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S E M I C O N D U C T O R
ICL7106, ICL7107
31/2 Digit LCD/LED Display A/D Converter
Description
The Harris ICL7106 and ICL7107 are high performance, low power 31/2 digit A/D converters. Included are seven segment decoders, display drivers, a reference, and a clock. The ICL7106 is designed to interface with a liquid crystal display (LCD) and includes a multiplexed backplane drive; the ICL7107 will directly drive an instrument size light emitting diode (LED) display. The ICL7106 and ICL7107 bring together a combination of high accuracy, versatility, and true economy. It features auto-zero to less than 10µV, zero drift of less than 1µV/C, input bias current of 10pA max., and rollover error of less than one count. True differential inputs and reference are useful in all systems, but give the designer an uncommon advantage when measuring load cells, strain gauges and other bridge type transducers. Finally, the true economy of single power supply operation (ICL7106), enables a high performance panel meter to be built with the addition of only 10 passive components and a display.
January 1994
Features
· Guaranteed Zero Reading for 0V Input on All Scales · True Polarity at Zero for Precise Null Detection · 1pA Typical Input Current · True Differential Input and Reference, Direct Display Drive - LCD ICL7106 - LED lCL7l07 · Low Noise - Less Than 15µVp-p · On Chip Clock and Reference · Low Power Dissipation - Typically Less Than 10mW · No Additional Active Circuits Required · New Small Outline Surface Mount Package Available
Ordering Information
PART NUMBER ICL7106CPL ICL7106RCPL ICL7106CM44 ICL7107CPL ICL7107RCPL ICL7107CM44 TEMPERATURE RANGE 0oC to +70oC 0oC to +70oC 0oC to +70oC 0 C to +70 C 0oC to +70oC 0 C to +70 C
o o o o
PACKAGE 40 Lead Plastic DIP 40 Lead Plastic DIP (Note 1) 44 Lead Metric Plastic Quad Flatpack 40 Lead Plastic DIP 40 Lead Plastic DIP (Note 1) 44 Lead Metric Plastic Quad Flatpack
NOTE: 1. "R" indicates device with reversed leads.
Pinouts
ICL7106, ICL7107 (PDIP) TOP VIEW
REF LO REF HI CREF+ V+ D1 C1 B1 (1's) A1 F1 G1 E1 D2 C2 (10's) B2 A2 F2 E2 D3 (100's) B3 F3 E3 (1000) AB4 (MINUS) POL 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 40 OSC 1 39 OSC 2 38 OSC 3 37 TEST 36 REF HI 35 REF LO 34 CREF+ 33 CREF32 COMMON 31 IN HI 30 IN LO 29 A-Z 28 BUFF 27 INT 26 V25 G2 (10's) 24 C3 23 A3 22 G3 21 BP/GND A1 F1 G1 E1 D2 C2 B2 A2 F2 E2 D3 (100's) NC NC TEST OSC 3 NC OSC 2 OSC 1 V+ D1 C1 B1 1 44 43 42 41 40 39 38 37 36 35 34 33 2 32 3 4 5 6 7 8 9 10 31 30 29 28 27 26 25 24 NC G2 C3 A3 G3 BP/GND POL AB4 E3 F3 B3
ICL7106, ICL7107 (MQFP) TOP VIEW
COMMON CREFIN LO BUFF
IN HI
A-Z
INT
11 23 12 13 14 15 16 17 18 19 20 21 22
V-
CAUTION: These devices are sensitive to electrostatic discharge. Users should follow proper I.C. Handling Procedures. Copyright
© Harris Corporation 1993
File Number
3082
2-33
Specifications ICL7106, ICL7107
Absolute Maximum Ratings
Supply Voltage ICL7106, V+ to V- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15V ICL7107, V+ to GND. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6V ICL7107, V- to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .-9V Analog Input Voltage (Either Input) (Note 1). . . . . . . . . . . . . V+ to VReference Input Voltage (Either Input) . . . . . . . . . . . . . . . . . V+ to VClock Input ICL7106 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TEST to V+ ICL7107 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . GND to V+
Thermal Information
Thermal Resistance (MAX, See Note 1) JA 40 Pin Plastic Package . . . . . . . . . . . . . . . . . . . . . . . . 50oC/W 44 Pin MQFP Package . . . . . . . . . . . . . . . . . . . . . . . . 80oC/W Maximum Power Dissipation ICL7106 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0W ICL7107 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2W Operating Temperature Range . . . . . . . . . . . . . . . . . . 0oC to +70oC Storage Temperature Range. . . . . . . . . . . . . . . . . . -65oC to +150oC Lead Temperature (Soldering 10s Max) . . . . . . . . . . . . . . . . +265oC Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +150oC
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.
