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FEATURES Complete 12-Bit A/D Converter with Reference and Clock 8- and 16-Bit Microprocessor Bus Interface Guaranteed Linearity Over Temperature 0 C to +70 C - AD574AJ, K, L -55 C to +125 C - AD574AS, T, U No Missing Codes Over Temperature 35 s Maximum Conversion Time Buried Zener Reference for Long-Term Stability and Low Gain T.C. 10 ppm/ C max AD574AL 12.5 ppm/ C max AD574AU Ceramic DIP, Plastic DIP or PLCC Package Available in Higher Speed, Pinout-Compatible Versions (15 s AD674B, 80 s AD774B; 10 s (with SHA) AD1674) Available in Versions Compliant with MIL-STD-883 and JAN QPL
+5V SUPPLY VLOGIC DATA MODE SELECT 12/8 CHIP SELECT CS BYTE ADDRESS/ SHORT CYCLE AO READ/CONVERT R/C CHIP ENABLE CE +12/+15V SUPPLY VCC +10V REFERENCE REF OUT ANALOG COMMON AC REFERENCE INPUT REF IN -12/-15V SUPPLY VEE BIPOLAR OFFSET BIP OFF 10V SPAN INPUT 10VIN 1 2 3 4 5 6 7
Complete 12-Bit A/D Converter AD574A*
BLOCK DIAGRAM AND PIN CONFIGURATION
STATUS STS DB11 27 MSB 26 DB10 25 DB9 24 DB8 23 DB7 22 DB6 21 DB5 20 DB4 19 DB3 18 DB2 17 DB1 DB0 16 LSB 15 DIGITAL COMMON DC DIGITAL DATA OUTPUTS 28
MSB
CONTROL 3 S T A T E O U T P U T B U F F E R S
CLOCK 3k
SAR
12
N I B B L E A N I B B L E B N I B B L E C
LSB
COMP 12 8 9 10 19.95k 11 12 13 5k 9.95k 5k DAC N VEE 10V REF IDAC IDAC = 4 x N x IREF IREF 8k
20V SPAN INPUT 14 20VIN
AD574A
12
PRODUCT DESCRIPTION
PRODUCT HIGHLIGHTS
The AD574A is a complete 12-bit successive-approximation analog-to-digital converter with 3-state output buffer circuitry for direct interface to an 8- or 16-bit microprocessor bus. A high precision voltage reference and clock are included on-chip, and the circuit guarantees full-rated performance without external circuitry or clock signals. The AD574A design is implemented using Analog Devices' Bipolar/I2L process, and integrates all analog and digital functions on one chip. Offset, linearity and scaling errors are minimized by active laser-trimming of thin-film resistors at the wafer stage. The voltage reference uses an implanted buried Zener for low noise and low drift. On the digital side, I2L logic is used for the successive-approximation register, control circuitry and 3-state output buffers. The AD574A is available in six different grades. The AD574AJ, K, and L grades are specified for operation over the 0C to +70C temperature range. The AD574AS, T, and U are specified for the -55C to +125C range. All grades are available in a 28-pin hermetically-sealed ceramic DIP. Also, the J, K, and L grades are available in a 28-pin plastic DIP and PLCC, and the J and K grades are available in ceramic LCC. The S, T, and U grades in ceramic DIP or LCC are available with optional processing to MIL-STD-883C Class B; the T and U grades are available as JAN QPL. The Analog Devices' Military Products Databook should be consulted for details on /883B testing of the AD574A.
*Protected by U.S. Patent Nos. 3,803,590; 4,213,806; 4,511,413; RE 28,633 .
1. The AD574A interfaces to most 8- or 16-bit microprocessors. Multiple-mode three-state output buffers connect directly to the data bus while the read and convert commands are taken from the control bus. The 12 bits of output data can be read either as one 12-bit word or as two 8-bit bytes (one with 8 data bits, the other with 4 data bits and 4 trailing zeros). 2. The precision, laser-trimmed scaling and bipolar offset resistors provide four calibrated ranges: 0 volts to +10 volts and 0 volts to +20 volts unipolar, -5 volts to +5 volts and -10 volts to +10 volts bipolar. Typical bipolar offset and full-scale calibration errors of 0.1% can be trimmed to zero with one external component each. 3. The internal buried Zener reference is trimmed to 10.00 volts with 0.2% maximum error and 15 ppm/C typical T.C. The reference is available externally and can drive up to 1.5 mA beyond the requirements of the reference and bipolar offset resistors. 4. AD674B (15 s) and AD774B (8 s) provide higher speed, pin compatibility; AD1674 (10 s) includes on-chip SampleHold Amplifier (SHA).
