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ICL8052/ICL71C03, ICL8068/ICL71C03
August 1997
Precision 4 1/2 Digit, A/D Converter
Description
The ICL8052 or ICL8068/lCL71C03 chip pairs with their multiplexed BCD output and digit drivers are ideally suited for the visual display DVM/DPM market. The outstanding 41/2 digit accuracy, 200.00mV to 2.0000V full scale capability, auto-zero and auto-polarity combine with true ratiometric operation, almost ideal differential linearity and time-proven dual slope conversion. Use of these chip pairs eliminates clock feedthrough problems, and avoids the critical board layout usually required to minimize charge injection. When only 2000 counts of resolution are required, the 71C03 can be wired for 31/2 digits and give up to 30 readings/sec., making it ideally suited for a wide variety of applications. The ICL71C03 is an improved CMOS plug-in replacement for the lCL7103 and should be used in all new designs.
Features
* Typically Less Than 2VP-P Noise (200.00mV Full Scale, lCL8068) * Accuracy Guaranteed to 1 Count Over Entire 20,000 Counts (2.0000V Full Scale) * Guaranteed Zero Reading for 0V Input * True Polarity at Zero Count for Precise Null Detection * Single Reference Voltage Required * Over-Range and Under-Range Signals Available for Auto-Ranging Capability * All Outputs TTL Compatible * Medium Quality Reference, 40ppm (Typ) on Board * Blinking Display Gives Visual Indication of Over Range * Six Auxiliary Inputs/Outputs are Available for Interfacing to UARTs, Microprocessors or Other Complex Circuitry * 5pA Input Current (Typ) (8052A)
Ordering Information
PART NUMBER ICL8052CPD lCL8052CDD lCL8052ACPD ICL8052ACDD ICL8068CDD ICL8068ACDD lCL8068ACJD ICL71C03CPl lCL71C03ACPl TEMP. RANGE (oC) 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 0 to 70 PACKAGE 14 Ld PDIP 14 Ld CERDIP 14 Ld PDIP 14 Ld CERDIP 14 Ld CERDIP 14 Ld CERDIP 14 Ld CERDIP 28 Ld PDIP 28 Ld PDIP PKG. NO. E14.3 F14.3 E14.3 F14.3 F14.3 F14.3 F14.3 E28.6 E28.6
Pinouts
ICL8052/ICL8068 (CERDIP, PDIP) TOP VIEW
V+ 1 V- 1 -1.2V COMP OUT 2 REF CAP 3 REF BYPASS 4 GND 5 REF OUT 6 REF SUPPLY 7 VREF 13 +BUFF IN 12 +INT IN 11 -INT IN 10 -BUFF IN 9 BUFF OUT ICL8052/ 8 V++ ICL8068 14 INT OUT 41/2 / 31/2 2 POL 3 RUN/HOLD 4 COMP IN 5 V- 6 REFERENCE 7 REF. CAP. 1 8 REF. CAP. 2 9 ANALOG IN 10 ANALOG GND 11 CLOCK IN 12 UNDER-RANGE 13 OVER-RANGE 14
ICL71C03 (PDIP) TOP VIEW
28 BUSY 27 D1 (LSD) 26 D2 25 D3 24 D4 23 B8 (MSB) 22 B4 21 B2 20 B1 (LSB) 19 D5 (MSD) 18 STROBE 17 A-Z IN 16 A-Z OUT 15 DIGITAL GND
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. http://www.intersil.com or 407-727-9207 | Copyright (c) Intersil Corporation 1999
File Number
3081.1
3-34
ICL8052/ICL71C03, ICL8068/ICL71C03 Functional Block Diagram
10k 90k 100k 0.22F
+15V -15V -BUF IN REF OUT 6 8 7 1 10 BUFFER BUF OUT 9 -INT IN 11 INTEG. INT OUT POLARITY 14 COMP. SEVENSEGMENT DECODER
INT. 3 REF. 300pF 10k 1k 10F REF CAP 1 REF ANALOG INPUT 10k 0.1F ANALOG GND 11 8 7 4 10 1 5 5
A1 + ICL8052/8068
A2 + -1.2V
A3 + 2
3
D5 19 MSD
D4 24
D3 25
D2 26
D1 27 LSD
20 B1 21 B2 22 B3 23 B4
+BUF IN 13 10F (TYP) REF CAP 2 9 2
+INT IN 12
COMP 1F (TYP) OUT AZ OUT 16 AZ IN COMP IN 17 5 ZERO CROSSING DETECTOR LATCH LATCH
MULTIPLEXER
LATCH
LATCH
LATCH
SW3 6 ICL71C03
COUNTERS
CONTROL LOGIC
1
15
6
4 RUN/ HOLD
12
2
14
13
18
28
+5V
-15V
CLOCK 4 1/2 DIGIT/ OVER UNDER STROBE BUSY IN 3 1/2 DIGIT RANGE RANGE
FIGURE 1.
3-35
ICL8052/ICL71C03, ICL8068/ICL71C03
Absolute Maximum Ratings
ICL8052, ICL8068 Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18V Differential Input Voltage (8068) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30V (8052) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6V Input Voltage (Note 1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15V Output Short Circuit Duration All Outputs (Note 2). . . . . . . Indefinite ICL71C03 Power Supply Voltage (GND to V+) . . . . . . . . . . . . . . . . . . . . . 6.5V Negative Supply Voltage (GND to V-). . . . . . . . . . . . . . . . . . . . .-17V Analog Input Voltage (Note 3) . . . . . . . . . . . . . . . . . . . . . . . V+ to VDigital Input Voltage (Note 4) . . . . . . . . (GND - 0.3V) to (V+ + 0.3V)
Thermal Information
Thermal Resistance (Typical, Note 5) JA (oC/W) JC (oC/W) CERDIP Package . . . . . . . . . . . . . . . . 75 20 14 Ld PDIP Package . . . . . . . . . . . . . . 100 N/A 28 Ld PDIP Package . . . . . . . . . . . . . . 65 N/A Maximum Storage Temperature . . . . . . . . . . . . . . . .-65oC to 150oC Maximum Lead Temperature (Soldering, 10s) . . . . . . . . . . . . 300oC
Operating Conditions
Temperature Range . . . . . . . . . . . . . . . . . . . . . . . . . . . .0oC to 70oC
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTES: 1. For supply voltages less than 15V, the absolute maximum input voltage is equal to the supply voltage. 2. Short circuit may be to ground or either supply. Rating applies to 70oC ambient temperature. 3. Input voltages may exceed the supply voltages provided the input current is limited to 100A. 4. Connecting any digital inputs or outputs to voltages greater then V+ or less than GND may cause destructive device latchup. For this reason it is recommended that the power supply to the ICL71C03 be established before any inputs from sources not on that supply are applied. 5. JA is measured with the component mounted on an evaluation PC board in free air.
