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19-0960; Rev 2; 1/00
Chopper-Stabilized Op Amps
General Description
Maxim's ICL7650/ICL7653 are chopper-stabilized amplifiers, ideal for low-level signal processing applications. Featuring high performance and versatility, these devices combine low input offset voltage, low input bias current, wide bandwidth, and exceptionally low drift over time and temperature. Low offset is achieved through a nulling scheme that provides continuous error correction. A nulling amplifier alternately nulls itself and the main amplifier. The result is an input offset voltage that is held to a minimum over the entire operating temperature range. The ICL7650B/ICL7653B are exact replacements for Intersil's ICL7650B/ICL7653B. These devices have a 10V max offset voltage, a 0.1V/C max input offset voltage temperature coefficient, and a 20pA max bias current--all specified over the commercial temperature range. A 14-pin version is available that can be used with either an internal or external clock. The 14-pin version has an output voltage clamp circuit to minimize overload recovery time.
Features
o ICL7650/53 are Improved Second Sources to ICL7650B/53B o Lower Supply Current: 2mA o Low Offset Voltage: 1V o No Offset Voltage Trimming Needed o High-Gain CMRR and PSRR: 120dB min o Lower Offset Drift with Time and Temperature o Extended Common-Mode Voltage Range o Low DC Input Bias Current: 10pA o Monolithic, Low-Power CMOS Design
ICL7650/ICL7650B/ICL7653/ICL7653B
Ordering Information
PART ICL7650CSA ICL7650CSD ICL7650CPA ICL7650CPD ICL7650CTV ICL7650C/D ICL7650IJA ICL7650IJD ICL7650MTV ICL7650MJD ICL7650BCSA ICL7650BCSD ICL7650BCPA ICL7650BCPD ICL7650BCTV ICL7650BC/D ICL7653CSA ICL7653CPA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -20C to +85C -20C to +85C -55C to +125C -55C to +125C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -20C to +85C -55C to +125C 0C to +70C 0C to +70C 0C to +70C PIN-PACKAGE 8 SO 14 SO 8 Plastic DIP 14 Plastic DIP 8 TO-99 Dice 8 CERDIP 14 CERDIP 8 CERDIP 14 CERDIP 8 SO 14 SO 8 Plastic DIP 14 Plastic DIP 8 TO-99 Dice 8 SO 8 Plastic DIP 8 TO-99 8 CERDIP 8 CERDIP 8 SO 8 Plastic DIP 8 TO-99
Applications
Condition Amplifier Precision Amplifier Instrumentation Amplifier Thermocouples Thermistors Strain Gauges
Typical Operating Circuit
CLAMP INPUT OUTPUT ICL7650 ICL7653 R C INVERTING AMPLIFIER WITH OPTIONAL CLAMP C
ICL7653CTV ICL7653IJA ICL7653MTV ICL7653BCSA ICL7653BCPA ICL7653BCTV
Pin Configurations appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
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Chopper-Stabilized Op Amps ICL7650/ICL7650B/ICL7653/ICL7653B
ABSOLUTE MAXIMUM RATINGS
