LOG100

® LOG100 Precision LOGARITHMIC AND LOG RATIO AMPLIFIER FEATURES q ACCURACY 0.37% FSO max Total Error Over 5 Decades q LINEARITY 0.1% max Log Conformity Over 5 Decades q EASY TO USE Pin-selectable Gains Internal Laser-trimmed Resistors q WIDE INPUT DYNAMIC RANGE 6 Decades, 1nA to 1mA q HERMETIC CERAMIC DIP APPLICATIONS q LOG, LOG RATIO AND ANTILOG COMPUTATIONS q ABSORBANCE MEASUREMENTS q DATA COMPRESSION q OPTICAL DENSITY MEASUREMENTS q DATA LINEARIZATION q CURRENT AND VOLTAGE INPUTS DESCRIPTION The LOG100 uses advanced integrated circuit technologies to achieve high accuracy, ease of use, low cost, and small size. It is the logical choice for your logarithmic-type computations. The amplifier has guaranteed maximum error specifications over the full sixdecade input range (1nA to 1mA) and for all possible combinations of I1 and I2. Total error is guaranteed so that involved error computations are not necessary. The circuit uses a specially designed compatible thinfilm monolithic integrated circuit which contains amplifiers, logging transistors, and low drift thin-film 9 –VCC 1 I1 A1 Q1 Q2 resistors. The resistors are laser-trimmed for maximum precision. FET input transistors are used for the amplifiers whose low bias currents (1pA typical) permit signal currents as low as 1nA while maintaining guaranteed total errors of 0.37% FSO maximum. Because scaling resistors are self-contained, scale factors of 1V, 3V or 5V per decade are obtained simply by pin selections. No other resistors are required for log ratio applications. The LOG100 will meet its guaranteed accuracy with no user trimming. Provisions are made for simple adjustments of scale factor, offset voltage, and bias current if enhanced performance is desired. 7 VOUT 3 K=1 4 K=3 A2 I2 +VCC 14 6 270Ω 10 VOUT = K LOG I1 I2 220Ω 7.5kΩ 24kΩ 5 K=5 39kΩ Scale Factor 2 Trim Com Resistor values nominal only; laser-trimmed for precision gain. International Airport Industrial Park • Mailing Address: PO Box 11400 Tel: (520) 746-1111 • Twx: 910-952-1111 • Cable: BBRCORP • © 1981 Burr-Brown Corporation • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706 Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 PDS-437E Printed in U.S.A. January, 1995 SPECIFICATIONS ELECTRICAL TA = +25°C and ±VCC = ±15V, after 15 minute warm-up, unless otherwise specified. LOG100JP PARAMETER TRANSFER FUNCTION Log Conformity Error(1) Initial Over Temperature K Range(2) Accuracy Temperature Coefficient ACCURACY Total Error(3) Initial K = 1,(4) Current Input Operation I1, I2 = 1mA I1, I2 = 100µA I1, I2 = 10µA I1, I2 = 1µA I1, I2 = 100nA I1, I2 = 10nA I1, I2 = 1nA I1, I2 = 1mA I1, I2 = 100µA I1, I2 = 10µA I1, I2 = 1µA I1, I2 = 100nA I1, I2 = 10nA I1, I2 = 1nA I1, I2 = 1mA I1, I2 = 100µA I1, I2 = 10µA I1, I2 = 1µA I1, I2 = 100nA I1, I2 = 10nA I1, I2 = 1nA ±0.20 ±0.37 ±0.28 ±0.033 ±0.28 ±0.51 ±1.26 ±4.3 ±1.5 ±0.37 ±0.11 ±0.61 ±0.91 ±2.6 CONDITIONS Either I1 or I2 1nA to 100µA (5 decades) 1nA to 1mA (6 decades) 1nA to 100µA (5 decades) 1nA to 1mA (6 decades) MIN TYP VOUT = K Log (I1/I2) 0.04 0.15 0.002 0.001 1, 3, 5 0.3 0.03 0.1 0.25 % % %/°C %/°C V/decade % %/°C MAX UNITS ±55 ±30 ±25 ±20 ±25 ±30 ±37 mV mV mV mV mV mV mV mV/°C mV/°C mV/°C mV/°C mV/°C mV/°C mV/°C mV/V mV/V mV/V mV/V mV/V mV/V mV/V vs Temperature vs Supply INPUT CHARACTERISTICS (of Amplifiers A1 and A2) Offset Voltage Initial vs Temperature Bias Current Initial vs Temperature Voltage Noise 10Hz to 10kHz, RTI Current Noise 10Hz to 10kHz, RTI AC PERFORMANCE 3dB Response(6), I2 = 10µA 1nA 1µA 10µA 1mA Step Response(6) Increasing 1µA to 1mA 100nA to 1µA 10nA to 100nA Decreasing 1mA to 