LM108A/LM208A/LM308A Operational Amplifiers General Description The LM108/LM108A series are precision operational amplifiers having specifications about a factor of ten better than FET amplifiers over their operating temperature range. In addition to low input currents, these devices have extremely low offset voltage, making it possible to eliminate offset adjustments, in most cases, and obtain performance approaching chopper stabilized amplifiers. The devices operate with supply voltages from g 2V to g 18V and have sufficient supply rejection to use unregulated supplies. Although the circuit is interchangeable with and uses the same compensation as the LM101A, an alternate compensation scheme can be used to make it particularly insensitive to power supply noise and to make supply bypass capacitors unnecessary. The low current error of the LM108A series makes possible many designs that are not practical with conventional amplifiers. In fact, it operates from 10 MX source resistances, introducing less error than devices like the 709 with 10 kX sources. Integrators with drifts less than 500 mV/sec and analog time delays in excess of one hour can be made using capacitors no larger than 1 mF. The LM208A is identical to the LM108A, except that the LM208A has its performance guaranteed over a b25§ C to a 85§ C temperature range, instead of b 55§ C to a 125§ C. The LM308A devices have slightly-relaxed specifications and performances over a 0§ C to a 70§ C temperature range. Features Y Y Y Y Y Offset voltage guaranteed less than 0.5 mV Maximum input bias current of 3.0 nA over temperature Offset current less than 400 pA over temperature Supply current of only 300 mA, even in saturation Guaranteed 5 mV/§ C drift Compensation Circuits Standard Compensation Circuit Alternate* Frequency Compensation Cf t R1 CO R1 a R2 CO e 30 pF *Improves rejection of power supply noise by a factor of ten. TL/H/7759 – 1 **Bandwidth and slew rate are proportional to 1/Cf . TL/H/7759 – 2 **Bandwidth and slew rate are proportional to 1/Cs . Feedforward Compensation TL/H/7759 – 3 C1995 National Semiconductor Corporation TL/H/7759 RRD-B30M115/Printed in U. S. A. LM108A/LM208A/LM308A Operational Amplifiers May 1989 LM108A/LM208A Absolute Maximum Ratings b 65§ C to a 150§ C Storage Temperature Range Lead Temperature (Soldering, 10 sec.) (DIP) 260§ C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. (Note 5) g 20V Supply Voltage Soldering Information Dual-In-Line Package Soldering (10 sec.) Small Outline Package Vapor Phase (60 sec.) Infrared (15 sec.) Power Dissipation (Note 1) 500 mW g 10 mA Differential Input Current (Note 2) g 15V Input Voltage (Note 3) Output Short-Circuit Duration Continuous Operating Free Air Temperature Range b 55§ C to a 125§ C LM108A b 25§ C to a 85§ C LM208A 260§ C 215§ C 220§ C See An-450 ‘‘Surface Mounting Methods and Their Effect on Product Reliability’’ for other methods of soldering surface mount devices. ESD Tolerance (Note 6) 2000V Electrical Characteristics (Note 4) Typ Max Units Input Offset Voltage Parameter TA e 25§ C Conditions Min 0.3 0.5 mV Input Offset Current TA e 25§ C 0.05 0.2 nA Input Bias Current TA e 25§ C 0.8 2.0 Input Resistance TA e 25§ C Supply Current TA e 25§ C Large Signal Voltage Gain TA e 25§ C, VS e g 15V, VOUT e g 10V, RL t 10 kX 30 70 0.3 80 Average Temperature Coefficient of Input Offset Voltage 1.0 Input Offset Current Average Temperature Coefficient of Input Offset Current 0.5 Input Bias Current Supply Current TA e 125§ C Large Signal Voltage Gain VS e g 15V, VOUT e g 10V, RL t 10 kX Output Voltage Swing VS e g 15V, RL e 10 kX Input Voltage Range VS e g 15V 0.15 40 g 13 0.6 300 Input Offset Voltage nA MX mA V/mV 1.0 mV 5.0 mV/§ C 0.4 nA 2.5 pA/§ C 3.0 nA 0.4 mA V/mV g 14 g 13.5 V V Common Mode Rejection Ratio 96 110 dB Supply Voltage Rejection Ratio 96 110 dB Note 1: The maximum junction temperature of the LM108A is 150§ C, while that of the LM208A is 100§ C. For operating at elevated temperatures, devices in the H08 package must be derated based on a thermal resistance of 160§ C/W, junction to ambient, or 20§ C/W, junction to case. The thermal resistance of the dual-in-line package is 100§ C/W, junction to ambient. Note 2: The inputs are shunted with back-to-back diodes for overvoltage protection. Therefore, excessive current will flow if a differential input voltage in excess of 1V is applied between the inputs unless some limiting resistance is used. Note 3: For supply voltages less than g 15V, the absolute maximum input voltage is equal to the supply voltage. Note 4: These specifications apply for g 5V s VS s g 20V and b 55§ C s TA s 125§ C, unless otherwise specified. With the LM208A, however, all temperature specifications are limited to b 25§ C s TA s 85§ C. Note 5: Refer to RETS108AX for LM108AH and LM108AJ-8 military specifications. Note 6: Human body model, 1.5 kX in series with 100 pF. 2 LM308A Absolute Maximum Ratings Lead Temperature (Soldering, 10 sec.) (DIP) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Supply Voltage Power Dissipation (Note 1) Differential Input Current (Note 2) Input Voltage (Note 3) Output Short-Circuit Duration Operating Temperature Range Storage Temperature Range H-Package Lead Temperature (Soldering, 10 sec.) Soldering Information Dual-In-Line Package Soldering (10 sec.) Small Outline Package Vapor phase (60 sec.) Infrared (15 sec.) g 18V 500 mW g 10 mA g 15V Continuous 0§ C to a 70§ C b 65§ C to a 150§ C 260§ C 260§ C 215§ C 220§ C See An-450 ‘‘Surface Mounting Methods and Their Effect on Product Reliability’’ for other methods of soldering surface mount devices. ESD rating to be determined. 