LT1497 Dual 125mA, 50MHz Current Feedback Amplifier U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Minimum Output Current: ±125mA Maximum Supply Current per Amp: 7mA, VS = ±5V Bandwidth: 50MHz, VS = ± 15V Slew Rate: 900V/µs, VS = ±15V Wide Supply Range: VS = ±2.5V to ±15V (Enhanced θJA 16-Pin SO Package) Enhanced θJA SO-8 Package for ±5V Operation 0.02% Differential Gain: AV = 2, RL = 150Ω 0.015° Differential Phase: AV = 2, RL = 150Ω ±13V Output Swing: IL = 100mA, VS = ±15V ±3.1V Output Swing: IL = 100mA, VS = ±5V 55ns Settling Time to 0.1%, 10V Step Thermal Shutdown Protection The LT®1497 dual current feedback amplifier features low power, high output drive, excellent video characteristics and outstanding distortion performance. From a low 7mA maximum supply current per amplifier, the LT1497 drives ±100mA with only 1.9V of headroom. Twisted pairs can be driven differentially with – 70dBc distortion up to 1MHz for ±40mA peak signals. The LT1497 is available in a low thermal resistance 16-pin SO package for operation with supplies up to ±15V. For ±5V operation the device is also available in a low thermal resistance SO-8 package. The device has thermal and current limit circuits that protect against fault conditions. The LT1497 is manufactured on Linear Technology’s complementary bipolar process. The device has characteristics that bridge the performance between the LT1229 and LT1207 dual current feedback amplifiers. The LT1229 has 30mA output drive, 100MHz bandwidth and 12mA supply current. The LT1207 has 250mA output drive, 60MHz bandwidth and 40mA supply current. U APPLICATIONS ■ ■ ■ ■ Twisted-Pair Drivers Video Amplifiers Cable Drivers Test Equipment Amplifiers Buffers , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ TYPICAL APPLICATION HDSL2 Single Pair Line Driver 2nd and 3rd Harmonic Distortion of HDSL2 Single Pair Line Driver 560Ω 560Ω – 40 – – 50 VS = ± 5V VIN = ±1.25V VOUT = ± 2.5V VIN + 1:1* 560Ω 135Ω 560Ω DISTORTION (dBc) 68.1Ω 1/2 LT1497 – 60 – 70 2ND 3RD – 80 – 68.1Ω *MIDCOM 671-7807 1/2 LT1497 – 90 100k + 1M 2M FREQUENCY (Hz) 1419 TA01 1497 TA02 1 LT1497 W W U W ABSOLUTE MAXIMUM RATINGS Total Supply Voltage (V + to V –) LT1497CS8.......................................................... 14V LT1497CS............................................................ 36V Noninverting Input Current ................................... ±2mA Output Short-Circuit Duration (Note 1) .......... Continuous Operating Temperature Range (Note 2) ... – 40°C to 85°C Specified Temperature Range ...................... 0°C to 70°C Maximum Junction Temperature (See Below) ....... 150°C Storage Temperature Range .................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................... 