Electrical Specifications
PARAMETER Clock In, Run/Hold, 4 1/2 / 3 1/2 SYMBOL IINL IINH Comp. In Current IINL IINH Threshold Voltage All Outputs B1 , B2 , B4 , B8 , D1 , D2 , D3 , D4 , D5 Busy, Strobe, Over-Range, Under-Range Polarity Switches 1, 3, 4, 5, 6 Switch 2 Switch Leakage (All) +5V Supply Range -15V Supply Range +5V Supply Current -15V Supply Current Power Dissipation Capacitance Clock Frequency (Note 6) VINTH VOL VOH VOH rDS(ON) rDS(ON) ID(OFF) V+ VI+ ICPD fCLK = 0 fCLK = 0 vs Clock Frequency IOL = 1.6mA IOH = -1mA IOH = -10A TEST CONDITIONS VIN = 0 VIN = +5V VIN = 0 VIN = +5V MIN 2.4 4.9 4 -5 DC TYP 0.2 0.1 0.1 0.1 2.5 0.25 4.2 4.99 400 1200 2 5 -15 1.1 0.8 40 2000 MAX 0.6 10 10 10 0.40 6 -18 3 3 1200 UNITS mA A A A V V V V pA V V mA mA pF kHz
NOTE: 6. This specification relates to the clock frequency range over which the ICL71C03(A) will correctly perform its various functions. See the "Max Clock Frequency" section under Component Value Selection for limitations on the clock frequency range in a system.
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ICL8052/ICL71C03, ICL8068/ICL71C03
ICL8068 Electrical Specifications
VSUPPLY = 15V, TA = 25oC, Unless Otherwise Specified ICL8068 PARAMETER EACH OPERATIONAL AMPLIFIER Input Offset Voltage Input Current (Either Input) (Note 7) Common-Mode Rejection Ratio Non-Linear Component of CommonMode Rejection Ratio (Note 8) Large Signal Voltage Gain Slew Rate Unity Gain Bandwidth Output Short-Circuit Current COMPARATOR AMPLIFIER Small-Signal Voltage Gain Positive Output Voltage Swing Negative Output Voltage Swing VOLTAGE REFERENCE Output Voltage Output Resistance Temperature Coefficient Supply Voltage (V++ -V-) Supply Current Total VO RO TC VSUPPLY ISUPPLY 1.5 10 1.75 5 50 2.0 16 14 1.60 10 1.75 5 40 8 1.90 16 14 V ppm/oC V mA AVOL +VO -VO RL = 30k 12 -2.0 13 -2.6 4000 12 -2.0 13 -2.6 V/V V V AV SR GBW ISC VOS IIN CMRR VCM = 0V VCM = 0V VCM = 10V VCM = 2V 70 20 175 90 110 65 250 70 20 80 90 110 65 150 mV pA dB dB SYMBOL TEST CONDITIONS MIN TYP MAX MIN ICL8068A TYP MAX UNITS
RL = 50k
20,000 -
6 2 5
-
20,000 -
6 2 5
-
V/V V/s MHz mA
ICL8052 Electrical Specifications
VSUPPLY = 15V, TA = 25oC, Unless Otherwise Specified TEST CONDITIONS ICL8052 MIN TYP MAX MIN ICL8052A TYP MAX UNITS
PARAMETER EACH OPERATIONAL AMPLIFIER Input Offset Voltage Input Current (Either Input) (Note 7) Common-Mode Rejection Ratio Non-Linear Component of CommonMode Rejection Ratio (Note 8) Large Signal Voltage Gain Slew Rate Unity Gain Bandwidth Output Short-Circuit Current
SYMBOL
VOS IIN CMRR
VCM = 0V VCM = 0V VCM = 10V VCM = 2V
70 20,000 -
20 5 90 110 6 1 20
75 50 -
70 20,000 -
20 2 90 110 6 1 20
75 10 -
mV pA dB dB V/V V/s MHz mA
AV SR GBW ISC
RL = 50k
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ICL8052/ICL71C03, ICL8068/ICL71C03
ICL8052 Electrical Specifications
VSUPPLY = 15V, TA = 25oC, Unless Otherwise Specified (Continued) TEST CONDITIONS ICL8052 MIN TYP MAX MIN ICL8052A TYP MAX UNITS
PARAMETER COMPARATOR AMPLIFIER Small-Signal Voltage Gain Positive Output Voltage Swing Negative Output Voltage Swing VOLTAGE REFERENCE Output Voltage Output Resistance Temperature Coefficient Supply Voltage (V++ -V-) Supply Current Total NOTES:
SYMBOL
AVOL +VO -VO
RL = 30k
12 -2.0
4000 13 -2.6
-
12 -2.0
13 -2.6
-
V/V V V
VO RO TC VSUPPLY ISUPPLY
1.5 10 -
1.75 5 50 6
2.0 16 12
1.60 10 -
1.75 5 40 6
1.90 16 14
V ppm/oC V mA
7. The input bias currents are junction leakage currents which approximately double for every 10oC increase in the junction temperature, TJ . Due to limited production test time, the input bias currents are measured with junctions at ambient temperature. In normal operation the junction temperature rises above the ambient temperature as a result of internal power dissipation, PD. TJ = TA + RJAPD, where RJA is the thermal resistance from junction to ambient. A heat sink can be used to reduce temperature rise. 8. This is the only component that causes error in dual-slope converter.
