LT1638/LT1639 1.2MHz, 0.4V/µs Over-The-TopTM Micropower Rail-to-Rail Input and Output Op Amps DESCRIPTION U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Operates with Inputs Above V + Rail-to-Rail Input and Output Low Power: 230µA per Amplifier Max Gain Bandwidth Product: 1.2MHz Slew Rate: 0.4V/µs High Output Current: 25mA Min Specified on 3V, 5V and ±15V Supplies Reverse Battery Protection to 18V No Supply Sequencing Problems High Voltage Gain: 1500V/mV Single Supply Input Range: – 0.4V to 44V High CMRR: 98dB No Phase Reversal The LT ®1638 is a low power dual rail-to-rail input and output operational amplifier available in the standard 8-pin PDIP and SO packages as well as the 8-lead MSOP package. The LT1639 is a low power quad rail-to-rail input and output operational amplifier offered on the standard 14-pin PDIP and surface mount packages. The LT1638/LT1639 op amps operate on all single and split supplies with a total voltage of 2.5V to 44V drawing only 170µA of quiescent current per amplifier. These amplifiers are reverse battery protected and draw no current for reverse supply up to 18V. The input range of the LT1638/LT1639 includes both supplies, and a unique feature of this device is its capability to operate over the top with either or both of its inputs above V +. The inputs handle 44V, both differential and common mode, independent of supply voltage. The input stage incorporates phase reversal protection to prevent false outputs from occurring even when the inputs are 22V below the negative supply. Protective resistors are included in the input leads so that current does not become excessive when the inputs are forced below the negative supply. The LT1638/LT1639 can drive loads up to 25mA and still maintain rail-to-rail capability. The op amps are unity-gain stable and drive all capacitive loads up to 1000pF when optional output compensation is used. U APPLICATIONS ■ ■ ■ ■ ■ Battery- or Solar-Powered Systems Portable Instrumentation Sensor Conditioning Supply Current Sensing Battery Monitoring Micropower Active Filters 4mA to 20mA Transmitters , LTC and LT are registered trademarks of Linear Technology Corporation. Over-The-Top is a trademark of Linear Technology Corporation. U TYPICAL APPLICATION Output Voltage vs Input Voltage Over-The-Top Comparator with 100mV Hysteresis Centered at 0mV 10k 1M 5V VCC V1 VCC VCC 1M + + A 1/2 LT1638 B 1/2 LT1638 – 1M V0 – 0V 10k 1M 1638/39 TA01 V2 VCC = 5V, VCM = 0V TO 44V, tPD = 27µs 1638/39 TA02 1 LT1638/LT1639 U W W W ABSOLUTE MAXIMUM RATINGS (Note 1) Total Supply Voltage (V + to V –) .............................. 44V Input Differential Voltage ......................................... 44V Input Current ...................................................... ±25mA Output Short-Circuit Duration (Note 2) ......... Continuous Operating Temperature Range ................ – 40°C to 85°C Specified Temperature Range (Note 3) .. – 40°C to 85°C Junction Temperature ........................................... 