LT1792 Low Noise, Precision, JFET Input Op Amp U FEATURES ■ ■ ■ ■ ■ ■ DESCRIPTIO The LT®1792 achieves a new standard of excellence in noise performance for a JFET op amp. The 4.2nV/√Hz voltage noise combined with low current noise and picoampere bias currents make the LT1792 an ideal choice for amplifying low level signals from high impedance capacitive transducers. 100% Tested Low Voltage Noise: 6nV/√Hz Max A Grade 100% Temperature Tested Voltage Gain: 1.2 Million Min Offset Voltage Over Temp: 800µV Max Gain-Bandwidth Product: 5.6MHz Typ Guaranteed Specifications with ±5V Supplies U APPLICATIO S ■ ■ ■ ■ ■ ■ Photocurrent Amplifiers Hydrophone Amplifiers High Sensitivity Piezoelectric Accelerometers Low Voltage and Current Noise Instrumentation Amplifier Front Ends Two and Three Op Amp Instrumentation Amplifiers Active Filters The LT1792 is unconditionally stable for gains of 1 or more, even with load capacitances up to 1000pF. Other key features are 600µV VOS and a voltage gain of over 4 million. Each individual amplifier is 100% tested for voltage noise, slew rate and gain bandwidth. The design of the LT1792 has been optimized to achieve true precision performance with an industry standard pinout in the SO-8 package. Specifications are also provided for ±5V supplies. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO Low Noise Hydrophone Amplifier with DC Servo R3 3.9k 5V TO 15V 2 – 40 7 LT1792 3 C1* 6 + R2 200Ω OUTPUT C2 0.47µF 4 –5V TO –15V R6 100k 6 2 3 R5 1M LT1097 R7 1M DC OUTPUT ≤ 2.5mV FOR TA < 70°C OUTPUT VOLTAGE NOISE = 128nV/√Hz AT 1kHz (GAIN = 20) C1 ≈ CT ≈ 100pF TO 5000pF; R4C2 > R8CT; *OPTIONAL + R8 100M – CT HYDROPHONE R4 1M PERCENT OF UNITS (%) R1* 100M 1kHz Input Noise Voltage Distribution VS = ±15V TA = 25°C 270 OP AMPS TESTED 30 20 10 0 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 INPUT VOLTAGE NOISE (nV/√Hz) 1792 TA02 1792 TA01 1 LT1792 W W W AXI U U ABSOLUTE RATI GS (Note 1) Supply Voltage ..................................................... ±20V Differential Input Voltage ...................................... ±40V Input Voltage (Equal to Supply Voltage) ............... ±20V Output Short-Circuit Duration ........................ Indefinite Operating Temperature Range ............... – 40°C to 85°C Specified Temperature Range Commercial (Note 8) ......................... – 40°C to 85°C Industrial ........................................... – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec) ................ 300°C W U U PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW VOS ADJ 1 8 NC –IN A 2 + +IN A 3 V – A 7 V 6 OUT 5 VOS ADJ 4 LT1792ACN8 LT1792CN8 LT1792AIN8 LT1792IN8 ORDER PART NUMBER TOP VIEW VOS ADJ 1 8 NC –IN A 2 7 V+ +IN A 3 V – A LT1792ACS8 LT1792CS8 LT1792AIS8 LT1792IS8 6 OUT 5 VOS ADJ 4 N8 PACKAGE 8-LEAD PDIP S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 140°C, θJA = 130°C/W TJMAX = 160°C, θJA = 190°C/W S8 PART MARKING 1792A 1792 1792AI 1792I Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS TA = 25°C, VS = ±15V, VCM = 0V, unless otherwise noted. (Note 9) LT1792AC/LT1792AI MIN TYP MAX LT1792C/LT1792I MIN TYP MAX VS = ± 5V 0.2 0.4 0.6 1.0 0.2 0.4 0.8 1.3 mV mV Input Offset Current Warmed Up (Note 3) 100 400 100 400 pA IB Input Bias Current Warmed Up (Note 3) 300 800 