Electrical Specifications (Note 3)
PARAMETERS SYSTEM PERFORMANCE Zero Input Reading VIN = 0.0V, Full-Scale = 200mV VlN = VREF, VREF = 100mV -VIN = +VlN 200mV Difference in Reading for Equal Positive and Negative Inputs Near Full-Scale Full-Scale = 200mV or Full-Scale = 2V Maximum Deviation from Best Straight Line Fit (Note 5) VCM = 1V, VIN = 0V, Full-Scale = 200mV (Note 5) VIN = 0V, Full-Scale = 200mV (Pk-Pk Value Not Exceeded 95% of Time) VlN = 0 (Note 5) VlN = 0, 0 < TA < +70 C (Note 5) VIN = 199mV, 0o < TA < +70oC, (Ext. Ref. 0ppm/oC) (Note 5)
o o
TEST CONDITIONS
MIN
TYP
MAX
UNIT
-000.0
±000.0 999/ 1000 ±0.2
+000.0
Digital Reading Digital Reading Counts
Ratiometric Reading
999
1000 ±1
Rollover Error
-
Linearity
-
±0.2 50 15
±1 -
Counts µV/V µV pA µV/oC ppm/oC
Common Mode Rejection Ratio Noise
-
Leakage Current Input Zero Reading Drift Scale Factor Temperature Coefficient
-
1 0.2 1
10 1 5
End Power Supply Character V+ Supply Cur- VIN = 0 (Does Not Include LED Current for ICL7107) rent End Power Supply Character V- Supply Current ICL7107 Only COMMON Pin Analog Common Voltage 25k Between Common and Positive Supply (With Respect to + Supply) 25k Between Common and Positive Supply (With Respect to + Supply)
-
0.8
1.8
mA
2.4
0.6 2.8
1.8 3.2
mA V ppm/oC
Temperature Coefficient of Analog Common
-
80
-
DISPLAY DRIVER ICL7106 ONLY Pk-Pk Segment Drive Voltage Pk-Pk Backplane Drive Voltage V+= to V- = 9V, (Note 4) 4 5 6 V
2-34
ICL7106, ICL7107
Electrical Specifications (Note 3) (Continued)
PARAMETERS ICL7107 ONLY Segment Sinking Current (Except Pin 19 and 20) Pin 19 Only Pin 20 Only V+ = 5V, Segment Voltage = 3V 5 10 4 8 16 7 mA mA mA TEST CONDITIONS MIN TYP MAX UNIT
NOTES: 1. Input voltages may exceed the supply voltages provided the input current is limited to ±100µA. 2. Dissipation rating assumes device is mounted with all leads soldered to printed circuit board. 3. Unless otherwise noted, specifications apply to both the ICL7106 and ICL7107 at TA = +25oC, fCLOCK = 48kHz. ICL7106 is tested in the circuit of Figure 1. ICL7107 is tested in the circuit of Figure 2. 4. Back plane drive is in phase with segment drive for `off' segment, 180o out of phase for `on' segment. Frequency is 20 times conversion rate. Average DC component is less than 50mV. 5. Not tested, guaranteed by design.