Total Supply Voltage (V+ to V-)..............................................18V Input Voltage ........................................(V+ + 0.3V) to (V- - 0.3V) Voltage on Oscillator Control Pins (except EXT/CLOCK IN).............................................V+ to VVoltage on EXT/CLOCK IN ..................(V+ + 0.3V) to (V+ - 6.0V) Duration of Output Short Circuit ....................................Indefinite Current into Any Pin ............................................................10mA Current into Any Pin while Operating (Note 1)...................100A Continuous Total Power Dissipation (TA = +70C) 8-Pin SO (derate 5.88mW/C above +70C)...............471mW 8-Pin PDIP (derate 6.9mW/C above +70C)...............552mW 8-Pin CERDIP (derate 8.0mW/C above +70C).........640mW 8-Pin TO-99 (derate 6.7mW/C above +70C)............533mW 14-Pin SO (derate 8.3mW/C above +70C)...............667mW 14-Pin PDIP (derate 10.0mW/C above +70C)..........800mW 14-Pin CERDIP (derate 9.1mW/C above +70C).......727mW Operating Temperature Ranges ICL765_C_ _/ICL755_BC_ _ ...............................0C to +70C ICL765_I_ _/ICL755_BI_ _................................-20C to +85C ICL765_M_ _/ICL755_BM_ _..........................-55C to +125C Storage Temperature Range .............................-65C to +150C Junction Temperature ......................................................+150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: Maxim recommends limiting the input current to 100A to avoid latchup problems. A value of 1mA is typically safe; however, this is not guaranteed.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS--ICL7650B/ICL7653B
(Circuit of Figure 1, V+ = +5V, V- = -5V, TA = +25C, unless otherwise noted.) PARAMETER Input Offset Voltage Average Temperature Coefficient of Input Offset Voltage Input Bias Current Input Offset Current (Note 2) Input Resistance Large-Signal Voltage Gain Output Voltage Swing (Note 3) Common-Mode Voltage Range Common-Mode Rejection Ratio Power-Supply Rejection Ratio Input Noise Voltage Input Noise Current Unity-Gain Bandwidth Slew Rate Rise Time Overshoot Operating Supply Range Supply Current V+ to VISUPP No load 4.5 2.0 SYMBOL TA = +25C VOS VOS T IBIAS IOS RIN AVOL VOUT CMVR CMRR PSRR enp-p In GBW SR tr CL = 50pF, RL = 10k CMVR = -5V to +1.6V V+ to V- = 3V to 8V RS = 100, f = 0 to 10Hz f = 10Hz RL = 10k RL = 10k RL = 100k 120 120 1* 4.7 105 -55C < TA < +85C -55C < TA < +125C TA = +25C -20C < TA < +85C TA = +25C Doubles every 10 TA = +25C 0C < TA < +70C -20C < TA < +85C 50 0.01 1.5 35 100 0.5 1012 5* 4.85 108 pA V/V V 1.6 V dB dB Vp-p pA/Hz MHz V/s s % 16 3.5 V mA 0.05 10 pA CONDITIONS MIN TYP 0.7 10 5.0 V/C MAX 5 V UNITS
4.95 -5.0 -5.2 to +2.0 130 130 2 0.01 2.0 2.5 0.2 20
2
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Chopper-Stabilized Op Amps
ELECTRICAL CHARACTERISTICS--ICL7650B/ICL7653B (continued)
(Circuit of Figure 1, V+ = +5V, V- = -5V, TA = +25C, unless otherwise noted.) PARAMETER Internal Chopping Frequency Clamp On Current (Note 4) Clamp Off Current (Note 4) Offset Voltage vs. Time SYMBOL fch CONDITIONS Pins 12-14 open (DIP) RL = 100k -4.0V < VOUT < +4.0V No load MIN 120 25 TYP 200 70 1 100 MAX 375 200 UNITS Hz A pA nV/ month
ICL7650/ICL7650B/ICL7653/ICL7653B
Note 2: IOS = 2 * IBIAS Note 3: OUTPUT and CLAMP pins not connected. Note 4: See Output Clamp section for details.