System Electrical Specifications: ICL8068/ICL71C03
V++ = +15V, V+ = +5V, V- = -15V, TA = 25oC, fCLK Set for 3 Readings/Sec. ICL8068A/ICL71C03 (NOTE 9) MIN -000.0 0.999 TYP 000.0 1.000 0.2 0.01 MAX +000.0 1.001 1 ICL8068A/ICL71C03 (NOTE 10) MIN -000.0 0.9999 TYP 000.0 1.0000 0.5 0.01 MAX 000.0 1.0001 1 UNITS Digital Reading Digital Reading Counts Counts
PARAMETER Zero Input Reading Ratiometric Error (Note 11) Linearity Over Full Scale (Error of Reading from Best Straight Line) Differential Linearity (Difference between Worst Case Step of Adjacent Counts and Ideal Step) Rollover Error (Difference in Reading for Equal Positive & Negative Voltage Near Full Scale) Noise (P-P Value Not Exceeded 95% of Time) Leakage Current at Input Zero Reading Drift (Note 12) Scale Factor Temperature Coefficient (Note 12)
TEST CONDITIONS VIN = 0V, Full Scale = 200mV VIN = VREF Full Scale = 2V -2V VIN +2V -2V VIN +2V
-VIN +VIN 2V
-
0.2
1
-
0.5
1
Counts
VIN = 0V, Full Scale = 200mV VIN = 0V VIN = 0V, 0oC TA 50oC VIN = 2V, 0oC TA 50oC Ext. Ref. 0ppm/oC
-
3 200 1 3
300 5 15
-
2 100 0.5 2
200 2 5
V pA V/oC ppm/oC
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ICL8052/ICL71C03, ICL8068/ICL71C03
System Electrical Specifications: ICL8052/ICL71C03
V++ = +15V, V+ = +5V, V- = -15V, TA = 25oC, fCLK Set for 3 Reading/Sec. ICL8068A/ICL71C03 (NOTE 9) MIN -0.000 0.999 TYP 0.000 1.000 0.2 0.01 MAX +0.000 1.001 1 ICL8068A/ICL71C03 (NOTE 10) MIN -0.000 0.9999 TYP 0.000 1.0000 0.5 0.01 MAX 0.000 1.0001 1 UNITS Digital Reading Digital Reading Counts Counts
PARAMETER Zero Input Reading Ratiometric Error (Note 11) Linearity Over Full Scale (Error of Reading from Best Straight Line) Differential Linearity (Difference between Worst Case Step of Adjacent Counts and Ideal Step) Rollover Error (Difference in Reading for Equal Positive & Negative Voltage Near Full Scale) Noise (Peak-To-Peak Value Not Exceeded 95% of Time) Leakage Current at Input Zero Reading Drift Scale Factor Temperature Coefficient
TEST CONDITIONS VIN = 0V, Full Scale = 2V VIN = VREF Full Scale = 2V -2V VIN +2V -2V VIN +2V
-VIN +VIN 2V
-
0.2
1
-
0.5
1
Counts
VIN = 0V, Full Scale = 200mV, Full Scale = 2V VIN = 0V VIN = 0V, 0oC To 70oC VIN = 2V, 0oC To 70oC, Ext. Ref. 0ppm/ oC
-
20 50 5 1 3
30 5 15
-
30 3 0.5 2
10 2 5
V pA V/oC ppm/oC
NOTES: 9. Tested in 31/2 digit (2,000 count) circuit shown in Figure 5, clock frequency 12kHz. Pin 2 71C03 connected to GND. 10. Tested in 41/2 digit (20,000 count) circuit shown in Figure 5, clock frequency 120kHz. Pin 2 71C03A open. 11. Tested with a low dielectric absorption integrating capacitor. See Component Selection Section. 12. The temperature range can be extended to 70oC and beyond if the Auto-Zero and Reference capacitors are increased to absorb the high temperature leakage of the 8068.
Detailed Description
ANALOG SECTION Figure 2 shows the equivalent Circuit of the Analog Section of both the ICL71C03/8052 and the ICL71C03/8068 in the 3 different phases of operation. IF the RUN/HOLD pin is left open or tied to V+, the system will perform conversions at a rate determined by the clock frequency: 40,0002 at 41/2 digit and 4002 at 31/2 digit clock periods per cycle (see Figure 3 for details of conversion timing). Auto-zero Phase I (Figure 2A) During the Auto-Zero, the input of the buffer is connected to VREF through switch 2, and switch 3 closes a loop around the integrator and comparator, the purpose of which is to charge the auto-zero capacitor until the integrator output does not change with time. Also, switches 1 and 2 recharge the reference capacitor to VREF . Input Integrate Phase II (Figure 2B) During Input Integrate the auto-zero loop is opened and the ANALOG INPUT is connected to the BUFFER INPUT through switch 4 and CREF . If the input signal is zero, the buffer, integrator and comparator will see the same voltage
that existed in the previous state (Auto-Zero). Thus, the integrator output will not change but will remain stationary during the entire Input Integrate cycle. If VIN is not equal to zero, and unbalanced condition exists compared to the Auto Zero phase, and the integrator will generate a ramp whose slope is proportional to VIN . At the end of this phase, the sign of the ramp is latched into the polarity F/F. Deintegrate Phase II (Figures 2C and 2D) During the Deintegrate phase, the switch drive logic uses the output of the polarity F/F in determining whether to close switch 6 or 5. If the input signal is positive, switch 6 is closed and a voltage which is VREF more negative than during Auto-Zero is impressed on the BUFFER INPUT. Negative Inputs will cause +2(VREF) to be applied to the BUFFER INPUT via switch 5. Thus, the reference capacitor generates the equivalent of a (+) or (-) reference from the single reference voltage with negligible error. The reference voltage returns the output of the integrator to the zero-crossing point established in Phase I. The time, or number of counts, required to do this is proportional to the input voltage. Since the Deintegrate phase can be twice as long as the Input Integrate Phase, the input voltage required to give a full scale reading is 2VREF .
