LT1880 SOT-23, Rail-to-Rail Output, Picoamp Input Current Precision Op Amp U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®1880 op amp brings high accuracy input performance and rail-to-rail output swing to the SOT-23 package. Input offset voltage is trimmed to less than 150µV and the low drift maintains this accuracy over the operating temperature range. Input bias current is an ultra low 900pA maximum. Offset Voltage: 150µV Max Input Bias Current: 900pA Max Offset Voltage Drift: 1.2µV/°C Max Rail-to-Rail Output Swing Operates with Single or Split Supplies Open-Loop Voltage Gain: 1 Million Min 1.2mA Supply Current Slew Rate: 0.4V/µs Gain Bandwidth: 1.1MHz Low Noise: 13nV/√Hz at 1kHz Low Profile (1mm) ThinSOTTM Package The amplifier works on any total power supply voltage between 2.7V and 36V (fully specified from 5V to ±15V). Output voltage swings to within 55mV of the negative supply and 250mV of the positive supply, which makes the amplifier a good choice for low voltage single supply operation. U APPLICATIO S ■ ■ ■ ■ Slew rates of 0.4V/µs with a supply current of 1.2mA give superior response and settling time performance in a low power precision amplifier. Thermocouple Amplifiers Bridge Transducer Conditioners Instrumentation Amplifiers Battery-Powered Systems Photocurrent Amplifiers The LT1880 is available in a 5-lead SOT-23 package. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. U ■ TYPICAL APPLICATIO Precision Photodiode Amplifier Distribution of Input Offset Voltage C1 39pF 35 VS+ Vλ – LT1880 S1 + OUT VOUT = 0.1V/µA VS PERCENT OF UNITS (%) 30 R1 100k, 1% 25 20 15 10 5 – 1880 TA01 320µV OUTPUT OFFSET, WORST CASE OVER 0°C TO 70°C 60kHz BANDWIDTH 5.8µs RISE TIME, 10% TO 90%, 100mV OUTPUT STEP 52µVRMS OUTPUT NOISE, MEASURED ON A 100kHz BW VS = ±1.5V TO ±18V S1: SIEMENS INFINEON BPW21 PHOTODIODE (~580pF) 0 –140 –100 100 60 –60 –20 20 INPUT OFFSET VOLTAGE (µV) 140 1880 TA01b 1 LT1880 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART NUMBER Supply Voltage (V + to V –) ....................................... 40V Differential Input Voltage (Note 2) ......................... ±10V Input Voltage .................................................... V + to V – Input Current (Note 2) ........................................ ±10mA Output Short-Circuit Duration (Note 3) ............ Indefinite Operating Temperature Range (Note 4) .. – 40°C to 85°C Specified Temperature Range (Note 5) ... – 40°C to 85°C Maximum Junction Temperature .......................... 150°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C TOP VIEW V– LT1880CS5 LT1880IS5 5 V+ OUT 1 2 +IN 3 4 –IN S5 PART MARKING S5 PACKAGE 5-LEAD PLASTIC SOT-23 TJMAX = 150°C, θJA = 250°C/W LTUM LTVW Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, 0V; VCM = 2.5V unless otherwise noted. (Note 5) SYMBOL PARAMETER VOS Input Offset Voltage Input Offset Voltage Drift (Note 6) IOS IB CONDITIONS MIN 0°C < TA < 70°C –40°C < TA < 85°C ● ● 0°C < TA < 70°C –40°C < TA < 85°C ● ● 0°C < TA < 70°C –40°C < TA < 85°C ● ● 0°C < TA < 70°C –40°C < TA < 85°C ● ● Input Offset Current Input Bias Current TYP MAX UNITS 40 150 200 250 µV µV µV 0.3 0.3 1.2 1.2 µV/°C µV/°C 150 900 