REV. B
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: 617/329-4700 Fax: 617/326-8703
C with V = +15 AD574A-SPECIFICATIONS (@ +25otherwise noted) V or +12 V, V unless
CC
LOGIC
= +5 V, VEE = -15 V or -12 V
AD574AL Typ
Model RESOLUTION LINEARITY ERROR @ +25C TMIN to TMAX DIFFERENTIAL LINEARITY ERROR (Minimum Resolution for Which No Missing Codes are Guaranteed) TMIN to TMAX UNIPOLAR OFFSET (Adjustable to Zero) BIPOLAR OFFSET (Adjustable to Zero) FULL-SCALE CALIBRATION ERROR (With Fixed 50 Resistor from REF OUT to REF IN) (Adjustable to Zero) TEMPERATURE RANGE TEMPERATURE COEFFICIENTS (Using Internal Reference) TMIN to TMAX Unipolar Offset Bipolar Offset Full-Scale Calibration POWER SUPPLY REJECTION Max Change in Full-Scale Calibration VCC = 15 V 1.5 V or 12 V 0.6 V VLOGIC = 5 V 0.5 V VEE = -15 V 1.5 V or -12 V 0.6 V ANALOG INPUT Input Ranges Bipolar Unipolar Input Impedance 10 Volt Span 20 Volt Span DIGITAL CHARACTERISTICS 1 (TMIN-TMAX) Inputs2 (CE, CS, R/C, A0) Logic "1" Voltage Logic "0" Voltage Current Capacitance Output (DB11-DB0, STS) Logic "1" Voltage (I SOURCE 500 A) Logic "0" Voltage (I SINK 1.6 mA) Leakage (DB11-DB0, High-Z State) Capacitance POWER SUPPLIES Operating Range VLOGIC VCC VEE Operating Current ILOGIC ICC IEE POWER DISSIPATION INTERNAL REFERENCE VOLTAGE Output Current (Available for External Loads) 3 (External Load Should not Change During Conversion) PACKAGE OPTIONS 4 Ceramic (D-28) Plastic (N-28) PLCC (P-28A) LCC (E-28A)
1 2
Min
AD574AJ Typ
Max 12 1 1
Min
AD574AK Typ
Max 12 1/2 1/2
Min
Max 12 1/2 1/2
Units Bits LSB LSB
11 2 4
12 1 4
12 1 2
Bits LSB LSB
0.25 0 +70 0
0.25 +70 0
0.125 +70
% of FS C
2 (10) 2 (10) 9 (50)
1 (5) 1 (5) 5 (27)
1 (5) LSB (ppm/C) 1 (5) LSB (ppm/C) 2 (10) LSB (ppm/C)
2 1/2 2
1 1/2 1
1 1/2 1
LSB LSB LSB
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
Volts Volts Volts Volts k k
+2.0 -0.5 -20 5 +2.4 -20 5
+5.5 +0.8 +20
+2.0 -0.5 -20 5 +2.4
+5.5 +0.8 +20
+2.0 -0.5 -20 5 +2.4
+5.5 +0.8 +20
Volts Volts A pF Volts Volts A pF
+0.4 +20
-20 5
+0.4 +20
-20 5
+0.4 +20
+4.5 +11.4 -11.4 30 2 18 390 9.98 10.0
+5.5 +16.5 -16.5 40 5 30 725 10.02 1.5
+4.5 +11.4 -11.4 30 2 18 390 9.98 10.0
+5.5 +16.5 -16.5 40 5 30 725 10.02 1.5
+4.5 +11.4 -11.4 30 2 18 390 9.99 10.0
+5.5 +16.5 -16.5 40 5 30 725 10.01 1.5
Volts Volts Volts mA mA mA mW Volts mA
AD574ASD AD574AJN AD574AJP AD574AJE
AD574AKD AD574AKN AD574AKP AD574AKE
AD574ALD AD574ALN
NOTES Detailed Timing Specifications appear in the Timing Section. 12/8 Input is not TTL-compatible and must be hard wired to V LOGIC or Digital Common. 3 The reference should be buffered for operation on 12 V supplies. 4 D = Ceramic DIP; N = Plastic DIP; P = Plastic Leaded Chip Carrier. Specifications subject to change without notice.
-2-
REV. B
AD574A
Model RESOLUTION LINEARITY ERROR @ +25C TMIN to TMAX DIFFERENTIAL LINEARITY ERROR (Minimum Resolution for Which No Missing Codes are Guaranteed) TMIN to TMAX UNIPOLAR OFFSET (Adjustable to Zero) BIPOLAR OFFSET (Adjustable to Zero) FULL-SCALE CALIBRATION ERROR (With Fixed 50 Resistor from REF OUT to REF IN) (Adjustable to Zero) TEMPERATURE RANGE TEMPERATURE COEFFICIENTS (Using Internal Reference) (TMIN to TMAX) Unipolar Offset Bipolar Offset Full-Scale Calibration POWER SUPPLY REJECTION Max Change in Full-Scale Calibration VCC = 15 V 1.5 V or 12 V 0.6 V VLOGIC = 5 V 0.5 V VEE = -15 V 1.5 V or -12 V 0.6 V ANALOG INPUT Input Ranges Bipolar Unipolar Input Impedance 10 Volt Span 20 Volt Span DIGITAL CHARACTERISTICS 1 (TMIN-TMAX) Inputs2 (CE, CS, R/C, A0) Logic "1" Voltage Logic "0" Voltage Current Capacitance Output (DB11-DB0, STS) Logic "1" Voltage (I SOURCE 500 A) Logic "0" Voltage (I SINK 1.6 mA) Leakage (DB11-DB0, High-Z State) Capacitance POWER SUPPLIES Operating Range VLOGIC VCC VEE Operating Current ILOGIC ICC IEE POWER DISSIPATION INTERNAL REFERENCE VOLTAGE Output Current (Available for External Loads) 3 (External Load Should not Change During Conversion) PACKAGE OPTION4 Ceramic (D-28) 9.98 -55 Min AD574AS Typ Max 12 1 1 Min AD574AT Typ Max 12 1/2 1 Min AD574AU Typ Max 12 1/2 1 Units Bits LSB LSB
11 2 4
12 1 4
12 1 2
Bits LSB LSB
0.25 +125 -55
0.25 +125 -55
0.125 +125
% of FS C
2 (5) 4 (10) 20 (50)
1 (2.5) 2 (5) 10 (25)
1 (2.5) LSB (ppm/C) 1 (2.5) LSB (ppm/C) 5 (12.5) LSB (ppm/C)
2 1/2 2
1 1/2 1
1 1/2 1
LSB LSB LSB
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
-5 -10 0 0 3 6 5 10
+5 +10 +10 +20 7 14
Volts Volts Volts Volts k k
+2.0 -0.5 -20 5 +2.4 -20 5
+5.5 +0.8 +20
+2.0 -0.5 -20 5 +2.4
+5.5 +0.8 +20
+2.0 -0.5 -20 5 +2.4
+5.5 +0.8 +20
Volts Volts A pF Volts Volts A pF
+0.4 +20
-20 5
+0.4 +20
-20 5
+0.4 +20
+4.5 +11.4 -11.4 30 2 18 390 10.0
+5.5 +16.5 -16.5 40 5 30 725 10.02 1.5
+4.5 +11.4 -11.4 30 2 18 390 9.98 10.0
+5.5 +16.5 -16.5 40 5 30 725 10.02 1.5
+4.5 +11.4 -11.4 30 2 18 390 9.99
+5.5 +16.5 -16.5 40 5 30 725
Volts Volts Volts mA mA mA mW Volts mA
10.0 10.01 1.5
AD574ASD
AD574ATD
AD574AUD
NOTES 1 Detailed Timing Specifications appear in the Timing Section. 2 12/8 Input is not TTL-compatible and must be hard wired to V LOGIC or Digital Common. 3 The reference should be buffered for operation on 12 V supplies. 4 D = Ceramic DIP. Specifications subject to change without notice.