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ICL8052/ICL71C03, ICL8068/ICL71C03
RINT VREF (+1.000V) BUFFER 4 VIN 5 2 1F CREF 6 CSTRAY CAZ INTEGRATOR COMPARATOR CINT
A1 +
A2 +
A3 +
ZERO CROSSING DETECTOR
1
3
FIGURE 2A. PHASE I AUTO-ZERO
RINT VREF (+1.000V) BUFFER 4 VIN 5 2 1F CREF 1 6 CSTRAY
CINT INTEGRATOR
A1 +
A2 +
COMPARATOR
A3 +
ZERO CROSSING DETECTOR
CAZ POLARITY FF
3
FIGURE 2B. PHASE II INTEGRATE INPUT
RINT VREF (+1.000V) BUFFER 4 VIN 5 2 1F CREF 6 CSTRAY
CINT INTEGRATOR
A1 +
A2 +
COMPARATOR
A3 +
ZERO CROSSING DETECTOR
1
CAZ POLARITY FF
3
FIGURE 2C. PHASE III + DEINTEGRATE
RINT VREF (+1.000V) BUFFER 4 VIN 5 2 1F CREF 6 CSTRAY
CINT INTEGRATOR
A1 +
A2 +
COMPARATOR
A3 +
ZERO CROSSING DETECTOR
1
CAZ POLARITY FF
3
FIGURE 2D. PHASE III - DEINTEGRATE FIGURE 2. ANALOG SECTION OF EITHER ICL8052 OR ICL8068 WITH ICL71C03
3-40
ICL8052/ICL71C03, ICL8068/ICL71C03
COUNTS PHASE I 41/2 DIGIT 31/2 DIGIT 10,001 1,001
POLARITY DETECTED INTEGRATOR OUTPUT
PHASE II 10,000 1,000
PHASE III 20,001 2,001
ZERO CROSSING OCCURS ZERO CROSSING DETECTED
AZ PHASE I CLOCK
INT PHASE II
DEINT PHASE III
AZ
INTERNAL LATCH
BUSY OUTPUT AFTER ZERO CROSSING, ANALOG SECTION WILL BE IN AUTOZERO CONFIGURATION
NUMBER OF COUNTS TO ZERO CROSSING PROPORTIONAL TO VIN
FIGURE 3. CONVERSION TIMING
Zero-Crossing Flip-Flop Figure 4 shows the problem that the zero-crossing F/F is designated to solve. The integrator output is approaching the zero-crossing point where the count will be latched and the reading displayed. For a 20,000 count instrument, the ramp is changing approximately 0.50mV per clock pulse (10V Max integrator output divided by 20,000 counts). The clock pulse feedthrough superimposed upon this ramp would have to be less than 100mV peak to avoid causing significant errors. The flip-flop interrogates the data once every clock pulse after the transients of the previous clock pulse and half-clock pulse have died down. False zero-crossings caused by clock pulses are not recognized. Of course, the flip-flop delays the true zero-crossing by one count in every instance, and if a correction were not made, the display would always be one count too high. Therefore, the counter is disabled for one clock pulse at the beginning of phase 3. This one count delay compensates for the delay of the zero crossing flipflop, and allows the correct number to be latched into the display. Similarly, a one count delay at the beginning of phase 1 gives an overload display of 0000 instead of 0001. No delay occurs during phase 2, so that true ratiometric readings result.
CLOCK PULSE FEEDTHROUGH
Detailed Description
DIGITAL SECTION The 71C03 includes several pins which allow it to operate conveniently in more sophisticated systems. These include: 4-1/2 / 3-1/2 (Pin 2) When high (or open) the internal counter operates as a full 41/2 decade counter, with a complete measurement cycle requiring 40,002 counts. When held low, the least significant decade is cleared and the clock is fed directly into the next decade. A measurement cycle now requires only 4,0002 clock pulses. All 5 digit drivers are active in either case, with each digit lasting 200 counts with Pin 2 high (41/2 digit) and 20 counts for Pin 2 low (31/2 digit). RUN/HOLD (Pin 4) When high (or open) the A/D will free-run with equally spaced measurement cycles every 40,0002/4,002 clock pulses. If taken low, the converter will continue the full measurement cycle that it is doing and then hold this reading as long as Pin 4 is held low. A short positive pulse (greater then 300ns) will now initiate a new measurement cycle beginning with up to 10,001/1,001 counts of auto zero. Of course if the pulse occurs before the full measurement cycle (40,002/4,002 counts) is completed, it will not be recognized and the converter will simply complete the measurement it is doing. An external indication that full measurement cycle has been completed is that the first STROBE pulse (see below) will occur 101/11 counts after the end of this cycle. Thus, if RUN/HOLD is low and has been low for at least 101/11 counts, converter is holding and ready to start a new measurement when pulsed high. STROBE (Pin 18) This is a negative-going output pulse that aids in transferring the BCD data to external latches, UARTs or microprocessors. There are 5 negative-going STROBE pulses that occur
TRUE ZERO CROSSING FALSE ZERO CROSSING
FIGURE 4. INTEGRATOR OUTPUT NEAR ZERO-CROSSING
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ICL8052/ICL71C03, ICL8068/ICL71C03
once and only once for each measurement cycle starting 101/11 pulses after the end of the full measurement cycle. Digit 5 (MSD) goes high at the end of the measurement cycle and stays on for 201/21 counts. In the center of this digit pulse (to avoid race conditions between changing BCD and digit drives) the first STROBE pulse goes negative for 1/ clock pulse width. Similarly, after Digit 5, Digit 4 goes 2 high (for 200/20 clock pulses) and 100/10 pulses later the STROBE goes negative for the second time. This continues through Digit 1 (LSD) when the fifth and last STROBE pulse is sent. The digit drive will continue to scan (unless the previous signal was over-range) but no additional STROBE pulses will be sent until a new measurement is available. Busy (Pin 28) BUSY goes high at the beginning of signal integrate and stays high until the first clock pulse after zero-crossing (or after end of measurement in the case of an OVER-RANGE). The internal latches are enabled (i.e., loaded) during the first clock pulse after BUSY and are latched at the end of this clock pulse. The circuit automatically reverts to auto-zero when not BUSY so it may also be considered an A-Z signal. A very simple means for transmitting the data down a single wire pair from a remote location would be to AND BUSY with clock and subtract 10,001/1,001 counts from the number of pulses received - as mentioned previously there is one "NOcount" pulse in each Reference Integrate cycle. Over-Range (Pin 4) This pin goes positive when the input signal exceeds the range (20,000/2,000) of the converter. The output F-F is set
INTEGRATOR OUTPUT AUTO SIGNAL ZERO REFERENCE INTEG. INTEGRATE 10,001 10,000 20,001 / 2,001 / 1,001 / 1,000 COUNTS MAX COUNTS COUNTS FULL MEASUREMENT CYCLE 40,002/4,002 COUNTS BUSY OVER-RANGE WHEN APPLICABLE UNDER-RANGE WHEN APPLICABLE EXPANDED SCALE BELOW DIGIT SCAN FOR OVER-RANGE D5 D4 D3 D2 D1 1000/100 COUNTS STROBE DIGIT SCAN FOR OVER-RANGE D5 AUTO ZERO
at the end of BUSY and is reset to zero at the beginning of Reference Integrate in the next measurement cycle. Under-Range (Pin 13) This pin goes positive when the reading is 9% of range or less. The output F-F is set at the end of BUSY (if the new reading is 1800/180 or less) and is reset a the beginning of Signal Integrate of the next reading. Polarity (Pin 3) This pin is positive for a positive input signal. It is valid even for a zero reading. In other words, +0000 means the signal is positive but less than the least significant bit. The converter can be used as null detector by forcing equal (+) and (-) readings. The null at this point should be less than 0.1 LSB. This output becomes valid at the beginning of Reference Integrate and remains correct until it is revalidated for the next measurement. Digit Drives (Pins 19, 24, 25, 26, and 27) Each digit drive is a positive-going signal which lasts for 200/20 clock pulses. The scan sequence is D5 (MSD), D4 , D3 , D2 , and D1 (LSD). All five digits are scanned even when operating in the 31/2 digit mode, and this scan is continuous unless and OVER-RANGE occurs. Then all Digit drives are blanked from the end of the STROBE sequence until the beginning of Reference Integrate, at which time D5 will start the scan again. This gives a blinking display as a visual indication of OVER-RANGE. BCD (Pins 20, 21, 22 and 23) The Binary coded decimal bit B8 , B4 , B2 , and B1 are positive logic signals that go on simultaneously with the Digit driver.