150°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C W U U PACKAGE/ORDER INFORMATION TOP VIEW TOP VIEW OUT A –IN A +IN A V– 1 2 3 4 V+ OUT B –IN B +IN B MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 150°C, θJA = 250°C/ W (MS8) ORDER PART NUMBER LT1638CMS8 MS8 PART MARKING LTCY 8 1 OUT A 8 7 6 5 7 2 –IN A TOP VIEW V+ OUT A 1 OUT B –IN A 2 +IN A 3 V+ 4 A 6 3 +IN A –IN B B V– 5 4 +IN B +IN B 5 S8 PACKAGE 8-LEAD PLASTIC SO –IN B 6 TJMAX = 150°C, θJA = 130°C/ W (N8) TJMAX = 150°C, θJA = 190°C/ W (S8) OUT B 7 N8 PACKAGE 8-LEAD PDIP D 13 –IN D 12 +IN D 11 V – 10 +IN C B C 9 – IN C 8 OUT C S PACKAGE 14-LEAD PLASTIC SO TJMAX = 150°C, θJA = 110°C/ W (N) TJMAX = 150°C, θJA = 150°C/ W (S) LT1638CS8 LT1638IS8 ORDER PART NUMBER S8 PART MARKING 1638 A N PACKAGE 14-LEAD PDIP ORDER PART NUMBER LT1638CN8 LT1638IN8 14 OUT D LT1639CN LT1639IN 1638I LT1639CS LT1639IS Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS VS = 3V, 0V; VS = 5V, 0V; VCM = VOUT = half supply, TA = 25°C, unless otherwise noted. (Note 3) SYMBOL VOS IOS PARAMETER Input Offset Voltage Input Offset Voltage Drift (Note 7) Input Offset Current CONDITIONS LT1638 N, S Packages 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C LT1639 N, S Packages 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C LT1638C MS8 Package 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C LT1638/LT1639 N, S Packages LT1638CMS8 VCM = 44V (Note 4) 2 MIN TYP 200 ● ● 300 ● ● 350 ● ● ● ● ● ● 2 2.5 1 MAX 600 850 950 700 950 1050 900 1150 1250 6 7 6 2.5 UNITS µV µV µV µV µV µV µV µV µV µV/°C µV/°C nA µA LT1638/LT1639 ELECTRICAL CHARACTERISTICS VS = 3V, 0V; VS = 5V, 0V; VCM = VOUT = half supply, TA = 25°C, unless otherwise noted. (Note 3) SYMBOL IB PARAMETER Input Bias Current Input Noise Voltage en in RIN Input Noise Voltage Density Input Noise Current Density Input Resistance CIN Input Capacitance Input Voltage Range CONDITIONS VCM = 44V (Note 4) VS = 0V 0.1Hz to 10Hz f = 1kHz f = 1kHz Differential Common Mode, VCM = 0V to 44V CMRR Common Mode Rejection Ratio VCM = 0V to VCC – 1V VCM = 0V to 44V (Note 8) AVOL Large-Signal Voltage Gain VS = 3V, VO = 500mV to 2.5V, RL = 10k 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C VS = 5V, VO = 500mV to 4.5V, RL = 10k 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C VS = 3V, No Load VS = 3V, ISINK = 5mA VS = 5V, No Load VS = 5V, ISINK = 10mA VS = 3V, No Load VS = 3V, ISOURCE = 5mA VS = 5V, No Load VS = 5V, ISOURCE = 10mA VS = 3V, Short to GND VS = 3V, Short to VCC VS = 5V, Short to GND VS = 5V, Short to VCC VS = 3V to 12.5V, VCM = VO = 1V IS = – 100µA per Amplifier VOL VOH Output Voltage Swing Low Output Voltage Swing High ISC Short-Circuit Current (Note 2) PSRR Power Supply Rejection Ratio Reverse Supply Voltage IS GBW SR Minimum Operating Supply Voltage Supply Current per Amplifier (Note 5) Gain Bandwidth Product (Note 4) Slew Rate (Note 6) MIN ● ● 1 1.4 TYP 20 8 0.1 1 20 0.3 2.5 5.5 5 ● 0 ● ● 88 80 98 88 200 133 100 400 250 200 1500 ● ● ● ● ● ● ● ● ● ● ● ● ● ● 2.94 2.25 4.94 3.8 10 15 15 15 90 18 ● MAX 50 30 44 3 250 3 500 2.98 2.40 4.98 4.0 15 25 20 25 100 27 8 450 8 700 2.4 170 2.7 230 275 ● 650 550 500 1075 ● ● AV = – 1, RL = ∞ 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C 0.210 0.185 0.170 0.38 ● ● nV/√Hz pA/√Hz MΩ MΩ pF V dB dB 1500 f = 1kHz 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C UNITS nA µA nA µVP-P V/mV V/mV V/mV V/mV V/mV V/mV mV mV mV mV V V V V mA mA mA mA dB V V µA µA kHz kHz kHz V/µs V/µs V/µs 3 LT1638/LT1639 