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ICL7650BC/D [MAXIM]

Chopper-Stabilized Op Amps; 斩波稳零运算放大器
ICL7650BC/D
型号： ICL7650BC/D
厂家： MAXIM INTEGRATED PRODUCTS    MAXIM INTEGRATED PRODUCTS
描述：

Chopper-Stabilized Op Amps
斩波稳零运算放大器

运算放大器
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19-0960; Rev 2; 1/00  
Chopper-Stabilized Op Amps  
General Description  
Features  
Maxim’s ICL7650/ICL7653 are chopper-stabilized  
amplifiers, ideal for low-level signal processing applica-  
tions. 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 operat-  
ing temperature range.  
ꢀ ICL7650/53 are Improved Second Sources to  
ICL7650B/53B  
ꢀ Lower Supply Current: 2mA  
ꢀ Low Offset Voltage: 1µV  
ꢀ No Offset Voltage Trimming Needed  
ꢀ High-Gain CMRR and PSRR: 120dB min  
ꢀ Lower Offset Drift with Time and Temperature  
ꢀ Extended Common-Mode Voltage Range  
ꢀ Low DC Input Bias Current: 10pA  
ꢀ Monolithic, Low-Power CMOS Design  
The ICL7650B/ICL7653B are exact replacements for  
Intersil’s ICL7650B/ICL7653B. These devices have a  
10µV max offset voltage, a 0.1µV/°C max input offset  
voltage temperature coefficient, and a 20pA max bias  
current—all specified over the commercial temperature  
range.  
Ordering Information  
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 over-  
load recovery time.  
PART  
TEMP. RANGE  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
-20°C to +85°C  
-20°C to +85°C  
-55°C to +125°C  
-55°C to +125°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
-20°C to +85°C  
-55°C to +125°C  
0°C to +70°C  
0°C to +70°C  
0°C to +70°C  
PIN-PACKAGE  
8 SO  
ICL7650CSA  
ICL7650CSD  
ICL7650CPA  
ICL7650CPD  
ICL7650CTV  
ICL7650C/D  
ICL7650IJA  
14 SO  
8 Plastic DIP  
14 Plastic DIP  
8 TO-99  
Applications  
Condition Amplifier  
Precision Amplifier  
Instrumentation Amplifier  
Thermocouples  
Dice  
8 CERDIP  
14 CERDIP  
8 CERDIP  
14 CERDIP  
8 SO  
ICL7650IJD  
ICL7650MTV  
ICL7650MJD  
ICL7650BCSA  
ICL7650BCSD  
ICL7650BCPA  
ICL7650BCPD  
ICL7650BCTV  
ICL7650BC/D  
ICL7653CSA  
ICL7653CPA  
ICL7653CTV  
ICL7653IJA  
Thermistors  
Strain Gauges  
14 SO  
8 Plastic DIP  
14 Plastic DIP  
8 TO-99  
Typical Operating Circuit  
Dice  
8 SO  
8 Plastic DIP  
8 TO-99  
CLAMP  
INPUT  
8 CERDIP  
8 CERDIP  
8 SO  
OUTPUT  
ICL7653MTV  
ICL7653BCSA  
ICL7653BCPA  
ICL7653BCTV  
ICL7650  
ICL7653  
C
8 Plastic DIP  
8 TO-99  
R
C
INVERTING AMPLIFIER  
WITH OPTIONAL CLAMP  
Pin Configurations appear at end of data sheet.  
________________________________________________________________ Maxim Integrated Products  
1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.  
For small orders, phone 1-800-835-8769.  
Chopper-Stabilized Op Amps  
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 V-  
Voltage 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)...................100µA  
8-Pin TO-99 (derate 6.7mW/°C above +70°C)............533mW  
14-Pin SO (derate 8.3mW/°C above +70°C)...............667mW  
14-Pin PDIP (derate 10.0mW/°C above +70°C)..........800mW  
14-Pin CERDIP (derate 9.1mW/°C above +70°C).......727mW  
Operating Temperature Ranges  
ICL765_C__/ICL755_BC__ ...............................0°C to +70°C  
ICL765_I__/ICL755_BI__................................-20°C to +85°C  
ICL765_M__/ICL755_BM__..........................-55°C to +125°C  
Storage Temperature Range.............................-65°C to +150°C  
Junction Temperature......................................................+150°C  
Lead Temperature (soldering, 10s) .................................+300°C  
Continuous Total Power Dissipation (T = +70°C)  
A
8-Pin SO (derate 5.88mW/°C above +70°C)...............471mW  
8-Pin PDIP (derate 6.9mW/°C above +70°C)...............552mW  
8-Pin CERDIP (derate 8.0mW/°C above +70°C).........640mW  
Note 1: Maxim recommends limiting the input current to 100µA 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, T = +25°C, unless otherwise noted.)  