REV. B
-3-
AD574A
+5V SUPPLY VLOGIC DATA MODE SELECT 12/8 CHIP SELECT CS BYTE ADDRESS/ SHORT CYCLE AO READ/CONVERT R/C CHIP ENABLE CE +12/+15V SUPPLY VCC +10V REFERENCE REF OUT ANALOG COMMON AC REFERENCE INPUT REF IN -12/-15V SUPPLY VEE BIPOLAR OFFSET BIP OFF 10V SPAN INPUT 10VIN 1 2 3 4 5 6 7 COMP 12 8 9 10 19.95k 11 12 13 5k 9.95k 5k DAC N VEE 10V REF IDAC IDAC = 4 x N x IREF IREF 8k CLOCK 3k SAR 12 CONTROL 3 S T A T E O U T P U T B U F F E R S
MSB
28
N I B B L E A N I B B L E B N I B B L E C
LSB
STATUS STS DB11 27 MSB 26 DB10 25 DB9 24 DB8 23 DB7 22 DB6 21 DB5 20 DB4 DIGITAL DATA OUTPUTS
19 DB3 18 DB2 17 DB1 DB0 16 LSB 15 DIGITAL COMMON DC
20V SPAN INPUT 14 20VIN
AD574A
12
AD574A Block Diagram and Pin Configuration
ABSOLUTE MAXIMUM RATINGS*
(Specifications apply to all grades, except where noted)
VCC to Digital Common . . . . . . . . . . . . . . . . . . 0 V to +16.5 V VEE to Digital Common . . . . . . . . . . . . . . . . . . . 0 V to -16.5 V VLOGIC to Digital Common . . . . . . . . . . . . . . . . . . 0 V to +7 V Analog Common to Digital Common . . . . . . . . . . . . . . . 1 V Control Inputs (CE, CS, AO 12/8, R/C) to Digital Common . . . . . . . . . . . . . . -0.5 V to VLOGIC + 0.5 V Analog Inputs (REF IN, BIP OFF, 10 VIN) to Analog Common . . . . . . . . . . . . . . . . . . . . . . . . . VEE to VCC 20 VIN to Analog Common . . . . . . . . . . . . . . . . . . . . . . 24 V REF OUT . . . . . . . . . . . . . . . . . . Indefinite Short to Common Momentary Short to VCC
Chip Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175C Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825 mW Lead Temperature (Soldering, 10 sec). . . . . . . . . . . . . +300C Storage Temperature (Ceramic) . . . . . . . . . . -65C to +150C (Plastic) . . . . . . . . . . . . . . . . . . . . . . . . . . . -25C to +100C
*Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ORDERING GUIDE
Model1 AD574AJ(X) AD574AK(X) AD574AL(X) AD574AS(X)2 AD574AT(X)2 AD574AU(X)2
Temperature Range 0C to +70C 0C to +70C 0C to +70C -55C to +125C -55C to +125C -55C to +125C
Linearity Error Max (TMIN to TMAX) 1 LSB 1/2 LSB 1/2 LSB 1 LSB 1 LSB 1 LSB
Resolution No Missing Codes (TMIN to TMAX) 11 Bits 12 Bits 12 Bits 11 Bits 12 Bits 12 Bits
Max Full Scale T.C. (ppm/C) 50.0 27.0 10.0 50.0 25.0 12.5
NOTES 1 X = Package designator. Available packages are: D (D-28) for all grades. E (E-28A) for J and K grades and /883B processed S, T and U grades. N (N-28) for J, K, and L grades. P (P-28A) for PLCC in J, K grades. Example: AD574AKN is K grade in plastic DIP. 2 For details on grade and package offerings screened in accordance with MIL-STD-883, refer to Analog Devices Military Products Databook.
-4-
REV. B
AD574A
THE AD574A OFFERS GUARANTEED MAXIMUM LINEARITY ERROR OVER THE FULL OPERATING TEMPERATURE RANGE
DEFINITIONS OF SPECIFICATIONS QUANTIZATION UNCERTAINTY
LINEARITY ERROR Linearity error refers to the deviation of each individual code from a line drawn from "zero" through "full scale". The point used as "zero" occurs 1/2 LSB (1.22 mV for 10 volt span) before the first code transition (all zeros to only the LSB "on"). "Full scale" is defined as a level 1 1/2 LSB beyond the last code transition (to all ones). The deviation of a code from the true straight line is measured from the middle of each particular code. The AD574AK, L, T, and U grades are guaranteed for maximum nonlinearity of 1/2 LSB. For these grades, this means that an analog value which falls exactly in the center of a given code width will result in the correct digital output code. Values nearer the upper or lower transition of the code width may produce the next upper or lower digital output code. The AD574AJ and S grades are guaranteed to 1 LSB max error. For these grades, an analog value which falls within a given code width will result in either the correct code for that region or either adjacent one. Note that the linearity error is not user-adjustable.
DIFFERENTIAL LINEARITY ERROR (NO MISSING CODES)
Analog-to-digital converters exhibit an inherent quantization uncertainty of 1/2 LSB. This uncertainty is a fundamental characteristic of the quantization process and cannot be reduced for a converter of given resolution.