300°C W U U PACKAGE/ORDER INFORMATION ORDER PART NUMBER 1 16 V – NC 2 15 NC OUT A 3 14 V + TOP VIEW OUT A LT1497CS8 8 V+ 1 –IN A 2 7 OUT B –IN A 4 A +IN A 3 V– 4 B 6 –IN B +IN A 5 5 +IN B V– 6 S8 PACKAGE 8-LEAD PLASTIC SO S8 PART MARKING TJMAX = 150°C, θJA = 80°C/ W (NOTE 3) ORDER PART NUMBER TOP VIEW V– 1497 LT1497CS 13 OUT B A B 12 –IN B 11 +IN B NC 7 10 NC V– 8 9 V– S PACKAGE 16-LEAD PLASTIC SO TJMAX = 150°C, θJA = 40°C/ W (NOTE 3) Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS VCM = 0V, ±2.5V ≤ VS ≤ ±15V (LT1497CS), ±2.5V ≤ VS ≤ ±5V (LT1497CS8), pulse tested unless otherwise noted. SYMBOL PARAMETER CONDITIONS VOS Input Offset Voltage TA = 25°C MIN TYP MAX UNITS ±3 ±10 ±15 mV mV ±1 ±3.5 ±5.0 mV mV ● Input Offset Voltage Matching TA = 25°C ● Input Offset Voltage Drift IIN+ Noninverting Input Current TA = 25°C ±1 ±3 ±10 µA µA ±0.3 ±1.0 ±1.5 µA µA ±7 ±20 ±40 µA µA ±3 ±10 ±15 µA µA ● Noninverting Input Current Matching TA = 25°C ● IIN– Inverting Input Current TA = 25°C ● Inverting Input Current Matching µV/°C 10 ● TA = 25°C ● en Input Noise Voltage Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 0Ω 3 nV/√Hz + in Noninverting Input Noise Current Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 10k 2 pA/√Hz – in Inverting Input Noise Current Density f = 1kHz, RF = 1k, RG = 10Ω, RS = 10k 20 pA/√Hz RIN Input Resistance VIN = ±13V, VS = ±15V VIN = ±3V, VS = ±5V VIN = ±0.5V, VS = ±2.5V 10 8 8 MΩ MΩ MΩ CIN Input Capacitance 3 pF 2 ● ● ● 1.5 1.5 1.5 LT1497 ELECTRICAL CHARACTERISTICS VCM = 0V, ±2.5V ≤ VS ≤ ±15V (LT1497CS), ±2.5V ≤ VS ≤ ±5V (LT1497CS8), pulse tested unless otherwise noted. SYMBOL CMRR PARAMETER CONDITIONS Input Voltage Range VS = ±15V VS = ±5V VS = ±2.5V Common Mode Rejection Ratio VS = ±15V, VCM = ±13V, TA = 25°C MIN TYP ● ● ● ±13 ±3.0 ±0.5 ±14 ±4.0 ±1.5 V V V 55 53 62 ● dB dB 54 52 60 ● dB dB 52 50 56 ● dB dB VS = ±5V, VCM = ±3V, TA = 25°C VS = ±2.5V, VCM = ±0.5V, TA = 25°C PSRR Inverting Input Current Common Mode Rejection VS = ±15V, VCM = ±13V VS = ±5V, VCM = ±3V VS = ±2.5V, VCM = ±0.5V Power Supply Rejection Ratio VS = ±2V to ±15V, TA = 25°C 2.0 2.5 3.0 ● ● ● MAX 10 10 10 UNITS µA/V µA/V µA/V 66 63 76 ● dB dB 66 63 76 ● dB dB VS = ±2V to ±5V, TA = 25°C Noninverting Input Current Power Supply Rejection VS = ±2V to ±15V VS = ±2V to ±5V ● ● 5 5 50 50 nA/V nA/V Inverting Input Current Power Supply Rejection VS = ±2V to ±15V VS = ±2V to ±5V ● ● 0.1 0.1 2 2 µA/V µA/V AVOL Large-Signal Voltage Gain VS = ± 15V, VOUT = ±10V, RL = 150Ω VS = ±5V, VOUT = ±2.5V, RL = 50Ω VS = ±2.5V, VOUT = ±0.5V, RL = 50Ω ● ● ● 66 66 66 80 80 80 dB dB dB ROL Transresistance, ∆VOUT/∆IIN– VS = ±15V, VOUT = ±10V, RL = 150Ω VS = ±5V, VOUT = ±2.5V, RL = 50Ω VS = ±2.5V, VOUT = ±0.5V, RL = 50Ω ● ● ● 100 100 100 500 500 300 kΩ kΩ kΩ VOUT Maximum Output Swing VS = ±15V, RL = 150Ω, TA = 25°C ±12.80 ±12.60 ±13.15 ● V V ±12.65 ±12.55 ±13.0 ● V V ±3.20 ±3.10 ±3.45 ● V V ±2.75 ±2.65 ±3.10 ● V V ±1.25 ±1.15 ±1.45 ● V V ±1.00 ±0.90 ±1.15 ● V V ● ● ± 125 ± 125 ± 220 ± 220 ± 140 mA mA mA VS = ±15V, IL = ±100mA, TA = 25°C VS = ±5V, RL = 50Ω, TA = 25°C VS = ±5V, IL = ±100mA, TA = 25°C VS = ±2.5V, RL = 50Ω, TA = 25°C VS = ±2.5V, IL = ±50mA, TA = 25°C IOUT Maximum Output Current RL = 1Ω, VS = ±15V RL = 1Ω, VS = ±5V RL = 1Ω, VS = ±2.5V IS Supply Current per Amplifier VS = ±2.5V to ±5V, TA = 25°C 6.0 7.0 8.0 mA mA 7.0 9.0 10.5 mA mA ● VS = ±15V, TA = 25°C ● Channel Separation VS = ±15V, VOUT = ±10V, RL = 150Ω VS = ±5V, VOUT = ±2.5V, RL = 50Ω ● ● 100 100 120 115 dB dB 3 LT1497 ELECTRICAL CHARACTERISTICS VCM = 0V, ±2.5V ≤ VS ≤ ±15V (LT1497CS), ±2.5V ≤ VS ≤ ±5V (LT1497CS8), pulse tested unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP SR Slew Rate VS = ±15V, TA = 25°C (Note 4) 900 ● 500 400 V/µs V/µs 200 150 350 ● V/µs V/µs VS = ±5V, TA = 25°C (Note 4) MAX UNITS BW Small-Signal Bandwidth VS = ±15V, RF = RG = 560Ω, RL = 100Ω VS = ±5V, RF = RG = 560Ω, RL = 100Ω VS = ±2.5V, RF = RG = 560Ω, RL = 100Ω 50 35 30 MHz MHz MHz tr Small-Signal Rise Time VS = ±15V, RF = RG = 560Ω, RL = 100Ω VS = ±5V, RF = RG = 560Ω, RL = 100Ω VS = ±2.5V, RF = RG = 560Ω, RL = 100Ω 7.5 9.5 11 ns ns ns Overshoot VS = ±15V, RF = RG = 560Ω, RL = 100Ω VS = ±5V, RF = RG = 560Ω, RL = 100Ω VS = ±2.5V, RF = RG = 560Ω, RL = 100Ω 15 12 10 % % % Propagation Delay VS = ±15V, RF = RG = 560Ω, RL = 100Ω VS = ±5V, RF = RG = 560Ω, RL = 100Ω VS = ±2.5V, RF = RG = 560Ω, RL = 100Ω 6.8 8.4 9.7 ns ns ns Settling Time VS = ±15V, 10V Step, 0.1%, AV = – 1 VS = ±5V, 5V Step, 0.1%, AV = – 1 55 50 ns ns Differential Gain (Note 5) VS = ±15V, RF = RG = 510Ω, RL = 150Ω VS = ±15V, RF = RG = 510Ω, RL = 50Ω VS = ±5V, RF = RG = 510Ω, RL = 150Ω VS = ±5V, RF = RG = 510Ω, RL = 50Ω 0.02 0.19 0.08 0.41 % % % % Differential Phase (Note 5) VS = ±15V, RF = RG = 510Ω, RL = 150Ω VS = ±15V, RF = RG = 510Ω, RL = 50Ω VS = ±5V, RF = RG = 510Ω, RL = 150Ω VS = ±5V, RF = RG = 510Ω, RL = 50Ω 0.015 0.235 0.045 0.310 Deg Deg Deg Deg ts The ● denotes specifications which apply over the full operating temperature range. Note 1: Applies to short circuits to ground only. A short circuit between the output and either supply may damage the part when operated on supplies greater than ±10V Note 2: The LT1497 is designed, characterized and expected to operate over the temperature range of – 40°C to 85°C, but is not tested at – 40°C and 85°C. Guaranteed industrial grade parts are available, consult factory. Note 3: Thermal resistance varies depending upon the amount of PC board metal attached to the device. θJA is specified for a 2500mm2 test board covered with 2oz copper on both sides. 4 Note 4: Slew rate is measured between ±5V on a ±10V output signal while operating on ±15V supplies with RF = 453Ω, RG = 49.9Ω and RL = 150Ω. On ±5V supplies slew rate is measured between ±1V on a ±3V output signal. The slew rate is much higher when the input is overdriven and when the amplifier is operated inverting. See the Applications Information section. Note 5: NTSC composite video with an amplifier output level of 2V peak. LT1497 W SMALL-SIGNAL BANDWIDTH U U VS = ±15V, Peaking ≤ 1dB AV –1 RL 150 50 20 150 50 20 150 50 20 150 50 20 1 2 10 VS = ±5V, Peaking ≤ 1dB RF 560 560 620 560 560 560 510 560 620 270 270 270 RG 560 560 620 – – – 510 560 620 30 30 30 – 3dB BW (MHz) 59.2 43.1 30.0 57.0 42.7 30.3 59.1 41.7 20.7 43.4 30.9 19.0 AV –1 RL 150 50 20 150 50 20 150 50 20 150 50 20 1 2 10 RF 510 560 560 510 560 560 510 560 560 270 270 270 RG 510 560 560 – – – 510 560 560 30 30 30 – 3dB BW (MHz) 45.0 32.0 23.2 44.3 31.7 22.9 41.7 30.4 21.9 28.1 21.9 14.6 U W TYPICAL PERFORMANCE CHARACTERISTICS – 3dB Bandwidth vs Supply Voltage Voltage Gain and Phase vs Frequency, Gain = 6dB 0 90 45 80 8 ±15V ± 5V 135 5 180 4 225 ± 5V 3 270 ±15V 2 1 0 – 3dB BANDWIDTH (MHz) 90 GAIN 6 PHASE SHIFT (DEG) VOLTAGE GAIN (dB) 7 RL = 100Ω RF = RG = 560Ω –1 0.1 PEAKING ≤ 1dB PEAKING ≤ 5dB 90 GAIN = 2 RL = 1k 70 RF = 