LM134 Series Constant Current Source and Temperature Sensor U FEATURES ■ ■ ■ ■ ■ ■ DESCRIPTIO 1µA to 10mA Operation 0.02%/V Regulation 0.8V to 40V Operating Voltage Can be Used as Linear Temperature Sensor Draws No Reverse Current Supplied in Standard Transistor Packages The LM134 is a three-terminal current source designed to operate at current levels from 1µA to 10mA, as set by an external resistor. The device operates as a true twoterminal current source, requiring no extra power connections or input signals. Regulation is typically 0.02%/V and terminal-to-terminal voltage can range from 800mV to 40V. U APPLICATIO S ■ ■ ■ ■ ■ ■ ■ Current Mode Temperature Sensing Constant Current Source for Shunt References Cold Junction Compensation Constant-Gain Bias for Bipolar Differential Stage Micropower Bias Networks Buffer for Photoconductive Cell Current Limiter , LTC and LT are registered trademarks of Linear Technology Corporation. Because the operating current is directly proportional to absolute temperature in degrees Kelvin, the device will also find wide applications as a temperature sensor. The temperature dependence of the operating current is 0.336%/°C at room temperature. For example, a device operating at 298µA will have a temperature coefficient of 1µA/°C. The temperature dependence is extremely accurate and repeatable. Devices specified as temperature sensors in the 100µA to 1mA range are the LM134-3, LM234-3 and the LM134-6, LM234-6, with the dash numbers indicating ±3°C and ±6°C accuracies, respectively. If a zero temperature coefficient current source is required, this is easily achieved by adding a diode and a resistor. U TYPICAL APPLICATIO Remote Temperature Sensor with Voltage Output Operating Current vs Temperature 225 500 VIN ≥ 5V 125 RSET 226Ω 10mV/°K LM234-3 V – R1 10k RSET = 226Ω 300 25 200 –75 100 –175 TEMPERATURE (°C) R TEMPERATURE (°K) 400 V+ TA01a 0 0 100 300 400 200 OPERATING CURRENT (µA) –275 500 TA01b 1 LM134 Series W W U W ABSOLUTE AXI U RATI GS (Note 1) V + to V – Forward Voltage LM134 ................................................................. 40V LM134-3/LM134-6/LM234-3/ LM234-6/LM334 ................................................. 30V + V to V – Reverse Voltage ........................................ 20V R Pin to V – Voltage.................................................... 5V Set Current ........................................................... 10mA Power Dissipation .............................................. 200mW Operating Temperature Range LM134 (OBSOLETE) ................... –55°C to 125°C LM234-3/LM234-6 ............................–25°C to 100°C LM334 ..................................................... 0°C to 70°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C U W U PACKAGE/ORDER I FOR ATIO BOTTOM VIEW R V+ V– H PACKAGE 3-LEAD TO-46 METAL CAN ORDER PART NUMBER CURRENT SOURCE TEMP SENSOR LM134H LM334H LM134H-3 LM234H-3 LM134H-6 LM234H-6 TJMAX = 150°C, θJA = 440°C/W, θJA = 80°C/W BOTTOM VIEW V+ R V– ORDER PART NUMBER CURRENT SOURCE TEMP SENSOR LM334Z LM234Z-3 LM234Z-6 Z PACKAGE 3-LEAD PLASTIC TO-92 TJMAX = 100°C, θJA = 160°C/W OBSOLETE PACKAGE Consider the S8 or Z Packages for Alternate Source ORDER PART NUMBER V– 1 8 NC R 2 7 NC V+ 3 6 NC NC 4 5 NC S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 100°C, θJA = 180°C/W Consult LTC Marketing for