LT1187 Low Power Video Difference Amplifier U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Differential or Single-Ended Gain Block (Adjustable) –3dB Bandwidth, AV = ±2 50MHz Slew Rate 165V/µs Low Supply Current 13mA Output Current ± 20mA CMRR at 10MHz 40dB LT1193 Pin Compatible Low Cost Single 5V Operation Drives Cables Directly Output Shutdown UO APPLICATI ■ ■ ■ The LT1187’s high slew rate, 165V/µs, wide bandwidth, 50MHz, and ±20mA output current require only 13mA of supply current. The shutdown feature reduces the power dissipation to a mere 15mW, and allows multiple amplifiers to drive the same cable. The LT1187 is a low power version of the popular LT1193, and is available in 8-pin miniDIPs and SO packages. For applications with gains of 10 or more, see the LT1189 data sheet. Line Receivers Video Signal Processing Cable Drivers Tape and Disc Drive Systems UO ■ S The LT1187 is a difference amplifier optimized for operation on ±5V, or a single 5V supply, and gain ≥2. This versatile amplifier features uncommitted high input impedance (+) and (–) inputs, and can be used in differential or single-ended configurations. Additionally, a second set of inputs give gain adjustment and DC control to the difference amplifier. TYPICAL APPLICATI Cable Sense Amplifier for Loop Through Connections with DC Adjust Closed-Loop Gain vs Frequency 40 V IN 30 CABLE 2 VDC 1 8 + 7 – LT1187 + – 6 VOUT 4 –5V 1k VOLTAGE GAIN (dB) 5V 3 VS = ±5V RL = 1k 20 10 0 1k –10 0.1 LT1187 • TA01 1 10 FREQUENCY (MHz) 100 LT1187 • TA02 1 LT1187 W U U W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO RATI GS Total Supply Voltage (V + to V –) ............................. 18V Differential Input Voltage ........................................ ±6V Input Voltage .......................................................... ±VS Output Short Circuit Duration (Note 1) ........ Continuous Operating Temperature Range LT1187M ..................................... – 55°C to 150°C LT1187C............................................. 0°C to 70°C Junction Temperature (Note 2) Plastic Package (CN8,CS8) ......................... 150°C Ceramic Package (CJ8,MJ8) ....................... 175°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec.)................ 300°C ORDER PART NUMBER TOP VIEW +/REF 1 8 –/FB –IN 2 7 V+ +IN 3 6 OUT V– 4 5 S/D LT1187MJ8 LT1187CJ8 LT1187CN8 LT1187CS8 J8 PACKAGE N8 PACKAGE 8-LEAD HERMETIC DIP 8-LEAD PLASTIC DIP S8 PACKAGE 8-LEAD PLASTIC SOIC S8 PART MARKING LT1187 • POI01 TJMAX = 175°C, θJA = 100°C/W (J8) TJMAX = 150°C, θJA = 100°C/W (N8) TJMAX = 150°C, θJA = 150°C/W (S8) 1187 Consult factory for Industrial grade parts. + – 5V ELECTRICAL CHARACTERISTICS TA = 25°C, (Note 3) VS = ±5V, VREF = 0V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to ground, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open. PARAMETER Input Offset Voltage CONDITIONS Either Input, (Note 