Typical Applications and Test Circuits
+ IN R1 R3 OSC 1 40 OSC 2 39 OSC 3 38 C4 TEST 37 R4 C1 R5 C5 C2 R2 C3 DISPLAY 9V
ICL7106
20 POL 19 AB4 G1 D1 C1 B1 A1 D2 10 C2 11 B2 12 A2 15 D3 16 B3 V+ E1 14 E2 18 E3 F1 13 F2 17 F3
C1 = 0.1µF C2 = 0.47µF C3 = 0.22µF C4 = 100pF C5 = 0.02µF R1 = 24k R2 = 47k R3 = 100k R4 = 1k R5 = 1M
REF HI 36
REF LO 35
CREF+ 34
CREF- 33
COM 32
IN HI 31
IN LO 30
A-Z 29
BUFF 28
INT 27
V- 26
G2 25
C3 24
A3 23
G3 22
1
2
3
4
5
6
7
8
9
DISPLAY
FIGURE 1. ICL7106 TEST CIRCUIT AND TYPICAL APPLICATION WITH LCD DISPLAY COMPONENTS SELECTED FOR 200mV FULLSCALE
+5V R5 C1 C5 C2 R2 C3 DISPLAY + IN R1 R3 OSC 1 40 OSC 2 39 OSC 3 38 C4 TEST 37 R4 -5V
BP 21
ICL7107
20 POL 19 AB4 G1 D1 C1 B1 A1 D2 10 C2 11 B2 12 A2 15 D3 16 B3 V+ E1 14 E2 18 E3 F1 13 F2 17 F3
C1 = 0.1µF C2 = 0.47µF C3 = 0.22µF C4 = 100pF C5 = 0.02µF R1 = 24k R2 = 47k R3 = 100k R4 = 1k R5 = 1M
REF HI 36
REF LO 35
CREF+ 34
CREF- 33
COM 32
IN HI 31
IN LO 30
A-Z 29
BUFF 28
INT 27
V- 26
G2 25
C3 24
A3 23
G3 22
1
2
3
4
5
6
7
8
9
DISPLAY
FIGURE 2. ICL7107 TEST CIRCUIT AND TYPICAL APPLICATION WITH LED DISPLAY COMPONENTS SELECTED FOR 200mV FULLSCALE
2-35
GND 21
ICL7106, ICL7107 Design Information Summary Sheet
· OSCILLATOR FREQUENCY fOSC = 0.45/RC COSC > 50pF; ROSC > 50K fOSC Typ. = 48KHz · OSCILLATOR PERIOD tOSC = RC/0.45 · INTEGRATION CLOCK FREQUENCY fCLOCK = fOSC/4 · INTEGRATION PERIOD tINT = 1000 x (4/fOSC) · 60/50Hz REJECTION CRITERION tINT/t60Hz or tlNT/t60Hz = Integer · OPTIMUM INTEGRATION CURRENT IINT = 4.0µA · FULL-SCALE ANALOG INPUT VOLTAGE VlNFS Typically = 200mV or 2.0V · INTEGRATE RESISTOR V INFS R = INT I INT · INTEGRATE CAPACITOR (t ) (I ) INT INT C = INT V INT · INTEGRATOR OUTPUT VOLTAGE SWING (t ) (I ) INT INT V = INT C INT · VINT MAXIMUM SWING: (V- + 0.5V) < VINT < (V+ - 0.5V), VINT typically = 2.0V · DISPLAY COUNT COUNT = 1000 × V V IN
REF
· CONVERSION CYCLE tCYC = tCL0CK x 4000 tCYC = tOSC x 16,000 when fOSC = 48KHz; tCYC = 333ms · COMMON MODE INPUT VOLTAGE (V- + 1.0V) < VlN < (V+ - 0.5V) · AUTO-ZERO CAPACITOR 0.01µF < CAZ < 1.0µF · REFERENCE CAPACITOR 0.1µF < CREF < 1.0µF · VCOM Biased between Vi and V-. · VCOM V+ - 2.8V Regulation lost when V+ to V- < 6.8V. If VCOM is externally pulled down to (V + to V -)/2, the VCOM circuit will turn off. · ICL7106 POWER SUPPLY: SINGLE 9V V+ - V- = 9V Digital supply is generated internally VGND V+ - 4.5V · ICL7106 DISPLAY: LCD Type: Direct drive with digital logic supply amplitude. · ICL7107 POWER SUPPLY: DUAL ±5.0V V+ = +5.0V to GND V- = -5.0V to GND Digital Logic and LED driver supply V+ to GND · ICL7107 DISPLAY: LED Type: Non-Multiplexed Common Anode
Typical Integrator Amplifier Output Waveform (INT Pin)
AUTO ZERO PHASE (COUNTS) 2999 - 1000
SIGNAL INTEGRATE PHASE FIXED 1000 COUNTS
DE-INTEGRATE PHASE 0 - 1999 COUNTS
TOTAL CONVERSION TIME = 4000 x tCLOCK = 16,000 x tOSC
2-36
ICL7106, ICL7107 Detailed Description
Analog Section Figure 3 shows the Analog Section for the ICL7106 and ICL7107. Each measurement cycle is divided into three phases. They are (1) auto-zero (A-Z), (2) signal integrate (INT) and (3) de-integrate (DE). Auto-Zero Phase During auto-zero three things happen. First, input high and low are disconnected from the pins and internally shorted to analog COMMON. Second, the reference capacitor is charged to the reference voltage. Third, a feedback loop is closed around the system to charge the auto-zero capacitor CAZ to compensate for offset voltages in the buffer amplifier, integrator, and comparator. Since the comparator is included in the loop, the A-Z accuracy is limited only by the noise of the system. In any case, the offset referred to the input is less than 10µV. Signal Integrate Phase During signal integrate, the auto-zero loop is opened, the internal short is removed, and the internal input high and low are connected to the external pins. The converter then integrates the differential voltage between IN HI and IN LO for a fixed time. This differential voltage can be within a wide common mode range: up to 1V from either supply. If, on the other hand, the input signal has no return with respect to the converter power supply, IN LO can be tied to analog COMMON to establish the correct common mode voltage. At the end of this phase, the polarity of the integrated signal is determined. De-Integrate Phase The final phase is de-integrate, or reference integrate. Input low is internally connected to analog COMMON and input high is connected across the previously charged reference capacitor. Circuitry within the chip ensures that the capacitor will be connected with the correct polarity to cause the integrator output to return to zero. The time required for the output to return to zero is proportional to the input signal. Specifically the digital reading displayed is:
DISPLAYCOUNT = 1000 V IN . V REF
