AD421 Analog Devices, AD421 Datasheet - Page 12

• Manufacturer Part Number: AD421
• Description: Loop-Powered 4-20 mA DAC
• Manufacturer: Analog Devices

Specifications of AD421

• Resolution (bits): 16bit
• Dac Update Rate: 125SPS
• Dac Settling Time: 8ms
• Max Pos Supply (v): +5.05V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Ser

AD421
Current Source
Figure 18 shows an application circuit for the AD421 being
used as a current source. The current programmed to the
AD421 (4 mA to 20 mA) will develop a voltage across R1.
This same voltage due to negative feedback will be generated
SENSORS
AMBIENT
mV
SENSOR
TEMP
RTD
TC
CLOCK
LATCH
0.1 F
DATA
MCLK IN
MCLK OUT
DGND
DV
CONVERTER
AD7714/
AD7715
ANALOG
DIGITAL
DD
DATA OUT
TO
DATA IN
AV
REF IN
AGND
SCLK
DD
10k
CS
Figure 18. AD421 in Programmable Current Source/Sink
10k
100k
Figure 17. AD421 in HART Transmitter Application
10k
COM
4.7 F
4.7 F
DATA
LATCH
CLOCK
MICROCONTROLLER
REF IN
GND
V
COM
CC
REF OUT2
–12–
C1
across R2. The ratio of R1 to R2 determines the current that
flows in the load resistor R
is the current that flows in the load resistor R
current programmed to the AD421. R1 and R2 are external to
the AD421 and will need to be matched resistors to obtain a
highly accurate current source.
0.01 F
REF OUT1
AD421
1.25V
3.3V
C2
4.7 F
0.01 F
COM
2.2 F
BELL 202
MODEM
2.2 F
HART
LV
C3
REF OUT1
REF OUT2
REF IN
CLOCK
LATCH
DATA
COM
C1
0.0033 F
BOOST
BOOST
DRIVE
COMP
V
LOOP
DN25D
CC
RTN
C2
AD421
*FOR SELECTION OF C
+5V
L
V
C3
. I
CC
WAVEFORM
0.01 F
SHAPER
R1
L
= [1 + R1/R2] × I
OUT
LV
DRIVE
COMP
REGULATOR
LOOP
C
RTN
C
5 VOLT
*
COM
1000pF
0.01 F
HT20C12/20C15
C
V
IN
, REFER TO AN-534
1k
R2
S
R
RETURN
L
L
BANDPASS
and I
FILTER
PROG
V
S
PROG
POWER
LOOP
, where I
REV. C
is the
L