4) SOIC Package IOS IB Input Offset Current Input Bias Current Either Input Either Input en Input Noise Voltage fO = 10kHz 65 nV/√Hz in Input Noise Current fO = 10kHz 1.5 pA/√Hz RIN Input Resistance Differential 100 kΩ CIN Input Capacitance Either Input 2.0 pF VIN LIM Input Voltage Limit (Note 5) ±380 mV Input Voltage Range MIN LT1187M/C TYP MAX 2.0 10 2.0 11 SYMBOL VOS 0.2 ±0.5 –2.5 CMRR PSRR Common-Mode Rejection Ratio Power Supply Rejection Ratio VCM = –2.5V to 3.5V VS = ±2.375V to ±8V VOUT Output Voltage Swing 1.0 ±2.0 3.5 UNITS mV mV µA µA V 70 70 100 85 dB dB VS = ±5V, RL = 1k, AV = 50 ±3.8 ±4.0 V VS = ±8V, RL = 1k, AV = 50 ±6.7 ±7.0 VS = ±8V, RL = 300Ω, AV = 50, (Note 3) ±6.4 ± 6.8 GE Gain Error VO = ±1V, AV = 10, RL = 1k SR Slew Rate (Note 6, 10) FPBW Full Power Bandwidth VO = 1VP-P, (Note 7) BW tr, tf Small Signal Bandwidth Rise Time, Fall Time AV = 10 AV = 50, VO = ±1.5V, 20% to 80% (Note 10) tPD Propagation Delay RL= 1k, VO = ±125mV, 50% to 50% Overshoot VO = ± 50mV 0 % Settling Time 3V Step, 0.1%, (Note 8) 100 ns Diff AV Differential Gain RL = 1k, AV = 4, (Note 9) 0.6 % Diff Ph Differential Phase RL = 1k, AV = 4, (Note 9) 0.8 DEGP-P IS Supply Current ts Shutdown Supply Current 2 Pin 5 at V – 0.2 100 150 1.0 % 165 V/µs 53 MHz 5.7 230 325 26 MHz ns ns 13 16 mA 0.8 1.5 mA LT1187 + – 5V ELECTRICAL CHARACTERISTICS TA = 25°C, (Note 3) VS = ±5V, VREF = 0V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to ground, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open. SYMBOL PARAMETER CONDITIONS Shutdown Pin Current Pin 5 at V – tON Turn On Time tOFF Turn Off Time Pin 5 from V – to Ground, RL = 1k Pin 5 from Ground to V –, RL = 1k IS/D MIN LT1187M/C TYP MAX 5 25 UNITS µA 500 ns 600 ns 5V CHARACTERISTICS ELECTRICAL + – TA = 25°C, (Note 3) VS = 5V, VS = 0V, VREF = 2.5V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to VREF, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open. SYMBOL PARAMETER CONDITIONS VOS Input Offset Voltage Either Input, (Note 4) SOIC Package IOS Input Offset Current Either Input IB Input Bias Current Either Input MIN LT1187M/C TYP MAX 2.0 2.0 Input Voltage Range mV mV 0.2 1.0 µA ± 0.5 ± 2.0 µA 3.5 V 2.0 CMRR Common-Mode Rejection Ratio VCM = 2.0V to 3.5V VOUT Output Voltage Swing RL = 300Ω to Ground (Note 3) VOUT High UNITS 10 12 70 100 dB 3.6 4.0 V VOUT Low 0.15 0.4 SR Slew Rate VO = 1.5V to 3.5V 130 V/µs BW Small-Signal Bandwidth AV = 10 5.3 MHz IS Supply Current IS/D – Shutdown Supply Current Pin 5 at V Shutdown Pin Current Pin 5 at V – 12 15 mA 0.8 1.5 mA 5 25 µA + – 5V ELECTRICAL CHARACTERISTICS –55°C ≤ TA ≤ 125°C, (Note 3) VS = ±5V, VREF = 0V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to ground, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open. MIN LT1187M TYP MAX SYMBOL PARAMETER CONDITIONS VOS Input Offset Voltage Either Input, (Note 4) ∆VOS /∆T Input VOS Drift IOS Input Offset Current Either