A
PARAMETER  
SYMBOL  
CONDITIONS  
MIN  
TYP  
0.7  
10  
MAX  
UNITS  
T
A
= +25°C  
5
Input Offset Voltage  
V
OS  
-55°C < T < +85°C  
µV  
A
-55°C < T < +125°C  
5.0  
A
T
= +25°C  
50  
0.01  
1.5  
35  
A
∆V  
Average Temperature Coefficient  
of Input Offset Voltage  
OS  
∆T  
µV/°C  
pA  
-20°C < T < +85°C  
A
0.05  
10  
T
= +25°C  
A
Input Bias Current  
I
Doubles every 10°  
0°C < T < +70°C  
A
BIAS  
-20°C < T < +85°C  
100  
0.5  
A
Input Offset Current (Note 2)  
Input Resistance  
I
T
A
= +25°C  
pA  
Ω
OS  
12  
R
IN  
10  
5
8
Large-Signal Voltage Gain  
A
VOL  
R = 10kΩ  
L
V/V  
1 · 10  
5 · 10  
R = 10kΩ  
4.7  
4.85  
L
Output Voltage Swing (Note 3)  
V
OUT  
V
R = 100kΩ  
L
4.95  
Common-Mode Voltage Range  
Common-Mode Rejection Ratio  
Power-Supply Rejection Ratio  
Input Noise Voltage  
Input Noise Current  
Unity-Gain Bandwidth  
Slew Rate  
CMVR  
CMRR  
PSRR  
-5.0 -5.2 to +2.0 1.6  
V
dB  
CMVR = -5V to +1.6V  
V+ to V- = 3V to 8V  
120  
120  
130  
130  
2
dB  
e
np-p  
R = 100Ω, f = 0 to 10Hz  
S
µVp-p  
pA/√Hz  
MHz  
V/µs  
µs  
I
n
f = 10Hz  
0.01  
2.0  
2.5  
0.2  
20  
GBW  
SR  
C = 50pF, R = 10kΩ  
L
L
Rise Time  
t
r
Overshoot  
%
Operating Supply Range  
Supply Current  
V+ to V-  
4.5  
16  
V
I
No load  
2.0  
3.5  
mA  
SUPP  
2
_______________________________________________________________________________________  
Chopper-Stabilized Op Amps  
ELECTRICAL CHARACTERISTICS—ICL7650B/ICL7653B (continued)  
(Circuit of Figure 1, V+ = +5V, V- = -5V, T = +25°C, unless otherwise noted.)  