1200 1400 pA pA pA 150 900 1200 1500 pA pA pA Input Noise Voltage 0.1Hz to 10Hz 0.5 µVP-P en Input Noise Voltage Density f = 1kHz 13 nV/√Hz in Input Noise Current Density f = 1kHz 0.07 pA/√Hz RIN Input Resistance Differential Common Mode, VCM = 1V to 3.8V 380 210 MΩ GΩ CIN Input Capacitance 3.7 (V – pF (V+ – 1.2) VCM Input Voltage Range CMRR Common Mode Rejection Ratio 1V < VCM < 3.8V ● 116 135 dB PSRR Power Supply Rejection Ratio V – = 0V, VCM = 1.5V; 2.7V < V+ < 32V ● 110 135 dB 500 400 400 300 300 250 1600 ● Minimum Operating Supply Voltage AVOL Large Signal Voltage Gain ● ● RL = 1k; 1V < VOUT < 4V ● 2 Output Voltage Swing Low 2.4 ● RL = 10k; 1V < VOUT < 4V RL = 2k; 1V < VOUT < 4V VOL + 1.0) No Load ISINK = 100µA ISINK = 1mA ● ● ● 2.7 V V/mV V/mV V/mV V/mV V/mV V/mV 800 400 20 35 130 V 55 65 200 mV mV mV LT1880 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = 5V, 0V; VCM = 2.5V unless otherwise noted. (Note 5) SYMBOL PARAMETER CONDITIONS VOH Output Voltage Swing High (Referred to V+) V+ = 5V; No Load IS Supply Current per Amplifier MIN ● ● ● V+ = 5V; ISOURCE = 100µA V+ = 5V; ISOURCE = 1mA V+ = 3V TYP MAX UNITS 130 150 220 250 270 380 mV mV mV 1.2 1.8 2.2 mA mA 1.2 1.9 2.3 mA mA 1.35 2 2.4 mA mA ● V+ = 5V ● V+ = 12V ● ISC Short-Circuit Current VOUT Short to GND VOUT Short to V+ GBW Gain-Bandwidth Product f = 20kHz tS Settling Time 0.01%, VOUT = 1.5V to 3.5V AV = –1, RL = 2k FPBW Full Power Bandwidth (Note 7) VOUT = 4VP-P THD Total Harmonic Distortion and Noise VO = 2VP-P, AV = –1, f = 1kHz, Rf = 1k, BW = 22kHz VO = 2VP-P, AV = 1, f = 1kHz, RL = 10k, BW = 22kHz SR+ Slew Rate Positive AV = –1 SR – Slew Rate Negative ● ● 10 10 18 20 mA mA 0.8 1.1 MHz 10 µs 32 kHz 0.002 0.0008 % % 0.25 0.2 0.4 ● V/µs V/µs 0.25 0.25 0.55 ● V/µs V/µs AV = –1 The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS= ±15V, VCM = 0V unless otherwise noted. (Note 5) SYMBOL PARAMETER VOS Input Offset Voltage Input Offset Voltage Drift (Note 6) IOS IB CONDITIONS MIN 0°C < TA < 70°C –40°C < TA < 85°C ● ● 0°C < TA < 70°C –40°C < TA < 85°C ● ● 0°C < TA < 70°C –40°C < TA < 85°C ● ● 0°C < TA < 70°C –40°C < TA < 85°C ● ● Input Offset Current Input Bias Current TYP MAX UNITS 40 150 200 250 µV µV µV 0.3 0.3 1.2 1.2 µV/°C µV/°C 150 900 1200 1400 pA pA pA 150 900 1200 1500 pA pA pA Input Noise Voltage 0.1Hz to 10Hz 0.5 µVP-P en Input Noise Voltage Density f = 1kHz 13 nV/√Hz in Input Noise Current Density f = 1kHz 0.07 pA/√Hz RIN Input Resistance Differential Common Mode, VCM = –13.5V to 13.5V 380 190 MΩ GΩ CIN Input Capacitance VCM Input Voltage Range CMRR Common Mode Rejection Ratio +PSRR –PSRR 3.7 pF ● –13.5 –13.5V < VCM < 13.5V ● 118 135 dB Positive Power Supply Rejection Ratio V– ● 110 135 dB Negative Power Supply Rejection Ratio V+ = 15V, VCM = 0V; –1.5V < V – < –18V ● 110 135 dB Minimum Operating Supply Voltage = –15V, VCM = 0V; 1.5V < V+ < 18V ● 13.5 ±1.2 ±1.35 V V 3 LT1880 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VS = ± 15V; VCM = 0V unless otherwise noted. (Note 5) SYMBOL PARAMETER CONDITIONS AVOL Large Signal Voltage Gain RL = 10k; –13.5V < VOUT < 13.5V ● RL = 2k; –13.5V < VOUT < 13.5V ● MIN TYP 1000 700 500 300 1600 MAX UNITS V/mV V/mV