Differential Input The input can accept differential voltages anywhere within the common mode range of the input amplifier, or specifically from 0.5V below the positive supply to 1.0V above the negative supply. In this range, the system has a CMRR of 86dB typical. However, care must be exercised to assure the integrator output does not saturate. A worst case condition would be a large positive common mode voltage with a near full-scale negative differential input voltage. The negative input signal drives the integrator positive when most of its swing has been used up by the positive common mode voltage. For these critical applications the integrator output swing can be reduced to less than the recommended 2V fullscale swing with little loss of accuracy. The integrator output can swing to within 0.3V of either supply without loss of linearity.
STRAY
CREF
STRAY RINT CAZ A-Z 29 INTEGRATOR
+
CINT INT 27
CREF V+
+
REF HI 36 A-Z
REF LO 35 A-Z
CREF 33
BUFFER V+ 28 1
34
+
-
10µA 31 IN HI INT DEDE+ INPUT HIGH 6.2V 2.8V
-
+
-
TO DIGITAL SECTION
A-Z
A-Z N 32 COMMON INT 30 IN LO VA-Z AND DE(±) INPUT LOW DE+ DE+
-
COMPARATOR
FIGURE 3. ANALOG SECTION OF ICL7106 AND ICL7107
2-37
ICL7106, ICL7107
Differential Reference The reference voltage can be generated anywhere within the power supply voltage of the converter. The main source of common mode error is a roll-over voltage caused by the reference capacitor losing or gaining charge to stray capacity on its nodes. If there is a large common mode voltage, the reference capacitor can gain charge (increase voltage) when called up to de-integrate a positive signal but lose charge (decrease voltage) when called up to de-integrate a negative input signal. This difference in reference for positive or negative input voltage will give a roll-over error. However, by selecting the reference capacitor such that it is large enough in comparison to the stray capacitance, this error can be held to less than 0.5 count worst case. (See Component Value Selection.) Analog COMMON This pin is included primarily to set the common mode voltage for battery operation (ICL7106) or for any system where the input signals are floating with respect to the power supply. The COMMON pin sets a voltage that is approximately 2.8V more negative than the positive supply. This is selected to give a minimum end-of-life battery voltage of about 6V. However, analog COMMON has some of the attributes of a reference voltage. When the total supply voltage is large enough to cause the zener to regulate (>7V), the COMMON voltage will have a low voltage coefficient (0.001%/V), low output impedance (15), and a temperature coefficient typically less than 80ppm/oC. The limitations of the on chip reference should also be recognized, however. With the ICL7107, the internal heating which results from the LED drivers can cause some degradation in performance. Due to their higher thermal resistance, plastic parts are poorer in this respect than ceramic. The combination of reference Temperature Coefficient (TC), internal chip dissipation, and package thermal resistance can increase noise near full-scale from 25µV to 80µVp-p. Also the linearity in going from a high dissipation count such as 1000 (20 segments on) to a low dissipation count such as 1111(8 segments on) can suffer by a count or more. Devices with a positive TC reference may require several counts to pull out of an over-range condition. This is because over-range is a low dissipation mode, with the three least significant digits blanked. Similarly, units with a negative TC may cycle between over-range and a non-overrange count as the die alternately heats and cools. All these problems are of course eliminated if an external reference is used. The ICL7106, with its negligible dissipation, suffers from none of these problems. In either case, an external reference can easily be added, as shown in Figure 4. Analog COMMON is also used as the input low return during auto-zero and de-integrate. If IN LO is different from analog COMMON, a common mode voltage exists in the system and is taken care of by the excellent CMRR of the converter. However, in some applications IN LO will be set at a fixed known voltage (power supply common for instance). In this application, analog COMMON should be tied to the same point, thus removing the common mode voltage from the converter. The same holds true for the reference voltage. If reference can be conveniently tied to analog COMMON, it should be since this removes the common mode voltage from the reference system. Within the lC, analog COMMON is tied to an N channel FET that can sink approximately 30mA of current to hold the voltage 2.8V below the positive supply (when a load is trying to pull the common line positive). However, there is only 10µA of source current, so COMMON may easily be tied to a more negative voltage thus overriding the internal reference.