LEFT-JUSTIFIED DATA
The data format used in the AD574A is left-justified. This means that the data represents the analog input as a fraction of 4095 full-scale, ranging from 0 to 4096 . This implies a binary point to the left of the MSB.
FULL-SCALE CALIBRATION ERROR
The last transition (from 1111 1111 1110 to 1111 1111 1111) should occur for an analog value 1 1/2 LSB below the nominal full scale (9.9963 volts for 10.000 volts full scale). The full-scale calibration error is the deviation of the actual level at the last transition from the ideal level. This error, which is typically 0.05% to 0.1% of full scale, can be trimmed out as shown in Figures 3 and 4.
TEMPERATURE COEFFICIENTS
A specification which guarantees no missing codes requires that every code combination appear in a monotonic increasing sequence as the analog input level is increased. Thus every code must have a finite width. For the AD574AK, L, T, and U grades, which guarantee no missing codes to 12-bit resolution, all 4096 codes must be present over the entire operating temperature ranges. The AD574AJ and S grades guarantee no missing codes to 11-bit resolution over temperature; this means that all code combinations of the upper 11 bits must be present; in practice very few of the 12-bit codes are missing.
UNIPOLAR OFFSET
The temperature coefficients for full-scale calibration, unipolar offset, and bipolar offset specify the maximum change from the initial (25C) value to the value at TMIN or TMAX.
POWER SUPPLY REJECTION
The standard specifications for the AD574A assume use of +5.00 V and 15.00 V or 12.00 V supplies. The only effect of power supply error on the performance of the device will be a small change in the full-scale calibration. This will result in a linear change in all lower order codes. The specifications show the maximum full-scale change from the initial value with the supplies at the various limits.
CODE WIDTH
The first transition should occur at a level 1/2 LSB above analog common. Unipolar offset is defined as the deviation of the actual transition from that point. This offset can be adjusted as discussed on the following two pages. The unipolar offset temperature coefficient specifies the maximum change of the transition point over temperature, with or without external adjustment.
BIPOLAR OFFSET
A fundamental quantity for A/D converter specifications is the code width. This is defined as the range of analog input values for which a given digital output code will occur. The nominal value of a code width is equivalent to 1 least significant bit (LSB) of the full-scale range or 2.44 mV out of 10 volts for a 12-bit ADC.
In the bipolar mode the major carry transition (0111 1111 1111 to 1000 0000 0000) should occur for an analog value 1/2 LSB below analog common. The bipolar offset error and temperature coefficient specify the initial deviation and maximum change in the error over temperature.
REV. B
-5-
AD574A
CIRCUIT OPERATION DRIVING THE AD574 ANALOG INPUT
The AD574A is a complete 12-bit A/D converter which requires no external components to provide the complete successiveapproximation analog-to-digital conversion function. A block diagram of the AD574A is shown in Figure 1.
+5V SUPPLY VLOGIC DATA MODE SELECT 12/8 CHIP SELECT CS BYTE ADDRESS/ SHORT CYCLE AO READ/CONVERT R/C CHIP ENABLE CE +12/+15V SUPPLY VCC +10V REFERENCE REF OUT ANALOG COMMON AC REFERENCE INPUT REF IN -12/-15V SUPPLY VEE BIPOLAR OFFSET BIP OFF 10V SPAN INPUT 10VIN 1 2 3 4 5 6 7 COMP 12 8 9 10 19.95k 11 12 13 5k 9.95k 5k DAC N VEE 10V REF IDAC IDAC = 4 x N x IREF IREF 8k CLOCK 3k SAR 12 CONTROL 3 S T A T E O U T P U T B U F F E R S
MSB
28 27
N I B B L E A N I B B L E B N I B B L E C
LSB
STATUS STS DB11 MSB
The internal circuitry of the AD574 dictates that its analog input be driven by a low source impedance. Voltage changes at the current summing node of the internal comparator result in abrupt modulations of the current at the analog input. For accurate 12-bit conversions the driving source must be capable of holding a constant output voltage under these dynamically changing load conditions.
FEEDBACK TO AMPLIFIER V+
26 DB10 25 DB9 24 DB8 23 DB7 22 DB6 21 DB5 20 DB4 DIGITAL DATA OUTPUTS
AD574A
CURRENT LIMITING RESISTORS
RIN
IIN IS MODULATED BY
IIN iTEST
iDIFF
CURRENT OUTPUT DAC
19 DB3 18 DB2
V-
CHANGES IN TEST CURRENT. AMPLIFIER PULSE LOAD RESPONSE LIMITED BY OPEN LOOP OUTPUT IMPEDANCE.
COMPARATOR
17 DB1 DB0 16 LSB 15 DIGITAL COMMON DC
ANALOG COMMON
SAR
20V SPAN INPUT 14 20VIN
AD574A
12
Figure 2. Op Amp - AD574A Interface
Figure 1. Block Diagram of AD574A 12-Bit A-to-D Converter
When the control section is commanded to initiate a conversion (as described later), it enables the clock and resets the successiveapproximation register (SAR) to all zeros. Once a conversion cycle has begun, it cannot be stopped or restarted and data is not available from the output buffers. The SAR, timed by the clock, will sequence through the conversion cycle and return an end-of-convert flag to the control section. The control section will then disable the clock, bring the output status flag low, and enable control functions to allow data read functions by external command. During the conversion cycle, the internal 12-bit current output DAC is sequenced by the SAR from the most significant bit (MSB) to least significant bit (LSB) to provide an output current which accurately balances the input signal current through the 5 k (or 10 k) input resistor. The comparator determines whether the addition of each successively-weighted bit current causes the DAC current sum to be greater or less than the input current; if the sum is less, the bit is left on; if more, the bit is turned off. After testing all the bits, the SAR contains a 12-bit binary code which accurately represents the input signal to within 1/2 LSB. The temperature-compensated buried Zener reference provides the primary voltage reference to the DAC and guarantees excellent stability with both time and temperature. The reference is trimmed to 10.00 volts 0.2%; it can supply up to 1.5 mA to an external load in addition to the requirements of the reference input resistor (0.5 mA) and bipolar offset resistor (1 mA) when the AD574A is powered from 15 V supplies. If the AD574A is used with 12 V supplies, or if external current must be supplied over the full temperature range, an external buffer amplifier is recommended. Any external load on the AD574A reference must remain constant during conversion. The thin-film application resistors are trimmed to match the full-scale output current of the DAC. There are two 5 k input scaling resistors to allow either a 10 volt or 20 volt span. The 10 k bipolar offset resistor is grounded for unipolar operation and connected to the 10 volt reference for bipolar operation.