470Ω 60 RF = 560Ω 50 40 RF = 750Ω 30 RF = 1k 20 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE (± V) 1497 G01 0 ±15V 24 90 22 135 GAIN 20 180 18 225 16 12 10 8 0.1 270 ± 5V 14 ±15V RL = 100Ω RF = 270Ω RG = 30Ω PEAKING ≤ 1dB PEAKING ≤ 5dB 80 PHASE SHIFT (DEG) VOLTAGE GAIN (dB) ± 5V 90 45 – 3dB BANDWIDTH (MHz) PHASE 16 100 1497 G04 RF = 560Ω 40 30 RF = 750Ω 20 RF = 1k 0 18 2 4 6 8 10 12 14 SUPPLY VOLTAGE (± V) 60 RF = 560Ω 90 PEAKING ≤ 1dB PEAKING ≤ 5dB 80 RF = 430Ω 40 30 18 1497 G03 GAIN = 10 RL = 1k RF = 270Ω 50 16 – 3dB Bandwidth vs Supply Voltage 70 RF = 750Ω 20 RF = 1k 10 1 10 FREQUENCY (MHz) 50 – 3dB Bandwidth vs Supply Voltage 28 RF = 470Ω 60 1497 G02 Voltage Gain and Phase vs Frequency, Gain = 20dB 26 70 0 0 100 GAIN = 2 RL = 100Ω 10 10 1 10 FREQUENCY (MHz) PEAKING ≤ 1dB PEAKING ≤ 5dB 80 – 3dB BANDWIDTH (MHz) PHASE – 3dB BANDWIDTH (MHz) 9 – 3dB Bandwidth vs Supply Voltage 70 60 50 RF = 430Ω 40 RF = 270Ω RF = 560Ω 30 20 10 0 GAIN = 10 RL = 100Ω RF = 750Ω RF = 1k 0 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE (± V) 16 18 1497 G05 0 2 4 6 8 10 12 14 SUPPLY VOLTAGE (± V) 16 18 1497 G06 5 LT1497 U W TYPICAL PERFORMANCE CHARACTERISTICS Differential Phase vs Supply Voltage Differential Gain vs Supply Voltage 0.4 RL = 50Ω 0.3 0.2 0.1 0.3 RL = 50Ω 0.2 0.1 7 5 RL = 1k RL = 1k RL = 150Ω 11 13 9 SUPPLY VOLTAGE (± V) 0 15 –2 11 13 9 SUPPLY VOLTAGE (± V) –3 IL = 100mA 3 2 IL = 125mA 1 IL = 100mA IL = 50mA V– – 50 – 25 IL = 75mA 50 25 75 0 TEMPERATURE (°C) 100 IL = 50mA –1 IL = 75mA –2 IL = 125mA –3 IL = 100mA 3 2 IL = 125mA 1 IL = 100mA IL = 50mA IL = 75mA 50 25 75 0 TEMPERATURE (°C) V+ 8.0 – 0.5 COMMON MODE RANGE (V) SUPPLY CURRENT PER AMPLIFIER (mA) 8.5 6.5 VS = ± 5V VS = ± 2.5V 5.5 5.0 – 50 – 25 100 125 1497 G13 6 100 3 2 IL = 75mA 1 V– – 50 – 25 125 IL = 75mA –3 IL = 25mA IL = 50mA 50 25 75 0 TEMPERATURE (°C) 100 1497 G12 350 V + = 2V TO 18V –1.0 –1.5 1.5 1.0 V– – 50 – 25 V – = – 2V TO –18V 50 25 75 0 TEMPERATURE (°C) 125 Output Short-Circuit Current vs Junction Temperature 0.5 50 25 75 0 TEMPERATURE (°C) IL = 25mA IL = 50mA –2 Input Common Mode Limit vs Junction Temperature 7.0 VS = ±2.5V –1 1497 G11 Supply Current vs Ambient Temperature 6.0 Output Saturation Voltage vs Junction Temperature, ±2.5V V+ 1497 G10 VS = ±15V 3 1497 G09 VS = ± 5V V– – 50 – 25 125 7.5 1 2 FEEDBACK RESISTOR (kΩ) 0 15 OUTPUT SHORT-CIRCUIT CURRENT (mA) IL = 125mA 10 1 7 5 OUTPUT SATURATION VOLTAGE (V) OUTPUT SATURATION VOLTAGE (V) OUTPUT SATURATION VOLTAGE (V) V+ IL = 75mA VS = ±15V 100 Output Saturation Voltage vs Junction Temperature, ±5V VS = ± 15V IL = 50mA VS = ± 5V 1497 G08 Output Saturation Voltage vs Junction Temperature, ±15V –1 1000 RL = 150Ω 1497 G07 V+ RL = 1k AV = 2 PEAKING ≤ 5dB RF = RG = 510Ω AV = 2 AMPLIFIER OUTPUT = 2V PEAK CAPACITIVE LOAD (pF) 0.4 0 10000 0.5 RF = RG = 510Ω AV = 2 AMPLIFIER OUTPUT = 2V PEAK DIFFERENTIAL GAIN (%) DIFFERENTIAL PHASE (DEG) 0.5 Maximum Capacitive Load vs Feedback Resistor 100 125 1497 G14 VS = ±15V RL = 1Ω 300 250 SINKING 200 SOURCING 150 100 50 0 – 50 – 25 50 25 75 0 TEMPERATURE (°C) 100 125 1497 G15 LT1497 U W TYPICAL PERFORMANCE CHARACTERISTICS 10 AV = –1 AV = 1 6 4 2 0 –2 –4 AV = –1 –6 20 0 AV = –1 2 0 –2 –4 AV = –1 