A
PARAMETER  
SYMBOL  
CONDITIONS  
Pins 12–14 open (DIP)  
R = 100kΩ  
MIN  
120  
25  
TYP  
200  
70  
MAX  
375  
UNITS  
Hz  
Internal Chopping Frequency  
Clamp On Current (Note 4)  
Clamp Off Current (Note 4)  
f
ch  
200  
µA  
L
-4.0V < V  
< +4.0V  
1
pA  
OUT  
nV/  
√month  
Offset Voltage vs. Time  
No load  
100  
Note 2: I = 2 · I  
BIAS  
OS  
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, T = +25°C, unless otherwise noted.) (Note 5)  
A
PARAMETER  
SYMBOL  
CONDITIONS  
ICL765_  
ICL765_B  
0°C ≤ T ≤ +70°C  
MIN  
TYP  
0.7  
1.0  
1.0  
1.0  
10  
MAX  
5.0  
10  
UNITS  
T
= +25°C  
A
Input Offset Voltage  
V
OS  
10  
µV  
A
ICL765_  
(Note 6)  
-20°C ≤ T ≤ +85°C  
10  
A
-55°C ≤ T ≤ +125°C  
50  
A
ICL765_B, 0°C ≤ T ≤ +70°C  
0.01  
0.01  
0.01  
0.01  
0.25  
4
0.05  
0.1  
0.05  
0.05  
1.5  
10  
A
0°C ≤ T ≤ +70°C  
A
∆V  
∆T  
Average Temperature Coefficient  
of Input Offset Voltage (Note 6)  
OS  
-20°C ≤ T ≤ +85°C  
µV/°C  
A
ICL765_  
-55°C ≤ T ≤ +85°C  
A
+85°C ≤ T ≤ +125°C  
A
ICL765_  
T
A
= +25°C  
ICL765_B  
12  
20  
Input Bias Current  
I
B
0°C ≤ T ≤ +70°C  
20  
100  
200  
10  
pA  
A
ICL765_  
-20°C ≤ T ≤ +85°C  
50  
A
-55°C ≤ T ≤ +125°C  
0.3  
A
12  
Input Resistance  
R
IN  
Ω
10  
8
8
R = 10kΩ, T = +25°C  
1 · 10  
5 · 10  
L
A
8
8
8
0°C ≤ T ≤ +70°C  
0.5 · 10  
0.5 · 10  
0.2 · 10  
4.7  
A
Large-Signal Voltage Gain  
A
V/V  
VOL  
-20°C ≤ T ≤ +85°C  
A
-55°C ≤ T ≤ +125°C  
A
R = 10kΩ  
L
4.85  
4.95  
Output Voltage Swing (Note 3)  
Common-Mode Voltage Range  
V
OUT  
V
V
R = 100kΩ  
L
0°C ≤ T ≤ +70°C  
-5.0 -5.2 to +3.0 2.5  
-5.0 -5.2 to +3.0 2.5  
-4.5 -4.0 to +3.0 2.5  
A
CMVR  
-20°C ≤ T ≤ +85°C  
A
-55°C ≤ T ≤ +125°C  
A
_______________________________________________________________________________________  
3
Chopper-Stabilized Op Amps  
ELECTRICAL CHARACTERISTICS—ICL7650/ICL7653 (continued)  
(Circuit of Figure 1, V+ = +5V, V- = -5V, T = +25°C, unless otherwise noted.) (Note 5)  
A
PARAMETER  
Common-Mode Rejection Ratio  
Power-Supply Rejection Ratio  
Input Noise Voltage  
Input Noise Current  
Unity-Gain Bandwidth  
Slew Rate  
SYMBOL  
CMRR  
CONDITIONS  
CMVR = -5V to +2.5V  
V+ to V- = 3V to 8V  
MIN  
120  
120  
TYP  
130  
130  
2
MAX  
UNITS  
dB  
PSRR  
dB  
e
np-p  
R = 100Ω, f = 0 to 10Hz  
S
µVp-p  
pA/√Hz  
MHz  
V/µs  
µs  
I
n
f = 10Hz  
0.01  
2.0  
2.5  
0.2  
20  
GBW  
SR  
C = 50pF, R = 10kΩ  
L
L
Rise Time  
t
r
Overshoot  
%
Operating Supply Range  
Supply Current  
V+ to V-  
4.5  
16  
2.0  
V
I
No load  
1.2  
200  
70  
1
mA  
SUPP  
Internal Chopping Frequency  
Clamp On Current (Note 4)  
Clamp Off Current (Note 4)  
f
Pins 13 and 14 open (DIP)  
R = 100kΩ  
120  
25  
375  
200  
Hz  
CLKOUT  
µA  
L
-4.0 ≤ V  
≤ +4.0V  
pA  
OUT  
nV/  
√month  
Offset Voltage vs. Time  
100  
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, T = +25°C, unless otherwise noted.)  
A
MAXIMUM OUTPUT CURRENT  
SUPPLY CURRENT  
vs. SUPPLY VOLTAGE  
CLOCK RIPPLE REFERRED TO INPUT  
vs. SUPPLY VOLTAGE  
vs. TEMPERATURE  
4
3
1k  
100  
10  
3
2
1
0
0.1µF  
1µF  
SOURCE CURRENT  
2
1
BROADBAND  
NOISE  
0
(A = 1000)  
V
-10  
-20  
-30  
1
SINK CURRENT  
0.1  
2
4
6
8
10  
12  
14  
16  
25  
50  
75  
100  
125  
150  
4
6
8
10  
12  
14  
16  
TOTAL SUPPLY VOLTAGE (V)  
TEMPERATURE (°C)  
TOTAL SUPPLY VOLTAGE (V)  
4
_______________________________________________________________________________________  
Chopper-Stabilized Op Amps  
Typical Operating Characteristics (continued)  
(Circuit of Figure 1, V+ = +5V, V- = -5V, T = +25°C, unless otherwise noted.)  