FIRST D5 OF AZ AND REF INT
ONE COUNT LONGER REFERENCE INTEGRATE
SIGNAL INTEGRATE
D4 D3 D2 D1
FIGURE 5. TIMING DIAGRAM FOR OUTPUTS
3-42
ICL8052/ICL71C03, ICL8068/ICL71C03 Component Value Selection
For optimum performance of the analog section, care must be taken in the selection of values for the integrator capacitor and resistor, auto-zero capacitor, reference voltage, and conversion rate. These values must be chosen to suit the particular application. Integrating Resistor The integrating resistor is determined by the full scale input voltage and the output current of the buffer used to charge the integrator capacitor. This current should be small compared to the output short circuit current such that thermal effects are kept to a minimum and linearity is not affected. Values of 5A to 40A give good results with a nominal of 20A. The exact value may be chosen by:
Full Scale Voltage (See Note) R INT = -----------------------------------------------------------------------------20A NOTE: If gain is used in the buffer amplifier, then: ( Buffe rGain ) (Full Scale Voltage) R INT = ------------------------------------------------------------------------------------------20A
Auto-Zero and Reference Capacitor The size of the auto-zero capacitor has some influence on the noise of the system, with a larger value capacitor giving less noise. The reference capacitor should be large enough such that stray capacitance to ground from its nodes is negligible. When gain is used in the buffer amplifier the reference capacitor should be substantially larger than the auto-zero capacitor. As a rule of thumb, the reference capacitor should be approximately the gain times the value of the auto-zero capacitor. The dielectric absorption of the reference cap and auto-zero cap are only important at power-on or when the circuit is recovering from an overload. Thus, smaller or cheaper caps can be used here if accurate readings are not required for the first few seconds of recovery. Reference Voltage The analog input required to generate a full scale output is: VIN = 2VREF . The stability of the reference voltage is a major factor in the overall absolute accuracy of the converter. For this reason, it is recommended that an external high quality reference be used where ambient temperature is not controlled or where high-accuracy absolute measurements are being made. Buffer Gain At the end of the auto-zero interval, the instantaneous noise voltage on the auto-zero capacitor is stored and subtracted from the input voltage while adding to the reference voltage during the next cycle. The result of this is that the noise voltage is effectively somewhat greater than the input noise voltage of the buffer itself during integration. By introducing some voltage gain into the buffer, the effect of the auto-zero noise (referred to the input) can be reduced to the level of the inherent buffer noise. This generally occurs with a buffer gain of between 3 and 10. Further increase in buffer gain merely increases the total offset to be handled by the autozero loop, and reduces the available buffer and integrator swings, without improving the noise performance of the system. The circuit recommended for doing this with the ICL8068/ICL71C03 is shown in Figure 6.
Integrating Capacitor The product of integrating resistor and capacitor is selected to give 9V swing for full scale inputs. This is a compromise between possibly saturating the integrator (at +14V) due to tolerance buildup between the resistor, capacitor and clock and the errors a lower voltage swing could induce due to offsets referred to the output of the comparator. In general, the value of CINT is given by:
10,000(4-1/2 Digit) x Clock Period x ( 20A ) 1000(3-1/2 Digit) C INT = -----------------------------------------------------------------------------------------------------------------------Integrator Output Voltage Swing
A very important characteristic of the integrating capacitor is that it has low dielectric absorption to prevent roll-over or ratiometric errors. A good test for dielectric absorption is to use the capacitor with the input tied to the reference. This ratiometric condition should be read half scale 1.0000, and any deviation is probably due to dielectric absorption. Polypropylene capacitors give undetectable errors at reasonable cost. Polystyrene and polycarbonate capacitors may be used in less critical applications.
10-50K +15V -15V 100k -BUF IN REF OUT 300pF 10k 1k 5 6 8 7 1 10 BUFFER
BUF OUT 9
-INT IN 11 INTEG.
INT OUT 14 COMP.
INT. 3 REF.