AV = 1 60 40 SETTLING TIME (ns) 80 100 25 50 75 100 125 150 175 200 225 250 SETTLING TIME (ns) 0 VOUT = 7VRMS VOUT = 2VRMS – 60 AV = 1 2ND – 70 AV = –1 2ND – 80 AV = 1 3RD AV = –1 3RD 0.1 100k 1 FREQUENCY (MHz) 1497 G19 80 POWER SUPPLY REJECTION (dB) 10 1 RF = RG = 1.5k 0.1 RF = RG = 560Ω 100k 1M 10M FREQUENCY (Hz) 30 25 20 15 100M 1497 G22 0 10 15 20 FREQUENCY (MHz) 5 60 50 NEGATIVE POSITIVE 40 30 20 10 0 10k 30 Amplifier Crosstalk vs Frequency VS = ±15V RL = 50Ω RF = RG = 560Ω 70 25 1497 G21 Power Supply Rejection vs Frequency VS = ±15V 0.01 10k 35 10 10 VS = ±15V RL = 50Ω RF = 270Ω RG = 30Ω PO1 = PO2 = 4dBm 1497 G20 Output Impedance vs Frequency OUTPUT IMPEDANCE (Ω) 1497 G18 –100 1k 10k FREQUENCY (Hz) 100k 3rd Order Intercept vs Frequency – 50 – 90 100 1k 10k FREQUENCY (Hz) 100 40 VS = ±15V VOUT = 5VP-P RL = 50Ω RF = 560Ω – 30 DISTORTION (dBc) TOTAL HARMONIC DISTORTION (%) – 20 – 40 100 1 10 2nd and 3rd Harmonic Distortion vs Frequency VS = ± 15V RL = 100Ω RF = RG = 560Ω 0.001 10 en 1497 G17 Total Harmonic Distortion vs Frequency 0.01 10 + in 1497 G16 0.10 – in –8 –10 – 10 OUTPUT TO INPUT CROSSTALK (dB) –10 AV = 1 4 –6 AV = 1 –8 VS = ±15V RF = 560Ω 8 OUTPUT STEP (V) OUTPUT STEP (V) 6 100 10 VS = ±15V RF = 560Ω Spot Noise Voltage and Current vs Frequency 3RD ORDER INTERCEPT (dBm) 8 Settling Time to 1mV vs Output Step SPOT NOISE (nV/√Hz OR pA/√Hz) Settling Time to 10mV vs Output Step – 20 – 30 – 40 VS = ±15V AV = 10 RL = 100Ω RF = 560Ω RG = 62Ω – 50 – 60 – 70 – 80 – 90 –100 100k 1M 10M FREQUENCY (Hz) 100M 1497 G23 –110 10k 100k 1M 10M FREQUENCY (Hz) 100M 1497 G24 7 LT1497 U W U U APPLICATIONS INFORMATION The LT1497 is a dual current feedback amplifier with high output current drive capability. Bandwidth is maintained over a wide range of voltage gains by the appropriate choice of feedback resistor. These amplifiers will drive low impedance loads such as cables with excellent linearity at high frequencies. Feedback Resistor Selection The optimum value for the feedback resistor is a function of the operating conditions of the device, the load impedance and the desired flatness of frequency response. The Small-Signal Bandwidth table gives the values which result in the highest bandwidth with less than 1dB of peaking for various gains, loads and supply voltages. If this level of flatness is not required, a higher bandwidth can be obtained by use of a lower feedback resistor. The characteristic curves of Bandwidth vs Supply Voltage indicate feedback resistors for peaking up to 5dB. These curves use a solid line when the response has less than 1dB of peaking and a dashed line when the response has 1dB to 5dB of peaking. Note that in a gain of 10 peaking is always under 1dB for the resistor ranges shown. Reducing the feedback resistor further than 270Ω in a gain of 10 will increase the bandwidth, but it also loads the amplifier and reduces the maximum current available to drive the load. Capacitive Loads The LT1497 can drive capacitive loads directly when the proper value of feedback resistor is used. The graph of Maximum Capacitive Load vs Feedback Resistor should be used to select the appropriate value. The graph shows feedback resistor values for 5dB frequency