The output impedance of an op amp has an open-loop value which, in a closed loop, is divided by the loop gain available at the frequency of interest. The amplifier should have acceptable loop gain at 500 kHz for use with the AD574A. To check whether the output properties of a signal source are suitable, monitor the AD574's input with an oscilloscope while a conversion is in progress. Each of the 12 disturbances should subside in 1 s or less. For applications involving the use of a sample-and-hold amplifier, the AD585 is recommended. The AD711 or AD544 op amps are recommended for dc applications.
SAMPLE-AND-HOLD AMPLIFIERS
Although the conversion time of the AD574A is a maximum of 35 s, to achieve accurate 12-bit conversions of frequencies greater than a few Hz requires the use of a sample-and-hold amplifier (SHA). If the voltage of the analog input signal driving the AD574A changes by more than 1/2 LSB over the time interval needed to make a conversion, then the input requires a SHA. The AD585 is a high linearity SHA capable of directly driving the analog input of the AD574A. The AD585's fast acquisition time, low aperture and low aperture jitter are ideally suited for high-speed data acquisition systems. Consider the AD574A converter with a 35 s conversion time and an input signal of 10 V p-p: the maximum frequency which may be applied to achieve rated accuracy is 1.5 Hz. However, with the addition of an AD585, as shown in Figure 3, the maximum frequency increases to 26 kHz. The AD585's low output impedance, fast-loop response, and low droop maintain 12-bits of accuracy under the changing load conditions that occur during a conversion, making it suitable for use in high accuracy conversion systems. Many other SHAs cannot achieve 12-bits of accuracy and can thus compromise a system. The AD585 is recommended for AD574A applications requiring a sample and hold. An alternate approach is to use the AD1674, which combines the ADC and SHA on one chip, with a total throughput time of 10 s. -6- REV. B
AD574A
+VS TO A1 VREF AGND +VS 14 13 12 11 10 9 8 R2 100 GAIN +15V
R1 100k OFFSET
C1
A
+ + + C3
+15V +5V -15V
page. Analog input connections and calibration are easily accomplished; the unipolar operating mode is shown in Figure 4.
2 12/8 STS 28 HIGH 27 BIT 24 MIDDLE 23 BITS 20
-VS TO A1
C2
11 1 8 10 13 R4 100k 12 9 3 4 15
A
267
OFFSET R1 100k -12V/-15V +12V/+15V 3 CS 4 AO 5 R/C 6 CE GAIN
10k 10k 100pF A1 AD585
A2
27 16
12-BIT 3-STATE DATA
AD574A
100k
AD574A
10 REF IN 8 REF OUT 12 BIP OFF
1
2
3
4
5
6
7
R3 -15V 100
R2 100 100
LOW 19 BITS 16
-VS ANALOG INPUT 0V TO +10V CONVERT 7404 OR EQ.
28
5
0 TO +10V +5V 13 10VIN ANALOG INPUTS 0 TO +20V 9 ANA COM DIG COM 15 +15V 14 20VIN -15V 7 11 1
STATUS
NOTE 1. C1, C2, C3 ARE 47 F TANTALUM, BYPASSED BY 0.1 F CERAMIC. LOCATE AT ASSOCIATED A2 PINS.
Figure 3. AD574A with AD585 Sample and Hold
SUPPLY DECOUPLING AND LAYOUT CONSIDERATIONS
Figure 4. Unipolar Input Connections
It is critically important that the AD574A power supplies be filtered, well regulated, and free from high frequency noise. Use of noisy supplies will cause unstable output codes. Switching power supplies are not recommended for circuits attempting to achieve 12-bit accuracy unless great care is used in filtering any switching spikes present in the output. Remember that a few millivolts of noise represents several counts of error in a 12-bit ADC. Decoupling capacitors should be used on all power supply pins; the +5 V supply decoupling capacitor should be connected directly from Pin 1 to Pin 15 (digital common) and the +VCC and -VEE pins should be decoupled directly to analog common (Pin 9). A suitable decoupling capacitor is a 4.7 F tantalum type in parallel with a 0.1 F disc ceramic type. Circuit layout should attempt to locate the AD574A, associated analog input circuitry, and interconnections as far as possible from logic circuitry. For this reason, the use of wire-wrap circuit construction is not recommended. Careful printed circuit construction is preferred.
GROUNDING CONSIDERATIONS
All of the thin-film application resistors of the AD574A are trimmed for absolute calibration. Therefore, in many applications, no calibration trimming will be required. The absolute accuracy for each grade is given in the specification tables. For example, if no trims are used, the AD574AK guarantees 1 LSB max zero offset error and 0.25% (10 LSB) max full-scale error. (Typical full-scale error is 2 LSB.) If the offset trim is not required, Pin 12 can be connected directly to Pin 9; the two resistors and trimmer for Pin 12 are then not needed. If the full-scale trim is not needed, a 50 1% metal film resistor should be connected between Pin 8 and Pin 10. The analog input is connected between Pin 13 and Pin 9 for a 0 V to +10 V input range, between 14 and Pin 9 for a 0 V to +20 V input range. The AD574A easily accommodates an input signal beyond the supplies. For the 10 volt span input, the LSB has a nominal value of 2.44 mV; for the 20 volt span, 4.88 mV. If a 10.24 V range is desired (nominal 2.5 mV/bit), the gain trimmer (R2) should be replaced by a 50 resistor, and a 200 trimmer inserted in series with the analog input to Pin 13 for a full-scale range of 20.48 V (5 mV/bit), use a 500 trimmer into Pin 14. The gain trim described below is now done with these trimmers. The nominal input impedance into Pin 13 is 5 k, and 10 k into Pin 14.