A1 + ICL8068
A2 + -1.2V +INT IN 12
A3 + 2
COMP OUT
+BUF IN 13
-15V
TO ICL7104
FIGURE 6. ADDING BUFFER GAIN TO ICL8068
3-43
ICL8052/ICL71C03, ICL8068/ICL71C03
ICL8052 vs ICL8068 The ICL8052 offers significantly lower input leakage currents than the ICL8068, and may be found preferable in systems with high input impedances. However, the ICL8068 has substantially lower noise voltage, and is the device of choice for systems where noise is a limiting factor, particularly in low signal level conditions. Max Clock Frequency The maximum conversion rate of most dual-slope A/D converters is limited by frequency response of the comparator. The comparator in this circuit is no exception, even though it is entirely NPN with an open-loop, gain-bandwidth product of 300MHz. The comparator output follows the integrator ramp with a 3s delay, and at a clock frequency of 160kHz (6s period) half of the first reference integrate clock period is lost in delay. This means that the meter reading will change from 0 to 1 with 50V input, 1 to 2 with 150V, 2 to 3 at 250V, etc. This transition at midpoint is considered desirable by most users. However, if the clock frequency is increased appreciably above 160kHz, the instrument will flash "1" on noise peaks even when the input is shorted. For many dedicated applications where the input signal is always on one polarity, the dealy of the comparator need not be limitation. Since the non-linearity and noise do not increase substantially with frequency, clock rates of up to approximately 1MHz may be used. For a fixed clock frequency, the extra count or counts caused by comparator delay will be a constant and can be subtracted out digitally. The minimum clock frequency is established by leakage on the auto-zero and reference caps. With most devices, measurement cycles as long as 10 seconds give no measurable leakage error. To achieve maximum rejection of 60Hz pickup, the signal integrate cycle should be a multiple of 60Hz. Oscillator frequencies of 300kHz, 200kHz, 150kHz, 120kHz, 100kHz, 40kHz, 331/3kHz, etc, should be selected. For 50Hz rejection, oscillator frequencies of 250kHz, 1662/3kHz, 125kHz, 100kHz, etc. would be suitable. Note that 100kHz (2.5 readings/second) will reject both 50Hz and 60Hz. The clock used should be free from significant phase or frequency jitter. A simple two-gate oscillator and one based on CMOS 7555 timer are shown in the Applications section. The multiplexed output means that if the display takes significant current from the logic supply, the clock should have good PSRR. LED is driven from the 7-segment decoder, with a zero reading blanked by connecting a D5 signal to RBI input of the decoder. A voltage translation network is connected between the comparator output of the 8068/52 and the auto-zero input of the 71C03. The purpose of this network is to assure that, during auto-zero, the output of the comparator is at or near the threshold of the 71C03 logic (+2.5V) while the auto-zero capacitor is being charged to VREF (+100mV for a 200mV instrument). Otherwise, even with 0V in, some reference integrate period would be required to drive the comparator output to the threshold level. This would show up as an equivalent offset error. Once the divider network has been selected, the unit-to-unit variation should contribute less than a tenth of a count error. A second feature is the back-to-back diodes, used to lower the noise. In the normal operating mode they offer a high impedance and long integrating time constant to any noise pulses charging the auto-zero cap. At startup or recovery from an overload, their impedance is low to large signals so that the cap can be charged up in one auto-zero cycle. The buffer gain does not have to be set precisely at 10 since the gain is used in both the integrate and deintegrate phase. For scale factors other then 200mV the gain of the buffer should be changed to give a 2V buffer output. For 2.0000V full scale this means unity gain and for 20,000mV (1V resolution) a gain of 100 is necessary. Not all 8068As can operate properly at a gain of 100 since their offset should be less than 10mV in order to accommodate the auto-zero circuitry. However, for devices selected with less than 10mV offset, the noise performance is reasonable with approximately 1.5V near full scale. On all scales less than 200mV, the voltage translation network should be made adjustable as an offset trim. The auto-zero cap should be 1F for all scales and the reference capacitor should be 1F times the gain of the buffer amplifier. At this value if the input leakages of the 8052/8068 are equal, the droop effects will cancel giving zero offset. This is especially important at high temperature. Some typical component values are shown in Table 1. For 31/2 digit conversion, use 12kHz clock. V++ = +15V, V+ = 5V, V- = -15V Clock Freq. = 120kHz (41/2 Digit) or 12kHz (31/2 Digit)
TABLE 1. SPECIFICATION Full Scale VIN Buffer Gain ( RB1 + RB2 ) ----------------------------------RB2 RINT CINT CAZ CREF VREF Resolution (41/2 Digit) 20 100 (See Note) 100 0.22 1.0 10 10 1 VALVE 200 10 2000 1 UNITS mV V/V
Applications
Specific Circuits Using the 8068/71C03 8052/71C03 Figure 7 shows the complete circuit for a 41/2 digit (200mV full scale) A/D converter with LED readout using the internal reference of the 8068/52. If an external reference is used, the reference supply (pin 7) should be connected to ground and the 300pF reference cap deleted. The circuit also shows a typical RC input filter. Depending on the application, the time-constant of this filter can be made faster, slower, or the filter deleted completely. The 1/2 digit
100 0.22 1.0 10 100 10
100 0.22 1.0 1.0 1000 100
k F F F mV V
NOTE: Comment on offset limitations above. Buffer gain does not improve ICL8052 noise performance adequately.
3-44
ICL8052/ICL71C03, ICL8068/ICL71C03
+5V 5 150 4.7k 150 4 3 2 1 150 7447 a b B1 c B2 d B3 e B4 f g RBI
ICL71C03 +5V
1 V+ 2 41/2 / 31/2 3 POLARITY 4 RUN/HOLD 5 COMP IN
BUSY 28 (LSD) D1 27 D2 26 D3 25 D4 24 (MSB) B8 23 B4 22 B2 21 (LSB) B1 20 (MSD) D5 19 STROBE 18 A-Z IN 17 A-Z OUT 16
300 k -15V 36 k 10 k 10F -15V
47k
-15V 10F 10k SIGNAL INPUT 0.1F
6 V7 REFERENCE 8 REF. CAP. 1 9 REF. CAP. 2 10 ANALOG IN 11 ANALOG GND 12 CLOCK IN 13 UNDER-RANGE
1.0F
ICL8068
0.22F
1 V2 COMP OUT 3 REF CAP 4 REF BYPASS 5 GND 6 REF OUT
INT OUT 14 +BUFF IN 13 +INT IN 12 -INT IN 11 -BUFF IN 10 BUFF OUT 9 V++ 8 100 k 90k 10k
300F
14 OVER-RANGE DIGITAL GND 15
CLOCK IN 120kHz = 3 READINGS/SEC
1k
7 REF SUPPLY
+15V
NOTE: For 31/2 digit, tie pin 2 low and change clock to 12kHz. FIGURE 7. ICL8052A (8068A)/71C03A 41/2 DIGIT A/D CONVERTER
a POL
a DM8880 g RBI BI D
V+ 3k
+5V
PROG 0V A
g +5V HI VOLTAGE BUFFER DI 505 47k 5k 0.02F
2.5k GATES ARE 7409
0.02 F
0.02 F 0.02 F 0.02 F
POL D5 8052A/ 8068A
D4
D3
D2
D1
71C03A
B8 B4 B2 B1
FIGURE 8. ICL8052-8068/71C03A PLASMA DISPLAY CIRCUIT
3-45
ICL8052/ICL71C03, ICL8068/ICL71C03
A suitable circuit for driving a plasma-type display is shown in Figure 8. The high voltage anode driver buffer is made by Dionics. The 3 AND gates and caps driving "Bl" are needed for interdigit blanking of multiple-digit display elements, and can be omitted if not needed. The 2K and 3K resistors set the current levels in the display. A similar arrangement can be used with "Nixie(R)" tubes.