300 800 pA en Input Noise Voltage 0.1Hz to 10Hz 2.4 2.4 µVP-P Input Noise Voltage Density fO = 10Hz fO = 1000Hz 8.3 4.2 6.0 8.3 4.2 6.0 nV/√Hz nV/√Hz fO = 10Hz, fO = 1000Hz (Note 4) 10 10 1011 1011 1010 1011 1011 1010 Ω Ω Ω 14 27 14 27 pF pF SYMBOL PARAMETER VOS Input Offset Voltage IOS in Input Noise Current Density RIN Input Resistance Differential Mode Common Mode CIN Input Capacitance VCM Input Voltage Range (Note 5) CMRR Common Mode Rejection Ratio PSRR Power Supply Rejection Ratio 2 CONDITIONS (Note 2) VCM = –10V to 8V VCM = 8V to 11V VS = ±5V UNITS fA/√Hz 13.0 –10.5 13.5 –11.0 13.0 –10.5 13.5 –11.0 V V VCM = –10V to 13V 85 105 82 100 dB VS = ±4.5V to ±20V 88 105 83 98 dB LT1792 ELECTRICAL CHARACTERISTICS TA = 25°C, VS = ±15V, VCM = 0V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS LT1792AC/LT1792AI MIN TYP MAX LT1792C/LT1792I MIN TYP MAX AVOL Large-Signal Voltage Gain VO = ±12V, RL = 10k VO = ±10V, RL = 1k 1200 600 4800 4000 1000 500 4500 3000 V/mV V/mV VOUT Output Voltage Swing RL = 10k RL = 1k ±13.0 ±12.0 ±13.2 ±12.3 ±13.0 ±12.0 ±13.2 ±12.3 V V SR Slew Rate RL ≥ 2k (Note 7) 2.3 3.4 2.3 3.4 V/µs GBW Gain-Bandwidth Product fO = 100kHz 4.0 5.6 4.0 5.6 MHz IS Supply Current Offset Voltage Adjustment Range VS = ±5V 4.2 4.2 RPOT (to VEE) = 10k 10 5.20 5.15 4.2 4.2 5.20 5.15 10 UNITS mA mA mV The ● denotes specifications which apply over the temperature range 0°C ≤ TA ≤ 70°C. VS = ±15V, VCM = 0V, unless otherwise noted. (Note 9) SYMBOL PARAMETER VOS Input Offset Voltage ∆VOS ∆Temp Average Input Offset Voltage Drift IOS CONDITIONS (Note 2) MIN LT1792AC TYP MAX MIN LT1792C TYP MAX UNITS VS = ± 5V ● ● 0.4 0.6 0.8 1.2 0.8 1.2 2.7 3.2 mV mV (Note 6) ● 4 10 7 40 µV/°C Input Offset Current ● 180 500 180 500 pA IB Input Bias Current ● 500 1800 500 1800 pA VCM Input Voltage Range ● ● 12.9 –10.0 13.4 –10.8 CMRR Common Mode Rejection Ratio VCM = –10V to 12.9V ● 81 104 79 99 dB PSRR Power Supply Rejection Ratio VS = ±4.5V to ±20V ● 85 99 81 97 dB AVOL Large-Signal Voltage Gain VO = ±12V, RL = 10k VO = ±10V, RL = 1k ● ● 900 500 3600 2600 800 400 3400 2400 VOUT Output Voltage Swing RL = 10k RL = 1k ● ● SR Slew Rate RL ≥ 2k (Note 7) ● 2.1 3.1 2.1 3.1 V/µs GBW Gain-Bandwidth Product fO = 100kHz ● 3.2 4.5 3.2 4.5 MHz IS Supply Current VS = ±5V ● ● 12.9 –10.0 ±12.9 ±13.2 ±11.9 ±12.15 4.2 4.2 13.4 –10.8 V V V/mV V/mV ±12.9 ±13.2 ±11.9 ±12.15 5.30 5.25 4.2 4.2 V V 5.30 5.25 mA mA 3 LT1792 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the temperature range – 40°C ≤ TA ≤ 85°C. VS = ±15V, VCM = 0V, unless otherwise noted. (Notes 8, 9) LT1792AC/LT1792AI MIN TYP MAX LT1792C/LT1792I MIN TYP MAX VS = ±5V ● ● 0.5 0.8 1.0 1.4 1.2 1.5 3.7 4.2 mV mV (Note 6) ● 4 10 7 40 µV/°C Input Offset Current ● 300 800 300 800 pA IB Input Bias Current ● 1200 4000 1200 4000 pA VCM Input Voltage Range ● ● 12.6 –10.0 13.0 –10.5 12.6 –10.0 13.0 –10.5 V V CMRR Common Mode Rejection Ratio VCM = –10V to 12.6V ● 80 103 78 98 dB PSRR Power Supply Rejection Ratio VS = ±4.5V to ± 20V ● 83 98 79 96 AVOL Large-Signal Voltage Gain VO = ±12V, RL = 10k VO = ±10V, RL = 1k ● ● 850 400 3300 2200 750 300 3000 2000 V/mV V/mV VOUT Output Voltage Swing RL = 10k RL = 1k ● ● ±12.8 ±11.8 ±13.1 ±12.1 ±12.8 ±11.8 ±13.1 ±12.1 V V SR Slew Rate RL ≥ 2k ● 2.0 3.0 2.0 3.0 V/µs GBW Gain-Bandwidth