V/mV V/mV 1000 VOL Output Voltage Swing Low (Referred to VEE) No Load ISINK = 100µA ISINK = 1mA ● ● ● 25 35 130 65 75 200 mV mV mV VOH Output Voltage Swing High (Referred to VCC) No Load ISOURCE = 100µA ISOURCE = 1mA ● ● ● 185 195 270 350 370 450 mV mV mV IS Supply Current per Amplifier ● 1.5 1.8 2.3 2.8 mA mA ISC Short-Circuit Current VOUT Short to V – ● 10 10 25 25 mA mA ● 10 10 20 20 mA mA 9 kHz 1.1 MHz VOUT Short to V+ FPBW Full Power Bandwidth (Note 7) GBW Gain Bandwidth Product f = 20kHz THD Total Harmonic Distortion and Noise VO = 25VP-P, AV = –1, f = 100kHz, Rf = 10k, BW = 22kHz VO = 25VP-P, AV = 1, f = 100kHz, RL = 10k, BW = 22kHz SR+ Slew Rate Positive AV = –1 SR – Slew Rate Negative VOUT = 14VP-P 0.00029 0.00029 % % 0.25 0.2 0.4 ● V/µs V/µs 0.25 0.2 0.55 ● V/µs V/µs AV = –1 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The inputs are protected by back-to-back diodes. If the differential input voltage exceeds 10V, see Application Information, the input current should be limited to less than 10mA. Note 3: A heat sink may be required to keep the junction temperature below absolute maximum ratings. Note 4: The LT1880C and LT1880I are guaranteed functional over the operating temperature range of –40°C to 85°C. 4 0.8 Note 5: The LT1880C is guaranteed to meet specified performance from 0°C to 70°C and is designed, characterized and expected to meet specified performance from –40°C to 85°C but is not tested or QA sampled at these temperatures. The LT1880I is guaranteed to meet specified performance from –40°C to 85°C. Note 6: This parameter is not 100% tested. Note 7: Full power bandwidth is calculated from the slew rate. FPBW = SR/(2πVP) LT1880 U W TYPICAL PERFOR A CE CHARACTERISTICS Input Bias Current vs Common Mode Voltage Input Offset Voltage vs Temperature TA = 25°C TA = –40°C TA = 85°C 800 INPUT BIAS CURRENT (pA) 100 50 0 –50 –100 –150 600 400 IB – 200 0 –200 IB + –400 –600 5 25 45 65 85 105 125 TEMPERATURE (°C) VS = ±15V –1000 –15 –10 0 5 10 –5 COMMON MODE VOLTAGE (V) 1880 G01 IB+ –500 TA = –45°C TA = 25°C TA = 85°C INPUT BIAS CURRENT (pA) 150 IB– IB+ –1000 –14.6 TA = –40°C TA = 25°C TA = 85°C –13.8 –14.2 –13.4 COMMON MODE VOLTAGE (V) VS = ±15V IB – 100 50 0 –100 IB + –150 –200 –300 –50 –25 25 50 0 TEMPERATURE (°C) 75 CURRENT NOISE DENSITY (fA/√Hz) VOLTAGE NOISE DENSITY (nV/√Hz) VS = ±15V 4 3 2 VS = ±2.5V 1 0 1 2 3 4 TIME AFTER POWER ON (MIN) 5 1880 G05 TA = 25°C –1.5 1.5 TA = 25°C 1.0 TA = 85°C 0.5 TA = –40°C –10 –8 –6 –4 –2 0 2 4 6 OUTPUT CURRENT (mA) 100 8 10 1880 G04 en, in vs Frequency 1000 5 TA = 85°C –1.0 1880 G03 Warm Up Drift TA = 25°C TA = –40°C –0.5 –50 1880 G02B 6 14.6 Output Voltage Swing vs Load Current –250 –13.0 13.8 14.2 13.4 COMMON MODE VOLTAGE (V) 1880 G02A OUTPUT VOLTAGE SWING (V+) 200 500 –500 –1000 13.0 Input Bias Current vs Temperature VS = ±15V 0 15 OUTPUT VOLTAGE SWING (V–) 1000 INPUT BIAS CURRENT (pA) 0 1880 G02 Input Bias Current vs Common Mode Near VEE OFFSET VOLTAGE CHANGE (µV) 500 –800 –200 –55 –35 –15 0 VS = ±15V IB– 0.1 to 10Hz Noise VS = ±15V TA = 25°C NOISE VOLTAGE (0.2µV/DIV) INPUT OFFSET VOLTAGE (µV) 150 1000 1000 TEMPCO: –55°C TO 125°C 10 REPRESENTATIVE UNITS INPUT BIAS