Nixie(R) is a registered trademark of Burroughs Corporation.
driver circuit could be ganged to the one shown if required. This would be useful if additional annunciators were needed. Figure 10 shows the complete circuit for a 41/2 digit (2.000V) A/D, again using the internal reference of the 8052A/8068A. Figure 11 shows a more complicated circuit for driving LCD displays. Here the data is latched into the ICM7211 by the STROBE signal and "Overrange" is indicated by blanking the 4 digits. A clock oscillator circuit using the ICM7555 CMOS timer is shown. Some other suitable clock circuits are suggested in Figures 12 and 13. The 2-gate circuit should use CMOS gates to maintain good power supply rejection. A problem sometimes encountered with the 8052/68/71C03 A/D is that of gross over-voltage applied in the input. Voltage in excess of 2.000V may cause the integrator output to saturate. When this occurs, the integrator can no longer source (or sink) the current required to hold the summing junction (Pin 11) at the voltage stored on the auto zero capacitor. As a result, the voltage across the integrator capacitor decreases sufficiently to give a false voltage reading. This problem can also show up as large-signal instability on overrange conditions. A simple solution to this problem is to use junction FET transistors across the integrator capacitor to source (or sink) current into the summing junction and prevent the integrator amplifier from saturating, as shown in Figure 14.
Analog and Digital Grounds
Extreme care must be taken to avoid ground loops in the layout of 8068 or 8052/71C03A circuits, especially in high sensitivity circuits. It is most important that return currents from digital loads are not fed into the analog ground line. Both of the above circuits have considerable current flowing in the digital ground returns from drivers, etc. A recommended connection sequence for the ground lines is shown in Figure 9. Other Circuits for Display Applications Popular LCD displays can be interfaced to the Output of the ICL71C03 with suitable display drivers, such as the ICM7211A as shown in Figure 10. A standard CMOS 4000 series LCD driver circuit is used for displaying the 1/2 digit, the polarity, and the "over-range" flag. A similar circuit can be used with the ICM7212A LED driver. Of course, another full
BUFF OUT PIN 11 ICL71C03 AN GND BUFF -IN (IF USED)
REF VOLTAGE VREF
EXTERNAL REFERENCE (IF USED)
ANALOG SUPPLY BYPASS CAPACITORS +15V -15V
+ VIN
-
I/P FILTER CAP
CAZ
PIN 5 ICL8052/68 AN GND ANALOG SUPPLY RETURN BOARD EDGE DIGITAL SUPPLY RETURN
8068 PIN 2 COMPARATOR
DIGITAL LOGIC
DIG GND ICL7104 PIN 2
DEVICE PIN
+5V SUPPLY BYPASS CAPACITOR(S)
FIGURE 9. GROUNDING SEQUENCE
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ICL8052/ICL71C03, ICL8068/ICL71C03
41/2 DIGIT LCD DISPLAY 28 SEGMENTS D 1 - D4 +5V 1 16 15 14 12 5 3 4 CD4054A 7 8 13 11 10 9 2 6 0V +5V 1 V+ 2 41/2 / 31/2 3 POL 4 R/H 5 COMP IN -15V 6 V7 REF 8 REF. CAP. 1 1F 100k 10 INPUT INPUT 0.1F 9 REF. CAP. 2 ICL71C03 BUSY 28 D1 27 D2 26 D3 25 D4 24 B8 23 B4 22 B2 21 B1 20 D5 19 0V A-Z IN 17 A-Z OUT 16 DIG GND 15 0V CLOCK IN (120kHz = 3 READINGS/SEC) 1.0F -15V 300F 36k ICM7211A 5 BP 31 D1 32 D2 33 D3 34 D4 30 B3 OPTIONAL CAPACITOR +5V 28 B1 OSC 36 22-100pF 27 B0 29 B2 35 VV+ 1 +5V 2, 3, 4 6 - 26 37 - 40
BACKPLANE
11 ANALOG GND STROBE 18 12 CLOCK 13 UR 14 OR
1 2 3 4 ICL8052 (A) 8068 (A)
14 0.22F 13 12 11 10 9 8 +15V 100k
300k 5 -15V 5k 10k 10F 6 7
ANALOG GND
FIGURE 10. DRIVING LCD DISPLAYS
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ICL8052/ICL71C03, ICL8068/ICL71C03
+5V 41/2 DIGIT LCD DISPLAY 28 SEGMENTS D1 - D4
1/ CD4030 2
BACKPLANE
+5V 1 V+
ICM7211A ICL71C03(A) BUSY 28 D1 27 D2 26 D3 25 D4 24 B8 23 B4 22 B2 21 B1 20 D5 19 CD4071 35 V0V A-Z IN 17 A-Z OUT 16 DIG GND 15 0V +5V
1/ CD4030 4
5 BP CD4081
1/ CD4030 4
2 41/2 / 31/2 3 POL 4 R/H 5 COMP IN -15V 6 V7 REF 8 REF. CAP. 1 1F 9 REF. CAP. 2 100k 10 INPUT INPUT 0.1F
31 D1 32 D2 33 D3 34 D4 2, 3, 4 6 - 26 37 - 40 OPTIONAL CAPACITOR +5V OSC 36 22-100pF
CD4071
30 B3 29 B2 28 B1 27 B0
V+ 1 +5V
11 ANALOG GND STROBE 18 12 CLOCK 13 UR 14 OR
+5V 4.7k 0V 1 V2 ICM7555 V+ 8 7 6 5 10 TO 15k ADJUST TO FCL = 120kHz
1.0F +5V -15V 300F 36k 1 2 3 4 300k 5 -15V 5k 10k 10F 6 7 10 9 8 +15V 100k ICL8052 (A) 8068 (A) 14 0.22F 13 12 11
3 OUT 4 RESET
300pF 0V
ANALOG GND
FIGURE 11. 41/2 DIGIT LCD DPM WITH DIGIT BLANKING ON OVERRANGE
3-48
ICL8052/ICL71C03, ICL8068/ICL71C03
+5V
16k 56k 2 0.22F +8 7 LM311 1 3 4 16k
1k
30k
R 37.5k C 100pF
fOSC = 0.45/RC
390pF
FIGURE 12. CMOS OSCILLATOR
FIGURE 13. LM311 OSCILLATOR
D D +15V -15V -BUF IN REF OUT 300pF REF COMP 5 6 8 7 1 10 BUFFER 100K BUF OUT 9 0.22F
S 2N5461 S 2N5458
-INT IN 11 INTEG.
INT OUT 14 COMP.
INT. 3 REF.