peaking when driving a 1k load at a gain of 2. This is a worst-case condition. The amplifier is more stable at higher gains and driving heavier loads (smaller load resistors). Alternatively, a small resistor (10Ω to 20Ω) can be put in series with the output to isolate the capacitive load from the amplifier output. This has the advantage in that the amplifier bandwidth is only reduced when the capacitive load is present, and the disadvantage that the gain is a function of the load resistance. 8 Capacitance on the Inverting Input Current feedback amplifiers require resistive feedback from the output to the inverting input for stable operation. Take care to minimize the stray capacitance between the output and the inverting input. Capacitance on the inverting input to ground will cause peaking in the frequency response (and overshoot in the transient response), but it does not degrade the stability of the amplifier. Power Supplies The LT1497 will operate on single or split supplies from ±2V (4V total) to ±15V (30V total). It is not necessary to use equal value split supplies, however, the offset voltage and inverting input bias current will change. The offset voltage changes about 1mV per volt of supply mismatch. The inverting bias current can change as much as 10µA per volt of supply mismatch, though typically the change is less than 2.5µA per volt. Thermal Considerations The LT1497 contains a thermal shutdown feature that protects against excessive internal (junction) temperature. If the junction temperature of the device exceeds the protection threshold, the device will begin cycling between normal operation and an off state. The cycling is not harmful to the part. The thermal cycling occurs at a slow rate, typically 10ms to several seconds, depending upon the power dissipation and the thermal time constants of the package and the amount of copper on the board under the package. Raising the ambient temperature until the device begins thermal shutdown gives a good indication of how much margin there is in the thermal design. For surface mount devices heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Experiments have shown that the heat spreading copper layer does not need to be electrically connected to the leads of the device. The PCB material can be very effective at transmitting heat between the pad area attached to V – pins of the device and a ground LT1497 U W U U APPLICATIONS INFORMATION or power plane layer either inside or on the opposite side of the board. Copper board stiffeners and plated throughholes can also be used to spread the heat generated by the device. Table 1 lists the thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 3/32" FR-4 board with 2oz copper. This data can be used as a rough guideline in estimating thermal resistance. The thermal resistance for each application will be affected by thermal interactions with other components as well as board size and shape. Table 1. Fused 16-lead and 8-lead SO Packages COPPER AREA (2oz) TOPSIDE BACKSIDE TOTAL COPPER AREA θJA (16-LEAD) θJA (8-LEAD) 2500mm2 2500mm2 5000mm2 40°C/W 80°C/W 1000mm2 2500mm2 3500mm2 46°C/W 92°C/W 600mm2 2500mm2 3100mm2 48°C/W 96°C/W 180mm2 2500mm2 2680mm2 