V+
V REF HI REF LO 6.8V ZENER IZ
ICL7106 ICL7107
V-
FIGURE 4A.
V+
V ICL7106 ICL7107 REF HI REF LO COMMON 20k
6.8k
ICL8069 1.2V REFERENCE
FIGURE 4B. FIGURE 4. USING AN EXTERNAL REFERENCE
TEST The TEST pin serves two functions. On the ICL7106 it is coupled to the internally generated digital supply through a 500 resistor. Thus it can be used as the negative supply for externally generated segment drivers such as decimal points or any other presentation the user may want to include on the LCD display. Figures 5 and 6 show such an application. No more than a 1mA load should be applied.
V+
1M TO LCD DECIMAL POINT
ICL7106 BP TEST 21 37
TO LCD BACKPLANE
FIGURE 5. SIMPLE INVERTER FOR FIXED DECIMAL POINT
2-38
ICL7106, ICL7107
The second function is a "lamp test". When TEST is pulled high (to V+) all segments will be turned on and the display should read "1888". The TEST pin will sink about 15mA under these conditions.
CAUTION: In the lamp test mode, the segments have a constant DC voltage (no square-wave). This may burn the LCD display if maintained for extended periods.
Digital Section
Figures 7 and 8 show the digital section for the ICL7106 and ICL7107, respectively. In the ICL7106, an internal digital ground is generated from a 6V Zener diode and a large Pchannel source follower. This supply is made stiff to absorb the relative large capacitive currents when the back plane (BP) voltage is switched. The BP frequency is the clock frequency divided by 800. For three readings/second this is a 60Hz square wave with a nominal amplitude of 5V. The segments are driven at the same frequency and amplitude and are in phase with BP when OFF, but out of phase when ON. In all cases negligible DC voltage exists across the segments. Figure 8 is the Digital Section of the ICL7107. It is identical to the ICL7106 except that the regulated supply and back plane drive have been eliminated and the segment drive has been increased from 2mA to 8mA, typical for instrument size common anode LED displays. Since the 1000 output (pin 19) must sink current from two LED segments, it has twice the drive capability or 16mA. In both devices, the polarity indication is "on" for negative analog inputs. If IN LO and IN HI are reversed, this indication can be reversed also, if desired.
V+ V+ BP
ICL7106
DECIMAL POINT SELECT
TO LCD DECIMAL POINTS
TEST CD4030 GND
FIGURE 6. EXCLUSIVE `OR' GATE FOR DECIMAL POINT DRIVE
a a b f g e d c b c f
a b g e d c e f
a b g c d
21 BACKPLANE
LCD PHASE DRIVER 7 SEGMENT DECODE 7 SEGMENT DECODE 7 SEGMENT DECODE
TYPICAL SEGMENT OUTPUT V+ 0.5mA SEGMENT OUTPUT 2.0mA 1000's COUNTER INTERNAL DIGITAL GROUND TO SWITCH DRIVERS FROM COMPARATOR OUTPUT CLOCK
÷200
LATCH
100's COUNTER
10's COUNTER
1's COUNTER
1 V+
÷4
INTERNAL DIGITAL GROUND
LOGIC CONTROL
6.2V 500
THREE INVERTERS ONE INVERTER SHOWN FOR CLARITY
TEST VTH = 1V 37
26 40 OSC 1 OSC 2 39 OSC 3 38
V-
FIGURE 7. ICL7106 DIGITAL SECTION
2-39
ICL7106, ICL7107
a a b f g e d c b c f g e d c e d a b f g c a b
7 SEGMENT DECODE TYPICAL SEGMENT OUTPUT V+ 0.5mA TO SEGMENT 8.0mA DIGITAL GROUND TO SWITCH DRIVERS FROM COMPARATOR OUTPUT V+ THREE INVERTERS ONE INVERTER SHOWN FOR CLARITY 40 OSC 1 OSC 2 39 OSC 3 38 CLOCK ÷4 1000's COUNTER 100's COUNTER
7 SEGMENT DECODE
7 SEGMENT DECODE
LATCH
10's COUNTER
1's COUNTER
1 V+ LOGIC CONTROL 500 27 DIGITAL GROUND 37 TEST
FIGURE 8. ICL7107 DIGITAL SECTION
System Timing Figure 9 shows the clocking arrangement used in the ICL7106 and ICL7107. Two basic clocking arrangements can be used: 1. An external oscillator connected to pin 40. 2. An R-C oscillator using all three pins. The oscillator frequency is divided by four before it clocks the decade counters. It is then further divided to form the three convert-cycle phases. These are signal integrate (1000 counts), reference de-integrate (0 to 2000 counts) and autozero (1000 to 3000 counts). For signals less than full-scale, auto-zero gets the unused portion of reference de-integrate. This makes a complete measure cycle of 4,000 counts (16,000 clock pulses) independent of input voltage. For three readings/second, an oscillator frequency of 48kHz would be used. To achieve maximum rejection of 60Hz pickup, the signal integrate cycle should be a multiple of 60Hz. Oscillator frequencies of 240kHz, 120kHz, 80kHz, 60kHz, 48kHz, 40kHz, 331/3kHz, etc. should be selected. For 50Hz rejection, Oscillator frequencies of 200kHz, 100kHz, 662/3kHz, 50kHz, 40kHz, etc. would be suitable. Note that 40kHz (2.5 readings/second) will reject both 50Hz and 60Hz (also 400Hz and 440Hz).