ELECTRICAL CHARACTERISTICS SYMBOL VOS IOS IB PARAMETER Input Offset Voltage Input Offset Voltage Drift (Note 7) Input Offset Current Input Bias Current Input Noise Voltage en in RIN Input Noise Voltage Density Input Noise Current Density Input Resistance CIN Input Capacitance Input Voltage Range CMRR AVOL Common Mode Rejection Ratio Large-Signal Voltage Gain VS = ±15V, VCM = 0V, VOUT = 0V, TA = 25°C, unless otherwise noted. (Note 3) CONDITIONS LT1638 N, S Packages 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C LT1639 N, S Packages 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C LT1638C MS8 Package 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C LT1638/LT1639 N, S Packages LT1638CMS8 MIN TYP 250 ● ● 350 ● ● 400 ● ● 2 2.5 1 20 1 ● ● ● ● 0.1Hz to 10Hz f = 1kHz f = 1kHz Differential Common Mode, VCM = – 15V to 14V 1 MAX 800 1000 1100 900 1100 1200 1050 1250 1350 6 7 6 50 20 0.3 2.5 500 4.5 ● – 15 VCM = –15V to 29V VO = ±14V, RL = 10k 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C ● 88 500 ● ● 80 200 125 100 29 UNITS µV µV µV µV µV µV µV µV µV µV/°C µV/°C nA nA µVP-P nV/√Hz pA/√Hz MΩ MΩ pF V dB V/mV V/mV V/mV VOL Output Voltage Swing No Load IOUT = ±10mA ● ● 14.9 13.7 14.95 14.0 ISC Short-Circuit Current (Note 2) Short to GND 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C 25 20 15 40 ● ● mA mA mA VS = ±1.5V to ±22V ● 90 100 dB PSRR Power Supply Rejection Ratio IS Supply Current per Amplifier 205 ● GBW SR Gain Bandwidth Product Slew Rate 280 350 µA µA f = 1kHz 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C 750 650 600 1200 ● ● kHz kHz kHz AV = – 1, RL = ∞, VO = ±10V, 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C 0.225 0.2 0.18 0.4 ● ● V/µs V/µs V/µs The ● denotes specifications which apply over the full specified temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: A heat sink may be required to keep the junction temperature below absolute maximum. This depends on the power supply voltage and how many amplifiers are shorted. Note 3: The LT1638C/LT1639C are guaranteed to meet 0°C to 70°C specifications and are designed, characterized and expected to meet the extended temperature limits, but are not tested at – 40°C and 85°C. The LT1638I/LT1639I are guaranteed to meet the extended temperature limits. 4 V V Note 4: VS = 5V limits are guaranteed by correlation to VS = 3V and VS = ±15V tests. Note 5: VS = 3V limits are guaranteed by correlation to VS = 5V and VS = ±15V tests. Note 6: Guaranteed by correlation to slew rate at VS = ±15V and GBW at VS = 3V and VS = ±15V tests. Note 7: This parameter is not 100% tested. Note 8: The spec implies a typical offset voltage at VCM = 44 of 2mV and a maximum offset voltage at VCM = 44 of 5mV. LT1638/LT1639 U W TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Supply Voltage 260 TA = 125°C 240 220 TA = 25°C 200 180 TA = –55°C 160 140 120 400 10000 300 8000 200 100 0 0 5 10 15 20 25 30 35 SUPPLY VOLTAGE (V) 40 TA = 25°C –100 TA = 125°C TA = –55°C –200 –300 – 400 100 INPUT BIAS CURRENT (nA) CHANGE IN INPUT OFFSET VOLTAGE (µV) SUPPLY CURRENT PER AMPLIFIER (µA) 300 280 Input Bias Current vs Common Mode Voltage Minimum Supply Voltage 45 0 1 3 4 2 TOTAL SUPPLY VOLTAGE (V) TA = –55°C 0.01 0.1 1 SOURCING LOAD CURRENT (mA) 10 TA = 125°C TA = 25°C 0.01 TA = –55°C 0.001 0.001 7 8 10 OUTPUT LOW 10 9 10 1638/39 G07 0 10 20 30 40 50 60 70 80 90 100 INPUT OVERDRIVE (mV) 1638/39 G06 1638/39 G05 Input Noise Current Density vs Frequency 4.5 INPUT NOISE CURRENT DENSITY (pA/√Hz) INPUT NOISE VOLTAGE DENSITY (nV/√Hz) 4 5 6 TIME (SEC) OUTPUT HIGH 1 0.01 0.1 1 SINKING LOAD CURRENT (mA) 70 3 44 VS = ±2.5V NO LOAD Noise Voltage Density vs Frequency VS = ±2.5 4.4 5.2 5.6 4.8 COMMON MODE VOLTAGE (V) 100 0.1 0.1Hz to 10Hz Noise Voltage 2 TA = 25°C Output Saturation Voltage vs Input Overdrive VS = ±2.5V VOD = 30mV 1638/39 G04 1 TA = 125°C 0 1638/39 G03 OUTPUT SATURATION VOLTAGE (mV) OUTPUT SATURATION VOLTAGE (V) TA = 25°C 0 20 –40 4.0 5 1 NOISE VOLTAGE (400nV/DIV) OUTPUT SATURATION VOLTAGE (V) 1 0.01 0.001 40 Output Saturation Voltage vs Load Current (Output Low) TA = 125°C TA = –55°C 60 1638/39 G02 Output Saturation Voltage vs Load Current (Output High) 0.1 6000 –20 1638/39 G01 VS = ±2.5V VOD = 30mV VS = 5V, 0V 60 50 40 30 20 10 0 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 1 10 100 FREQUENCY (Hz) 1k 1638/39 G09 1 10 100 FREQUENCY (Hz) 1k 1638/39 G08 5 LT1638/LT1639 U W TYPICAL PERFORMANCE CHARACTERISTICS Gain and Phase Shift vs Frequency Gain Bandwith Product vs Temperature 100 80 PHASE 50 70 40 60 50 GAIN 20 40 10 30 0 20 10 –10 0 1000 –20 10 100 FREQUENCY (kHz) 1 1400 0.55 1300 VS = ±15V 1200 1100 1000 VS = ±2.5V 900 800 –50 –25 50 0 75 25 TEMPERATURE (°C) 1638/39 G12 GAIN BANDWIDTH 30 20 1100 5 10 15 20 25 30 35 40 TOTAL SUPPLY VOLTAGE (V) GAIN BANDWIDTH PRODUCT (kHz) 40 1300 0 VS = ± 2.5V AV = –1 RF = RG = 100k f = 1kHz 1400 1300 50 25 0 75 TEMPERATURE (°C) 1100 20 GAIN BANDWIDTH PRODUCT 1000 90 50 30 10 900 0 800 –10 100 1 10 LOAD RESISTANCE (kΩ) VS = ±15V 125 70 60 POSITIVE SUPPLY 50 40 30 NEGATIVE SUPPLY 20 10 0 –10 1 10 100 FREQUENCY (kHz) 1000 1638/39 G16 Output Impedance vs Frequency Channel Separation vs Frequency 130 100 VS = ±2.5V 80 1638/39 G17 10k VS = ±15V VS = ± 2.5V 90 80 70 60 50 40 OUTPUT IMPEDANCE (Ω) 120 CHANNEL SEPARATION (dB) COMMON MODE REJECTION RATIO (dB) FALLING, VS = ±15V PSRR vs Frequency 1200 10 45 100 110 100 90 80 1k 100 AV = 10 AV = 100 10 AV = 1 1 70 30 20 1 10 100 FREQUENCY (kHz) 1000 1638/39 G18 6 FALLING, VS = ±2.5V 0.35 1638/39 G14 60 PHASE MARGIN CMRR vs Frequency 110 0.40 0.25 –50 –25 125 40 1638/39 G15 120 100 PHASE MARGIN (DEG) PHASE MARGIN PHASE MARGIN (DEG) GAIN BANDWIDTH PRODUCT (kHz) 1500 50 1400 1000 RISING, VS = ±2.5V 0.45 Gain Bandwidth Product and Phase Margin vs Load Resistance 60 1200 0.50 1638/39 G13 Gain Bandwidth Product and Phase Margin vs Supply Voltage 1500 RISING, VS = ±15V 0.30 POWER SUPPLY REJECTION RATIO (dB) 30 PHASE SHIFT (DEG) GAIN (dB) f = 1kHz 90 60 0.60 SLEW RATE (V/µs) VS = ±2.5V 70 Slew Rate vs Temperature 1500 GAIN BANDWIDTH PRODUCT (kHz) 80 60 0.1 1 10 FREQUENCY (kHz) 100 1638/39 G19 0.1 0.1 1 10 100 FREQUENCY (kHz) 1000 1638/39 G20 LT1638/LT1639 U W TYPICAL PERFORMANCE CHARACTERISTICS Settling Time to 0.1% vs Output Step 100 VS = ±15V 8 OVERSHOOT (%) 2 0 –2 –4 AV = –1 –6 60 AV = 5 AV = 1 40 30 AV = 10 5 20 15 10 25 SETTLING TIME (µs) 15 10 VS = ± 2.5V 0 0.1 0 –10 0 20 5 10 10 35 30 100 1000 CAPACITIVE LOAD (pF) 10000 DISTORTION ≤ 1% RL = 20k 25 20 AV = 1 –8 70 50 VS = ±15V 30 1 10 FREQUENCY (kHz) 100 1638/39 G21 1638/39 G22 1638/39 G23 Total Harmonic Distortion + Noise vs Frequency Total Harmonic Distortion + Noise vs Load Resistance Total Harmonic Distortion + Noise vs Output Voltage 10 10 10 VS = 3V TOTAL AV = 1 VIN = 2VP-P AT 1kHz VS = 3V, 0V VOUT = 2VP-P VCM = 1.2V RL = 20k 0.1 0.01 VS = ±1.5V VIN = ±1V 0.1 VS = 3V, 0V VIN = 0.5V TO 2.5V 0.01 AV = –1 0.1 1 10 FREQUENCY (Hz) 100 0.001 0.1 CHANGE IN INPUT OFFSET VOLTAGE (50µV/DIV) Open-Loop Gain 0.001 1 10 LOAD RESISTANCE TO GROUND (kΩ) 1638/39 G24 0.1 0.01 VS = 3V, 0V VIN = 0.2V TO 2.2V AV = 1 0.001 0.01 RL = 10k, f = 1kHz VCM = HALF SUPPLY A V = –1, VS = ±1.5V AV = –1, VS = 3V, 0V AV = 1, VS = ±1.5V AV = 1, VS = 3V, 0V 1 1 THD + NOISE (%) 1 THD + NOISE (%) OUTPUT STEP (V) 80 AV = –1 4 35 VS = 5V, 0V VCM = 2.5V ISOURCE = 150µA 90 AV = 1 6 THD + NOISE (%) Undistorted Output Swing vs Frequency OUTPUT SWING (VP-P) 10 Capacitive Load Handling, Overshoot vs Capacitive Load 100 0 2 1 OUTPUT VOLTAGE (VP-P) 1638/39 G26 1638/39 G25 Large-Signal Response 3 Small-Signal Response VS = ±15V RL = 2k RL = 10k RL = 50k VS = ±15V AV = 1 –20V –10V 10V 0V OUTPUT VOLTAGE (5V/DIV) 1638/39 G28 VS = ±15V AV = 1 CL = 15pF 1638/39 G29 20V 1638/39 G27 7 LT1638/LT1639 U W U U APPLICATIONS INFORMATION Supply Voltage The positive supply pin of the LT1638/LT1639 should be bypassed with a small capacitor (typically 0.1µF) within an inch of the pin. When driving heavy loads an additional 4.7µF electrolytic capacitor should be used. When using split supplies, the same is true for the negative supply pin. The LT1638/LT1639 are protected against reverse battery voltages up to 18V. In the event a reverse battery condition occurs, the supply current is less than 1nA. The LT1638/LT1639 can be shut down by removing V +. In this condition the input bias current is less than 0.1nA, even if the inputs are 44V above the negative supply. At temperatures greater than 70°C, when operating the LT1638/LT1639 on total supplies of 10V or more, the supply must not be brought up faster than 1V/µs. Increasing the bypass capacitor and/or adding a small resistor in series with the supply will limit the rise time. Inputs The LT1638/LT1639 have two input stages, NPN and PNP (see the Simplified Schematic), resulting in three distinct operating regions as shown in the Input Bias Current vs Common Mode typical performance curve. For input voltages about 0.8V or more below V +, the PNP input stage is active and the input bias current is typically – 20nA. When the input common mode voltage is within 0.5V of the positive rail, the NPN stage is operating and the input bias current is typically 40nA. Increases in temperature will cause the voltage at which operation switches from the PNP input stage to the NPN input stage to move towards V +. The input offset voltage of the NPN stage is untrimmed and is typically 600µV. A Schottky diode in the collector of each NPN transistor allow the LT1638/LT1639 to operate over the top, with either or both of its inputs above V +. At about 0.3V above V + the NPN input transistor is fully saturated and the input bias current is typically 8µA at room temperature. The input offset voltage is typically 2mV when operating above V +. The LT1638/LT1639 will operate with its inputs 44V above V – regardless of V +. 