49°C/W 98°C/W 180mm2 1000mm2 1180mm2 56°C/W 112°C/W 180mm2 600mm2 780mm2 58°C/W 116°C/W 180mm2 300mm2 480mm2 59°C/W 118°C/W 180mm2 100mm2 280mm2 60°C/W 120°C/W 180mm2 0mm2 180mm2 61°C/W 122°C/W thermal resistance is 40°C/W. The junction temperature TJ is: TJ = (1.24W)(40°C/W) + 85°C = 135°C The maximum junction temperature for the LT1497 is 150°C, so the heat sinking capability of the board is adequate for the application. If the copper area on the PC board is reduced to 180mm2 the thermal resistance increases to 61°C/W and the junction temperature becomes: TJ = (1.24W)(61°C/W) + 85°C = 161°C which is above the maximum junction temperature indicating that the heat sinking capability of the board is inadequate and should be increased. 560Ω 560Ω A – 15V 86.4mA + 200Ω 10V 560Ω –10V 560Ω – f = 2MHz Calculating Junction Temperature + The junction temperature can be calculated from the equation: – 15V TJ = (PD)(θJA) + TA TJ = Junction Temperature TA = Ambient Temperature PD = Power Dissipation θJA = Thermal Resistance (Junction-to-Ambient) As an example, calculate the junction temperature for the circuit in Figure 1 assuming an 85°C ambient temperature. The device dissipation can be found by measuring the supply currents, calculating the total dissipation and then subtracting the dissipation in the load and feedback network. Both amplifiers are in a gain of –1. The dissipation for each amplifier is: PD = (1/2)(86.4mA)(30V) – (10V)2/(200||560) = 0.62W The total dissipation is 1.24W. When a 2500mm2 PC board with 2oz copper on top and bottom is used, the 200Ω 1497 F01 Figure 1. Thermal Calculation Example Slew Rate Unlike a traditional op amp, the slew rate of a current feedback amplifier is not independent of the amplifier gain configuration. There are slew rate limitations in both the input stage and the output stage. In the inverting mode and for higher gains in the noninverting mode, the signal amplitude on the input pins is small and the overall slew rate is that of the output stage. The input stage slew rate is related to the quiescent current in the input devices. Referring to the Simplified Schematic, for noninverting applications the two current sources in the input stage slew the parasitic internal capacitances at the bases of Q3 and Q4. Consider a positive going input at the base of Q1 and Q2. If the input slew rate exceeds the internal slew rate, 9 LT1497 U U W U APPLICATIONS INFORMATION the normally active emitter of Q2 will turn off as the entire current available from the current source is used to slew the base of Q3. The base of Q4 is driven by Q1 without slew limitation. When the differential input voltage exceeds two diode drops (about 1.4V) the extra clamp emitter on Q1 turns on and drives the base of Q3 directly. Once the base of Q3 has been driven within 1.4V of its final value, the clamp emitter of Q1 turns off and the node must finish slewing using the current source. This effect can be seen in Figure 2 which shows the large signal behavior in a gain of 1 on ±15V supplies. The clamping action enhances the slew rate beyond the input limitation, but always leads to slew overshoot after the clamps turn off. Figure 3 shows that for higher