ELECTRICAL CHARACTERISTICS--ICL7650/ICL7653
(Circuit of Figure 1, V+ = +5V, V- = -5V, TA = +25C, unless otherwise noted.) (Note 5) PARAMETER SYMBOL TA = +25C Input Offset Voltage VOS ICL765_ (Note 6) CONDITIONS ICL765_ ICL765_B 0C TA +70C -20C TA +85C -55C TA +125C 0C TA +70C ICL765_ -20C TA +85C -55C TA +85C +85C TA +125C TA = +25C Input Bias Current IB ICL765_ Input Resistance RIN RL = 10k, TA = +25C Large-Signal Voltage Gain AVOL 0C TA +70C -20C TA +85C -55C TA +125C Output Voltage Swing (Note 3) VOUT RL = 10k RL = 100k 0C TA +70C Common-Mode Voltage Range CMVR -20C TA +85C -55C TA +125C 1 * 108 0.5 * 108 0.5 * 108 0.2 * 108 4.7 4.85 4.95 -5.0 -5.2 to +3.0 -5.0 -5.2 to +3.0 -4.5 -4.0 to +3.0 2.5 2.5 2.5 V ICL765_ ICL765_B 0C TA +70C -20C TA +85C -55C TA +125C MIN TYP 0.7 1.0 1.0 1.0 10 0.01 0.01 0.01 0.01 0.25 4 12 20 50 0.3 1012 5 * 108 V/V MAX 5.0 10 10 10 50 0.05 0.1 0.05 0.05 1.5 10 20 100 200 10 pA V/C V UNITS
ICL765_B, 0C TA +70C Average Temperature Coefficient of Input Offset Voltage (Note 6) VOS T
V
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Chopper-Stabilized Op Amps ICL7650/ICL7650B/ICL7653/ICL7653B
ELECTRICAL CHARACTERISTICS--ICL7650/ICL7653 (continued)
(Circuit of Figure 1, V+ = +5V, V- = -5V, TA = +25C, unless otherwise noted.) (Note 5) PARAMETER Common-Mode Rejection Ratio Power-Supply Rejection Ratio Input Noise Voltage Input Noise Current Unity-Gain Bandwidth Slew Rate Rise Time Overshoot Operating Supply Range Supply Current Internal Chopping Frequency Clamp On Current (Note 4) Clamp Off Current (Note 4) Offset Voltage vs. Time V+ to VISUPP fCLKOUT No load Pins 13 and 14 open (DIP) RL = 100k -4.0 VOUT +4.0V 120 25 4.5 1.2 200 70 1 100 SYMBOL CMRR PSRR enp-p In GBW SR tr CL = 50pF, RL = 10k CONDITIONS CMVR = -5V to +2.5V V+ to V- = 3V to 8V RS = 100, f = 0 to 10Hz f = 10Hz MIN 120 120 TYP 130 130 2 0.01 2.0 2.5 0.2 20 16 2.0 375 200 MAX UNITS dB dB Vp-p pA/Hz MHz V/s s % V mA Hz A pA nV/ month
Note 3: OUTPUT and CLAMP pins not connected. Note 4: See Output Clamp section for details. Note 5: All pins are designed to withstand electrostatic discharge (ESD) levels in excess of 2000V (MIL STD 8838 Method 3015.1 test circuit). Note 6: Sample tested. Limits are not used to calculate outgoing quality level.
Typical Operating Characteristics
(Circuit of Figure 1, V+ = +5V, V- = -5V, TA = +25C, unless otherwise noted.)
MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE
ICL7650toc01
CLOCK RIPPLE REFERRED TO INPUT vs. TEMPERATURE
ICL7650toc02
SUPPLY CURRENT vs. SUPPLY VOLTAGE
ICL7650toc03
4 MAXIMUM OUTPUT CURRENT (mA) 3 2 1 0 -10 -20 -30 2 4 6 8 10 12 14 SINK CURRENT SOURCE CURRENT
1k 0.1F CLOCK RIPPLE (Vp-p) 100 BROADBAND NOISE (AV = 1000) 1 1F
3
SUPPLY CURRENT (mA) 150
2
10
1
0.1 16 25 50 75 100 125 TOTAL SUPPLY VOLTAGE (V) TEMPERATURE (C)
0 4 6 8 10 12 14 16 TOTAL SUPPLY VOLTAGE (V)
4
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Chopper-Stabilized Op Amps
Typical Operating Characteristics (continued)
(Circuit of Figure 1, V+ = +5V, V- = -5V, TA = +25C, unless otherwise noted.)