Input 0.2 1.5 µA IB Input Bias Current Either Input ± 0.5 ±3.5 µA 2.0 15 –2.5 mV µV/°C 8.0 Input Voltage Range UNITS 3.5 V CMRR Common-Mode Rejection Ratio VCM = –2.5V to 3.5V 70 100 dB PSRR Power Supply Rejection Ratio VS = ±2.375V to ±8V 60 85 dB VOUT Output Voltage Swing VS = ±5V, RL = 1k, AV = 50 ±3.7 ± 4.0 V VS = ±8V, RL = 1k, AV = 50 ±6.6 ±7.0 VS = ±8V, RL = 300Ω, AV = 50, (Note 3) ±6.4 ± 6.8 GE Gain Error IS Supply Current Shutdown Supply Current IS/D Shutdown Pin Current VO = ±1V, AV = 10, RL = 1k 0.2 1.2 % 13 17 mA Pin 5 at V –, (Note 11) 0.8 1.5 mA – 5 25 µA Pin 5 at V 3 LT1187 + ELECTRICAL CHARACTERISTICS 0°C ≤ TA ≤ 70°C, (Note 3) –V 5V = ±5V, V = 0V, R = 900Ω from pins 6 to 8, R = 100Ω from pin 8 to ground, R = R S REF FB1 FB2 L SYMBOL PARAMETER CONDITIONS VOS Input Offset Voltage Either Input, (Note 4) ∆VOS /∆T Input VOS Drift IOS Input Offset Current Either Input IB Input Bias Current Either Input Common-Mode Rejection Ratio + RFB2 = 1k, CL ≤ 10pF, pin 5 open. MIN LT1187C TYP MAX 2.0 12 70 mV 0.2 1.5 µA ± 0.5 ±3.5 µA 3.5 V – 2.5 VCM = –2.5V to 3.5V UNITS µV/°C 9.0 Input Voltage Range CMRR FB1 100 dB PSRR Power Supply Rejection Ratio VS = ±2.375V to ±8V 65 85 dB VOUT Output Voltage Swing VS = ±5V, RL = 1k, AV = 50 ±3.7 ±4.0 V VS = ±8V, RL = 1k, AV = 50 ±6.6 ±7.0 VS = ±8V, RL = 300Ω, AV = 50, (Note 3) ±6.4 ± 6.8 GE Gain Error IS Supply Current IS/D VO = ±1V, AV = 10, RL = 1k – Shutdown Supply Current Pin 5 at V , (Note 11) Shutdown Pin Current Pin 5 at V – 0.2 1.0 % 13 17 mA 0.8 1.5 mA 5 25 µA CHARACTERISTICS ELECTRICAL 5V + – 0°C ≤ TA ≤ 70°C, (Note 3) VS = 5V, VS = 0V, VREF = 2.5V, RFB1 = 900Ω from pins 6 to 8, RFB2 = 100Ω from pin 8 to VREF, RL = RFB1 + RFB2 = 1k, CL ≤ 10pF, pin 5 open. SYMBOL PARAMETER CONDITIONS VOS Input Offset Voltage Either Input, (Note 4) SOIC Package ∆VOS/∆T Input VOS Drift IOS Input Offset Current Either Input IB Input Bias Current Either Input MIN 2.0 2.0 Common-Mode Rejection Ratio VCM = 2.0V to 3.5V VOUT Output Voltage Swing RL = 300Ω to Ground VOUT High (Note 3) VOUT Low Supply Current Shutdown Supply Current Pin 5 at V –, (Note 11) Shutdown Pin Current Pin 5 at V – Note 1: A heat sink may be required to keep the junction temperature below absolute maximum when the output is shorted continuously. Note 2: TJ is calculated from the ambient temperature T A and power dissipation PD according to the following formulas: LT1187MJ8,LT1187CJ8: TJ = TA + (PD × 100°C/W) LT1187CN8: TJ = TA + (PD × 100°C/W) LT1187CS8: TJ = TA + (PD × 150°C/W) Note 3: When RL = 1k is specified, the load resistor is RFB1 + RFB2, but when RL = 300Ω is specified, then an additional 430Ω is added to the output such that (RFB1 + RFB2) in parallel with 430Ω is RL = 300Ω. Note 4: VOS measured at the output (pin 6) is the contribution from both input pair, and is input referred. Note 5: VIN LIM is the maximum voltage between –V IN and +VIN (pin 2 and pin 3) for which the output can respond. 