gain 1497 F02 RF = 560Ω AV = 1 VS = ±15V RL = 100Ω RF = 560Ω AV = 10 VS = ±15V RL = 100Ω Figure 2. Large-Signal Response configurations there is much less slew rate enhancement because the input only moves 2V, barely enough to turn on the input clamps. In inverting configurations as shown in Figure 4 the noninverting input does not move so there is no input slew rate limitation. Slew overshoot is due to capacitance on the inverting input and can be reduced with a larger feedback resistor. The output slew rate is set by the value of the feedback resistors and the internal capacitance. Larger feedback resistors will reduce the slew rate as will lower supply voltages, similar to the way the bandwidth is reduced. The larger feedback resistors will also cut back on slew overshoot. 1497 F03 RG = 62Ω RF = RG = 560Ω AV = – 1 VS = ±15V RL = 100Ω Figure 3. Large-Signal Response Figure 4. Large-Signal Response W W SI PLIFIED SCHE ATIC One Amplifier V+ Q6 Q5 Q7 Q13 Q3 Q8 Q2 – IN +IN VOUT Q1 Q9 Q4 Q14 Q10 Q11 Q12 V– 1497 SS 10 1497 F04 LT1497 U TYPICAL APPLICATIONS Differential Input/Differential Output Power Amp (AV = 2) Paralleling Both Amplifiers for Guaranteed 250mA Output Drive + VIN + VIN VOUT 1/2 LT1497 3Ω VOUT 1/2 LT1497 – – 560Ω 560Ω 560Ω 1.1k 560Ω + – – VOUT 1/2 LT1497 560Ω + – VIN 3Ω 1/2 LT1497 – 1497 TA03 560Ω 1497 TA04 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 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) 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) *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 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 0996 1 3 2 4 S Package 16-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.386 – 0.394* (9.804 – 10.008) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.004 – 0.010 (0.101 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 16 15 14 13 12 11 10 9 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 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) S16 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 8 11 LT1497 U TYPICAL APPLICATION ±4A Current Boosted Power Amp (AV = 10) Frequency Response of Current Boosted Power Amp 22 15V 21 + VIN 200Ω 0.033Ω 20 Q1 D45VH4 19 0.01µF V+ 3Ω VOUT 1/2 LT1497 – 1.8K VOLTAGE GAIN (dB) 6.2Ω 200Ω 17 16 15 14 VS = ±15V AV = 10 RF = 1.8k RG = 200Ω VOUT = 6VP-P 12 10k 3Ω 1/2 LT1497 – RL = 2.5Ω 18 13 + RL = 50Ω 100k 1M FREQUENCY (Hz) 10M 1497 TA06 V– 1.8k Q2 D44VH4 0.01µF 6.2Ω 0.033Ω 1497 TA05 – 15V RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1206 Single 250mA, 60MHz Current Feedback Amplifier Shutdown Function, Stable with CL = 10,000pF, 900V/µs Slew Rate LT1207 Dual 250mA, 60MHz Current Feedback Amplifier Dual Version of LT1206 LT1210 Single 1A, 30MHz Current Feedback Amplifier Higher Output Version of LT1206 LT1229/LT1230 Dual/Quad 100MHz Current Feedback Amplifiers 30mA Output Current, 1000V/µs Slew Rate LT1363/LT1364/LT1365 Single/Dual/Quad 70MHz, 1000V/µs, C-LoadTM Amplifiers 50mA Output Current, 1.5mV Max VOS, 2µA Max IB C-Load is a trademark of Linear Technology Corporation. 12 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com 1497f LT/TP 1097 4K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1997