ICL7650/ICL7650B/ICL7653/ICL7653B
SUPPLY CURRENT vs. AMBIENT TEMPERATURE
ICL7650toc04
COMMON-MODE INPUT VOLTAGE RANGE vs. SUPPLY VOLTAGE
ICL7650toc05
COMMON-MODE INPUT VOLTAGE RANGE (V)
3
8 7 6 NEGATIVE LIMIT 5 4 3 POSITIVE LIMIT 2 1 0 0 1 2 3 4 5 6 7 8
INPUT OFFSET VOLTAGE vs. CHOPPING FREQUENCY
ICL7650toc06
-10
SUPPLY CURRENT (mA)
-8 OFFSET VOLTAGE (V)
2
-6
1
-4
-2
0 -50 -25 0 25 50 75 100 125 AMBIENT TEMPERATURE (C)
0 10 100 1k 10k CHOPPING FREQUENCY (CLOCK OUT) (Hz)
SUPPLY VOLTAGE (V)
INPUT OFFSET VOLTAGE CHANGE vs. SUPPLY VOLTAGE
ICL7650toc07
10Hzp-p NOISE VOLTAGE vs. CHOPPING FREQUENCY
DC TO 10Hz P-P NOISE VOLTAGE (V)
ICL7650toc08
OPEN-LOOP GAIN AND PHASE SHIFT vs. FREQUENCY
160 140 120 70 100 90 80 110 60 130 40 RL = 10k CEXT = 0.1F 0.01 0.1 1 10 100 1k 10k 100k PHASE SHIFT (DEGREES) 50 OPEN-LOOP GAIN (dB)
ICL7650toac09
-3 INPUT OFFSET VOLTAGE CHANGE (V) -2 -1 0 1 2 3 4 6 8 10 12 14
5
4
3
2
1
0 16 10 100 1k 10k TOTAL SUPPLY VOLTAGE (V) CHOPPING FREQUENCY (CLOCK-OUT) (Hz)
20 FREQUENCY (Hz)
OPEN-LOOP GAIN AND PHASE SHIFT vs. FREQUENCY
160 140 PHASE SHIFT (DEGREES) OUTPUT VOLTAGE (V) 50 OPEN-LOOP GAIN (dB) 120 70 100 90 80 110 60 130 40 20 0.01 0.1 1 10 100 1k 10k 100k FREQUENCY (Hz) RL = 10k CEXT = 1.0F -2 -3
ICL7650toac10
VOLTAGE FOLLOWER LARGE-SIGNAL PULSE RESPONSE
ICL7650toc11
VOLTAGE FOLLOWER LARGE-SIGNAL PULSE RESPONSE
ICL7650toc12
3 2 CLOCK OUT LOW 1 0 -1 CLOCK OUT HIGH
3 2 OUTPUT VOLTAGE (V) 1 0 -1 -2 -3 CLOCK OUT HIGH
CLOCK OUT LOW
-1.0 -0.5
0
0.5
1.0
1.5
2.0
2.5
3.0
-1.0 -0.5
0
0.5
1.0
1.5
2.0
2.5
3.0
TIME (s)
TIME (s)
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Chopper-Stabilized Op Amps ICL7650/ICL7650B/ICL7653/ICL7653B
R2 1M
ICL7650 INT/EXT EXT CLK IN OSC CLK OUT OUTPUT
A A B C
R1 1M ICL7650 ICL7653 CR C -IN 0.1F 0.1F A
C +IN
INTERNAL BIAS + MAIN + A NULL B CEXTA CEXTB C
P OUTPUT CLAMP N
Figure 1. ICL7650 Test Circuit
CAP RETURN
Detailed Description
Figure 2 shows the major elements of the ICL7650/ ICL7653. Two amplifiers are illustrated, the main amplifier and the nulling amplifier, both of which have offsetnull capability. The main amplifier is connected full time from the input to the output. The nulling amplifier, under control of the chopper-frequency oscillator and clock circuit, alternately nulls itself and the main amplifier. This nulling arrangement, which is independent of the output level, operates over the full power-supply and commonmode ranges. The ICL7650/ICL7653 exhibit an exceptionally high CMRR, PSRR, and A VOL . Their nulling connections, which are MOSFET back gates, have inherently high impedance. Two external capacitors provide storage for the nulling potentials and the necessary nulling-loop time constants. The ICL7650/ICL7653 minimize chopper-frequency charge injection at the input terminals by carefully balancing the input switches. Feed-forward injection into the compensation capacitor, the main cause of output spikes in this type of circuit, is also minimized.
EXT CLK IN A = CLK OUT A B C
Figure 2. Block Diagram
Intermodulation
Intermodulation effects can cause problems in older chopper-stabilized amplifier modules. Intermodulation occurs since the amplifier has a finite AC gain, and therefore will have a small AC signal at the input. In a chopper-stabilized module, this small AC signal is detected, chopped, and fed into the offset-correction circuit. This results in spurious outputs at the sum and difference frequencies of the chopping and input signal frequencies. Other intermodulation effects in chopperstabilized modules include gain and phase anomalies near the chopping frequency. These effects are substantially reduced in the ICL7650/ICL7653, which add to the nulling circuit a dynamic current that compensates for the AC signal on the inputs. Unlike modules, the ICL7650/ICL7653 can precisely compensate for the finite AC gain, since both the AC gain rolloff and the intermodulation compensation current are controlled by internal matched capacitors.