4 UNITS mV mV µV/°C 0.2 1.5 µA ± 0.5 ± 3.5 µA 3.5 V 2.0 CMRR IS/D 12.0 13.0 9.0 Input Voltage Range IS LT1187C TYP MAX 70 100 dB 3.5 4.0 V 0.15 0.4 12 16 mA 0.8 1.5 mA 5 25 µA Note 6: Slew rate is measured between ±0.5V on the output, with a VIN step of ±0.75V, AV = 3 and RL = 1k. Note 7: Full power bandwidth is calculated from the slew rate measurement: FPBW = SR/2πVp. Note 8: Settling time measurement techniques are shown in “Take the Guesswork Out of Settling Time Measurements,” EDN, September 19, 1985. Note 9: NTSC (3.58MHz). Note 10: AC parameters are 100% tested on the ceramic and plastic DIP packaged parts (J8 and N8 suffix) and are sample tested on every lot of the SO packaged parts (S8 suffix). Note 11: See Application section for shutdown at elevated temperatures. Do not operate shutdown above T J > 125°C. LT1187 U W TYPICAL PERFOR A CE CHARACTERISTICS Input Bias Current vs Common-Mode Voltage Common-Mode Voltage vs Temperature Input Bias Current vs Temperature V+ 100 3.0 VS = ±5V 1.5 –55°C 1.0 0.5 25°C 0 +IB 0 –100 COMMON-MODE RANGE (V) INPUT BIAS CURRENT (nA) –IB IOS –200 –300 125°C –5 –4 –3 –2 –1 0 1 2 3 COMMON-MODE VOLTAGE (V) 4 – 400 –50 5 –25 0 25 75 50 TEMPERATURE (°C) V + = –1.8V TO –9V 1.0 400 300 200 100 0 1k 10k FREQUENCY (Hz) 8 6 4 25°C 12 125°C 10 2 0 Shutdown Supply Current vs Temperature 100 1k 10k FREQUENCY (Hz) 8 100k Open-Loop Gain vs Temperature VS = ±5V VOUT = ±2V AV = 10 RL = 1k VS = ±5V 2 GAIN ERROR (%) –0.05 VS/D = –VEE + 0.2V 10 8 5 VS/D = –VEE + 0.4V 4 6 8 ±SUPPLY VOLTAGE (V) LT1187 • TPC06 Gain Error vs Temperature 3 2 0 0 VS/D = –VEE + 0.6V – 55°C 14 LT1187 • TPC05 6 125 Supply Current vs Supply Voltage VS = ±5V TA = 25°C RS = 100k 10 10 100k 100 16 SUPPLY CURRENT (mA) VS = ±5V TA = 25°C RS = 0Ω 0 25 75 50 TEMPERATURE (°C) LT1187 • TPC03 12 LT1187 • TPC04 SHUTDOWN SUPPLY CURRENT (mA) 2.0 1.5 Equivalent Input Noise Current vs Frequency EQUIVALENT INPUT NOISE CURRENT (pA/√Hz) EQUIVALENT INPUT NOISE VOLTAGE (nV/√Hz) 600 4 –2.0 LT1187 • TPC02 Equivalent Input Noise Voltage vs Frequency 100 –1.5 V– – 50 –25 125 100 LT1187 • TPC01 500 –1.0 0.5 –0.5 VS = ±5V VO = ±3V OPEN-LOOP GAIN (kV/V) INPUT BIAS CURRENT (µA) 2.0 10 V + = 1.8V TO 9V –0.5 2.5 –0.10 –0.15 RL = 1k 6 4 RL = 500Ω 2 1 VS/D = –VEE 0 –50 –25 50 0 25 75 TEMPERATURE (°C) 100 125 LT1187 • TPC07 –0.20 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 LT1187 • TPC08 0 –50 –25 25 75 0 50 TEMPERATURE (°C) 100 125 LT1187 • TPC09 5 LT1187 U W TYPICAL PERFOR A CE CHARACTERISTICS Open-Loop Voltage Gain vs Load Resistance Gain, Phase vs Frequency 100 80 40 40 GAIN 20 20 0 PHASE MARGIN (DEG) 60 60 0 –20 100k 16k –20 1M 10M FREQUENCY (Hz) 60 12k 8k 4k TA = 25°C 50 TA = 125˚C 40 30 0 100 100M TA = – 55°C AV = 20dB VS = ±5V VO = ±3V TA = +25˚C GAIN BANDWIDTH PRODUCT (MHz) PHASE 80 VOLTAGE GAIN (dB) VS = ±5V TA = 25°C RL = 1k OPEN-LOOP