EVAL-AD7892-3CB 반도체 회로 부품 판매점
LC2MOS Single Supply/ 12-Bit 600 kSPS ADC
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 Analog Devices |
a
Loop-Powered
4 mA to 20 mA DAC
AD421
FEATURES
4 mA to 20 mA Current Output
HART® Compatible
16-Bit Resolution and Monotonicity
؎0.01% Integral Nonlinearity
5 V or 3 V Regulator Output
2.5 V and 1.25 V Precision Reference
750 A Quiescent Current max
Programmable Alarm Current Capability
Flexible High Speed Serial Interface
16-Lead SOIC and PDIP Packages
GENERAL DESCRIPTION
The AD421 is a complete, loop-powered, digital to 4 mA to
20 mA converter, designed to meet the needs of smart trans-
mitter manufacturers in the Industrial Control industry. It pro-
vides a high precision, fully integrated, low cost solution in a
compact 16-lead package. The AD421 is ideal for extending the
resolution of smart 4 mA to 20 mA transmitters at very low cost.
The AD421 includes a selectable regulator that is used to power
itself and other devices in the transmitter. This regulator pro-
vides either a +5 V, +3.3 V or +3 V regulated output voltage.
The part also contains +1.25 V and +2.5 V precision references.
The AD421 thus eliminates the need for a discrete regulator
and voltage reference. The only external components required
are a number of passive components and a pass transistor to
span large loop voltages.
The AD421 can be used with standard HART FSK protocol
communication circuitry without any degradation in specified
performance. The high speed serial interface is capable of oper-
ating at 10 Mbps and allows for simple connection to com-
monly-used microprocessors and microcontrollers via a standard
three-wire serial interface.
The sigma-delta architecture of the DAC guarantees 16-bit
monotonicity while the integral nonlinearity for the AD421 is
± 0.01%. The part provides a zero scale 4 mA output current
with ± 0.1% offset error and a 20 mA full-scale output current
with ± 0.2% gain error.
The AD421 is available in a 16-lead, 0.3 inch-wide, plastic DIP
and in a 16-lead, 0.3 inch-wide, SOIC package. The part is speci-
fied over the industrial temperature range of –40°C to +85°C.
FUNCTIONAL BLOCK DIAGRAM
REF IN REF OUT1 REF OUT2
(+2.5V) (+1.25V) (+2.5V)
LV
VCC
AD421
112.5k⍀ 75k⍀
134k⍀
BANDGAP
REFERENCE
121k⍀
DATA
CLOCK
LATCH
INPUT SHIFT
REGISTER
DAC LATCH
POWER-ON
RESET
LOCAL
OSCILLATOR
16-BIT
SIGMA-
DELTA DAC
SWITCHED
CURRENT
SOURCES
AND
FILTERING
40⍀
80k⍀
DRIVE
COMP
BOOST
LOOP
RTN
COM
C1 C2 C3
PRODUCT HIGHLIGHTS
1. The AD421 is a single chip, high performance, low cost
solution for generating 4 mA to 20 mA signals for smart
industrial control transmitters.
2. The AD421’s regulated supply voltage can be used to power
any additional circuits in the transmitter. The regulated
output value is pin selectable as either +3 V, +3.3 V or +5 V.
3. The AD421’s on-chip references can provide a precision
reference voltage to other devices in the system. This refer-
ence voltage can be either +1.25 V or +2.5 V.
4. The AD421 is fully compatible with standard HART cir-
cuitry or other similar FSK protocols.
5. With the addition of a single discrete transistor, the AD421
can be operated from VCC + 2 V min to a maximum of the
breakdown voltage of the pass transistor.
6. The AD421 converts the digital data to current with 16-bit
resolution and monotonicity. Full-scale settling time to
± 0.1% typically occurs within 8 ms.
7. The AD421 features a programmable alarm current capabil-
ity that allows the transmitter to send out of range currents to
indicate a transducer fault.
HART is a registered trademark of the HART Communication
Foundation.