Product fO = 100kHz ● 2.9 4.3 2.9 4.3 MHz IS Supply Current VS = ±5V ● ● SYMBOL PARAMETER VOS Input Offset Voltage ∆VOS ∆Temp Average Input Offset Voltage Drift IOS CONDITIONS (Note 2) Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Typical parameters are defined as the 60% yield of parameter distributions of individual amplifiers. Note 3: Warmed-up IB and IOS readings are extrapolated to a chip temperature of 32°C from 25°C measurements and 32°C characterization data. Note 4: Current noise is calculated from the formula: in = (2qIB)1/2 where q = 1.6 • 10 –19 coulomb. The noise of source resistors up to 200M swamps the contribution of current noise. Note 5: Input voltage range functionality is assured by testing offset voltage at the input voltage range limits to a maximum of 2.3mV (A grade), to 2.8mV (C grade). 4 4.2 4.2 5.40 5.35 4.2 4.2 UNITS dB 5.40 5.35 mA mA Note 6: This parameter is not 100% tested. Note 7: Slew rate is measured in AV = – 1; input signal is ±7.5V, output measured at ±2.5V. Note 8: The LT1792AC and LT1792C are guaranteed to meet specified performance from 0°C to 70°C and are designed, characterized and expected to meet these extended temperature limits, but are not tested at – 40°C and 85°C. The LT1792I is guaranteed to meet the extended temperature limits. The LT1792AC and LT1792AI grade are 100% temperature tested for the specified temperature range. Note 9: The LT1792 is measured in an automated tester in less than one second after application of power. Depending on the package used, power dissipation, heat sinking, and air flow conditions, the fully warmed-up chip temperature can be 10°C to 50°C higher than the ambient temperature. LT1792 U W TYPICAL PERFOR A CE CHARACTERISTICS Voltage Noise vs Chip Temperature Voltage Noise vs Frequency VOLTAGE NOISE (1µV/DIV) RMS VOLTAGE NOISE DENSITY (nV/√Hz) 100 10 VS = ±15V TA = 25°C 9 VOLTAGE NOISE (AT 1kHz) (nV/√Hz) 0.1Hz to 10Hz Voltage Noise 10 1/f CORNER 30Hz 8 7 6 5 4 3 2 1 1 2 0 6 4 TIME (SEC) 8 1 10 10 100 1k FREQUENCY (Hz) 300 200 BIAS CURRENT 100 OFFSET CURRENT V+ VS = ±15V 30 10 3 1 IB 0.3 IOS 0.1 0.03 100 125 1792 G22 60 40 20 0 100k 1M FREQUENCY (Hz) 4.0 3.5 3.0 10M 1792 G06 V – = – 5V TO – 20V –20 60 100 20 TEMPERATURE (°C) 140 1792 G05 Voltage Gain vs Frequency 180 TA = 25°C 160 100 140 VOLTAGE GAIN (dB) 80 10k –1.5 V –+ 2.0 – 60 120 POWER SUPPLY REJECTION RATIO (dB) COMMON MODE REJECTION RATIO (dB) TA = 25°C VS = ± 15V V + = 5V TO 20V – 2.0 Power Supply Rejection Ratio vs Frequency 120 1k –1.0 1792 G04 Common Mode Rejection Ratio vs Frequency 100 0 – 0.5 2.5 0.01 – 75 – 50 – 25 0 25 50 75 TEMPERATURE (°C) 15 Common Mode Limit vs Temperature COMMON MODE LIMIT REFERRED TO POWER SUPPLY (V) INPUT BIAS AND OFFSET CURRENT (nA) INPUT BIAS AND OFFSET CURRENTS (pA) 100 10 –10 –5 0 5 COMMON-MODE RANGE (V) 1792 G03 Input Bias and Offset Current vs Chip Temperature TA = 25°C VS = ±15V NOT WARMED UP 100 125 1792 G02 Input Bias and Offset Current Over the Common Mode Range 0 –15 0 –75 –50 –25 0 25 50 75 TEMPERATURE (°C) 10k 1792 G01 400 VS = ±15V 80 +PSRR 60 –PSRR 40 120 100 80 60 40 20 20 0 0 10 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 1792 G07 – 20 0.01 1 10k 100 FREQUENCY (Hz) 1M 100M 1792 G08 5 LT1792 U W TYPICAL PERFOR A CE CHARACTERISTICS