A
SUPPLY CURRENT vs.  
AMBIENT TEMPERATURE  
COMMON-MODE INPUT VOLTAGE RANGE  
vs. SUPPLY VOLTAGE  
INPUT OFFSET VOLTAGE  
vs. CHOPPING FREQUENCY  
8
7
6
5
4
3
2
1
0
3
2
1
0
-10  
-8  
-6  
-4  
-2  
0
NEGATIVE LIMIT  
POSITIVE LIMIT  
-50 -25  
0
25  
50  
75 100 125  
0
1
2
3
4
5
6
7
8
10  
100  
1k  
10k  
AMBIENT TEMPERATURE (°C)  
SUPPLY VOLTAGE (V)  
CHOPPING FREQUENCY (CLOCK OUT) (Hz)  
INPUT OFFSET VOLTAGE CHANGE  
vs. SUPPLY VOLTAGE  
10Hzp-p NOISE VOLTAGE  
vs. CHOPPING FREQUENCY  
OPEN-LOOP GAIN AND PHASE SHIFT  
vs. FREQUENCY  
ICL7650toac09  
-3  
-2  
-1  
0
5
4
3
2
1
0
160  
140  
120  
100  
80  
50  
70  
90  
110  
130  
1
60  
2
R = 10kΩ  
EXT  
40  
L
C
= 0.1µF  
3
20  
4
6
8
10  
12  
14  
16  
10  
100  
1k  
10k  
0.01 0.1  
1
10 100 1k  
FREQUENCY (Hz)  
10k 100k  
TOTAL SUPPLY VOLTAGE (V)  
CHOPPING FREQUENCY (CLOCK-OUT) (Hz)  
OPEN-LOOP GAIN AND PHASE SHIFT  
vs. FREQUENCY  
VOLTAGE FOLLOWER LARGE-SIGNAL  
PULSE RESPONSE  
VOLTAGE FOLLOWER LARGE-SIGNAL  
PULSE RESPONSE  
ICL7650toac10  
160  
140  
120  
100  
80  
3
3
2
2
1
50  
CLOCK OUT LOW  
1
70  
CLOCK OUT LOW  
90  
0
0
110  
130  
CLOCK OUT HIGH  
-1  
-2  
-3  
-1  
-2  
-3  
60  
CLOCK OUT HIGH  
R = 10kΩ  
EXT  
40  
L
C
= 1.0µF  
20  
0.01 0.1  
1
10 100 1k  
FREQUENCY (Hz)  
10k 100k  
-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 (µs)  
TIME (µs)  
_______________________________________________________________________________________  
5
Chopper-Stabilized Op Amps  
R2  
1M  
ICL7650  
A
A
B
C
INT/EXT  
EXT CLK IN  
CLK OUT  
OSC  
R1  
1M  
OUTPUT  
ICL7650  
ICL7653  
INTERNAL  
BIAS  
P
C
+
+IN  
C
R
OUTPUT  
CLAMP  
MAIN  
C
-
-IN  
A
+
C
N
0.1µF 0.1µF  
NULL  
A
-
B
Figure 1. ICL7650 Test Circuit  
CAP RETURN  
C
EXTA  
C
EXTB  
Detailed Description  
Figure 2 shows the major elements of the ICL7650/  
ICL7653. Two amplifiers are illustrated, the main amplifi-  
er and the nulling amplifier, both of which have offset-  
null 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 common-  
mode ranges. The ICL7650/ICL7653 exhibit an excep-  
EXT CLK IN  
A = CLK OUT  
A
B
C
Figure 2. Block Diagram  
tionally high CMRR, PSRR, and A  
. Their nulling  
VOL  
connections, which are MOSFET back gates, have inher-  
ently high impedance. Two external capacitors provide  
storage for the nulling potentials and the necessary  
nulling-loop time constants.  