1µA 1µA to 100nA 100nA to 10nA OUTPUT CHARACTERISTICS Full Scale Output (FSO) Rated Output Voltage Current Current Limit Positive Negative Impedance ±0.7 ±80 1 Doubles Every 10°C 3 0.5 ±5 mV µV/°C pA µVrms pArms 5(5) CC = 4500pF CC = 150pF CC = 150pF CC = 50pF CC = 150pF 0.11 38 27 45 kHz kHz kHz kHz 11 7 110 CC = 150pF 45 20 550 ±10 IOUT = ±5mA VOUT = ±10V ±10 ±5 12.5 15 0.05 µs µs µs µs µs µs V V mA mA mA Ω ® LOG100 2 SPECIFICATIONS ELECTRICAL (CONT) TA = +25°C and ±VCC = ±15V, after 15 minute warm-up, unless otherwise specified. LOG100JP PARAMETER POWER SUPPLY REQUIREMENTS Rated Voltage Operating Range Quiescent Current AMBIENT TEMPERATURE RANGE Specification Operating Range Storage CONDITIONS MIN TYP ±15 ±7 MAX UNITS VDC VDC mA °C °C °C Derated Performance ±12 ±18 ±9 +70 +85 +85 Derated Performance 0 –25 –40 NOTES: (1) Log Conformity Error is the peak deviation from the best-fit straight line of the VOUT vs Log IIN curve expressed as a percent of peak-to-peak full scale output. (2) May be trimmed to other values. See Applications section. (3) The worst-case Total Error for any ratio of I1/I2 is the largest of the two errors when I1 and I2 are considered separately. (4) Total Error at other values of K is K times Total Error for K = 1. (5) Guaranteed by design. Not directly measurable due to amplifier’s committed configuration. (6) 3dB and transient response are a function of both the compensation capacitor and the level of input current. See Typical Performance Curves. ABSOLUTE MAXIMUM RATINGS Supply ................................................................................................ ±18V Internal Power Dissipation .............................................................. 600mV Input Current ..................................................................................... 10mA Input Voltage Range .......................................................................... ±18V Storage Temperature Range ........................................... –40°C to +85°C Lead Temperature (soldering, 10s) ............................................... +300°C Output Short-circuit Duration .................................. Continuous to ground Junction Temperature ...................................................................... 175°C PIN CONFIGURATION Bottom View I2 Input 14 NC 13 NC 12 NC 11 Common 10 1 2 3 4 5 6 7 NC = No Connection I1 Input Scale Factor Trim K=1 K=3 K=5 +VCC Output SCALE FACTOR PIN CONNECTIONS K, V/DECADE 5 3 1.9 1 0.85 0.77 0.68 CONNECTIONS 5 to 7 4 to 7 4 and 5 to 7 3 to 7 3 and 5 to 7 3 and 4 to 7 3 and 4 and 5 to 7 –VCC NC 9 8 FREQUENCY COMPENSATION 9 1 LOG100 14 6 5 4 3 10 7 ELECTROSTATIC DISCHARGE SENSITIVITY Any integral circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet published specifications. PACKAGE INFORMATION CC ORDERING INFORMATION SPECIFIED TEMPERATURE RANGE 0°C to +70°C MODEL LOG100JP PACKAGE 14-Pin Hermetic Ceramic DIP PACKAGE DRAWING NUMBER(1) 148(2) MODEL LOG100JP PACKAGE 14-Pin Hermetic Ceramic DIP NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix D of Burr-Brown IC Data Book. (2) During 1994, the package was changed from plastic to hermetic ceramic. Pinout, model number, and specifications remained unchanged. The metal lid of the new package is internally connected to common, pin 10. ® 3 LOG100 TYPICAL PERFORMANCE CURVES TA = +25°C, VCC = ±15VDC, unless otherwise noted. NORMALIZED TRANSFER FUNCTION 1 (K) ONE CYCLE OF NORMALIZED TRANSFER FUNCTION 0.9 (K) 0.8 (K) 0.7 (K) 0.6 (K) 0.5 (K) 0.4 (K) 0.3 (K) 0.2 (K) 0.1 (K) 0 1 2 3 4 6 8 10 Normalized Output Voltage (V) 2 (K) 1 (K) 0 (K) –1 (K) –2 (K) –3 (K) I1 VOUT = K Log I2 0.001 0.01 0.1 1 10 100 1000 Normalized Output Voltage (V) 3 (K) I Current Ratio, 1 I2 I Current Ratio, 1 I2 TOTAL ERROR vs INPUT CURRENT ±75 Trimmed Output Error (mV) 60 50 TRIMMED OUTPUT ERROR vs INPUT CURRENT –60 Gain Error and Offset Error Trimmed to Zero –50 –40 –30 Maximum Total Error (mV) 40 30 ±50 I1 20 10 0 –10 I2 1nA 100nA 10µA 1mA Input Current (I1 or I2) –20 –10 0 10 20 ±25 0 1nA 100nA 10µA 1mA Input Current ( I1 or I2) –20 MINIMUM VALUE OF COMPENSATION CAPACITOR 1M Compensation Capacitor, CC (pF) 3dB Frequency Response (Hz) 1M 3dB FREQUENCY RESPONSE 10µA 100k 10k 1k 100 10 1 0.1 1nA 10nA I1 = 1nA 100µA 1µA 100µA 100µA 1mA I1 = 1mA 100k 10k 1k 100 Select CC for I1 min and I2 max I1 = 1nA I1 = 10nA I1 = 100nA Values below 2pF may be ignored. I1 = 1µA I1 = 10µA CC =1 F 0p 100µA 1µ to µA 10 10nA A 1µA 1mA to 10µA 100nA 10nA I1 = 1nA 10 I1 = 100µA to 1mA 1 1nA 10nA 100nA 1µA 10µA 100µA 1mA Input Current, I2 CC 0 =1 0 F 0p = F 1µ CC 10nA 100nA 1µA I2 1nA 10µA 100µA 1mA ® LOG100 4 THEORY OF OPERATION The base-emitter voltage of a bipolar transistor is IC KT VBE = VT l n where: VT = q IS K = Boltzman’s constant = 1.381 x 10–23 T = Absolute temperature in degrees Kelvin q = Electron charge = 1.602 x 10–19 Coulombs IC = Collector current IS = Reverse saturation current From the circuit in Figure 1, we see that VOUT' = VBE1 – VBE2 Substituting (1) into (2) yields I1 I1 – VT2 l n VOUT' = VT1 l n IS1 IS2 (2) (1) It should be noted that the temperature dependance associated with VT = KT/q is compensated by making R1 a temperature sensitive resistor with the required positive temperature coefficient. DEFINITION OF TERMS TRANSFER FUNCTION The ideal transfer function is VOUT = K log where: I1 = numerator input current I2 = denominator input current. (3) ACCURACY Accuracy considerations for a log ratio amplifier are somewhat more complicated than for other amplifiers. The reason is that the transfer function is nonlinear and has two inputs, each of which can vary over a wide dynamic range. The accuracy for any combination of inputs is determined from the total error specification. I1 I2 K = the scale factor with units of volts/decade If the transistors are matched and isothermal and VT1 = VT2, then (3) becomes: I1 I2 VOUT' = VT [ l n – ln ] (4) IS IS I1 VOUT' = VT l n and since (5) I2 ln x = 2.3 log10 x VOUT' = n VT log where n = 2.3 also VOUT = VOUT' R1 + R2 R1 n VT log I1 I2 I1 I2 (6) (7) (8) VOUT (V) 10 8 6 4 2 0 –2 –4 –6 1µA 1nA 10nA 100nA K=5 K=3 K=1 I1 10µA 100µA VOUT = K LOG I2 = 1µA Fixed value of I2. I1 I2 1mA (9) = or R1 + R2 R1 I1 I2 (10) –8 –10 VOUT = K log (11) FIGURE 2. Transfer Function with Varying K and I1. 10 I2 = 10nA I2 = 1µA I1 I1 A1 Q1 + – VBE – VBE Q2 + I2 VOUT VOUT (V) 8 6 A2 2 4 2 0 –2 –4 –6 –8 –10 K=3 1nA 10nA 100nA 1µA 10µA 100µA I2 = 100µA 1mA I1 1 I1 VOUT = K LOG I2 I2 R2 VOUT R1 VOUT = K LOG I1 I2 Fixed value of K. FIGURE 1. Simplified Model of Log Amplifier. FIGURE 3. Transfer Function with Varying I2 and I1. ® 5 LOG100 TOTAL ERROR The total error is the deviation (expressed in mV) of the actual output from the ideal output of VOUT = K log (I1/I2). Thus, VOUT (ACTUAL) = VOUT (IDEAL) ± Total Error. It represents the sum of all the individual components of error normally associated with the log amp when operated in the current input mode. The worst-case error for any given ratio of I1/I2 is the largest of the two errors when I1 and I2 are considered separately. Example: I1 varies over a range of 10nA to 1µA and I2 varies from 100nA to 10µA. What is the maximum error? Table I shows the maximum errors for each decade combination