availability of LM234Z-3 and LM234Z-6 2 LM334S8 S8 PART MARKING 334 LM134 Series ELECTRICAL CHARACTERISTICS CURRENT SOURCE (Note 2) SYMBOL PARAMETER CONDITIONS ∆ISET Set Current Error, V+ = 2.5V 10µA ≤ ISET ≤ 1mA 1mA < ISET ≤ 5mA 2µA ≤ ISET < 10µA (Note 3) MIN LM134 TYP MAX MIN LM334 TYP 3 5 8 MAX UNITS 6 8 12 % % % Ratio of Set Current to V– Current 10µA ≤ ISET ≤ 1mA 1mA ≤ ISET ≤ 5mA 2µA ≤ ISET ≤ 10µA VMIN Minimum Operating Voltage 2µA ≤ ISET ≤ 100µA 100µA < ISET ≤ 1mA 1mA < ISET ≤ 5mA 0.8 0.9 1.0 ∆ISET ∆VIN Average Change in Set Current with Input Voltage 1.5V ≤ V+ ≤ 5V 2µA ≤ ISET ≤ 1mA 5V ≤ V+ ≤ VMAX (Note 5) 0.02 0.05 0.02 0.1 %/V 0.01 0.03 0.01 0.05 %/V 14 1.5V ≤ V ≤ 5V 1mA < ISET ≤ 5mA 5V ≤ V ≤ VMAX (Note 5) Temperature Dependence of Set Current (Note 4) CS 25µA ≤ ISET ≤ 1mA 18 14 18 14 23 18 14 18 26 26 0.8 0.9 1.0 V V V 0.03 0.03 %/V 0.02 0.02 %/V 0.96 Effective Shunt Capacitance 23 1.04 0.96 1.04 15 15 pF LM134-3,LM234-3 MIN TYP MAX LM134-6, LM234-6 MIN TYP MAX TEMPERATURE SENSOR (Note 2) SYMBOL PARAMETER CONDITIONS ∆ISET Set Current Error, V+ = 2.5V (Note 3) 100µA ≤ ISET ≤ 1mA Tj = 25°C Equivalent Temperature Error VMIN ∆ISET ∆VIN ±2 % ±3 ±6 °C Ratio of Set Current to V – Current 100µA ≤ ISET ≤ 1mA Minimum Operating Voltage 100µA ≤ ISET ≤ 1mA 0.9 Average Change in Set Current with Input Voltage 1.5V ≤ V+ ≤ 5V 0.02 0.05 0.02 0.1 %/V 0.01 0.03 0.01 0.05 %/V Temperature Dependence of Set Current (Note 4) CS UNITS ±1 14 100µA ≤ ISET ≤ 1mA 5V ≤ V+ ≤ 30V 100µA ≤ ISET ≤ 1mA 18 0.98 26 14 18 26 0.9 1.02 0.97 V 1.03 Equivalent Slope Error ±2 ±3 % Effective Shunt Capacitance 15 15 pF Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Unless otherwise specified, tests are performed at Tj = 25°C with pulse testing so that junction temperature does not change during test. Note 3: Set current is the current flowing into the V+ pin. It is determined by the following formula: ISET = 67.7mV/RSET (at 25°C). Set current error is expressed as a percent deviation from this amount. ISET increases at 0.336%/°C at Tj = 25°C. Note 4: ISET is nominally directly proportional to absolute temperature (°K). ISET at any temperature can be calculated from: ISET = IO (T/TO) where IO is ISET measured at TO (°K). Note 5: VMAX = 40V for LM134 and 30V for other grades. 3 LM134 Series U W TYPICAL PERFOR A CE CHARACTERISTICS Maximum Slew Rate for Linear Operation Output Impedance 109 Start-Up 10 10µA I = 10µA I = 100µA 107 100µA ISET SLEW RATE (V/µs) IMPEDANCE (Ω) 108 200µs 0µA 1.0 0.1 50µs 0µA 1mA 0.01 I = 1mA 5µs 0mA 5V 106 0.001 100 1k FREQUENCY (Hz) 10 10k 1 10 100 ISET (µA) 1000 134 G03 86 2µs 82 ISET = 1mA 0 78 V + TO V – = 5V ∆V = 0.4V tr, f = 500ns 5 0 ISET = 100µA 10µs –5 1k 74 VOLTAGE (mV) –1 10k CURRENT (pA/√Hz) 1 ∆ISET (%) Current Noise Voltage Across RSET Transient Response 70 66 62 58 10 ISET = 10µA –10 ISET = 1mA 100 ISET = 100µA 10 ISET = 10µA 50 50µs –20 46 –50 TIME (*NOTE SCALE CHANGES FOR EACH CURRENT LEVEL) 1 –25 50 25 0 75 TEMPERATURE (°C) 100 125 10 RSET = 226Ω RATIO 18 17 16 15 14 10µA RSET = 6.8k 13 400 125 300 25 200 –75 100 –175 TEMPERATURE (°C) RSET = 68Ω TEMPERATURE (°K) 19 RSET = 680Ω 225 500 20 RSET = 14Ω 100k Operating Current vs Temperature 21 Tj = 25°C 100µA 1k 10k FREQUENCY (Hz) 134 G06 Ratio of ISET to V – Current Turn-On Voltage 1mA 100 1314/15 G01 134 G04 ISET ISET = 5mA 54 0 10mA TIME (*NOTE SCALE