Gain and Phase Shift vs Frequency TA = 25°C VS = ±15V CL = 10pF 100 120 30 140 20 GAIN 10 160 0 180 1 10 FREQUENCY (MHz) 0.1 AV = 1 CL = 10pF VS = ±15V, ±5V 200 100 –10 5V/DIV PHASE PHASE SHIFT (DEG) VOLTAGE GAIN (dB) 40 Large-Signal Transient Response Small-Signal Transient Response 80 20mV/DIV 50 1µs/DIV 1792 G10 AV = 1 CL = 10pF RL = 2k VS = ±15V 1792 G11 5µs/DIV 1792 G09 Output Voltage Swing vs Load Current 40 –55°C – 1.4 –1.6 OVERSHOOT (%) VS = ±5V TO ±20V 2.0 1.8 125°C 1.6 30 20 10 –55°C 1.2 SR 6 3 GBWP 2 4 0 0.1 1 100 1000 10 CAPACITIVE LOAD (pF) TOTAL HARMONIC DISTROTION + NOISE (%) SO-8 PACKAGE 60 45 N8 PACKAGE 30 15 0 0 25 50 75 – 75 – 50 – 25 0 TEMPERATURE (°C) 5 2 3 4 1 TIME AFTER POWER ON (MINUTES) 6 1792 G15 0 100 125 1792 G14 THD and Noise vs Frequency for Noninverting Gain VS = ±15V TA = 25°C 75 10000 1792 G13 Warm-Up Drift 90 2 AV = 10 1792 G12 CHANGE IN OFFSET VOLTAGE (µV) 8 4 1 25°C V – +1.0 –10 –8 –6 –4 –2 0 2 4 6 8 10 ISINK ISOURCE OUTPUT CURRENT (mA) 6 10 AV = 1 1.4 0 12 VS = ± 15V 5 1 ZL = 2k 15pF VO = 20VP-P AV = 1, 10, 100 MEASUREMENT BANDWIDTH = 10Hz TO 80kHz 0.1 AV = 100 0.01 AV = 10 0.001 AV = 1 NOISE FLOOR THD and Noise vs Frequency for Inverting Gain TOTAL HARMONIC DISTROTION + NOISE (%) OUTPUT VOLTAGE SWING (V) –1.2 6 VS = ±15V TA = 25°C RL ≥ 10k VO = 100mVP-P AV = 10 RF = 10k CF = 20pF SLEW RATE (V/µs) 50 125°C 25°C GAIN-BANDWIDTH PRODUCT (fO = 100kHz) (MHz) V + – 0.8 –1.0 Slew Rate and Gain-Bandwidth Product vs Temperature Capacitive Load Handling 1 ZL = 2k 15pF VO = 20VP-P AV = – 1, – 10, – 100 MEASUREMENT BANDWIDTH = 10Hz TO 80kHz 0.1 0.01 AV = – 100 AV = – 10 0.001 AV = – 1 NOISE FLOOR 0.0001 0.0001 20 100 1k FREQUENCY (Hz) 10k 20k 1792 G16 20 100 1k FREQUENCY (Hz) 10k 20k 1792 G17 LT1792 U W TYPICAL PERFOR A CE CHARACTERISTICS THD and Noise vs Output Amplitude for Inverting Gain 1 TOTAL HARMONIC DISTORTION + NOISE (%) TOTAL HARMONIC DISTORTION + NOISE (%) THD and Noise vs Output Amplitude for Noninverting Gain ZL = 2k 15pF, fO = 1kHz AV = 1, 10, 100 MEASUREMENT BANDWIDTH = 10Hz TO 22kHz 0.1 AV = 100 0.01 AV = 10 0.001 AV = 1 0.0001 0.3 1 10 OUTPUT SWING (VP-P) 1 ZL = 2k 15pF, fO = 1kHz AV = – 1, – 10, – 100 MEASUREMENT BANDWIDTH = 10Hz TO 22kHz 0.1 AV = –100 0.01 AV = –10 0.001 AV = –1 0.0001 30 0.3 1 10 OUTPUT SWING (VP-P) 30 1792 G18 1792 G19 Short-Circuit Output Current vs Temperature 40 Supply Current vs Temperature 5 VS = ±15V SUPPLY CURRENT (mA) OUTPUT CURRENT (mA) 35 30 SINK SOURCE 25 20 VS = ±15V 4 VS = ± 5V 15 10 – 75 – 50 – 25 0 25 50 75 TEMPERATURE (°C) 3 – 75 – 50 – 25 0 25 50 75 TEMPERATURE (°C) 100 125 100 125 1792 G20 U W U UO APPLICATI 1792 G21 S I FOR ATIO The LT1792 may be inserted directly into OPA124, AD743, AD745, AD645, AD544 and AD820 sockets with improved noise performance. Offset nulling will be compatible with these devices with the wiper of the potentiometer tied to the negative supply (Figure 1a). No appreciable change in offset voltage drift with temperature will occur when the device is nulled with a potentiometer ranging from 10k to 200k. Finer adjustments can be made with resistors in series with the potentiometer (Figure 1b). Being a low voltage noise JFET op amp, the LT1792 can replace many bipolar op amps that are used in amplifying low level signals from