of I1 and I2. I1 (maximum error)(1) I2 (maximum error)(1) 10nA (30mV) 100nA (25mV) 1µA (20mV) 10µA (25mV) 0.1 (30mV) 0.01 (30mV) 0.001 (30mV) 100nA (25mV) 1 (25mV) 0.1 (25mV) 0.01 (25mV) 1µA (20mV) 10 (25mV) 1 (20mV) 0.1 (25mV) Log conformity is defined as the peak deviation from the best-fit straight line of the VOUT versus log (I1/I2) curve. This is expressed as a percent of peak-to-peak full scale output. Thus, the nonlinearity error expressed in volts over m decades is VOUT (NONLIN) = K 2Nm V where N is the log conformity error, in percent. INDIVIDUAL ERROR COMPONENTS The ideal transfer function with current input is VOUT = K Log I1 I2 (13) (12) The actual transfer function with the major components of error is I1 – IB1 VOUT = K (1 ± ∆K) log ±K 2Nm ± VOS OUT (14) I2 – IB2 The individual component of error is ∆K = scale factor error (0.3%, typ) IB1 = bias current of A1 (1pA, typ) IB2 = bias current of A2 (1pA, typ) N = log conformity error ( 0.05%, 0.1%, typ) VOS OUT = output offset voltage (1mV, typ) m = number of decades over which N is specified: 0.05% for m = 5, 0.1% for m = 6 Example: what is the error with K = 3 when I1 = 1µA and I2 = 100nA VOUT = 3(1 ± 0.003) log ≈ 3.009 log 10–6 –10–12 ±3(2)(0.0005)5±1mV 10–7 –10–12 (15) (16) (17) (18) NOTE: (1) Maximum errors are in parenthesis. TABLE I. I1/I2 and Maximum Errors. Since the largest value of I1/I2 is 10 and the smallest is 0.001, K is set at 3V per decade so the output will range from +3V to –9V. The maximum total error occurs when I1 = 10nA and is equal to K x 30mV. This represents a 0.75% of peak-topeak FSO error 3 x 0.030/12 x 100% = 0.75% where the full scale output is 12V (from +3V to –9V). ERRORS RTO AND RTI As with any transfer function, errors generated by the function itself may be Referred-to-Output (RTO) or Referred-to-Input (RTI). In this respect, log amps have a unique property: Given some error voltage at the log amp’s output, that error corresponds to a constant percent of the input regardless of the actual input level. Refer to: Yu Jen Wong and William E. Ott, “Function Circuits: Design & Applications”, McGraw-Hill Book, 1976. LOG CONFORMITY Log conformity corresponds to linearity when VOUT is plotted versus I1/I2 on a semilog scale. In many applications, log conformity is the most important specification. This is true because bias current errors are negligible (1pA compared to input currents of 1nA and above) and the scale factor and offset errors may be trimmed to zero or removed by system calibration. This leaves log conformity as the major source of error. ® 10–6 + 0.015 + 0.001 10–7 = 3.009 (1) + 0.015 + 0.001 = 3.025V Since the ideal output is 3.000V, the error as a percent of reading is % error = 0.025 x 100% = 0.83% 3 (19) For the case of voltage inputs, the actual transfer function is V1 VOUT = K(1 ± ∆K) log R1 V2 R2 – IB1 ± – IB2 ± EOS1 R1 EOS2 R2 (20) FREQUENCY RESPONSE The 3dB frequency response of the LOG100 is a function of the magnitude of the input current levels and of the value of the frequency compensation capacitor. See Typical Performance Curves for details. ±K 2Nm ±VOS OUT LOG100 6 The frequency response curves are shown for constant DC I1 and I2 with a small signal AC current on one of them. The transient response of the LOG100 is different for increasing and decreasing signals. This is due to the fact that a log amp is a nonlinear gain element and has different gains at different levels of input signals. Frequency response decreases as the gain increases. A voltage divider may be used to reduce the value of the resistor. When this is done, one must be aware of possible