40 39 38 INTERNAL TO PART
÷4
CLOCK
GND ICL7107 TEST ICL7106
INTERNAL TO PART
÷4
CLOCK
40
39 R
38 C RC OSCILLATOR
FIGURE 9. CLOCK CIRCUITS
2-40
ICL7106, ICL7107 Component Value Selection
Integrating Resistor Both the buffer amplifier and the integrator have a class A output stage with 100µA of quiescent current. They can supply 4µA of drive current with negligible nonlinearity. The integrating resistor should be large enough to remain in this very linear region over the input voltage range, but small enough that undue leakage requirements are not placed on the PC board. For 2V full-scale, 470k is near optimum and similarly a 47k for a 200mV scale. Integrating Capacitor The integrating capacitor should be selected to give the maximum voltage swing that ensures tolerance buildup will not saturate the integrator swing (approximately. 0.3V from either supply). In the ICL7106 or the ICL7107, when the analog COMMON is used as a reference, a nominal +2V fullscale integrator swing is fine. For the ICL7107 with +5V supplies and analog COMMON tied to supply ground, a ±3.5V to +4V swing is nominal. For three readings/second (48kHz clock) nominal values for ClNT are 0.22µF and 0.10µF, respectively. Of course, if different oscillator frequencies are used, these values should be changed in inverse proportion to maintain the same output swing. An additional requirement of the integrating capacitor is that it must have a low dielectric absorption to prevent roll-over errors. While other types of capacitors are adequate for this application, polypropylene capacitors give undetectable errors at reasonable cost. Auto-Zero Capacitor The size of the auto-zero capacitor has some influence on the noise of the system. For 200mV full-scale where noise is very important, a 0.47µF capacitor is recommended. On the 2V scale, a 0.047µF capacitor increases the speed of recovery from overload and is adequate for noise on this scale. Reference Capacitor A 0.1µF capacitor gives good results in most applications. However, where a large common mode voltage exists (i.e. the REF LO pin is not at analog COMMON) and a 200mV scale is used, a larger value is required to prevent roll-over error. Generally 1.0µF will hold the roll-over error to 0.5 count in this instance. Oscillator Components
ICL7107
Reference Voltage The analog input required to generate full-scale output (2000 counts) is: VlN = 2VREF . Thus, for the 200mV and 2V scale, VREF should equal 100mV and 1V, respectively. However, in many applications where the A/D is connected to a transducer, there will exist a scale factor other than unity between the input voltage and the digital reading. For instance, in a weighing system, the designer might like to have a full-scale reading when the voltage from the transducer is 0.662V. Instead of dividing the input down to 200mV, the designer should use the input voltage directly and select VREF = 0.341V. Suitable values for integrating resistor and capacitor would be 1 20k and 0.22µF. This makes the system slightly quieter and also avoids a divider network on the input. The ICL7107 with ±5V supplies can accept input signals up to ±4V. Another advantage of this system occurs when a digital reading of zero is desired for VIN 0. Temperature and weighing systems with a variable fare are examples. This offset reading can be conveniently generated by connecting the voltage transducer between IN HI and COMMON and the variable (or fixed) offset voltage between COMMON and IN LO. ICL7107 Power Supplies The ICL7107 is designed to work from ±5V supplies. However, if a negative supply is not available, it can be generated from the clock output with 2 diodes, 2 capacitors, and an inexpensive l.C. Figure 10 shows this application. See ICL7660 data sheet for an alternative. In fact, in selected applications no negative supply is required. The conditions to use a single +5V supply are: 1. The input signal can be referenced to the center of the common mode range of the converter. 2. The signal is less than ±1.5V. 3. An external reference is used.