high impedance transducers. The 15V 15V 2 – 2 7 – 7 6 6 3 + 3 4 5 ∆VOS = ±10mV 1 4 5 1792 F01a ∆VOS = ±1mV 1 10k 50k – 15V + 10k 50k – 15V (a) 1792 F01b (b) Figure 1 7 LT1792 U W U UO S I FOR ATIO APPLICATI 1k best bipolar op amps, with higher current noise, will eventually lose out to the LT1792 when transducer impedance increases. The low voltage noise of the LT1792 allows it to surpass most single JFET op amps available. For the best performance versus area available anywhere, the LT1792 is offered in the SO-8 surface mount package with no degradation in performance. H z) INPUT NOISE VOLTAGE (nV/√ The low voltage and current noise offered by the LT1792 makes it useful in a wide range of applications, especially where high impedance, capacitive transducers are used such as hydrophones, precision accelerometers and photo diodes. The total output noise in such a system is the gain times the RMS sum of the op amp input referred voltage noise, the thermal noise of the transducer, and the op amp bias current noise times the transducer impedance. Figure 2 shows total input voltage noise versus source resistance. In a low source resistance (<5k) application the op amp voltage noise will dominate the total noise. This means the LT1792 will beat out any JFET op amp, only the lowest noise bipolar op amps have the edge at low source resistances. As the source resistance increases from 5k to 50k, the LT1792 will match the best bipolar op amps for noise performance, since the thermal noise of the transducer (4kTR) begins to dominate the total noise. A further increase in source resistance, above 50k, is where the op amp’s current noise component (2qIB RTRANS) will eventually dominate the total noise. At these high source resistances, the LT1792 will out perform the lowest noise bipolar op amp due to the inherently low LT1007* – 100 + CS LT1792† 10 LT1792 LT1007 RESISTOR NOISE ONLY 1 100 1k 10k 100k 1M 10M SOURCE RESISTANCE (Ω) 1792 F02 Vn = AV √Vn2(OP AMP) + 4kTR + 2qIB • R2 Figure 2. Comparison of LT1792 and LT1007 Total Output 1kHz Voltage Noise Versus Source Resistance current noise of FET input op amps. Clearly, the LT1792 will extend the range of high impedance transducers that can be used for high signal-to-noise ratios. This makes the LT1792 the best choice for high impedance, capacitive transducers. The high input impedance JFET front end makes the LT1792 suitable in applications where very high charge sensitivity is required. Figure 3 illustrates the LT1792 in its inverting and noninverting modes of operation. A charge amplifier is shown in the inverting mode example; here the gain depends on the principal of charge conservation at RF CF RB – – R1 OUTPUT + RS TRANSDUCER CB ≅ CS RB = RS RS > R1 OR R2 100M SOURCE RESISTANCE = 2RS = R * PLUS RESISTOR † PLUS RESISTOR 1000pF CAPACITOR CB CS RS + TRANSDUCER CB RB 1792 F03 Figure 3. Noninverting and Inverting Gain Configurations 8 LT1007† VO RS R2 CS LT1792* CS RS OUTPUT CB = CF CS RB = RF RS dQ dV Q = CV; = I = C dt dt LT1792 W U U UO APPLICATI S I FOR ATIO the input of the LT1792. The charge across the transducer capacitance, CS, is transferred to the feedback capacitor CF, resulting in a change in voltage, dV, equal to dQ/CF. The gain therefore is CF/CS. For unity gain, the CF should equal