UNIPOLAR CALIBRATION
The analog common at Pin 9 is the ground reference point for the internal reference and is thus the "high quality" ground for the AD574A; it should be connected directly to the analog reference point of the system. In order to achieve all of the high accuracy performance available from the AD574A in an environment of high digital noise content, the analog and digital commons should be connected together at the package. In some situations, the digital common at Pin 15 can be connected to the most convenient ground reference point; analog power return is preferred.
UNIPOLAR RANGE CONNECTIONS FOR THE AD574A
The AD574A is intended to have a nominal 1/2 LSB offset so that the exact analog input for a given code will be in the middle of that code (halfway between the transitions to the codes above and below it). Thus, the first transition (from 0000 0000 0000 to 0000 0000 0001) will occur for an input level of +1/2 LSB (1.22 mV for 10 V range). If Pin 12 is connected to Pin 9, the unit will behave in this manner, within specifications. If the offset trim (R1) is used, it should be trimmed as above, although a different offset can be set for a particular system requirement. This circuit will give approximately 15 mV of offset trim range.
The AD574A contains all the active components required to perform a complete 12-bit A/D conversion. Thus, for most situations, all that is necessary is connection of the power supplies (+5 V, +12 V/+15 V and -12 V/-15 V), the analog input, and the conversion initiation command, as discussed on the next REV. B -7-
AD574A
The full-scale trim is done by applying a signal 1 1/2 LSB below the nominal full scale (9.9963 for a 10 V range). Trim R2 to give the last transition (1111 1111 1110 to 1111 1111 1111).
BIPOLAR OPERATION
STATUS R/C CE CS
CONVERT
START CONVERT
The connections for bipolar ranges are shown in Figure 5. Again, as for the unipolar ranges, if the offset and gain specifications are sufficient, one or both of the trimmers shown can be replaced by a 50 1% fixed resistor. Bipolar calibration is similar to unipolar calibration. First, a signal 1/2 LSB above negative full scale (-4.9988 V for the 5 V range) is applied and R1 is trimmed to give the first transition (0000 0000 0000 to 0000 0000 0001). Then a signal 1 1/2 LSB below positive full scale (+4.9963 V the 5 V range) is applied and R2 trimmed to give the last transition (1111 11111110 to 1111 1111 1111).
2 12/8 3 CS 4 AO 5 R/C 6 CE R2 100 GAIN STS 28 27 HIGH BIT 24 MIDDLE 23 BITS 20
LOW IF CONVERSION IN PROGRESS
A0 READ
VALUE OF A0 AT LAST CONVERT COMMAND EOC8 EOC12 FROM NOTE 1
12/8 (NOTE 2)
NIBBLE A, B, ENABLE NIBBLE C ENABLE NIBBLE B = O ENABLE TO OUTPUT BUFFERS
NOTE 1: WHEN START CONVERT GOES LOW, THE EOC (END OF CONVERSION) SIGNALS GO LOW. EOC8 RETURNS HIGH AFTER AN 8-BIT CONVERSION CYCLE IS COMPLETE, AND EOC12 RETURNS HIGH WHEN ALL 12-BITS HAVE BEEN CONVERTED. THE EOC SIGNALS PREVENT DATA FROM BEING READ DURING CONVERSIONS. NOTE 2: 12/8 IS NOT A TTL-COMPATABLE INPUT AND SHOULD ALWAYS BE WIRED DIRECTLY TO VLOGIC OR DIGITAL COMMON.
AD574A
10 REF IN 8 REF OUT
LOW 19 BITS 16
Figure 6. AD574A Control Logic
OFFSET 5V ANALOG INPUTS 10V
12 BIP OFF R1 100 +5V 13 10VIN +15V 14 20VIN 9 ANA COM 7 -15V 11 DIG COM 15 1
An output signal, STS, indicates the status of the converter. STS goes high at the beginning of a conversion and returns low when the conversion cycle is complete.
Table I. AD574A Truth Table
CE CS R/C 12/8
Figure 5. Bipolar Input Connections
CONTROL LOGIC
AO X X 0 1
Operation None None Initiate 12-Bit Conversion Initiate 8-Bit Conversion Enable 12-Bit Parallel Output Enable 8 Most Significant Bits Enable 4 LSBs + 4 Trailing Zeroes
0 X 1 1 1 1 1
X 1 0 0 0 0 0
X X 0 0 1 1 1
X X X X
The AD574A contains on-chip logic to provide conversion initiation and data read operations from signals commonly available in microprocessor systems. Figure 6 shows the internal logic circuitry of the AD574A. The control signals CE, CS, and R/C control the operation of the converter. The state of R/C when CE and CS are both asserted determines whether a data read (R/C = 1) or a convert (R/C = 0) is in progress. The register control inputs AO and 12/8 control conversion length and data format. The AO line is usually tied to the least significant bit of the address bus. If a conversion is started with AO low, a full 12-bit conversion cycle is initiated. If AO is high during a convert start, a shorter 8-bit conversion cycle results. During data read operations, AO determines whether the three-state buffers containing the 8 MSBs of the conversion result (AO = 0) or the 4 LSBs (AO = 1) are enabled. The 12/8 pin determines whether the output data is to be organized as two 8-bit words (12/8 tied to DIGITAL COMMON) or a single 12-bit word (12/8 tied to VLOGIC). The 12/8 pin is not TTL-compatible and must be hard-wired to either VLOGIC or DIGITAL COMMON. In the 8-bit mode, the byte addressed when AO is high contains the 4 LSBs from the conversion followed by four trailing zeroes. This organization allows the data lines to be overlapped for direct interface to 8-bit buses without the need for external three-state buffers. It is not recommended that AO change state during a data read operation. Asymmetrical enable and disable times of the three-state buffers could cause internal bus contention resulting in potential damage to the AD574A.