CURRENT (pA) 200 Input Bias Current vs Common Mode Near VCC CURRENT NOISE 100 VOLTAGE NOISE 10 VS = ±15V TA = 25°C 1 1 10 100 FREQUENCY (Hz) 1k 1880 G08 0 2 6 4 TIME (SEC) 8 10 1880 G09a 5 LT1880 U W TYPICAL PERFOR A CE CHARACTERISTICS PSRR vs Frequency Gain vs Frequency 140 160 VS = ±15V POWER SUPPLY REJECTION RATIO (dB) 0.01 to 1Hz Noise NOISE VOLTAGE (0.2µV/DIV) 120 100 GAIN (dB) 80 60 40 20 0 VS = ±15V TA = 25°C 60 40 TIME (SEC) 80 0.1 10 1 VOLTAGE GAIN (dB) 100 80 60 40 20 40 PHASE SHIFT 1M –10 5 20 10 25 15 SETTLING TIME (µs) 30 35 1880 G15 6 4 10 –20 GAIN 0 –40 –10 –60 –20 –80 0.1% 0.01% 2 0 –2 –4 0.01% 0.1% –8 –100 10M 100k 1M FREQUENCY (Hz) VS = ±15V AV = –1 –6 –10 0 5 10 35 15 20 25 30 SETTLING TIME (µs) 0.5 Slew Rate, Gain-Bandwidth Product and Phase Margin vs Power Supply VS = ±15V SLEW RATE 0.4 68 0.3 64 ΦM 1.14 60 1.12 1.10 –50 GBW –25 25 50 0 TEMPERATURE (°C) 75 40 1880 G14 100 1880 G16 SLEW RATE (V/µs) SLEW RATE (V/µs) OUTPUT STEP (V) –8 100k 1M 1880 G13 GAIN BANDWIDTH PRODUCT (MHz) 0.01% 10 100 1k 10k FREQUENCY (Hz) 0.5 TA = 25°C 0.4 SLEW RATE 64 0.3 ΦM 60 1.12 56 1.11 GBW 1.10 0 2.5 7.5 10 5 POWER SUPPLY (±V) 12.5 15 1880 G17 PHASE MARGIN (DEG) –2 0 6 40 0 0 0.1% 60 PHASE MARGIN (DEG) 0.01% 2 –6 8 Slew Rate, Gain-Bandwidth Product and Phase Margin vs Temperature VS = ±15V AV = 1 –4 80 20 Settling Time vs Output Step 4 10 20 1880 G12 0.1% 100 30 –30 10k 0 100k 1 1880 G11 OUTPUT STEP (V) 50 6 20 Settling Time vs Output Step VS = ±15V 60 120 8 40 0 0.1 PHASE SHIFT (DEG) POWER SUPPLY REJECTION RATIO (dB) VS = ±15V 100 1k 10k FREQUENCY (Hz) +PSRR 60 Gain and Phase vs Frequency 70 140 10 –PSRR 80 1880 G10 CMRR vs Frequency 160 10 100 100 1k 10k 100k 1M 10M FREQUENCY (Hz) 1880 G09b 1 120 –40 100 GAIN BANDWIDTH PRODUCT (MHz) 20 0 –20 VS = ±15V 140 LT1880 U W TYPICAL PERFOR A CE CHARACTERISTICS Gain vs Frequency with CLOAD, AV = –1 Gain vs Frequency with CLOAD, AV = 1 Output Impedance vs Frequency 100 10 0 0 1000pF –10 500pF 500pF 0pF GAIN (dB) GAIN (dB) 1000pF –20 –10 0pF –20 VS = ±15V 10 AV = 100 AV = 10 1.0 AV = 1 0.1 –30 –30 –40 OUTPUT IMPEDANCE (Ω) 10 –40 10k 1k 100k 1M FREQUENCY (Hz) 10M 100M 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M 0.01 0.01 0.1 1.0 10 FREQUENCY (MHz) 1880 G19 1880 G18 Total Harmonic Distortion + Noise vs Frequency 100 1880 G17A Small Signal Response Small Signal Response 10 THD + NOISE (%) VS = 5V, 0V VCM = 2.5V R = R = 1k 1.0 V f =G 2V OUT P-P RL = 10k VOUT (20mV/DIV) VOUT (20mV/DIV) 0.1 0.01 AV = –1 0.001 AV = –1 NO LOAD AV = 1 0.0001 10 100 1k 10k FREQUENCY (Hz) TIME (2µs/DIV) AV = 1 NO LOAD 1880 G20 TIME (2µs/DIV) 1880 G21 100k 1880 G17B Small Signal Response Large Signal Response Large Signal Response VOUT (5V/DIV) VOUT (20mV/DIV) AV = 1 CL = 500pF TIME (2µs/DIV) 1880 G22 VOUT (5V/DIV) AV = –1 TIME (50µs/DIV) 1880 G23 AV = 1 TIME (50µs/DIV) 1880 G24 7 LT1880 U W U U APPLICATIO S I FOR ATIO Preserving Input Precision Preserving the input voltage accuracy of the LT1880 requires that the applications circuit and PC board layout do not introduce errors comparable to or greater than the 40µV offset. Temperature differentials across the input connections can generate thermocouple voltages