A1 + 8052A/ 8068A
A2 + -1.2V
A3 + 2
COMP OUT
+BUF IN 13
+INT IN 12
TO ICL71C03
FIGURE 14. GROSS OVERVOLTAGE PROTECTION CIRCUIT
Interfacing with UARTs and Microprocessors
Figure 15 shows a very simple interface between a free-running 8068/8052/71C03A and a UART. The five STROBE pulses start the transmission of the five data words. The digit 5 word is 0000XXXX, digit 4 is 1000XXXX, digit 3 is 0100XXXX, etc. Also, the polarity is transmitted indirectly by using it to drive the Even Parity Enable Pin (EPE). If EPE of the receiver is held low, a parity flag at the receiver can be decoded as a positive signal, no flag as negative. A complex arrangement is shown in Figure 14. Here the UART can instruct the A/D to begin a measurement sequence by a word on RRI. The Busy signal resets the Data Ready Reset (DRR). Again STROBE starts the transmit sequence. A quad 2 input multiplexer is used to superimpose polarity, over-range, and under-range onto the D5 word since in this instance it is known that B2 = B4 = B8 = 0. For correct operation it is important that the UART clock be fast enough that each word is transmitted before the next STROBE pulse arrives. Parity is locked into the UART at load time but does not change in this connection during an output stream. Circuits to interface the 71C03(A) directly with three popular microprocessors are shown in Figures 17, 18 and 19. The main differences in the circuits are that the IM6100 with its
12-bit word capability can accept polarity, over-range, underrange, 4 bits of BCD and 5 digits simultaneously where the 8080/8048 and the MC6800 groups with 8-bit words need to have polarity, over-range and under-range multiplexed onto the Digit 5 word - as in the UART circuits. In each case the microprocessor can instruct the A/D when to begin a measurement and when to hold this measurement.
Application Notes
NOTE # AN016 AN017 AN018 DESCRIPTION "Selecting A/D Converters" "The Integrating A/D Converter" "Do's and Don'ts of Applying A/D Converters" "Low Cost Digital Panel Meter Designs" "Build an Auto-Ranging DMM Using the 8052A / 7103A A/D Converter Pair," by Larry Goff AnswerFAX DOC. # 9016 9017 9018
AN023 AN028
9023 9028
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ICL8052/ICL71C03, ICL8068/ICL71C03
SERIAL OUTPUT TO RECEIVING UART
TRO UART IM6402/3 EPE TBR 1 2 3 4 5 6 7 8 TBRL
D4 NC D5
D3
D2
D1
B1
B2
B4
B8 STROBE
71C03/A POL RUN/HOLD +5V
FIGURE 15. SIMPLE ICL71C03/71C03A TO UART INTERFACE
TRO
RRI UART IM6402/3
DRR DR TBRL 5 6 7 8
EPE TBR 1 2 3 4
1Y
2Y
3Y ENABLE 74C157
1A
2A
3A SELECT 1B
2B
3B
D4 D5
D3
D2
D1
B1
B2
B4
B8
POL OVER UNDER
71C03/A STROBE RUN/HOLD BUSY 100pF 10k
+5V
FIGURE 16. COMPLEX ICL71C03/7103A TO UART INTERFACE
3-50
ICL8052/ICL71C03, ICL8068/ICL71C03
12
12 1 80C95 15 80C95 15 1
12
READ 1 IM6101 D1 D2 D3 D4 D5 B1 B2 B4 B8 POL OVER 71C03/A STROBE RUN/HOLD SENSE 1 7 WRITE 1 IM6100
FIGURE 17. IM6100 TO ICL71C03A/71C03A INTERFACE
EN 74C157
1Y 2Y
PA0 PA1 PA2 PA3 MC680X OR MCS650X
EN 74C157
1Y 2Y
PA0 PA1 PA2 PA3 8255 (MODE 1) PA4 PA5 PA6 PA7 STBA PB0 8080, 8085, ETC.
1B 2B 3B SEL 1A 2A 3A 3Y
1B 2B 3B SEL 1A 2A 3A 3Y
POL
OVER
POL
UNDER
OVER
71C03
RUN/ HOLD
STROBE
D1 D2 D3 D4
PA4 PA5 PA6 PA7 CA1 CA2
UNDER
D5 B8 B4 B2 B1
MC6820
D5 B8 B4 B2 B1 71C03 D1 D2 D3 D4
RUN/ HOLD
STROBE
FIGURE 18. ICL71C03 TO MC6800, MCS650X INTERFACE
FIGURE 19. ICL71C03 TO MCS-48, -80, -85 INTERFACE
3-51
ICL8052/ICL71C03, ICL8068/ICL71C03 ICL71C03 with ICL8052/8068 Integrating A/D Converter Equations
The ICL71C03 does not have an internal crystal or RC oscillator. It has a clock input only. Integration Period
10, 000 t INT = -------------------- ( 4-1/2 Digit ) f CLOCK 1, 000 t INT = -------------------- ( 3-1/2 Digit ) f CLOCK
Integrator Output Voltage
( t INT ) ( I INT ) V INT = ------------------------------C INT
VINT (Typ) = 9V Output Count
V IN Count = 10, 000 x -------------- (4-1/2 Digit) V REF V IN Count = 1, 000 x -------------- (3-1/2 Digit) V REF NOTE: The 41/2 digit mode's LSD will be output as a zero in the 31/2 digit mode.
Integration Clock Period tCLOCK = 1/fCLOCK 60/50Hz Rejection Criterion tINT/t60Hz or tINT/t50Hz = Integer
Output Type: Optimum Integration Current 4 Nibbles BCD with Polarity and Over-range. IINT = 20A Full Scale Analog Input Voltage VINFS (Typ) = 200mV to 2.0V = 2VREF Integrate Resistor
( Buffe rGain ) x V INFS R INT = -----------------------------------------------------------I INT
Power Supply: 15V, +5V V++ = +15V V- = -15V V+ = +5V VREF 1.75V If VREF not used, float output pin. Auto Zero Capacitor Values 0.01F < CAZ < 1F Reference Capacitor Value CREF = (Buffer Gain) x CAZ
Integrate Capacitor
( t INT ) ( I INT ) C INT = ------------------------------V INT
AUTO ZERO (COUNTS) 30,001 - 10,001 3,001 - 1,001
INTEGRATE (FIXED COUNT) 10,000 1,000
DEINTEGRATE (COUNTS) 1 - 20,001 1 - 2,001
(41/2 DIGIT) (31/2 DIGIT)
TOTAL CONVERSION TIME (tCONV) (IN CONTINUOUS MODE) tCONV = 40,002 * tCLOCK (41/2 DIGIT MODE) tCONV = 4,002 * tCLOCK (31/2 DIGIT MODE)
FIGURE 20. INTEGRATOR OUTPUT
All Intersil semiconductor products are manufactured, assembled and tested under ISO9000 quality systems certification.
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries 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 Intersil or its subsidiaries.
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