the transducer capacitance plus the input capacitance of the LT1792 and RF should equal RS. In the noninverting mode example, the transducer current is converted to a change in voltage by the transducer capacitance; this voltage is then buffered by the LT1792 with a gain of 1 + R1/R2. A DC path is provided by RS, which is either the transducer impedance or an external resistor. Since RS is usually several orders of magnitude greater than the parallel combination of R1 and R2, RB is added to balance the DC offset caused by the noninverting input bias current and RS. The input bias currents, although small at room temperature, can create significant errors at higher temperature, especially with transducer resistances of up to 100M or more. The optimum value for RS is determined by equating the thermal noise (4kTRS) to the current noise times RS, [(2qIB) • RS], resulting in RB = 2VT/IB (VT = 26mV at 25°C). A parallel capacitor, CB, is used to cancel the phase shift caused by the op amp input capacitance and RB. Reduced Power Supply Operation expense of reduced dynamic range. To illustrate this benefit, let’s take the following example: An LT1792CS8 operates at an ambient temperature of 25°C with ±15V supplies, dissipating 159mW of power (typical supply current = 5.3mA). The SO-8 package has a θJA of 190°C/W, which results in a die temperature increase of 30.2°C or a room temperature die operating temperature of 55.2°C. At ±5V supplies, the die temperature increases by only one third of the previous amount or 10.1°C resulting in a typical die operating temperature of only 35.1°C. A 20 degree reduction of die temperature is achieved at the expense of a 20V reduction in dynamic range. To take full advantage of a wide input common mode range, the LT1792 was designed to eliminate phase reversal. Referring to the photographs shown in Figure 4, the LT1792 is shown operating in the follower mode (AV = 1) at ±5V supplies with the input swinging ±5.2V. The output of the LT1792 clips cleanly and recovers with no phase reversal. This has the benefit of preventing lock-up in servo systems and minimizing distortion components. High Speed Operation The LT1792 can be operated from ±5V supplies for lower power dissipation resulting in lower IB and noise at the The low noise performance of the LT1792 was achieved by making the input JFET differential pair large to maximize the first stage gain. Increasing the JFET geometry INPUT: ±5.2V Sine Wave LT1792 Output 1792 F04a 1792 F03b Figure 4. Voltage Follower with Input Exceeding the Common Mode Range ( VS = ±5V) 9 LT1792 W U U UO APPLICATI S I FOR ATIO CF also increases the parasitic gate capacitance, which if left unchecked, can result in increased overshoot and ringing. When the feedback around the op amp is resistive (RF), a pole will be created with RF, the source resistance and capacitance (RS, CS), and the amplifier input capacitance (CIN = 27pF). In low gain configurations and with RS and RF in the kilohm range (Figure 5), this pole can create excess phase shift and even oscillation. A small capacitor (CF) in parallel with RF eliminates this problem. With RS(CS + CIN) = RFCF, the effect of the feedback pole is completely removed. RF – RS CIN + CS OUTPUT 1792 F05 Figure 5 UO TYPICAL APPLICATI S