300§ C Electrical Characteristics (Note 4) Typ Max Units Input Offset Voltage Parameter TA e 25§ C Conditions Min 0.3 0.5 mV Input Offset Current TA e 25§ C 0.2 1 nA Input Bias Current TA e 25§ C 1.5 7 Input Resistance TA e 25§ C Supply Current TA e 25§ C, VS e g 15V Large Signal Voltage Gain TA e 25§ C, VS e g 15V, VOUT e g 10V, RL t 10 kX Input Offset Voltage VS e g 15V, RS e 100X Average Temperature Coefficient of Input Offset Voltage VS e g 15V, RS e 100X 10 40 0.3 80 Input Offset Current Average Temperature Coefficient of Input Offset Current 2.0 Input Bias Current Large Signal Voltage Gain VS e g 15V, VOUT e g 10V, RL t 10 kX Output Voltage Swing VS e g 15V, RL e 10 kX g 13 Input Voltage Range VS e g 15V g 14 0.8 300 2.0 60 nA MX mA V/mV 0.73 mV 5.0 mV/§ C 1.5 nA 10 pA/§ C 10 nA V/mV g 14 V V Common Mode Rejection Ratio 96 110 dB Supply Voltage Rejection Ratio 96 110 dB Note 1: The maximum junction temperature of the LM308A is 85§ C. For operating at elevated temperatures, devices in the H08 package must be derated based on a thermal resistance of 160§ C/W, junction to ambient, or 20§ C/W, junction to case. The thermal resistance of the dual-in-line package is 100§ C/W, junction to ambient. Note 2: The inputs are shunted with back-to-back diodes for overvoltage protection. Therefore, excessive current will flow if a differential input voltage in excess of 1V is applied between the inputs unless some limiting resistance is used. Note 3: For supply voltages less than g 15V, the absolute maximum input voltage is equal to the supply voltage. Note 4: These specifications apply for g 5V s VS s g 15V and 0§ C s TA s a 70§ C, unless otherwise specified. 3 Typical Applications Sample and Hold ² Teflon, polyethylene or polycarbonate dielectric capacitor. Worst case drift less than 2.5 mV/sec. TL/H/7759 – 4 High Speed Amplifier with Low Drift and Low Input Current TL/H/7759 – 5 4 Application Hints Resistors can cause other errors besides gradient generated voltages. If the gain setting resistors do not track with temperature a gain error will result. For example, a gain of 1000 amplifier with a constant 10 mV input will have a 10V output. If the resistors mistrack by 0.5% over the operating temperature range, the error at the output is 50 mV. Referred to input, this is a 50 mV error. All of the gain fixing resistor should be the same material. Testing low drift amplifiers is also difficult. Standard drift testing technique such as heating the device in an oven and having the leads available through a connector, thermoprobe, or the soldering iron methodÐdo not work. Thermal gradients cause much greater errors than the amplifier drift. Coupling microvolt signal through connectors is especially bad since the temperature difference across the connector can be 50§ C or more. The device under test along with the gain setting resistor should be isothermal. A very low drift amplifier poses some uncommon application and testing problems. Many sources of error can cause the apparent circuit drift to be much higher than would be predicted. Thermocouple effects caused by temperature gradient across dissimilar metals are perhaps the worst offenders. Only a few degrees gradient can cause hundreds of microvolts of error. The two places this shows up, generally, are the package-to-printed circuit board interface and temperature gradients across resistors. Keeping package leads short and the two input leads close together helps greatly. Resistor choice as well as physical placement is important for minimizing thermocouple effects. Carbon, oxide film and some metal film resistors can cause large thermocouple errors. Wirewound resistors of evanohm or manganin are best since they only generate about 2 mV/§ C referenced to copper. Of course, keeping the resistor ends at the same temperature is important. Generally, shielding a low drift stage electrically and thermally will yield good results. Schematic Diagram TL/H/7759 – 6 5 Connection Diagrams Dual-In-Line Package Metal Can Package TL/H/7759–7 Pin 4 is connected to the case. TL/H/7759 – 8 Top View **Unused pin (no internal connection) to allow for input anti-leakage guard ring on printed circuit board layout. Order Number LM108AJ-8, LM208AJ-8, LM308AJ-8, LM308AM or LM308AN See NS Package Number J08A, M08A or N08E Order Number LM108AH, LM208AH or LM208AH See NS Package Number H08C Physical Dimensions inches (millimeters) Metal Can Package (H) Order Number LM108AH, LM208AH or LM308AH NS Package Number H08C 6 Physical Dimensions inches (millimeters) (Continued) Ceramic Dual-In-Line Package (J) Order Number LM108AJ-8, LM208AJ-8 or LM308AJ-8 NS Package Number J08A S.O. Package (M) Order Number LM308AM NS Package Number M08A 7 LM108A/LM208A/LM308A Operational Amplifiers Physical Dimensions inches (millimeters) (Continued) Molded Dual-In-Line Package (N) Order Number LM308AN NS Package Number N08E LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation 1111 West Bardin Road Arlington, TX 76017 Tel: 1(800) 272-9959 Fax: 1(800) 737-7018 2. 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