Output Clamp (ICL7650 Only)
The output clamp reduces the overload recovery time inherent with chopper-stabilized amplifiers. When tied to the summing junction or inverting input pin, a current path between this point and the output occurs just before the output device saturates. This prevents uncontrolled input differential and the consequent charge build-up on the correction-storage capacitors, while causing only a slight reduction in the output swing.
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Chopper-Stabilized Op Amps
Nulling Capacitor Connection
Separate pins are provided for CRETN and CLAMP in the ICL7650. If you do not need the clamp feature, order the ICL7653; this device only offers the CRETN pin and will produce slightly lower noise and improved AC common-mode rejection. If you need to use the clamp feature, order the ICL7650 and connect the external capacitors to V-. To prevent load-current IR drops and other extraneous signals from being injected into the capacitors, use a separate PC board trace to connect the capacitor commons directly to the V- pin. The outside foil of the capacitors should be connected to the low-impedance side of the null storage circuit, V- or CRETN. This will act as an ESD voltage shield. leakage at the null capacitor pins) becomes excessive and 1F external capacitors are required.
ICL7650/ICL7650B/ICL7653/ICL7653B
Output Stage/Load Driving
The ICL7650/ICL7653 somewhat resemble a transconductance amplifier whose open-loop gain is proportional to load resistance. This behavior is apparent when loads are less than the high-impedance stage (approximately 18k for one output circuit). The open-loop gain, for example, will be 17dB lower with a 1k load than with a 10k load. This lower gain is of little consequence if the amplifier is used strictly for DC since the DC gain is typically greater than 120dB, even with a 1k load. For wideband applications, however, the best frequency response will be achieved with a load resistor of 10k or higher. The result will be a smooth 6dB per octave response from 0.1Hz to 2MHz, with phase shifts of less than 10 in the transition region where the main amplifier takes over from the null amplifier.
Clock Operation
The ICL7650's internal oscillator generates a 200Hz frequency, which is available at the CLK OUT pin. The device can also be operated with an external clock, if desired. An internal pull-up permits the INT/EXT pin to be left open for normal operation. However, the internal clock must be disabled and INT/EXT must be tied to Vif an external clock is used. An external clock signal may then be applied to the EXT CLK IN pin. The duty cycle of the external clock is not critical at low frequencies. However, a 50% to 80% positive duty cycle is preferred for frequencies above 500Hz, since the capacitors are charged only when EXT CLK IN is high. This ensures that any transients have time to settle before the capacitors are turned off. The external clock should swing between ground and V+ for power supplies up to 6V, and between V+ and (V+ - 6V) for higher supply voltages. To avoid a capacitor imbalance during overload, use a strobe signal. Neither capacitor will be charged if a strobe signal is connected to EXT CLK IN so that it is low while the overload signal is being applied to the amplifier. A typical amplifier will drift less than 10Vs since the leakage of the capacitor pins is quite low at room temperature. Relatively long measurements may be made with little change in offset.
Component Selection
CEXTA and CEXTB, the two required capacitors, have optimum values depending on the clock or chopping frequency. The correct value is 0.1F for the preset internal clock. When using an external clock, scale this component value in proportion to the relationship between the chopping frequency and the nulling time constant. A low-leakage ceramic capacitor may prove suitable for many applications; however, a high-quality film-type capacitor (such as mylar) is preferred. For lowest settling time at initial turn-on, use capacitors with low dielectric absorption (such as polypropylene types). With low-dielectric-absorption capacitors, the ICL7650/ICL7653 will settle to 1V offset in 100ms, but several seconds may be required if ceramic capacitors are used.