Pin 1 X Pin 15 0 Pin 15 1
TIMING
The AD574A is easily interfaced to a wide variety of microprocessors and other digital systems. The following discussion of the timing requirements of the AD574A control signals should provide the system designer with useful insight into the operation of the device.
Table II. Convert Start Timing--Full Control Mode Symbol tDSC tHEC tSSC tHSC tSRC tHRC tSAC tHAC tC Parameter STS Delay from CE CE Pulse Width CS to CE Setup CS Low During CE High R/C to CE Setup R/C Low During CE High AO to CE Setup AO Valid During CE High Conversion Time 8-Bit Cycle 12-Bit Cycle Min 300 300 200 250 200 0 300 10 15 24 35 Typ Max 400 Units ns ns ns ns ns ns ns ns s s
-8-
REV. B
AD574A
Figure 7 shows a complete timing diagram for the AD574A convert start operation. R/C should be low before both CE and CS are asserted; if R/C is high, a read operation will momentarily occur, possibly resulting in system bus contention. Either CE or CS may be used to initiate a conversion; however, use of CE is recommended since it includes one less propagation delay than CS and is the faster input. In Figure 7, CE is used to initiate the conversion.
Table III. Read Timing--Full Control Mode Symbol tDD1 tHD tHL2 tSSR tSRR tSAR tHSR tHRR tHAR Parameter Access Time (from CE) Data Valid After CE Low Output Float Delay CS to CE Setup R/C to CE Setup AO to CE Setup CS Valid After CE Low R/C High After CE Low AO Valid After CE Low Min Typ 25 100 150 0 150 50 0 50 Max Units 200 ns ns ns ns ns ns ns ns ns
NOTES 1 tDD is measured with the load circuit of Figure 9 and defined as the time required for an output to cross 0.4 V or 2.4 V. 2 tHL is defined as the time required for the data lines to change 0.5 V when loaded with the circuit of Figure 10.
Figure 7. Convert Start Timing
Once a conversion is started and the STS line goes high, convert start commands will be ignored until the conversion cycle is complete. The output data buffers cannot be enabled during conversion. Figure 8 shows the timing for data read operations. During data read operations, access time is measured from the point where CE and R/C both are high (assuming CS is already low). If CS is used to enable the device, access time is extended by 100 ns.
a. High-Z to Logic 1 b. High-Z to Logic 0 Figure 9. Load Circuit for Access Time Test
a. Logic 1 to High-Z b. Logic 0 to High-Z Figure 10. Load Circuit for Output Float Delay Test
"STAND-ALONE" OPERATION
The AD574A can be used in a "stand-alone" mode, which is useful in systems with dedicated input ports available and thus not requiring full bus interface capability. In this mode, CE and 12/8 are wired high, CS and AO are wired low, and conversion is controlled by R/C. The three-state buffers are enabled when R/C is high and a conversion starts when R/C goes low. This allows two possible control signals--a high pulse or a low pulse. Operation with a low pulse is shown in Figure 11. In this case, the outputs are forced into the high impedance state in response to the falling edge of R/C and return
Figure 8. Read Cycle Timing
In the 8-bit bus interface mode (12/8 input wired to DIGITAL COMMON), the address bit, AO, must be stable at least 150 ns prior to CE going high and must remain stable during the entire read cycle. If AO is allowed to change, damage to the AD574A output buffers may result.
Figure 11. Low Pulse for R/C--Outputs Enabled After Conversion
REV. B
-9-
AD574A
to valid logic levels after the conversion cycle is completed. The STS line goes high 600 ns after R/C goes low and returns low 300 ns after data is valid. If conversion is initiated by a high pulse as shown in Figure 12, the data lines are enabled during the time when R/C is high. The falling edge of R/C starts the next conversion, and the data lines return to three-state (and remain three-state) until the next high pulse of R/C.
GENERAL A/D CONVERTER INTERFACE CONSIDERATIONS
Figure 12. High Pulse for R/C--Outputs Enabled While R/C High, Otherwise High-Z
Table IV. Stand-Alone Mode Timing Symbol tHRL tDS tHDR tHL tHS tHRH tDDR Parameter Low R/C Pulse Width STS Delay from R/C Data Valid After R/C Low Output Float Delay STS Delay After Data Valid High R/C Pulse Width Data Access Time Min Typ Max 250 600 25 300 300 150 1000 250 Units ns ns ns ns ns ns ns
A typical A/D converter interface routine involves several operations. First, a write to the ADC address initiates a conversion. The processor must then wait for the conversion cycle to complete, since most ADCs take longer than one instruction cycle to complete a conversion. Valid data can, of course, only be read after the conversion is complete. The AD574A provides an output signal (STS) which indicates when a conversion is in progress. This signal can be polled by the processor by reading it through an external three-state buffer (or other input port). The STS signal can also be used to generate an interrupt upon completion of conversion, if the system timing requirements are critical (bear in mind that the maximum conversion time of the AD574A is only 35 microseconds) and the processor has other tasks to perform during the ADC conversion cycle. Another possible time-out method is to assume that the ADC will take 35 microseconds to convert, and insert a sufficient number of "do-nothing" instructions to ensure that 35 microseconds of processor time is consumed. Once it is established that the conversion is finished, the data can be read. In the case of an ADC of 8-bit resolution (or less), a single data read operation is sufficient. In the case of converters with more data bits than are available on the bus, a choice of data formats is required, and multiple read operations are needed. The AD574A includes internal logic to permit direct interface to 8-bit or 16-bit data buses, selected by connection of the 12/8 input. In 16-bit bus applications (12/8 high) the data lines (DB11 through DB0) may be connected to either the 12 most significant or 12 least significant bits of the data bus. The remaining four bits should be masked in software. The interface to an 8-bit data bus (12/8 low) is done in a left-justified format. The even address (A0 low) contains the 8 MSBs (DB11 through DB4). The odd address (A0 high) contains the 4 LSBs (DB3 through DB0) in the upper half of the byte, followed by four trailing zeroes, thus eliminating bit masking instructions. It is not possible to rearrange the AD574A data lines for right justified 8-bit bus interface.