V+ CD4009 V+ OSC 1 OSC 2 OSC 3 IN914 + 10 µF -
0.047 µF IN914
For all ranges of frequency a 100k resistor is recommended and the capacitor is selected from the equation 0.45 For48kHzClock(3Readings/second), f = RC C = 100pF
GND V-
V- = 3.3V
FIGURE 10. GENERATING NEGATIVE SUPPLY FROM +5V
2-41
ICL7106, ICL7107 Typical Applications
The ICL7106 and ICL7107 may be used in a wide variety of configurations. The circuits which follow show some of the possibilities, and serve to illustrate the exceptional versatility of these A/D converters. The following application notes contain very useful information on understanding and applying this part and are available from Harris semiconductor.
Application Notes
A016 "Selecting A/D Converters" A017 "The Integrating A/D Converter" A018 "Do's and Don'ts of Applying A/D Converters" A023 "Low Cost Digital Panel Meter Designs" A032 "Understanding the Auto-Zero and Common Mode
Performance of the ICL7106/7/9 Family"
A046 "Building a Battery-Operated Auto Ranging DVM with
the ICL7106"
A052 "Tips for Using Single Chip 31/2 Digit A/D Converters"
Typical Applications
TO PIN 1 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 BP 21 TO BACKPLANE TO DISPLAY 0.22µF 0.01µF 0.47µF 47K 9V 1K 0.1µF 1M + IN 22K 100pF SET VREF = 100mV 100K OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 1K 0.1µF 1M 0.01µF 0.47µF 47K + IN 22K +5V 100pF SET VREF = 100mV 100K TO PIN 1
-
IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 GND 21
-
0.22µF
-5V
TO DISPLAY
Values shown are for 200mV full-scale, 3 readings/sec., floating supply voltage (9V battery).
Values shown are for 200mV full-scale, 3 readings/sec. IN LO may be tied to either COMMON for inputs floating with respect to supplies, or GND for single ended inputs. (See discussion under Analog COMMON.) FIGURE 12. ICL7107 USING THE INTERNAL REFERENCE
FIGURE 11. ICL7106 USING THE INTERNAL REFERENCE
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ICL7106, ICL7107 Typical Applications (Continued)
TO PIN 1 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 GND 21 TO DISPLAY 0.22µF V0.01µF 0.47µF 47K 1K 0.1µF 1.2V (ICL8069) 1M + IN 10K 10K V+ 100pF SET VREF = 100mV 100K OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 GND 21 TO DISPLAY 0.22µF -5V 0.01µF 0.47µF 47K 1K 0.1µF 1M 100K 6.8V + IN +5V 100pF SET VREF = 100mV 100K TO PIN 1
-
-
IN LO is tied to supply COMMON establishing the correct common mode voltage. If COMMON is not shorted to GND, the input voltage may float with respect to the power supply and COMMON acts as a pre-regulator for the reference. If COMMON is shorted to GND, the input is single ended (referred to supply GND) and the pre-regulator is overridden. FIGURE 13. ICL7107 WITH AN EXTERNAL BAND-GAP REFERENCE (1.2V TYPE)
TO PIN 1 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 BP/GND 21 TO DISPLAY 0.22µF V0.01µF 0.047µF 470K 25K 0.1µF 1M + IN 24K V+ 100pF SET VREF = 100mV 100K
Since low TC zeners have breakdown voltages ~ 6.8V, diode must be plasced across the total supply (10V). As in the case of Figure 14, IN LO may be tied to either COMMON or GND
FIGURE 14. ICL7107 WITH ZENER DIODE REFERENCE