of 10’s of microvolts. PC board layouts should keep connections to the amplifier’s input pins close together and away from heat dissipating components. Air currents across the board can also generate temperature differentials. The extremely low input bias currents, 150pA, allow high accuracy to be maintained with high impedance sources and feedback networks. The LT1880’s low input bias currents are obtained by using a cancellation circuit onchip. This causes the resulting IBIAS+ and IBIAS– to be uncorrelated, as implied by the lOS specification being comparable to IBIAS. The user should not try to balance the input resistances in each input lead, as is commonly recommended with most amplifiers. The impedance at either input should be kept as small as possible to minimize total circuit error. PC board layout is important to insure that leakage currents do not corrupt the low IBIAS of the amplifier. In high precision, high impedance circuits, the input pins should be surrounded by a guard ring of PC board interconnect, with the guard driven to the same common mode voltage as the amplifier inputs. Input Common Mode Range The LT1880 output is able to swing nearly to each power supply rail, but the input stage is limited to operating between V – + 1V and V + – 1.2V. Exceeding this common 8 mode range will cause the gain to drop to zero, however no gain reversal will occur. Input Protection The inverting and noninverting input pins of the LT1880 have limited on-chip protection. ESD protection is provided to prevent damage during handling. The input transistors have voltage clamping and limiting resistors to protect against input differentials up to 10V. Short transients above this level will also be tolerated. If the input pins can see a sustained differential voltage above 10V, external limiting resistors should be used to prevent damage to the amplifier. A 1k resistor in each input lead will provide protection against a 30V differential voltage. Capacitive Loads The LT1880 can drive capacitive loads up to 600pF in unity gain. The capacitive load driving capability increases as the amplifier is used in higher gain configurations, see the graph labled Capacitive Load Response. Capacitive load driving may be increased by decoupling the capacitance from the output with a small resistance. Capacitance Load Response 30 VS = ±15V TA = 25°C 25 OVERSHOOT (%) The LT1880 single op amp features exceptional input precision with rail-to-rail output swing. Slew rate and small signal bandwidth are superior to other amplifiers with comparable input precision. These characteristics make the LT1880 a convenient choice for precision low voltage systems and for improved AC performance in higher voltage precision systems. Obtaining beneficial advantage of the precision inherent in the amplifier depends upon proper applications circuit design and board layout. 