errors caused by the amplifier’s input offset voltage. This is shown in Figure 5. In this case the voltage at pin 14 is not exactly zero, but is equal to the value of the input offset voltage of A1, which ranges from zero to ±5mV. VT must be kept much larger than 5mV in order to make this effect negligible. This concept also applies to pin 1. GENERAL INFORMATION INPUT CURRENT RANGE The stated input range of 1nA to 1mA is the range for specified accuracy. Smaller or larger input currents may be applied with decreased accuracy. Currents larger than 1mA result in increased nonlinearity. The 10mA absolute maximum is a conservative value to limit the power dissipation in the output stage of A1 and the logging transistor. Currents below 1nA will result in increased errors due to the input bias currents of A1 and A2 (1pA typical). These errors may be nulled. See Optional Adjustments section. FREQUENCY COMPENSATION Frequency compensation for the LOG100 is obtained by connecting a capacitor between pins 7 and 14. The size of the capacitor is a function of the input currents as shown in the Typical Performance Curves. For any given application, the smallest value of the capacitor which may be used is determined by the maximum value at I2 and the minimum value of I1. Larger values of CC will make the LOG100 more stable, but will reduce the frequency response. SETTING THE REFERENCE CURRENT When the LOG100 is used as a straight log amplifier I2 is constant and becomes the reference current in the expression I1 VOUT = K log (21) IREF IREF can be derived from an external current source (such as shown in Figure 4), or it may be derived from a voltage source with one or more resistors. When a single resistor is used, the value may be quite large when IREF is small. If IREF is 10nA and +15V is used RREF = 15V = 1500MΩ. 10nA R1 VT R3 14 IREF VOS + – A1 VREF R2 FIGURE 5. “T” Network for Reference Current. OPTIONAL ADJUSTMENTS The LOG100 will meet its specified accuracy with no user adjustments. If improved performance is desired, the following optional adjustments may be made. INPUT BIAS CURRENT The circuit in Figure 6 may be used to compensate for the input bias currents of A1 and A2. Since the amplifiers have FET inputs with the characteristic bias current doubling every 10°C, this nulling technique is practical only where the temperature is fairly stable. R2 10kΩ +VCC R1 1kMΩ 1 I1 LOG100 14 I2 R1' 1kMΩ 6 5 4 3 10 VOUT – –VCC 9 7 + CC –VCC IREF 2N2905 RREF +15V 6V IN834 2N2905 R2' 10kΩ +VCC FIGURE 6. Bias Current Nulling. 3.6kΩ –15V 6V = RREF IREF FIGURE 4. Temperature-Compensated Current Reference. 7 OUTPUT OFFSET The output offset may be nulled with the circuit in Figure 7. I1 and I2 are set equal at some convenient value in the range of 100nA to 100µA. R1 is then adjusted for zero output voltage. ® LOG100 –VCC –VCC 10kΩ +VCC –VCC R1 100kΩ 9 1 I1 LOG100 14 I2 6 5 4 3 10 VOUT – 2 7 + 9 LOG100 6 +VCC CC I1 = I2 +VCC FIGURE 8. Reverse Polarity Protection. techniques should be used to avoid damage caused by low energy electrostatic discharge (ESD). LOG RATIO One of the more common uses of log ratio amplifiers is to measure absorbance. A typical application is shown in Figure 9. Absorbance of the sample is A = log λ1' λ1 I1 I2 (22) . (23) FIGURE 7. Output Offset Nulling. ADJUSTMENTS OF SCALE FACTOR K The value of K may be changed by increasing or decreasing the voltage divider resistor normally connected to the output, pin 7. To increase K put resistance in series between pin 7 and the appropriate scaling resistor pin (3, 4 or 5). To decrease K place a parallel resistor between pin 2 and either