CHANGES FOR EACH CURRENT LEVEL) 134 G02 134 G01 2 INPUT 0V 10000 12 1µA 0.4 0.6 0.8 1.0 1.2 1.4 V+ TO V – VOLTAGE 0 100µA 1mA 10mA ISET 134 G02 4 11 10µA 134 G08 0 100 300 400 200 OPERATING CURRENT (µA) –275 500 134 G09 LM134 Series U U W U APPLICATIO S I FOR ATIO Basic Theory of Operation The equivalent circuit of the LM134 is shown in Figure 1. A reference voltage of 64mV is applied to the minus input of A1 with respect to the V – pin. A1 serves the drive to Q2 to keep the R pin at 64mV, independent of the value of RSET. Transistor Q1 is matched to Q2 at a 17:1 ratio so that the current flowing out of the V – pin is always 1/18 of the total current into the V+ pin. This total current is called ISET and is equal to: 64mV 18 67.7mV = RSET RSET 17 the device is ±2% when the room temperature current is set to the exact desired value. Supply Voltage Slew Rate At slew rates above a given threshold (see curve), the LM134 may exhibit nonlinear current shifts. The slewing rate at which this occurs is directly proportional to ISET. At ISET = 10µA, maximum dv/dt is 0.01V/µs; at ISET = 1mA, the limits is 1V/µs. Slew rates above the limit do not harm the LM134, or cause large currents to flow. Thermal Effects V+ ISET Q1 Q2 + R A1 – + RSET 64mV – V– 134 F01 Internal heating can have a significant effect on current regulation for ISET greater than 100µA. For example, each 1V increase across the LM134 at ISET = 1mA will increase junction temperature by ≈0.4°C in still air. Output current (ISET) has a temperature coefficient of ≈0.33%/°C, so the change in current due to temperature rise will be (0.4)(0.33) = 0.132%. This is a 10:1 degradation in regulation compared to true electrical effects. Thermal effects, therefore, must be taken into account when DC regulation is critical and ISET exceeds 100µA. Heat sinking of the TO-46 package or the TO-92 leads can reduce this effect by more than 3:1. Figure 1. Shunt Capacitance The 67.7mV equivalent reference voltage is directly proportional to absolute temperature in degrees Kelvin (see curve, “Operating Current vs Temperature”). This means that the reference voltage can be plotted as a straight line going from 0mV at absolute zero temperature to 67.7mV at 298°K (25°C). The slope of this line is 67.7mV/298 = 227µV/°C. The accuracy of the device is specified as a percent error at room temperature, or in the case of the -3 and -6 devices, as both a percent error and an equivalent temperature error. The LM134 operating current changes at a percent rate equal to (100)(227µV/°C)/(67.7mV) = 0.336%/ °C at 25°C, so each 1% operating current error is equivalent to ≈3°C temperature error when the device is used as a temperature sensor. The slope accuracy (temperature coefficient) of the LM134 is expressed as a ratio compared to unity. The LM134-3, for instance, is specified at 0.98 to 1.02, indicating that the maximum slope error of In certain applications, the 15pF shunt capacitance of the LM134 may have to be reduced, either because of loading problems or because it limits the AC output impedance of the current source. This can be easily accomplished by buffering the LM134 with a FET, as shown in the applications. This can reduce capacitance to less than 3pF and improve regulation by at least an order of magnitude. DC characteristics (with the exception of minimum input voltage) are not affected. Noise Current noise generated by the LM134 is approximately 4 times the shot noise of a transistor. If the LM134 is used as an active load for a transistor amplifier, input referred noise will be increased by about 12dB. In many cases, this is acceptable and a single stage amplifier can be built with a voltage gain exceeding 2000. 