TO PIN 1 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 GND 21 TO DISPLAY 0.22µF 0.01µF 0.47µF 47K 1K 0.1µF 1.2V (ICL8069) 1M + IN 10K 15K +5V 100pF SET VREF = 100mV 100k
-
-
An external reference must be used in this application, since the voltage between V+ and V- is insufficient for correct operation of the internal reference. FIGURE 15. ICL7106 AND ICL7107: RECOMMENDED COMPONENT VALUES FOR 2.0V FULL-SCALE FIGURE 16. ICL7107 OPERATED FROM SINGLE +5V
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ICL7106, ICL7107 Typical Applications (Continued)
TO PIN 1 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 GND 21 TO DISPLAY 0.22µF 47K 0.47µF 0.1µF 100pF 100K V+ TO PIN 1 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 BP 21 TO BACKPLANE TO DISPLAY 0.22µF 0.01µF 0.47µF 47K 9V ZERO ADJUST SILICON NPN MPS 3704 OR SIMILAR 0.1µF 100k 1M 100k 220k 100pF SCALE FACTOR ADJUST 22K 100K
The resistor values within the bridge are determined by the desired sensitivity.
A silicon diode-connected transistor has a temperature coefficient of about -2mV/oC. Calibration is achieved by placing the sensing transistor in ice water and adjusting the zeroing potentiometer for a 000.0 reading. The sensor should then be placed in boiling water and the scale-factor potentiometer adjusted for a 100.0 reading. FIGURE 18. ICL7106 USED AS A DIGITAL CENTIGRADE THERMOMETER
+5V
FIGURE 17. ICL7107 MEASUREING RATIOMETRIC VALUES OF QUAD LOAD CELL
V+ 1 V+ 2 D1 TO LOGIC VCC 3 C1 4 B1 5 A1 6 F1 7 G1 8 E1 9 D2 10 C2 11 B2 12 A2 13 F2 14 E2 15 D3 16 B3 17 F3 O /RANGE 18 E3 19 AB4 20 POL U /RANGE CD4023 OR 74C10 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 TO CREF 34 LOGIC GND CREF 33 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V- 26 G2 25 C3 24 A3 23 G3 22 BP 21 V-
1 V+ 2 D1 3 C1 4 B1 5 A1 6 F1 TO LOGIC VCC 12K 7 G1 8 E1 9 D2 10 C2
OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V- 26 G2 25 C3 24 A3 23 G3 22 BP 21 V-
COMMON 32
The LM339 is required to ensure logic compatibility with heavy display loading.
+ O /RANGE
11 B2 12 A2 13 F2 14 E2 15 D3 16 B3
+ + -
17 F3 18 E3 19 AB4 20 POL
U /RANGE CD4023 OR 74C10
+
33K
CD4077
FIGURE 19. CIRCUIT FOR DEVELOPING UNDERRANGE AND OVERRANGE SIGNAL FROM ICL7106 OUTPUTS
FIGURE 20. CIRCUIT FOR DEVELOPING UNDERRANGE AND OVERRANGE SIGNALS FROM ICL7107 OUTPUT
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ICL7106, ICL7107 Typical Applications (Continued)
TO PIN 1 OSC 1 40 OSC 2 39 OSC 3 38 TEST 37 REF HI 36 REF LO 35 CREF 34 CREF 33 COMMON 32 IN HI 31 IN LO 30 A-Z 29 BUFF 28 INT 27 V - 26 G2 25 C3 24 A3 23 G3 22 BP 21 TO BACKPLANE TO DISPLAY 0.22µF 47K 10µF 9V 100pF (FOR OPTIMUM BANDWIDTH) 0.47µF 1K 0.1µF 1µF 10K 4.3K 0.22µF 1µF 10K 1µF 22K 470K 2.2M 1N914 100pF 100k 10µF SCALE FACTOR ADJUST (VREF = 100mV FOR AC TO RMS) 5µF CA3140 + 100k AC IN
Test is used as a common-mode reference level to ensure compatibility with most op amps. FIGURE 21. AC TO DC CONVERTER WITH ICL7106
+5V
DM7407 ICL7107 130
LED SEGMENTS
130 130
FIGURE 22. DISPLAY BUFFERING FOR INCREASED DRIVE CURRENT
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