FEATURES
16-bit resolution and monotonicity ±0.012% max integral nonlinearity ±0.05% max offset (trimmable) ±0.15% max total output error (trimmable) Flexible serial digital interface (3.3 MBPS) On-Chip loop fault detection On-chip 5 V reference (25 ppm/°C max) Asynchronous CLEAR function Maximum power supply range 32 V Output loop compliance V to VCC V 24-Lead SOIC and PDIP packages
The is a complete digital to current loop output converter, designed to meet the needs of the industrial control market. It provides a high precision, fully integrated, low cost single-chip solution for generating current loop signals in a compact 24-lead SOIC or PDIP package.
The output current range can be programmed to 20 mA, to an overrange function to 24 mA. The AD420 can alternatively provide a voltage output from a separate pin that can be configured to provide ±10 V with the addition of a single external buffer amplifier.
The 3.3 M Baud serial input logic design minimizes the cost of galvanic isolation and allows for simple connection to commonly used microprocessors. It can be used 3-wire or asynchronous mode and a serial-out pin is provided to allow daisy chaining of multiple DACs on the current loop side of the isolation barrier.
The AD420 uses sigma-delta DAC technology to achieve 16-bit monotonicity at very low cost. Full-scale settling to 0.1% occurs within 3 ms. The only external components that are required (in addition to normal transient protection circuitry) are two low cost capacitors which are used in the DAC output filter.
If the AD420 is used at extreme temperatures and supply voltages, an external output transistor can be used to minimize power dissipation on the chip via the BOOST pin. The FAULT DETECT pin signals when an open circuit occurs in the loop. The on-chip voltage reference can be used to supply a precision V to external components in addition to the AD420 or, if the
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CLEAR LATCH CLOCK DATA IN RANGE SELECT 1 RANGE SELECT 2
user desires temperature stability exceeding 25 ppm/°C, an external precision reference such as the AD586 can be used as the reference. The AD420 is available a 24-lead SOIC and PDIP over the industrial temperature range to +85°C.
1. The is a single chip solution for generating 20 mA signals at the controller end of the current loop.
2. The AD420 is specified with a power supply range from 32 V. Output loop compliance V to VCC 2.75 V.
3. The flexible serial input can be used in 3-wire mode with SPI® or MICROWIRE® microcontrollers, or in asynchronous mode, which minimizes the number of control signals required.
4. The serial data out pin can be used to daisy chain any number of AD420s together in 3-wire mode.
6. The AD420 has an asynchronous CLEAR pin, which sends the output to the low end of the selected range (0 mA, 4 mA, or 0 V).
7. The AD420 BOOST pin accommodates an external transistor to off-load power dissipation from the chip.
8. The offset of ±0.05% and total output error of ±0.15% can be trimmed if desired, using two external potentiometers.
Features : 1 Functional Block Diagram : 1 General Description : 1 Product Highlights : 1 Revision History : 2 Specifications : 3 Absolute Maximum Ratings : 5
ESD Caution : 5 Pin Configuration and Function Descriptions : 6 Timing Requirements : 7
Three-Wire Interface : 7 Three-Wire Interface Fast Edges on Digital Input : 7 Asynchronous Interface : 7 Terminology : 8 Theory of Operation : 9 Applications Information : 10 Current Output : 10
H to Rev. I Changes to Three-Wire Interface Fast Edges on Digital Input Section G to Rev. H Changes to Figure : 13 Changes to Ordering Guide F to Rev. G Updated Format : Universal Changes to Table : 5 Updated Outline Dimensions : 15 Changes to Ordering Guide E to Rev. F
Driving Inductive Loads : 10 Voltage-Mode Output : 10 Optional Span and Zero Trim : 10 Three-Wire Interface : 11 Using Multiple DACS with Fault Detect : 11 Asynchronous Interface Using Optocouplers : 11 Microprocessor Interface 12 AD420-To-MC68HC11 (SPI Bus) Interface AD420 to Microwire Interface : 12 External Boost Function 13 AD420 Protection : 14 Transient Voltage Protection : 14 Board Layout And Grounding : 14 Power Supplies and Decoupling : 14 Outline Dimensions : 15 Ordering Guide : 15
SPECIFICATIONS
Current Loop Voltage Compliance Settling Time (to of FS)1 Output Impedance (Current Mode) Accuracy2
Monotonicity Integral Nonlinearity Offset or 4 mA) (TA = +25°C) Offset Drift Total Output Error or 24 mA) (TA = +25°C) Total Output Error Drift PSRR3 VOUT CHARACTERISTICS FS Output Voltage Range (Pin 17) VOLTAGE REFERENCE REF OUT Output Voltage (TA +25° C) Drift Externally Available Current Short Circuit Current REF IN Resistance VLL Output Voltage Externally Available Current Short Circuit Current DIGITAL INPUTS VIH (Logic 1) VIL (Logic 0) IIH (VIN 5.0 V) IIL (VIN 0 V) Data Input Rate (3-Wire Mode) Data Input Rate (Asynchronous Mode) DIGITAL OUTPUTS FAULT DEFECT VOH (10 k Pull-Up Resistor to VLL) VOL (10 k Pull-Up Resistor to VLL) VOL 2.5 mA DATA OUT VOH (IOH = -0.8 mA) VOL (IOL = 1.6 mA)
Required