VOLTAGE GAIN (V/V) 100 Gain Bandwidth Product vs Supply Voltage 1k LOAD RESISTANCE (Ω) 10k 0 2 4 8 6 ±SUPPLY VOLTAGE (V) LT1187 • TPC11 LT1187 • TPC12 Gain Bandwidth Product and Unity Gain Phase Margin vs Temperature 65 55 UNITY GAIN PHASE MARGIN 40 45 OUTPUT IMPEDANCE (Ω) GAIN BANDWIDTH PRODUCT COMMON-MODE REJECTION RATIO (dB) VS = ±5V TA = 25°C PHASE MARGIN (DEG) 10 AV = 10 1.0 AV = 2 30 –50 –25 25 75 0 50 TEMPERATURE (°C) 35 125 100 0.1 1k 10k 100k 1M FREQUENCY (Hz) LT1187 • TPC13 40 20 0 –20 1k 10k 1M 100k FREQUENCY (Hz) 10M 100M LT1187 • TPC16 OUTPUT SHORT CIRCUIT CURRENT (mA) POWER SUPPLY REJECTION RATIO (dB) +PSRR –PSRR 50 40 1M 10M FREQUENCY (Hz) V+ – 0.7 VS = ± 5V 35 34 33 32 31 30 – 50 –25 50 0 25 75 TEMPERATURE (°C) 100 125 LT1187 • TPC17 100M LT1187 • TPC15 36 60 60 30 100k 100M Output Short Circuit Current vs Temperature 80 VS = ±5V TA = 25°C VRIPPLE = ±300mV VS = ±5V TA = 25°C RL = 1k 70 LT1187 • TPC14 Power Supply Rejection Ratio vs Frequency 6 10M OUTPUT SATURATION VOLTAGE (V) GAIN BANDWIDTH PRODUCT (MHz) 80 100 VS = ±5V RL = 1k 50 Common-Mode Rejection Ratio vs Frequency Output Impedance vs Frequency 60 10 ± Output Swing vs Supply Voltage –0.8 125°C –0.9 25°C –1.0 –1.1 0.5 –55°C RL = 1k ±1.8V ≤ VS ≤ ±9V 0.4 125°C 25°C 0.3 –55°C 0.2 0.1 V– 0 2 4 6 8 ±SUPPLY VOLTAGE (V) 10 LT1187 • TPC18 LT1187 U W TYPICAL PERFOR A CE CHARACTERISTICS Output Voltage Swing vs Load Resistance 250 4 VS = ±5V TA = –55°C 3 SLEW RATE (V/µs) TA = 25°C TA = 125°C 1 –1 TA = 25°C –3 200 +SLEW RATE TA = –55°C TA = 125°C 150 –50 –25 –5 100 LOAD RESISTANCE (Ω) 1000 VS = ±5V TA = 25°C RL = 1k 10mV 2 0 –2 10mV –4 0 25 50 75 TEMPERATURE (°C) 100 125 40 50 60 70 80 SETTLING TIME (ns) LT1187 • TPC20 LT1187 • TPC19 Harmonic Distortion vs Output Voltage 90 100 LT1187 • TPC21 Large-Signal Transient Response –30 VS = ±5V TA = 25°C RL = 1k f = 1MHz AV = 10 –35 DISTORTION (dBc) 10 –SLEW RATE VS = ±5V RL = 1k VO = ± 0.5V AV = 2 OUTPUT VOLTAGE STEP (V) 5 OUTPUT VOLTAGE SWING (V) Output Voltage Step vs Settling Time, AV = 2 Slew Rate vs Temperature –40 HD3 HD2 –45 –50 –55 –60 0 1 4 3 5 2 OUTPUT VOLTAGE (VP-P) 6 7 INPUT IN LIMITING, AV = 3, SR = 180V/ µs LT1187 • TPC22 Small-Signal Transient Response LT1187 • TPC23 Small-Signal Transient Response AV = 2, RFB = 1k, OVERSHOOT = 25% AV = 2, RFB = 1k, OVERSHOOT = 25% LT1187 • TPC24 LT1187 • TPC25 7 LT1187 U W U U APPLICATIO S I FOR ATIO The primary use of the LT1187 is in converting high speed differential signals to a single-ended output. The LT1187 video difference amplifier has two uncommitted high input impedance (+) and (–) inputs. The amplifier has another set of inputs which can be used for reference and feedback. Additionally, this set of inputs give gain adjust and DC control to the difference amplifier. The voltage gain of the LT1187 is set like a conventional operational amplifier. Feedback is applied to pin 8, and it is optimized