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 chopper-  
stabilized modules include gain and phase anomalies  
near the chopping frequency.  
The ICL7650/ICL7653 minimize chopper-frequency  
charge injection at the input terminals by carefully bal-  
ancing the input switches. Feed-forward injection into  
the compensation capacitor, the main cause of output  
spikes in this type of circuit, is also minimized.  
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.  
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.  
6
_______________________________________________________________________________________  
Chopper-Stabilized Op Amps  
leakage at the null capacitor pins) becomes excessive  
and 1µF external capacitors are required.  
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 out-  
side foil of the capacitors should be connected to the  
low-impedance side of the null storage circuit, V- or  
Output Stage/Load Driving  
The ICL7650/ICL7653 somewhat resemble a transcon-  
ductance amplifier whose open-loop gain is proportional  
to load resistance. This behavior is apparent when loads  
are less than the high-impedance stage (approximately  
18kΩ for one output circuit). The open-loop gain, for  
example, will be 17dB lower with a 1kΩ load than with a  
10kΩ load. This lower gain is of little consequence if the  
amplifier is used strictly for DC since the DC gain is typi-  
cally greater than 120dB, even with a 1kΩ load. For  
wideband applications, however, the best frequency  
response will be achieved with a load resistor of 10kΩ 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.  
C
. This will act as an ESD voltage shield.  
RETN  
Clock Operation  
The ICL7650’s internal oscillator generates a 200Hz fre-  
quency, 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 V-  
if 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 frequen-  
cies. However, a 50% to 80% positive duty cycle is pre-  
ferred 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 sup-  
plies up to 6V, and between V+ and (V+ - 6V) for  
higher supply voltages.  
Component Selection  
, the two required capacitors, have  
EXTB  
C
and C  
EXTA  
optimum values depending on the clock or chopping  
frequency. The correct value is 0.1µF 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 1µV offset in 100ms, but  
several seconds may be required if ceramic capacitors  
are used.  
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 10µVs  
since the leakage of the capacitor pins is quite low at  
room temperature. Relatively long measurements may  
be made with little change in offset.  
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, ther-  
moelectric voltages (typically around 10µV/°C, but up  
to hundreds of µV/°C for some materials) will be gener-  
ated. In order to realize the extremely low offset volt-  
ages that the chopper amplifier can provide, take  
special precautions to avoid temperature gradients. To  
eliminate air movement, enclose all components (par-  
ticularly those caused by power-dissipating elements in  
the system). Minimize power-supply voltages and  
power dissipation, and use low-thermoelectric-coeffi-  
cient connections where possible. It is advisable to  
separate the device surrounding heat-dissipating ele-  
ments, and to use high-impedance loads.  
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 0.1µF capacitors before the clock ripple (due to  
_______________________________________________________________________________________  
7
Chopper-Stabilized Op Amps  
ing to decrease the voltage difference between inputs  
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 pre-  
vent contamination.  
and adjacent metal runs. Use a 10-lead pin circle, with  
the leads of the device formed so that the holes adja-  
cent 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 high-  
voltage pins. Typical guard connections are shown in  
Figure 3.  
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 guard-  
R2  
R1  
INPUT  
R3*  
OUTPUT  
OUTPUT  
INPUT  
R3*  
INVERTING AMPLIFIER  
FOLLOWER  
*
USE R3 TO COMPENSATE FOR LARGE  
SOURCE RESISTANCES, OR FOR CLAMP  
OPERATION (FIGURE 5).  
R2  
EXTERNAL  
CAPACITORS  
V+  
V-  
R3*  
OUTPUT  
OUTPUT  
7 8  
4
1
6
5
2
EXTERNAL  
CAPACITORS  
3
R1  
GUARD  
INPUT  
NONINVERTING AMPLIFIER  
BOTTOM VIEW  
R1 R2  
SHOULD BE LOW IMPEDANCE FOR  
R1 + R2 OPTIMUM GUARDING.  
BOARD LAYOUT FOR INPUT GUARDING  
WITH TO-99 PACKAGE.  
NOTE:  
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 cir-  
cuit’s DC offset characteristics are determined by the  
ICL7650/ICL7653, and its AC performance is deter-  
mined by the high-speed amplifier. While this circuit  
continuously and automatically adjusts the amplifier’s  
offset to less than 5µV, it does not correct for errors  
caused by the input bias current, so the value of resis-  
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.  
tor R should be as low as is practical. This technique  
F
can be used with any op amp that is configured as an  
inverting amplifier.  