5 LM134 Series U W U U APPLICATIO S I FOR ATIO Lead Resistance The sense voltage which determines the operating current of the LM134 is less than 100mV. At this level, thermocouple or lead resistance effects should be minimized by locating the current setting resistor physically close to the device. Sockets should be avoided if possible. It takes only 0.7Ω contact resistance to reduce output current by 1% at the 1mA level. Start-Up Time The LM134 is designed to operate at currents as low as 1µA. This requires that internal biasing current be well below that level because the device achieves its wide operating current range by using part of the operating current as bias current for the internal circuitry. To ensure start-up, however, a fixed trickle current must be provided internally. This is typically in the range of 20nA to 200nA and is provided by the special ultralow IDDS FETs shown in the Schematic Diagrams as Q7 and Q8. The start-up time of the LM134 is determined by the IDSS of these FETs and the capacitor C1. This capacitor must charge to approximately 500mV before Q3 turns on to start normal circuit operation. This takes as long as (500mV)(50pF)/(20nA) = 1.25ms for very low IDSS values. Using the LM134 as a Temperature Sensor Because it has a highly linear output characteristic, the LM134 makes a good temperature sensor. It is particularly useful in remote sensing applications because it is a current output device and is therefore not affected by long wire runs. It is easy to calibrate, has good long term stability and can be interfaced directly with most data acquisition systems, eliminating the expensive preamplifiers required for thermocouples and platinum sensors. A typical temperature sensor application is shown in Figure␣ 2. The LM134 operating current at 25°C is set at 298µA by the 226Ω resistor, giving an output of 1µA/°K. The current flows through the twisted pair sensor leads to the 10k termination resistor, which converts the current output to a voltage of 10mV/°K referred to ground. The 6 voltage across the 10k resistor will be 2.98V at 25°C, with a slope of 10mV/°C. The simplest way to convert this signal to a Centigrade scale is to subtract a constant 2.73V in software. Alternately, a hardware conversion can be used, as shown in Figure 3, using an LT1009 as a level shifter to offset the output to a Centigrade scale. The resistor (RSET) used to set the operating current of the LM134 in temperature sensing applications should have low temperature coefficient and good long term stability. A 30ppm/°C drift in the resistor will change the slope of the temperature sensor by 1%, assuming that the resistor is at the same temperature as the sensor, which is usually the case since the resistor should be located physically close to the LM134 to prevent errors due to wire resistance. A long term shift of 0.3% in the resistor will create a 1°C temperature error. The long term drift of the LM134 is typically much better than this, so stable resistors must be