8 The inputs are protected against excursions as much as 22V below V – by an internal 1k resistor in series with each input and a diode from the input to the negative supply. The input stage of the LT1638/LT1639 incorporates phase reversal protection to prevent the output from phase reversing for inputs up to 22V below V –. There are no clamping diodes between the inputs and the maximum differential input voltage is 44V. Output The output of the LT1638/LT1639 can swing within 20mV of the positive rail with no load, and within 3mV of the negative rail with no load. When monitoring voltages within 20mV of the positive rail or within 3mV of the negative rail, gain should be taken to keep the output from clipping. The LT1638/LT1639 are capable of sinking and sourcing over 40mA on ±15V supplies; sourcing current capability is reduced to 20mA at 5V total supplies as noted in the electrical characteristics. The LT1638/LT1639 are internally compensated to drive at least 200pF of capacitance under any output loading conditions. A 0.22µF capacitor in series with a 150Ω resistor between the output and ground will compensate these amplifiers for larger capacitive loads, up to 1000pF, at all output currents. Distortion There are two main contributors of distortion in op amps: output crossover distortion as the output transitions from sourcing to sinking current and distortion caused by nonlinear common mode rejection. If the op amp is operating inverting there is no common mode induced distortion. If the op amp is operating in the PNP input stage (input is not within 0.8V of V +), the CMRR is very good, typically 98dB. When the LT1638 switches between input stages there is significant nonlinearity in the CMRR. Lower load resistance increases the output crossover distortion, but has no effect on the input stage transition distortion. For lowest distortion the LT1638/LT1639 should be operated single supply, with the output always sourcing current and with the input voltage swing between ground and (V + – 0.8V). See the Typical Performance Characteristics curves. LT1638/LT1639 U U W U APPLICATIONS INFORMATION Gain The open-loop gain is almost independent of load when the output is sourcing current. This optimizes perfor- mance in single supply applications where the load is returned to ground. The typical performance curve of Open-Loop Gain for various loads shows the details. U TYPICAL APPLICATIONS With 1.2MHz bandwidth, Over-The-Top capability, reverse-battery protection and rail-to-rail input and output features, the LT1638/LT1639 are ideal candidates for general purpose applications. VCC R5 100k + 1/4 LT1639 The lowpass slope limiting filter in Figure 1 limits the maximum dV/dT (not frequency) that it passes. When the input signal differs from the output by one forward diode drop, D1 or D2 will turn on. With a diode on, the voltage across R2 will be constant and a fixed current, VDIODE/R2, will flow through capacitor C1, charging it linearly instead of exponentially. The maximum slope that the circuit will pass is equal to VDIODE divided by (R2)(C1). No matter how fast the input changes the output will never change any faster