Accelerometer Amplifier with DC Servo C1 1250pF R1 100M C2 2µF R3 2k R2 18k – 6 + 2 – 3 R5 20M R4C2 = R5C3 > R1 (1 + R2/R3) C1 OUTPUT = 0.8mV/pC* = 8.0mV/g** DC OUTPUT ≤ 2.7mV OUTPUT NOISE = 6nV/√ Hz AT 1kHz *PICOCOULOMBS **g = EARTH’S GRAVITATIONAL CONSTANT C3 2µF 7 6 LT1792 3 R4 20M LT1792 5V TO 15V ACCELEROMETER B & K MODEL 4381 OR EQUIVALENT 2 OUTPUT + 1792 TA03 4 – 5V TO –15V 10Hz Fourth Order Chebyshev Lowpass Filter (0.01dB Ripple) C1 33nF R2 237k R1 237k R3 249k VIN C2 100nF C3 10nF R5 154k 15V 2 – 7 LT1792 3 6 R4 154k R6 249k 2 – C4 330nF 3 + + 4 LT1792 6 VOUT –15V TYPICAL OFFSET ≈ 0.8mV 1% TOLERANCES FOR VIN = 10VP-P, VOUT = –121dB AT f > 330Hz = – 6dB AT f = 16.3Hz LOWER RESISTOR VALUES WILL RESULT IN LOWER THERMAL NOISE AND LARGER CAPACITORS 10 1792 TA06 LT1792 UO TYPICAL APPLICATI S Low Noise Light Sensor with DC Servo C1 2pF R1 1M 2 – 3 + 6 LT1792 OUTPUT C2 0.022µF D2 1N914 V+ R3 1k 2N3904 R5 1k HAMAMATSU S1336-5BK 7 6 2 + D1 1N914 – CD 3 R2 100k LT1792 4 R4 1k V– R2C2 > C1R1 CD = PARASITIC PHOTODIODE CAPACITANCE VO = 100mV/µWATT FOR 200nm WAVE LENGTH 330mV/µWATT FOR 633nm WAVE LENGTH V– 1792 TA05 Paralleling Amplifiers to Reduce Voltage Noise 3 2 + 6 An LT1792 1k – 51Ω 1k 10k 3 2 15V + 6 A2 LT1792 1k 2 – 3 + – 7 LT1792 1k 51Ω 6 OUTPUT 4 15V –15V 3 2 + 7 6 A1 LT1792 – 4 –15V 51Ω 1k 1k 1. ASSUME VOLTAGE NOISE OF LT1792 AND 51Ω SOURCE RESISTOR = 4.3nV/√ H z 2. GAIN WITH n LT1792s IN PARALLEL = n × 200 3. OUTPUT NOISE = √ n × 200 × 4.3nV/√ H z OUTPUT NOISE 4.3 4. INPUT REFERRED NOISE = = nV/√ Hz n × 200 √n 5. NOISE CURRENT AT INPUT INCREASES √ 1792 TA04 n TIMES 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 LT1792 UO TYPICAL APPLICATI S Light Balance Detection Circuit I1 Unity-Gain Buffer with Extended Load Capacitance Drive Capability R1 1M R2 1k C1 2pF TO 8pF C1 – PD1 – I2 VOUT LT1792 + + VIN VOUT LT1792 PD2 R1 33Ω CL 1792 TA08 C1 = CL ≤ 0.1µF OUTPUT SHORT-CIRCUIT CURRENT (∼ 30mA) WILL LIMIT THE RATE AT WHICH THE VOLTAGE CAN CHANGE ACROSS LARGE CAPACITORS 1792 TA07 VOUT = 1M × (I1 – I2) PD1,PD2 = HAMAMATSU S1336-5BK WHEN EQUAL LIGHT ENTERS PHOTODIODES, VOUT < 3mV. I=C U PACKAGE DESCRIPTIO ( ) dV dt Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1510) (LTC DWG # 05-08-1610) 0.400* (10.160) MAX 8 7 6 8 ( +0.035 0.325 –0.015 +0.889 8.255 –0.381 ) 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.009 – 0.015 (0.229 – 0.381) 5 5 0.255 ± 0.015* (6.477 ± 0.381) 0.300 – 0.325 (7.620 – 8.255) 0.189 – 0.197* (4.801 – 5.004) 7 6 2 3 4 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 0.008 – 0.010 (0.203 – 0.254) 0.065 (1.651) TYP 0.100 ± 0.010 (2.540 ± 0.254) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) N8 1197 2 3 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) *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 0.050 (1.270) TYP SO8 0996 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) RELATED PARTS PART NUMBER DESCRIPTION LT1113 Low Noise Dual JFET Op Amp Dual Version of LT1792, VNOISE = 4.5nV/√Hz LT1169 Low Noise Dual JFET Op Amp Dual Version of LT1793, IB = 10pA, VNOISE = 6nV/√Hz LT1793 Low Noise Single Op Amp Lower IB Version of LT1792, IB = 10pA, VNOISE = 6nV/√Hz 12 Linear Technology Corporation COMMENTS 1792f LTTP 0599 4K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1999