used for best long term performance. Calibration of the LM134 as a temperature sensor is extremely easy. Referring to Figure 2, calibration is achieved by trimming the termination resistor. This theoretically trims both zero and slope simultaneously for Centigrade and Fahrenheit applications. The initial errors in the LM134 are directly proportional to absolute temperature, just like the actual output. This allows the sensor to be trimmed at any temperature and have the slope error be corrected at the same time. Residual slope error is typically less than 1% after this single trim is completed. VS ≥ 5V V+ LM234-3 R TO DATA ACQUISITION SYSTEM 10mV/°K V– 9.53k RSET 226Ω I = 1µA/°K 1k CALIBRATE Figure 2 Kelvin Temperature Sensor 134 F02 LM134 Series U W U U APPLICATIO S I FOR ATIO If higher accuracy is required, a two point calibration technique can be used. In Figure 4, separate zero and slope trims are provided. Residual nonlinearity is now the limitation on accuracy. Nonlinearity of the LM134 in a 100°C span is typically less than 0.5°C. This particular method of trimming has the advantage that the slope trim does not interact with the zero trim. Trim procedure is to adjust for zero output with TSENSOR = 0°C, then trim slope for proper output at some convenient second temperature. No further trimming is required. The two trims shown in Figure 3 are still intended to be a “one point” temperature calibration, where the zero and the slope are trimmed at a single temperature. The LT1009 reference is adjusted to give 2.700V at node “a” at TSENSOR = 25°C. The 1k trimmer then adjusts the output for 0.25V, completing the calibration. If the calibration is to be done at a temperature other than 25°C , trim the LT1009 for 2.7025—(1µA)[TSENSOR (°C)](100Ω) at node “a”, then adjust the 1k trimmer for proper output. VS ≥ 4V V+ ≥ 5V V+ LM134-3 V+ R OUTPUT 10mV/°C V– 9.53k 1% R RSET 226Ω 226Ω* 1k SLOPE ADJ 100Ω “a” LM134-3 OUTPUT 10mV/°C V– 332k 1% 50k *LOW TC, STABLE RESISTOR LT1009 SLOPE TRIM 500k 11k* 1% 15k LT1009 ZERO TRIM 10k 10k 10k ZERO ADJ –15V –15V 134 F03 134 F04 Figure 4. Centigrade Temperature Sensor with 2 Point Trim Figure 3. Centigrade Temperature Sensor U TYPICAL APPLICATIO S Basic 2-Terminal Current Source Low Output Impedance Thermometer (Kelvin Output) VIN VIN ≥ 4.8V V+ LM334 V– RSET LM334 C1 0.1µF V– I+ V+ R 134 TA02 –VIN VIN V+ R ISET Zero Temperature Coefficient Current Source R3* 600Ω R1 230Ω 1% R VOUT = 10mV/°K ZOUT ≤ 100Ω V– RSET LM334 R2 10k 1% D1 1N457 R1* ≈10 RSET 134 TA03 –VIN *OUTPUT IMPEDANCE OF THE LM134 AT THE “R” PIN IS –RO APPROXIMATELY Ω, WHERE RO IS THE EQUIVALENT 16 EXTERNAL RESISTANCE CONNECTED TO THE V – PIN. THIS NEGATIVE RESISTANCE CAN BE REDUCED BY A FACTOR OF 5 OR MORE BY INSERTING AN EQUIVALENT RESISTOR IN SERIES WITH THE OUTPUT. 134 TA04 *SELECT RATIO OF R1 TO RSET TO OBTAIN ZERO DRIFT. I+ ≈2 ISET. 7 LM134 Series U TYPICAL APPLICATIO S Higher Output Current Low Input Voltage Reference Driver Low Output Impedance Thermometer VIN VIN ≥ VREF + 200mV VIN R1 15k 2N2905 R1 1.5k R2 300Ω C1 0.1 R1* 2N4250 V+ V+ C1* R LM334 RSET V– –VIN V+ VOUT = 10mV/°K ZOUT ≤ 2Ω R C1 0.0022 LM334 LM334 V R3 100Ω – Q1 2N4250 VOUT = VZ + 64mV AT 25°C IOUT ≤ 3mA LT1009 + VZ R – R2 120Ω V– R4 4.5k TA05 TA07 *SELECT R1 AND C1 FOR OPTIMUM STABILITY Micropower Bias TA06 Zener Biasing 1.2V Regulator with 1.8V