Usually the low pulse for R/C stand-alone mode will be used. Figure 13 illustrates a typical stand-alone configuration for 8086 type processors. The addition of the 74F/S374 latches improves bus access/release times and helps minimize digital feedthrough to the analog portion of the converter.
Figure 14. AD574A Data Format for 8-Bit Bus
SPECIFIC PROCESSOR INTERFACE EXAMPLES Z-80 System Interface
Figure 13. 8086 Stand-Alone Configuration
INTERFACING THE AD574A TO MICROPROCESSORS
The control logic of the AD574A makes direct connection to most microprocessor system buses possible. While it is impossible to describe the details of the interface connections for every microprocessor type, several representative examples will be described here.
The AD574A may be interfaced to the Z-80 processor in an I/O or memory mapped configuration. Figure 15 illustrates an I/O or mapped configuration. The Z-80 uses address lines A0-A7 to decode the I/O port address. An interesting feature of the Z-80 is that during I/O operations a single wait state is automatically inserted, allowing the AD574A to be used with Z-80 processors having clock speeds up to 4 MHz. For applications faster than 4 MHz use the wait state generator in Figure 16. In a memory mapped configuration the AD574A may be interfaced to Z-80 processors with clock speeds of up to 2.5 MHz.
-10-
REV. B
AD574A
Note: Due to the large number of options that may be installed in the PC, the I/O bus loading should be limited to one Schottky TTL load. Therefore, a buffer/driver should be used when interfacing more than two AD574As to the I/O bus.
8086 Interface
The data mode select pin (12/8) of the AD574A should be connected to VLOGIC to provide a 12-bit data output. To prevent possible bus contention, a demultiplexed and buffered address/ data bus is recommended. In the cases where the 8-bit short conversion cycle is not used, A0 should be tied to digital common. Figure 18 shows a typical 8086 configuration.
Figure 15. Z80--AD574A Interface
Figure 16. Wait State Generator
IBM PC Interface
The AD574A appears in Figure 17 interfaced to the 4 MHz 8088 processor of an IBM PC. Since the device resides in I/O space, its address is decoded from only the lower ten address lines and must be gated with AEN (active low) to mask out internal DMA cycles which use the same I/O address space. This active low signal is applied to CS. IOR and IOW are used to initiate the conversion and read, and are gated together to drive the chip enable, CE. Because the data bus width is limited to 8 bits, the AD574A data resides in two adjacent addresses selected by A0.
Figure 18. 8086--AD574A with Buffered Bus lnterface
For clock speeds greater than 4 MHz wait state insertion similar to Figure 16 is recommended to ensure sufficient CE and R/C pulse duration. The AD574A can also be interfaced in a stand-alone mode (see Figure 13). A low going pulse derived from the 8086's WR signal logically ORed with a low address decode starts the conversion. At the end of the conversion, STS clocks the data into the three-state latches.
68000 Interface
The AD574, when configured in the stand-alone mode, will easily interface to the 4 MHz version of the 68000 microprocessor. The 68000 R/W signal combined with a low address decode initiates conversion. The UDS or LDS signal, with the decoded address, generates the DTACK input to the processor, latching in the AD574A's data. Figure 19 illustrates this configuration.
Figure 17. IBM PC--AD574A Interface
Figure 19. 68000--AD574A Interface
REV. B
-11-
AD574A
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
28-Pin Ceramic DIP Package (D-28)
28-Lead Plastic DIP Package (N-28A)
C704d-10-8/88
28-Terminal PLCC Package (P-28A)
0.180 (4.57) 0.165 (4.19) 0.056 (1.42) 0.042 (1.07)
26 25
0.048 (1.21) 0.042 (1.07) 0.048 (1.21) 0.042 (1.07)
0.025 (0.63) 0.015 (0.38) 0.021 (0.53) 0.013 (0.33)
4 5 PIN 1 IDENTIFIER
TOP VIEW
(PINS DOWN) 11 12 19 18
0.050 (1.27) BSC
0.032 (0.81) 0.026 (0.66)
0.430 (10.92) 0.390 (9.91)
0.020 (0.50) R
0.456 (11.58) SQ 0.450 (11.43) 0.495 (12.57) SQ 0.485 (12.32)
0.040 (1.01) 0.025 (0.64) 0.110 (2.79) 0.085 (2.16)
28-Terminal LCC Package (E-28A)
0.458 (11.63) SQ 0.442 (11.23) 0.075 (1.91) REF 0.100 (2.54) 0.064 (1.63) 0.150 (3.81) BSC 0.095 (2.41) 0.075 (1.90)
0.300 (7.62) BSC
0.015 (0.38) MIN 0.028 (0.71) 0.022 (0.56)
28 1
TOP VIEW
0.458 (11.63) MAX SQ
0.011 (0.28) 0.007 (0.18) R TYP
BOTTOM VIEW
0.050 (1.27) BSC 12 45 TYP
18 0.055 (1.40) 0.045 (1.14) 0.075 (1.91) REF 0.088 (2.24) 0.054 (1.37)
0.200 (5.08) BSC
-12-
REV. B
PRINTED IN U.S.A.

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