50kΩ
50kΩ
C2
R1
R1'
A
+ R2
is able to deliver
OP2177
VL
B
V
V
V+
V–
, respectively.
B
DD
SS
10pF
1kΩ
A2
R2'
C1
R2
1kΩ
A
R2
10Ω
LOAD
B
IL
Rev. H | Page 19 of 24
(3)
(4)
PROGRAMMABLE DAC REFERENCE VOLTAGE
With a multichannel DAC, such as the quad, 12-bit voltage
output AD7398, one of its internal DACs, and an ADR42x
voltage reference can be used as a common programmable
V
shown in Figure 48. The relationship of V
on the digital code and the ratio of R1 and R , and is given by
where:
D is the decimal equivalent of input code.
N is the number of bits.
V
V
Table 9. V
R1, R2
R1 = R2
R1 = R2
R1 = R2
R1 = 3R2
R1 = 3R2
R1 = 3R2
REF
REF
REF
x is the reference voltage for DACs A to D.
x for the rest of the DACs. The circuit configuration is
is the applied external reference.
V
REF
x
ADR420/ADR421/ADR423/ADR425
REF
DACA
DACB
DACC
DACD
V
V
V
V
=
REF
REF
REF
REF
x vs. R1 and R2
V
⎛
⎜
⎝
A
B
C
Figure 48. Programmable DAC Reference
D
REF
1
+
×
2
D
⎛
⎜
⎝
N
Digital Code
0000 0000 0000
1000 0000 0000
1111 1111 1111
0000 0000 0000
1000 0000 0000
1111 1111 1111
1
×
+
R2
R1
R2
R1
AD7398
⎞
⎟
⎠
⎞
⎟
⎠
V
V
V
V
OUT
OUT
OUT
OUT
A
B
C
D
V
IN
±0.1%
R1
REF
ADR425
V
V
V
OB
OC
OD
x to V
V
2 V
1.3 V
V
4 V
1.6 V
V
= V
= V
= V
REF
REF
REF
R2
±0.1%
REF
REF
REF
REF
REF
V
REF
REF
REF
REF
x (D
x (D
x (D
depends
B
C
D
)
)
)
(5)