20 15 AV = 1 10 5 0 AV = 10 10 100 1000 CAPACITIVE LOAD (pF) 10000 1880 G25 Getting Rail-to-Rail Operation without Rail-to-Rail Inputs The LT1880 does not have rail-to-rail inputs, but for most inverting applications and noninverting gain applications, this is largely inconsequential. Figure 1 shows the basic op amp configurations, what happens to the op amp inputs, and whether or not the op amp must have rail-to-rail inputs. LT1880 U W U U APPLICATIO S I FOR ATIO + VREF RG + VIN – VIN + VIN – – RF RF RG VREF INVERTING: AV = –RF/RG OP AMP INPUTS DO NOT MOVE, BUT ARE FIXED AT DC BIAS POINT VREF NONINVERTING: AV = 1 + RF/RG INPUTS MOVE BY AS MUCH AS VIN, BUT THE OUTPUT MOVES MORE INPUT DOES NOT HAVE TO BE RAIL-TO-RAIL INPUT MAY NOT HAVE TO BE RAIL-TO-RAIL NONINVERTING: AV = +1 INPUTS MOVE AS MUCH AS OUTPUT INPUT MUST BE RAIL-TORAIL FOR OVERALL CIRCUIT RAIL-TO-RAIL PERFORMANCE Figure 1. Some Op Amp Configurations Do Not Require Rail-to Rail Inputs to Achieve Rail-to-Rail Outputs The circuit of Figure 2 shows an extreme example of the inverting case. The input voltage at the 1M resistor can swing ±13.5V and the LT1880 will output an inverted, divided-by-ten version of the input voltage. The input accuracy is limited by the resistors to 0.2%. Output referred, this error becomes 2.7mV. The 40µV input offset voltage contribution, plus the additional error due to input bias current times the ~100k effective source impedance, contribute only negligibly to error. 1.5V ±13.5V SWINGS WELL OUTSIDE SUPPLY RAILS ±1.35V OUTPUT SWING + LT1880 Precision Photodiode Amplifier Photodiode amplifiers usually employ JFET op amps because of their low bias current; however, when precision is required, JFET op amps are generally inadequate due to their relatively high input offset voltage and drift. The LT1880 provides a high degree of precision with very low bias current (IB = 150pA typical) and is therefore applicable to this demanding task. Figure 3 shows an LT1880 configured as a transimpedance photodiode amplifier. CF WORST-CASE OUTPUT OFFSET ≤196µV AT 25°C ≤262µV 0°C TO 70°C ≤323µV –40°C TO 85°C RF 51.1k 5V – VIN – 1M, 0.1% PHOTODIODE (SEE TEXT) CD 100k, 0.1% –1.5V Figure 2. Extreme Inverting Case: Circuit Operates Properly with Input Voltage Swing Well Outside Op Amp Supply Rails. LT1880 + OUT –5V Figure 3. Precision Photodiode Amplifier 9 LT1880 U W U U APPLICATIO S I FOR ATIO The transimpedance gain is set to 51.1kΩ by RF. The feedback capacitor, CF, may be as large as desired where response time is not an issue, or it may be selected for maximally flat response and highest possible bandwidth given a photodiode capacitance CD. Figure 4 shows a chart of CF and rise time versus CD for maximally flat response. Total output offset is below 262µV, worst-case, over temperature (0°C–70°C). With a 5V output swing, this guarantees a minimum 86dB dynamic range over temperature (0°C–70°C), and a full-scale photodiode current of 98µA. Single-Supply Current Source for Platinum RTD The precision, low bias current input stage of the LT1880 makes it ideal for precision integrators and current sources. Figure 5 shows the LT1880 providing a simple precision current source for a remote 1kΩ RTD on a 4-wire connection. The LT1634 reference places 1.25V at the noninverting input of the LT1880, which then maintains its inverting input at the same voltage by driving 1mA of current through the RTD and the total 1.25kΩ of resistance set by R1 and R2. Imprecise