for gains of 2 or greater. The amplifier can be operated single-ended by connecting either the (+) or (–) inputs to the +/REF (pin 1). The voltage gain is set by the resistors: (RFB + RG)/RG. Like the single-ended case, the differential voltage gain is set by the external resistors: (RFB + RG)/RG. The maximum input differential signal for which the output will respond is approximately ±0.38V. S/D 5 VIN S/D V+ 3 7 + 2 – LT1187 1 +/REF 8 –/FB 4 6 V+ 5 3 7 + 2 – LT1187 1 +/REF 8 –/FB 4 V IN VOUT V– RFB RG AV = + 6 VOUT RG RG AV = – The LT1187 is quite tolerant of power supply bypassing. In some applications a 0.1µF ceramic disc capacitor placed 1/2 inch from the amplifier is all that is required. In applications requiring good settling time, it is important to use multiple bypass capacitors. A 0.1µF ceramic disc in parallel with a 4.7µF tantalum is recommended. Calculating the Output Offset Voltage Both input stages contribute to the output offset voltage at pin 6. The feedback correction forces balance in the input stages by introducing an Input VOS at pin 8. The complete expression for the output offset voltage is: VOUT = (VOS + IOS(RS) + IB(RREF)) × (RFB+RG)/RG + IB(RFB) RS represents the input source resistance, typically 75Ω, and RREF represents the finite source impedance from the DC reference voltage, for VREF grounded, RREF = 0Ω. The IOS is normally a small contributor and the expression simplifies to: VOUT = VOS(RFB+RG)/RG + IB(RFB) If RFB is limited to 1k the last term of the equation contributes only 2mV, since IB is less than 2µA. V– RFB RFB + RG Power Supply Bypassing RFB + RG 7 V+ RG 6 S/D VIN DIFF VIN S/D V+ 5 3 7 + 2 – LT1187 1 +/REF 8 –/FB 4 6 V+ 5 3 7 + 2 – LT1187 1 +/REF 8 –/FB 4 VIN DIFF VOUT V IN RG V– RFB RFB 6 Q1 VOUT 3 V– RFB + RS 2 – RS Q2 RE 1.1k 345µA RG VO = (VIN DIFF + VIN) RFB + RG RG VO = ( RFB + RG RG (V IN DIFF – RFB ( R (V G IN Q3 + 1 REF RREF Q4 8 RG RE 1.1k 350µA 4 V– LT1187 • AI01 Figure 1. Simplified Input Stage Schematic 8 ILT1187 • AI02 LT1187 U W U U APPLICATIO S I FOR ATIO Operating with Low Closed-Loop Gains The LT1187 has been optimized for closed-loop gains of 2 or greater. For a closed-loop gain of 2 the response peaks about 2dB. Peaking can be eliminated by placing a capacitor across the feedback resistor, (feedback zero). This peaking shows up as time domain overshoot of about 25%. Small-Signal Transient Response Closed-Loop Voltage Gain vs Frequency CLOSED-LOOP VOLTAGE GAIN (dB) 9 8 CFB = 0pF 7 AV = 2, WITH 8pF FEEDBACK CAPACITOR 6 LT1187 • AI05 5 CFB = 5pF 4 Extending the Input Range CFB = 10pF 3 VS = ±5V TA = 25°C AV = 2 RFB = 900Ω RG = 900Ω 2 1 0 –1 100k 1M 10M FREQUENCY (Hz) Figure 1 shows a simplified schematic of the LT1187. In normal operation the REF pin 1 is grounded or taken to a DC offset control voltage and differential signals are applied between pins 2 and 3. The input responds linearly until all of the 345µA current flows through the 1.1k resistor and Q1 (or Q2) turns off. Therefore the maximum input swing is 380mVP or 760mVP-P. The second differential pair, Q3 and Q4, is running at slightly larger current so that when the first input stage limits, the second stage remains biased to maintain the feedback. 