Thermoelectric Effects
Thermoelectric effects developed in thermocouple junctions of dissimilar materials (metals, alloys, silicon, etc.) ultimately limit precision DC measurements. Unless all junctions are at the same temperature, thermoelectric voltages (typically around 10V/C, but up to hundreds of V/C for some materials) will be generated. In order to realize the extremely low offset voltages that the chopper amplifier can provide, take special precautions to avoid temperature gradients. To eliminate air movement, enclose all components (particularly those caused by power-dissipating elements in the system). Minimize power-supply voltages and power dissipation, and use low-thermoelectric-coefficient connections where possible. It is advisable to separate the device surrounding heat-dissipating elements, and to use high-impedance loads.
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Applications Information
Device Selection
In applications that require lowest noise, Maxim's ICL7652 may be preferred over the ICL7650/ICL7653. The ICL7650/ICL7653 offer a higher gain-bandwidth product and lower input bias currents, while the ICL7652 reduces noise by using larger input FETs. These larger FETs, however, increase the leakage at the ICL7652's external null pins. Therefore, the ICL7650/ICL7653 can operate to a higher temperature with 0.1F capacitors before the clock ripple (due to
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Chopper-Stabilized Op Amps ICL7650/ICL7650B/ICL7653/ICL7653B
Input Guarding
Low-leakage, high-impedance CMOS inputs allow the ICL7650/ICL7653 to measure high-impedance sources. Stray leakage paths can decrease input resistance and increase input currents unless inputs are guarded. Boards must be thoroughly cleaned with TCE or alcohol and blown dry with compressed air. The board should be coated with epoxy or silicone after cleaning to prevent contamination. Leakage currents may cause trouble even with properly cleaned and coated boards, particularly since the input pins are adjacent to pins that are at supply potentials. Leakage can be significantly reduced by using guarding to decrease the voltage difference between inputs and adjacent metal runs. Use a 10-lead pin circle, with the leads of the device formed so that the holes adjacent to the inputs are empty when it is inserted in the board to accomplish input guarding of the 8-pin TO-99 package. A conductive ring surrounding the inputs, the "guard," is connected to a low-impedance point that is approximately the same voltage as the inputs. The guard then absorbs the leakage current from the highvoltage pins. Typical guard connections are shown in Figure 3.
INPUT
R1
R2
R3* OUTPUT INPUT R3* OUTPUT
INVERTING AMPLIFIER * USE R3 TO COMPENSATE FOR LARGE SOURCE RESISTANCES, OR FOR CLAMP OPERATION (FIGURE 5). R2
FOLLOWER
EXTERNAL CAPACITORS R3* OUTPUT OUTPUT EXTERNAL CAPACITORS R1 INPUT V+ 67 8 1 5 2 43 VGUARD
IN PU TS
NONINVERTING AMPLIFIER NOTE: R1 R2 R1 + R2 SHOULD BE LOW IMPEDANCE FOR OPTIMUM GUARDING.
BOTTOM VIEW BOARD LAYOUT FOR INPUT GUARDING WITH TO-99 PACKAGE.
Figure 3. Input Guard Connection 8 _______________________________________________________________________________________
Chopper-Stabilized Op Amps
The 14-pin DIP configuration has been specifically designed to ease input guarding. The pins adjacent to the inputs are not used. the amplifier's inverting input, integrate the error, and drive the amplifier's noninverting input to correct for the offset voltage detected at the inverting input. The circuit's DC offset characteristics are determined by the ICL7650/ICL7653, and its AC performance is determined by the high-speed amplifier. While this circuit continuously and automatically adjusts the amplifier's offset to less than 5V, it does not correct for errors caused by the input bias current, so the value of resistor RF should be as low as is practical. This technique can be used with any op amp that is configured as an inverting amplifier. Figures 5 and 6 illustrate basic inverting and noninverting amplifier circuits. Both figures show an output clamping circuit being used to enhance overload recovery performance. Supply voltage (8V max) and output drive capability (10k load for full swing) are the only limitations to consider when replacing other op amps with the ICL7650/ICL7653. Use a simple booster circuit to overcome these limitations (Figure 7). This enables the full output capabilities of the LM118 (or any other standard device) to be combined with the input capabilities of the ICL7650/ICL7653. Observe the loop gain stability carefully when the feedback network is added, particularly when a slower amplifier such as the LM741 is used. A lower voltage supply is required when mixing the ICL7650/ICL7653 with circuits that operate at 15V supplies. One approach is to use a highly efficient voltage divider. This is illustrated in Figure 8, where the ICL7660 voltage converter is used to convert +15V to +7.5V.