pin 3, 4 or 5. If λ2 = λ1 and D1 and D2 are matched A ∝ K log APPLICATION INFORMATION WIRING PRECAUTIONS In order to prevent frequency instability due to lead inductance of the power supply lines, each power supply should be bypassed. This should be done by connecting a 10µF tantalum capacitor in parallel with a 1000pF ceramic capacitor from the +VCC and –VCC pins to the power supply common. The connection of these capacitors should be as close to the LOG100 as practical. CAPACITIVE LOADS Stable operation is maintained with capacitive loads of up to 100pF, typically. Higher capacitive loads can be driven if a 22Ω carbon resistor is connected in series with the LOG100’s output. This resistor will, of course, form a voltage divider with other resistive loads. CIRCUIT PROTECTION The LOG100 can be protected against accidental power supply reversal by putting a diode (1N4001 type) in series with each power supply line as shown in Figure 8. This precaution is necessary only in power systems that momentarily reverse polarity during turn-on or turn-off. If this protection circuit is used, the accuracy of the LOG100 will be degraded slightly by the voltage drops across the diodes as determined by the power supply sensitivity specification. The LOG100 uses small geometry FET transistors to achieve the low input bias currents. Normal FET handling ® –VCC I1 Sample λ1 Light λ 2 Source λ1 I2 D2 14 6 CC 5 4 3 D1 LOG100 10 VOUT – 9 1 7 + +VCC FIGURE 9. Absorbance Measurement. DATA COMPRESSION In many applications the compressive effects of the logarithmic transfer function is useful. For example, a LOG100 preceding an 8-bit analog-to-digital converter can produce equivalent 20-bit converter operation. SELECTING OPTIMUM VALUES OF I2 AND K In straight log applications (as opposed to log ratio), both K and I2 are selected by the designer. In order to minimize errors due to output offset and noise, it is normally best to 8 LOG100 scale the log amp to use as much of the ±10V output range as possible. Thus, with the range of I1 from I1 MIN to I1 MAX ; For I1 MAX IIN QA QB National LM394 + 10V = K log I1 – 10V = K log I1 MAX /I2 MIN (24) (25) D1 For I1 MIN /I2 D2 Addition of these two equations and solving for I2 shows that its optimum value, I2 OPT, is the geometric mean of I1 MAX and I1 MIN. I2 OPT = I1 MAX x I1 MIN KOPT = log 10 I1 MAX I2 OPT ANTILOG CONFIGURATION (an implicit technique) Since K is selectable in discrete steps, use the largest value of K available which does not exceed KOPT. NEGATIVE INPUT CURRENTS The LOG100 will function only with positive input currents (conventional current flow into pins 1 and 14). Some current sources (such as photomultiplier tubes) provide negative input currents. In such situations, the circuit in Figure 10 may be used.(1) VOLTAGE INPUTS The LOG100 gives the best performance with current inputs. Voltage inputs may be handled directly with series resistors, but the dynamic input range is limited to approximately three decades of input voltage by voltage noise and offsets. The transfer function of equation (20) applies to this configuration. NOTE: (1) More detailed information may be found in “Properly Designed Log Amplifiers Process Bipolar Input Signals” by Larry McDonald, EDN, 5 Oct. 80, pp 99–102. 9 1 IREF LOG100 14 6 5 4 3 R 10 VOUT – 7 + –VCC (26) (27) IOUT FIGURE 10. Current Inverter. +VCC VIN VIN K CC = 0.01µF VOUT = IREF R Antilog – K = 1 when VIN connected to pin 3. K = 3 when VIN connected to pin 4. K = 5 when VIN connected to pin 5. FIGURE 11. Connections for Antilog Function. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. ® 9 LOG100