100M LT1187 • AI03 Small-Signal Transient Response Occasionally it is necessary to handle signals larger than 760mVP-P at the input. The LT1187 input stage can be tricked to handle up to 1.5VP-P. To do this, it is necessary to ground pin 3 and apply the differential input signal between pin 1 and 2. The input signal is now applied across two 1.1k resistors in series. Since the input signal is applied to both input pairs, the first pair will run out of bias current before the second pair, causing the amplifier to go open-loop. The results of this technique are shown in the following scope photo. AV = 2, OVERSHOOT = 25%, RFB = RG = 1k LT1187 • AI04 9 LT1187 U W U U APPLICATIO S I FOR ATIO LT1187 in Unity Gain Performance Characteristics section. At very high elevated temperature it is important to hold the shutdown pin close to the negative supply to keep the supply current from increasing. A Send Color Video Over Twisted-Pair B C (A) STANDARD INPUTS, PINS 2 TO 3, VIN = 1.0VP-P (B) EXTENDED INPUTS, PINS 2 TO 2, VIN = 1.0VP-P (C) EXTENDED INPUTS, PINS 1 TO 2, VIN = 2.0VP-P LT1187 • AI06 Using the Shutdown Feature The LT1187 has a unique feature that allows the amplifier to be shutdown for conserving power, or for multiplexing several amplifiers onto a common cable. The amplifier will shutdown by taking pin 5 to V –. In shutdown, the amplifier dissipates 15mW while maintaining a true high impedance output state of 20k in parallel with the feedback resistors. For MUX applications, the amplifiers may be configured inverting, noninverting, or differential. When the output is loaded with as little 1k from the amplifier’s feedback resistors, the amplifier shuts off in 600ns. This shutoff can be under the control of HC CMOS operating between 0V and –5V. The ability to maintain shutoff is shown on the curve Shutdown Supply Current vs Temperature in the Typical 1MHz Sine Wave Gated Off with Shutdown Pin With an LT1187 it is possible to send and receive color composite video signals more than 1000 feet on a low cost twisted-pair. A bidirectional “video bus” consists of the LT1195 op amp and the LT1187 video difference amplifier. A pair of LT1195s at TRANSMIT 1, is used to generate differential signals to drive the line which is back-terminated in its characteristic impedance. The LT1187, twistedpair receiver, converts signals from differential to singleended. Topology of the LT1187 provides for cable compensation at the amplifier’s feedback node as shown. In this case, 1000 feet of twisted-pair is compensated with 1000pF and 50Ω to boost the 3dB bandwidth of