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 con-  
nected 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.  
Figures 5 and 6 illustrate basic inverting and noninvert-  
ing amplifier circuits. Both figures show an output  
clamping circuit being used to enhance overload  
recovery performance. Supply voltage ( 8V max) and  
output drive capability (10kΩ 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.  
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  
A lower voltage supply is required when mixing the  
ICL7650/ICL7653 with circuits that operate at 15V sup-  
plies. 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.  
R
F
R
IN  
R2  
V
HIGH-  
SPEED  
AMP  
OUT  
CLAMP  
R1  
1k  
INPUT  
OUTPUT  
ICL7650  
47Ω  
10k  
C
(R1 || R2) ≥ 100kΩ  
FOR FULL CLAMP EFFECT  
R
0.1µF  
100k  
C
NOTE: R1 || R2 INDICATES THE  
PARALLEL COMBINATION OF  
R1 || R2.  
0.1µF 0.1µF  
ICL7650  
ICL7653  
Figure 5. Inverting Amplifier with Optional Clamp  
Figure 4. Nulling a High-Speed Amplifier  
_______________________________________________________________________________________  
9
Chopper-Stabilized Op Amps  
0.1µF 0.1µF  
+7.5V  
CLAMP  
+15V  
-15V  
C
+
INPUT  
OUT  
R
741  
IN  
ICL7650  
C
OUTPUT  
-
ICL7650  
R2  
R1  
CLAMP  
R3  
-7.5V  
10k  
0.1µF 0.1µF  
10k  
R3 + (R1 || R2) > 100kΩ  
FOR FULL CLAMP EFFECT  
NOTE: R1 || R2 INDICATES THE  
PARALLEL COMBINATION OF  
R1 || R2.  
Figure 7. Using an Industry-Standard 741 to Boost Output  
Drive Capability  
Figure 6. Noninverting Amplifier with Optional Clamp  
Chip Topography  
INT/EXT  
EXT/CLK IN  
8
3
2
4
+15V  
C
EXTB  
INT/  
CLK OUT  
ICL7660  
10µF  
+7.5V  
0V  
C
EXTA  
10µF  
5
V+  
6
OUTPUT  
1M  
0.090"  
(2.29mm)  
Figure 8. Splitting +15V with an ICL7660, 95% Efficiency  
(Same for -15V)  
-INPUT  
+INPUT  
V-  
CLAMP  
C
RETN  
0.069"  
(1.75mm)  
10 ______________________________________________________________________________________  
Chopper-Stabilized Op Amps  
Pin Configurations  
TOP VIEW  
C
EXTB  
7
C
1
2
3
4
5
6
7
14 INT/EXT  
13 EXT/CLK IN  
12 INT/CLK OUT  
11 V+  
EXTB  
EXTA  
8
C
V+  
6
EXTA  
C
C
1
2
3
4
8
7
6
5
C
EXTB  
1
3
EXTA  
N.C. (GUARD)  
-INPUT  
-INPUT  
+INPUT  
V-  
V+  
ICL7650  
MAX7650  
-INPUT  
2
OUTPUT  
ICL7650  
OUTPUT  
CLAMP  
+INPUT  
10 OUTPUT  
N.C. (GUARD)  
V-  
9
8
CLAMP  
5
+INPUT  
CLAMP  
4
V-  
TO-99  
C
RETN  
SO/DIP/CERDIP  
SO/DIP/CERDIP  
N.C. = NO INTERNAL CONNECTION  
C
EXTB  
8
C
V+  
EXTA  
1
3
7
C
1
2
3
4
8
C
EXTB  
EXTA  
-INPUT  
+INPUT  
V-  
7
6
5
V+  
OUTPUT  
-INPUT  
2
6
OUTPUT  
ICL7653  
ICL7653  
5
C
RETN  
+INPUT  
C
RETN  
4
V-  
SO/DIP/CERDIP  
TO-99  
______________________________________________________________________________________ 11  
Chopper-Stabilized Op Amps  
Package Information  
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  
© 2000 Maxim Integrated Products  
Printed USA  
is a registered trademark of Maxim Integrated Products.  

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