REV. C
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2000
AD421–LOOP-POWERED SPECIFICATIONS (Using DN25D1 as pass transistor as per Figure 3;
REF IN = REF OUT2; TA = TMIN to TMAX unless otherwise noted)
Parameter
OUTPUT CHARACTERISTICS
Current Loop Voltage Compliance3
Full-Scale Settling Time
Output Impedance
AC Loop Voltage Sensitivity
VOLTAGE REGULATOR
Output Voltage (VCC)
3 V Mode
3.3 V Mode
5 V Mode
Externally Available Current
Line Regulation
Load Regulation
B Versions2 Units
VCC + 2
350
8
25
2
V min
V max
ms typ
MΩ typ
µA/V typ
2.95/3.05
3.25/3.35
4.95/5.05
3.25
1
15
V min/V max
V min/V max
V min/V max
mA min
µV/V typ
µV/mA typ
Conditions/Comments
DN25D Breakdown Voltage
Settling Time to ± 0.1%, C1 = C2 = 10 nF, C3 = 3.3 nF
1200 Hz to 2200 Hz
3 V Nominal. LV Pin Connected to VCC
3.3 V Nominal. LV Pin Connected Through 0.01 µF to VCC
5 V Nominal. LV Pin Connected to COM
Assuming 4 mA Flowing in the Loop
DAC SPECIFICATIONS (VCC = +3 V to +5 V; REF IN = REF OUT2; TA = TMIN to TMAX unless otherwise noted)
Parameter
B Versions2 Units
Conditions/Comments
ACCURACY
Resolution
Monotonicity
Integral Nonlinearity
Offset (4 mA) @ +25°C4
Offset Drift
Total Output Error (20 mA) @ +25°C4
Total Output Drift
VCC Supply Sensitivity
VOLTAGE REFERENCE
REF OUT2
Output Voltage
Drift
16
16
± 0.01
± 0.1
± 25
± 0.2
± 50
50
2.49/2.51
± 40
Externally Available Current
VCC Supply Sensitivity
Output Impedance
Noise (0.1 Hz–10 Hz)
REF OUT1
Output Voltage
Drift
0.5
150
3
6
1.24/1.26
± 50
Externally Available Current
VCC Supply Sensitivity
Output Impedance
Noise (0.1 Hz–10 Hz)
REF IN
Input Resistance
0.5
150
3
4
40
Bits
Bits min
% of FS max
% of FS max
ppm of FS/°C max
% of FS max
ppm of FS/°C max
nA/mV max
FS = Full-Scale Output Current
VCC = 5 V
Includes On-Chip Reference Drift
VCC = 5 V
Includes On-Chip Reference Drift
25 nA/mV Typical
V min/V max
ppm/°C max
mA min
µV/V max
Ω typ
µV (p-p) typ
V min/V max
ppm/°C max
mA min
µV/V max
Ω typ
µV (p-p) typ
kΩ typ
2.5 V Nominal
20 ppm/°C Typical from –40°C to +25°C and
–2.5 ppm/°C Typical from +25°C to +85°C
15 µV/V Typical
1.25 V Nominal, 100 kΩ Load to COM5
20 ppm/°C Typical from –40°C to +25°C and
2 ppm/°C Typical from +25°C to +85°C
15 µV/V Typical
DIGITAL INPUTS
VIH (Logic 1)
VIL (Logic 0)
IIH
IIL
Data Coding
Data Rate
0.75 × VCC
0.25 × VCC
± 10
± 10
Binary
10
V min
V max
µA max
µA max
Mbps max
VIN = VCC
VIN = 0 V
POWER SUPPLIES
Operating Range
+2.95 to +5.05 V min to V max Functional to 7 V
Quiescent Current
@ VCC = 3 V
@ VCC = 5 V
650
µA max
475 µA Typical
750
µA max
575 µA Typical
NOTES
1The DN25D is available from Supertex, Inc., 1350 Bordeaux Drive, Sunnyvale, CA 94089.
2Temperature range is –40°C to +85°C.
3The max current loop voltage compliance is determined by the pass transistor breakdown voltage and is 350 V for the DN25D.
4With VCC = 3 V, the transfer function shifts negative by typically 0.25%; a 16 kΩ resistor connected between COM and LOOPRTN will approximately compensate for the VCC
supply sensitivity in moving from 5 V to 3 V by skewing the gain of the AD421.
5100 kΩ resistor only required if this reference is being used in application circuits.
Specifications subject to change without notice.
–2– REV. C
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