Minimum Input VIN ≥ 1.8V VIN 100k VIN C1 0.001 LM4250 2N4250 R1 33k V+ VOUT = 1.2V IOUT ≤ 200µA R LM334 1N457** 1µA V+ V+ RSET R 68k LM334 R1* ≈6k 1% R LM134** VOUT VZ R2* 680Ω 1% V– V– RSET V– TA10 TA09 TA08 –VIN Alternate Trimming Technique *SELECT RATIO OF R1 TO R2 FOR ZERO TEMPERATURE DRIFT **LM134 AND DIODE SHOULD BE ISOTHERMAL Buffer for Photoconductive Cell High Precision Low TC Current Source + VIN ISET ≥ 50µA V+ V+ LM334 V– LM334 RSET R1* V– R 1.5V –VIN *FOR ±10% ADJUSTMENT, SELECT RSET 10% HIGH AND MAKE R1 ≈ 3RSET R1 6.8k LT1004-1.2 (1.235V) V– TA11 R LM334 V+ R TA12 R2* TA13 – *ISET = 1.37V + 10µA R2 ISET TC = 0.016%/°C + 33nA/°C REGULATION ≈ 0.001%/V 8 LM134 Series U TYPICAL APPLICATIO S Precision 10nA Current Source Micropower 5V Reference VIN = 6.5V TO 15V 15V V+ R3 1M R4 100MΩ IO 5.6k R1 2.7k V– R2 226k R LM334 R LM134 3 2 LT1004-1.2 (1.235V) 15V 6 LT1008 3 8 + VOUT = 5V 8 – 4 7 – 6 LM4250 LT1004-1.2 2 7 + 22M 150pF 3.01M 1% 1M 1% BUFFERED VOLTAGE OUTPUT TA15 200pF 4 IO = 10nA –15V ZO ≥ 1012Ω COMPLIANCE = –14V TO 12.5V TA14 FET Cascoding for Low Capacitance and/or Ultrahigh Output Impedance VIN VIN ISET V+ Q1* V+ LM334 R LM334 R V– RSET V– Q2* RSET ISET –VIN –VIN TA16 *SELECT Q1 OR Q2 TO ENSURE AT LEAST 1V ACROSS THE LM134. VP (1 – ISET/IDSS) ≥ 1.2V. W W SCHE ATIC DIAGRA V+ Q7 Q8 Q4 Q5 Q6 Q3 Q2 C1 50pF Q1 134 SD R V– 9 LM134 Series U PACKAGE DESCRIPTIO H Package 2-Lead and 3-Lead TO-46 Metal Can (Reference LTC DWG # 05-08-1340) 0.209 – 0.219 (5.309 – 5.537) 0.178 – 0.195 (4.521 – 4.953) REFERENCE PLANE 0.050 (1.270) TYP 0.085 – 0.105 (2.159 – 2.667) 0.100 (2.540) TYP 0.050 (1.270) TYP PIN 1 0.500 (12.700) MIN FOR 3-LEAD PACKAGE ONLY 45° * 0.028 – 0.048 (0.711 – 1.219) 0.036 – 0.046 (0.914 – 1.168) 0.025 (0.635) MAX H02/03(TO-46) 1098 0.016 – 0.021** (0.406 – 0.533) DIA *LEAD DIAMETER IS UNCONTROLLED BETWEEN THE REFERENCE PLANE AND 0.045" BELOW THE REFERENCE PLANE 0.016 – 0.024 **FOR SOLDER DIP LEAD FINISH, LEAD DIAMETER IS (0.406 – 0.610) OBSOLETE PACKAGE Z Package 3-Lead Plastic TO-92 (Similar to TO-226) (Reference LTC DWG # 05-08-1410) 0.180 ± 0.005 (4.572 ± 0.127) 0.060 ± 0.005 (1.524± 0.127) DIA 0.90 (2.286) NOM 0.180 ± 0.005 (4.572 ± 0.127) 0.500 (12.70) MIN 0.050 UNCONTROLLED (1.270) LEAD DIMENSION MAX 0.016 ± 0.003 (0.406 ± 0.076) 0.050 (1.27) BSC 0.060 ± 0.010 (1.524 ± 0.254) 0.140 ± 0.010 (3.556 ± 0.127) 10° NOM 10 5° NOM 0.015 ± 0.002 (0.381 ± 0.051) 0.098 +016/–0.04 (2.5 +0.4/–0.1) 2 PLCS Z3 (TO-92) 0401 TO-92 TAPE AND REEL REFER TO TAPE AND REEL SECTION OF LTC DATA BOOK FOR ADDITIONAL INFORMATION LM134 Series U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 1298 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 11 LM134 Series U TYPICAL APPLICATIO S In-Line Current Limiter Generating Negative Output Impedance RSET VIN R VIN V– V+ V+ R1* C1* R LM334 LM334 OP AMP V– –VIN TA17 RSET TA18 *ZOUT ≈ –16 • R1(R1/VIN MUST NOT EXCEED ISET). *USE MINIMUM VALUE REQUIRED TO ENSURE STABILITY OF PROTECTED DEVICE. THIS MINIMIZES INRUSH CURRENT TO A DIRECT SHORT. Ground Referred Fahrenheit Thermometer VIN ≥ 3V R4 56k C1 0.01 V+ R LM334 V– 2N4250 VOUT = 10mV/°F 10°F ≤ T ≤ 250°F R1 8.25k 1% VIN R5** R3* R2 100Ω 1% LT1009 2.5V* TA19 *SELECT R3 = VREF/583µA **SELECT FOR 1.2mA 12 Linear Technology Corporation 134sc LT/CP 1001 1.5K REV C • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 1991