than the dV/dT set by the diodes and (R2)(C). D1 R3 100k – R1 1k R4 100k D3 VD d = V dt OUT(MAX) (R2)(C1) FOR R1 = 10k, R2 = 100k, C1 = 1000pF d V = 0.006V/µs dt OUT(MAX) C1 LT1634-1.2V D4 – 1/4 LT1639 FOR R2 = 50k, C1 = 500pF, MAXIMUM SLOPE = 0.048V/µs 1.2V d = V dt OUT (R2)(C1) + VIN + C1 D2 R2 VOUT 1/4 LT1639 R2 VIN D1 R1 LT1634-1.2V – D2 1/2 LT1638 + R6 100k 1638/39 F02 VEE VOUT – Response of Slope Limiting Filter 1638/39 F01 Figure 1. Lowpass Slope Limiting Filter VOUT A modification of this application is shown in Figure 2 using references instead of diodes to set the maximum slope. By using references, the slope is independent of temperature. A scope photo shows a 1VP-P, 2kHz input signal with a 2V pulse added to the sine wave; the circuit passes the 2kHz signal but limits the slope of the pulse. The application in Figure 3 utilizes the Over-The-Top capabilities of the LT1638. The 0.2Ω resistor senses the load current while the op amp and NPN transistor form a closed loop making the collector current of Q1 VIN 1638/39 TA02 Figure 2. Lowpass Slope Limiting Filter with 0TC 9 LT1638/LT1639 U TYPICAL APPLICATIONS proportional to the load current. As a convenient monitor, the 2k load resistor converts the current into a voltage. The positive supply rail, V +, is not limited to the 5V supply of the op amp and could be as high as 44V. The Figure 4 application uses the LT1638 in conjunction with the LT1634 micropower shunt reference. The supply current of the op amp also biases the reference. The drop across resistor R1 is fixed at 1.2V generating an output current equal to 1.2V/R1. V+ 200Ω VCC LT1634-1.2 5V 0.2Ω R1 + Q1 2N3904 1/2 LT1638 200Ω LOAD VCC – + 0V TO 4.3V ILOAD IOUT = 1.2V R1 1/2 LT1638 2k – IOUT 1638/39 F03 VOUT = (2Ω)(ILOAD) 1638/39 F04 Figure 3. Positive Supply Rail Current Sense Figure 4. Current Source W W SI PLIFIED SCHE ATIC V+ Q2 Q1 D1 R1 6k Q3 Q22 D3 D2 R2 1k Q4 Q19 – IN Q17 Q7 R3 1k + Q8 Q11 OUT Q16 +IN 10µA Q6 Q18 Q15 Q9 Q5 Q20 Q12 D4 Q10 Q13 Q14 R4 8k D5 Q21 R5 8k V– ONE AMPLIFIER 1638/39 SS U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.034 ± 0.004 (0.86 ± 0.102) 8 7 6 5 0° – 6° TYP 0.021 ± 0.006 (0.53 ± 0.015) SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) TYP 0.006 ± 0.004 (0.15 ± 0.102) * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE 10 0.118 ± 0.004* (3.00 ± 0.102) 0.118 ± 0.004** (3.00 ± 0.102) 0.192 ± 0.004 (4.88 ± 0.10) MSOP (MS8) 1197 1 2 3 4 LT1638/LT1639 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.300 – 0.325 (7.620 – 8.255) 0.045 – 0.065 (1.143 – 1.651) 0.130 ± 0.005 (3.302 ± 0.127) 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) ( 0.400* (10.160) MAX +0.035 0.325 –0.015 +0.889 8.255 –0.381 ) 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) 0.100 ± 0.010 (2.540 ± 0.254) N8 1197 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.053 – 0.069 (1.346 – 1.752) 0.008 – 0.010 (0.203 – 0.254) 0.189 – 0.197* (4.801 – 5.004) 7 8 0.004 – 0.010 (0.101 – 0.254) 5 6 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 0.050 (1.270) 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 SO8 0996 1 3 2 4 N Package 14-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.130 ± 0.005 (3.302 ± 0.127) 0.300 – 0.325 (7.620 – 8.255) 