components R4 and C1 ensure circuit stability, which would otherwise be excessively dependant on the cable characteristics. R5 is also noncritical and is included to improve ESD immunity and decouple any cable capacitance from the LT1880’s output. The 4-wire cable allows Kelvin sensing of the RTD voltage while excluding the cable IR drops from the voltage reading. With 1mA excitation, a 1kΩ RTD will have 1V across it at 0°C, and +3.85mV/°C temperature response. This voltage can be easily read in myriad ways, with the best method depending on the temperature region to be emphasized and the particular ADC that will be reading the voltage. R5 180Ω, 5% + RISE TIME (µs), CF (pF) 100 1kΩ AT 0°C RTD* CF 10 VOUT = 1.00V AT 0°C + 3.85mV/°C – –50°C TO 600°C R4 1k, 5% R1 1.24K 0.1% RISE TIME 1 100mV OUTPUT STEP 0.1 0.1 1 10 CD (pF) 100 R2 10Ω 1% C1 0.1µF 5V – + LT1880 R3 150k, 1% 1000 LT1634ACS8 5V -1.25 Figure 4. Feedback CF and Rise Time vs Photodiode CD *OMEGA F3141 1kΩ, 0.1% PLATINUM RTD (800) 826-6342 Figure 5. Single Supply Current Source for Platinum RTD 10 LT1880 W W SI PLIFIED SCHE ATIC V+ 5 R3 R5 R4 R27 CX1 100µA Q41 Q23 Q6 Q38 RCM1 Q5 CM1 Q4 Q3 Q47 B A Q59 Q58 1 OUT 35µA Q48 Q12 RCM2 CM2 Q16 V– R1 500Ω CM3 Q46 C B A –IN 4 +IN 3 Q14 7µA R2 500Ω Q24 Q1 Q2 Q20 R22 500Ω 10µA Q45 Q44 Q7 Q8 R38 21µA V– 2 1880 SD U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic SOT-23 (Reference LTC DWG # 05-08-1633) (Reference LTC DWG # 05-08-1635) 2.80 – 3.10 (.110 – .118) (NOTE 3) A SOT-23 (Original) .90 – 1.45 (.035 – .057) SOT-23 (ThinSOT) 1.00 MAX (.039 MAX) A1 .00 – .15 (.00 – .006) .01 – .10 (.0004 – .004) A2 .90 – 1.30 (.035 – .051) .80 – .90 (.031 – .035) L .35 – .55 (.014 – .021) .30 – .50 REF (.012 – .019 REF) 2.60 – 3.00 (.102 – .118) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN (INCHES) 3. DRAWING NOT TO SCALE 4. DIMENSIONS ARE INCLUSIVE OF PLATING 5. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 6. MOLD FLASH SHALL NOT EXCEED .254mm 7. PACKAGE EIAJ REFERENCE IS: SC-74A (EIAJ) FOR ORIGINAL JEDEL MO-193 FOR THIN 1.50 – 1.75 (.059 – .069) (NOTE 3) PIN ONE .95 (.037) REF .25 – .50 (.010 – .020) (5PLCS, NOTE 2) .20 (.008) A DATUM ‘A’ L .09 – .20 (.004 – .008) (NOTE 2) A2 1.90 (.074) REF A1 S5 SOT-23 0401 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 LT1880 U TYPICAL APPLICATIO All SOT-23 JFET Input Transimpedance Photodiode Amplifier C4 1.2pF V+ R5 100k, 1% J1 1k TIME DOMAIN RESPONSE TRIM C5 1.2pF R2 220k, 5% C1 0.01µF + R7 47Ω 5% U1 LT1880 R1 220k, 5% – R3 10k 5% C2 0.1µF S1 N1 R6 47Ω 5% C3 0.01µF V– – U2 LT1806 VOUT + J1: ON SEMI MMBF4416 JFET N1:ON SEMI MMBT3904 NPN S1: SIEMENS/INFINEON SFH213FA PHOTODIODE (~3pF) VSUPPLY = ±5V BANDWIDTH = 7MHz NOISE FIGURE = 2dB AT 100kHz, 25°C AZ = 100kΩ 1880 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1782 Rugged, General Purpose SOT-23 Op Amp Rail-to-Rail I/O LT1792 Low Noise JFET Op Amp 4.2nV/√Hz LT1881/LT1882 Dual/Quad Precision Op Amps 50µV VOS(MAX), 200pA IB(MAX) Rail-to-Rail Output LTC2050 Zero Drift Op Amp in SOT-23 3µV VOS(MAX), Rail-to-Rail Output 12 Linear Technology Corporation 1880f LT/TP 0801 2K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2001