the system from 750kHz to 4MHz. This bandwidth is adequate to pass a 3.58MHz chroma subcarrier, and the 4.5MHz sound subcarrier. Attenuation in the cable can be compensated by lowering the gain set resistor RG. At TRANSMIT 2, another pair of LT1195s serve the dual function to provide cable termination via low output impedance, and generate differential signals for TRANSMIT 2. Cable termination is made up of a 15Ω and 33Ω attenuator to reduce the differential input signal to the LT1187. Maximum input signal for the LT1187 is 760mVP-P. 1.5MHz Square Wave Input and Unequalized Response Through 1000 Feet of Twisted-Pair SHUTDOWN VOUT AV = 2, RFB = RG = 1k LT1187 • AI07 10 LT1187 • AI08 LT1187 U W U U APPLICATIO S I FOR ATIO 1.5MHz Square Wave Input and Equalized Response Through 1000 Feet of Twisted-Pair Multiburst Pattern Passed Through 1000 Feet of Twisted-Pair LT1187 • AI10 LT1187 • AI09 Bidirectional Video Bus TRANSMIT 1 3 + 1k 75Ω TRANSMIT 2 + LT1195 2 6 6 3 1k LT1195 – – 1k 1k 1k 1k 1k 2 1k – 6 LT1195 3 + 6 33Ω S/D + – LT1187 + – R 5 75Ω 6 75Ω 2 33Ω 33Ω 15Ω 3 15Ω 2 1 15Ω 1 8 8 FB 300Ω 1000pF RG 300Ω RECEIVE 2 50Ω + – + – 1000pF 50Ω + 3 S/D 3 2 1000 FEET TWISTED-PAIR 2 LT1195 33Ω 15Ω – 5 LT1187 6 75Ω RFB 300Ω RG 300Ω RECEIVE 1 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. LT1187 • AI11 11 LT1187 W W SI PLIFIED SCHE ATIC 7 V+ VBIAS VBIAS CM + 3 CFF – 2 +V 6 VOUT +V * 4 V– 5 S/D 1 +/REF 8 –/FB * SUBSTRATE DIODE, DO NOT FORWARD BIAS LT1187 • SS U PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. 0.290 – 0.320 (7.366 – 8.128) J8 Package 8-Lead Hermetic DIP 0.200 (5.080) MAX CORNER LEADS OPTION (4 PLCS) 0.015 – 0.060 (0.381 – 1.524) 0.023 – 0.045 (0.58 – 1.14) HALF LEAD OPTION 0.008 – 0.018 (0.203 – 0.460) 0° – 15° 0.385 ± 0.025 (9.779 ± 0.635) 0.045 – 0.065 (1.14 – 1.65) FULL LEAD OPTION 0.300 – 0.320 (7.620 – 8.128) 0.045 – 0.065 (1.143 – 1.651) 8 6 7 5 0.025 (0.635) RAD TYP 0.220 – 0.310 (5.588 – 7.874) 2 3 4 0.125 3.175 0.100 ± 0.010 MIN (2.540 ± 0.254) 0.400 (10.160) MAX 0.130 ± 0.005 (3.302 ± 0.127) 8 7 6 5 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) ( 0.405 (10.287) MAX 1 0.045 – 0.065 (1.14 – 1.65) 0.014 – 0.026 (0.360 – 0.660) N8 Package 8-Lead Plastic DIP 0.005 (0.127) MIN +0.025 0.325 –0.015 +0.635 8.255 –0.381 0.250 ± 0.010 (6.350 ± 0.254) 0.125 (3.175) MIN 0.045 ± 0.015 (1.143 ± 0.381) ) 0.100 ± 0.010 (2.540 ± 0.254) 0.020 (0.508) MIN 1 2 4 3 0.018 ± 0.003 (0.457 ± 0.076) 0.189 – 0.197 (4.801 – 5.004) 0.010 – 0.020 × 45° (0.254 – 0.508) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 0.050 (1.270) BSC 12 6 5 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157 (3.810 – 3.988) 1 Linear Technology Corporation 7 0.004 – 0.010 (0.101 – 0.254) 0.008 – 0.010 (0.203 – 0.254) S8 Package 8-Lead Plastic SOIC 8 0.053 – 0.069 (1.346 – 1.752) 2 3 4 BA/LT/GP 0293 10K REV0 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1993