0.045 – 0.065 (1.143 – 1.651) 0.020 (0.508) MIN 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) +0.035 0.325 –0.015 ( +0.889 8.255 –0.381 ) 0.770* (19.558) MAX 0.125 (3.175) MIN 0.005 (0.125) MIN 0.100 ± 0.010 (2.540 ± 0.254) 14 13 12 11 10 9 8 1 2 3 4 5 6 7 0.255 ± 0.015* (6.477 ± 0.381) 0.018 ± 0.003 (0.457 ± 0.076) N14 1197 *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) S Package 14-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 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) 0.004 – 0.010 (0.101 – 0.254) 0.337 – 0.344* (8.560 – 8.738) 14 13 12 11 10 9 8 0° – 8° TYP 0.050 (1.270) 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 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157** (3.810 – 3.988) S14 0695 1 2 3 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. 4 5 6 7 11 LT1638/LT1639 U TYPICAL APPLICATION The battery monitor in Figure 5 also demonstrates the LT1638’s ability to operate with its inputs above the positive rail. In this application, a conventional amplifier would be limited to a battery voltage between 5V and ground, but the LT1638 can handle battery voltages as high as 44V. When the battery is charging, Amp B senses the voltage drop across RS. The output of Amp B causes Q2 to drain sufficient current through RB to balance the input of Amp B. Likewise, Amp A and Q1 form a closed RS, 0.2Ω CHARGER VOLTAGE RA, 2k RA', 2k IBATT loop when the battery is discharging. The current through Q1 or Q2 is proportional to the current in R S and this current flows into RG and is converted into a voltage. Amp D buffers and amplifies the voltage across RG. Amp C compares the output of Amp A and Amp B to determine the polarity of current through RS. The scale factor for VOUT with S1 open is 1V/A. With S1 closed the scale factor is 1V/100mA and currents as low as 500µA can be measured. Q1 2N3904 + A 1/4 LT1639 + C 1/4 LT1639 – LOGIC – RB, 2k RB', 2k LOAD + + Q2 2N3904 LOGIC HIGH (5V) = CHARGING LOGIC LOW (0V) = DISCHARGING B 1/4 LT1639 + – RG 10k VBATT = 12V D 1/4 LT1639 VOUT – S1 90.9k 10k 1638/39 F05 IBATT = VOUT V = OUT AMPS (RS)(RG /RA)(GAIN) GAIN S1 = OPEN, GAIN = 1 S1 = CLOSED, GAIN = 10 RA = RB VS = 5V, 0V Figure 5. Battery Monitor RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1078/LT1079 LT2078/LT2079 Dual/Quad 55µA Max, Single Supply, Precision Op Amps Input/Output Common Mode Includes Ground, 70µV VOS(MAX) and 2.5µV/°C Drift (Max), 200kHz GBW, 0.07V/µs Slew Rate LT1178/LT1179 LT2178/LT2179 Dual/Quad 17µA Max, Single Supply, Precison Op Amps Input/Output Common Mode Includes Ground, 70µV VOS(MAX) and 4µV/°C Drift (Max), 85kHz GBW, 0.04V/µs Slew Rate LT1366/LT1367 Dual/Quad Precision, Rail-to-Rail Input and Output Op Amps 475µV VOS(MAX), 500V/mV AVOL(MIN), 400kHz GBW LT1490/LT1491 Dual/Quad Over-The-Top Micropower, Rail-to-Rail Input and Output Op Amps Single Supply Input Range: – 0.4V to 44V, Micropower 50µA per Amplifier, Rail-to-Rail Input and Output, 200kHz GBW LT1636 Single Over-The-Top Micropower Rail-to-Rail Input and Output Op Amp 55µA Supply Current, VCM Extends 44V above VEE, Independent of VCC; MSOP Package, Shutdown Function 12 Linear Technology Corporation 16389f LT/TP 1098 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 1998