ICL7650/ICL7650B/ICL7653/ICL7653B
Pin Compatibility
The ICL7653's pinout generally corresponds to that of industry-standard 8-pin devices such as the LM741 or LM101. However, its external null storage capacitors are connected to pins 1 and 8; whereas most op amps leave these pins open or use them for offset null or compensation capacitors. The OP05 and OP07 op amps can be converted for ICL7650/ICL7653 operation. This can be accomplished by removing the offset null potentiometer, which is connected from pins 1 and 8 to V+, and replacing it with two capacitors connected from pins 1 and 8 to V-. For LM108 devices, the compensation capacitor is replaced by the external nulling capacitors. Pin 5 is the output clamp connection on the ICL7650/ICL7653. By removing any circuit connections from this pin, the LM101/LM748/LM709 devices can undergo a similar conversion.
Typical Applications
Figure 4 shows the ICL7650/ICL7653 automatically nulling the offset voltage of a high-speed amplifier. The ICL7650/ICL7653 continuously monitor the voltage at
RF
RIN HIGHSPEED AMP VOUT R1 1k CLAMP R2
INPUT
OUTPUT 47 100k 10k 0.1F ICL7650 R C NOTE: R1 || R2 INDICATES THE PARALLEL COMBINATION OF R1 || R2. C (R1 || R2) 100k FOR FULL CLAMP EFFECT
ICL7650 ICL7653
0.1F 0.1F
Figure 5. Inverting Amplifier with Optional Clamp
Figure 4. Nulling a High-Speed Amplifier _______________________________________________________________________________________ 9
Chopper-Stabilized Op Amps ICL7650/ICL7650B/ICL7653/ICL7653B
0.1F 0.1F CLAMP C INPUT R C ICL7650 R2 CLAMP R3 R3 + (R1 || R2) > 100k FOR FULL CLAMP EFFECT NOTE: R1 || R2 INDICATES THE PARALLEL COMBINATION OF R1 || R2. -7.5V OUTPUT -
+7.5V +15V + OUT IN ICL7650 741 -15V
0.1F 0.1F
10k 10k
R1
Figure 7. Using an Industry-Standard 741 to Boost Output Drive Capability
Figure 6. Noninverting Amplifier with Optional Clamp
Chip Topography
2 8 INT/EXT +15V +7.5V 10F 0V V+ 6 1M 0.090" (2.29mm) OUTPUT CEXTA CEXTB EXT/CLK IN INT/ CLK OUT
10F
ICL7660
3
4
5
Figure 8. Splitting +15V with an ICL7660, 95% Efficiency (Same for -15V)
-INPUT +INPUT VCRETN 0.069" (1.75mm) CLAMP
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Chopper-Stabilized Op Amps
Pin Configurations
TOP VIEW
ICL7650/ICL7650B/ICL7653/ICL7653B
CEXTB 1 CEXTA N.C. (GUARD) 2 3
14 INT/EXT 13 EXT/CLK IN 12 INT/CLK OUT CEXTA 1 -INPUT 2 8 7 CEXTB V+ -INPUT 2 6 5 OUTPUT CLAMP +INPUT 3 4 VCEXTA 8 1
CEXTB 7 V+
-INPUT 4 +INPUT 5 N.C. (GUARD) 6 V- 7
MAX7650
11 V+ 10 OUTPUT 9 8 CLAMP CRETN +INPUT 3
ICL7650
V- 4
ICL7650
5
6 OUTPUT
CLAMP
SO/DIP/CERDIP SO/DIP/CERDIP
N.C. = NO INTERNAL CONNECTION CEXTB CEXTA CEXTA 1 -INPUT 2 8 7 CEXTB V+ -INPUT 2 6 5 OUTPUT CRETN +INPUT 3 4 V5 CRETN 8 1 7 V+
TO-99
ICL7653
+INPUT 3 V- 4
ICL7653
6 OUTPUT
SO/DIP/CERDIP
TO-99
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11
Chopper-Stabilized Op Amps
Package Information
ICL7650/ICL7650B/ICL7653/ICL7653B
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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