Datasheet LT1190 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | Ultrahigh Speed Operational Amplifier |
| Pages / Page | 12 / 9 — APPLICATIO S I FOR ATIO. Cable Terminations. Using the Shutdown Feature. … |
| File Format / Size | PDF / 268 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Cable Terminations. Using the Shutdown Feature. Double Terminated Cable Driver
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LT1190
U U W U APPLICATIO S I FOR ATIO Cable Terminations Using the Shutdown Feature
The LT1190 operational amplifier has been optimized as a The LT1190 has a unique feature that allows the amplifier low cost video cable driver. The ±50mA guaranteed output to be shut down for conserving power or for multiplexing current enables the LT1190 to easily deliver 7.5VP-P into several amplifiers onto a common cable. The amplifier will 100Ω, while operating on ±5V supplies or 2.6VP-P on a shut down by taking Pin 5 to V –. In shutdown, the single 5V supply. amplifier dissipates 15mW while maintaining a true high impedance output state of 15kΩ in parallel with the
Double Terminated Cable Driver
feedback resistors. The amplifiers must be used in a 5V noninverting configuration for MUX applications. In in- 3 + 7 75Ω CABLE 6 verting configurations the input signal is fed to the output LT1190 2 – through the feedback components. The following scope 4 R 75 FB Ω RG –5V photos show that with very high RL, the output is truly high impedance; the output slowly decays toward ground.
Cable Driver Voltage Gain vs Frequency
Additionally, when the output is loaded with as little as 1kΩ 10 the amplifier shuts off in 400ns. This shutoff can be under AV = 2 VS = ±5V 8 RFB = 1k TA = 25°C the control of HC CMOS operating between 0V and – 5V. RG = 330Ω 6 4
Output Shutdown
AV = 1 2 RFB = 1k RG = 1k 0 0V –2 VSHDN – 5V –4 –6 CLOSED-LOOP VOLTAGE GAIN (dB) –8 VOUT –10 100k 1M 10M 100M FREQUENCY (Hz) LT1190 • TA08 When driving a cable it is important to terminate the cable to avoid unwanted reflections. This can be done in one of LT1190 • TA09 1MHz SINE WAVE GATED OFF WITH two ways: single termination or double termination. With SHUTDOWN PIN, AV = 1, RL = SCOPE PROBE single termination, the cable must be terminated at the
Output Shutdown
receiving end (75Ω to ground) to absorb unwanted en- ergy. The best performance can be obtained by double termination (75Ω in series with the output of the amplifier, 0V V and 75Ω to ground at the other end of the cable). This SHDN – 5V termination is preferred because reflected energy is ab- sorbed at each end of the cable. When using the double termination technique it is important to note that the signal VOUT is attenuated by a factor of 2, or 6dB. This can be compen- sated for by taking a gain of 2, or 6dB in the amplifier. The cable driver has a – 3dB bandwidth in excess of 30MHz while driving the 150Ω load. LT1190 • TA10 1MHz SINE WAVE GATED OFF WITH SHUTDOWN PIN, AV = 1, RL = 1kΩ 9
U U W U APPLICATIO S I FOR ATIO Cable Terminations Using the Shutdown Feature
The LT1190 operational amplifier has been optimized as a The LT1190 has a unique feature that allows the amplifier low cost video cable driver. The ±50mA guaranteed output to be shut down for conserving power or for multiplexing current enables the LT1190 to easily deliver 7.5VP-P into several amplifiers onto a common cable. The amplifier will 100Ω, while operating on ±5V supplies or 2.6VP-P on a shut down by taking Pin 5 to V –. In shutdown, the single 5V supply. amplifier dissipates 15mW while maintaining a true high impedance output state of 15kΩ in parallel with the
Double Terminated Cable Driver
feedback resistors. The amplifiers must be used in a 5V noninverting configuration for MUX applications. In in- 3 + 7 75Ω CABLE 6 verting configurations the input signal is fed to the output LT1190 2 – through the feedback components. The following scope 4 R 75 FB Ω RG –5V photos show that with very high RL, the output is truly high impedance; the output slowly decays toward ground.
Cable Driver Voltage Gain vs Frequency
Additionally, when the output is loaded with as little as 1kΩ 10 the amplifier shuts off in 400ns. This shutoff can be under AV = 2 VS = ±5V 8 RFB = 1k TA = 25°C the control of HC CMOS operating between 0V and – 5V. RG = 330Ω 6 4
Output Shutdown
AV = 1 2 RFB = 1k RG = 1k 0 0V –2 VSHDN – 5V –4 –6 CLOSED-LOOP VOLTAGE GAIN (dB) –8 VOUT –10 100k 1M 10M 100M FREQUENCY (Hz) LT1190 • TA08 When driving a cable it is important to terminate the cable to avoid unwanted reflections. This can be done in one of LT1190 • TA09 1MHz SINE WAVE GATED OFF WITH two ways: single termination or double termination. With SHUTDOWN PIN, AV = 1, RL = SCOPE PROBE single termination, the cable must be terminated at the
Output Shutdown
receiving end (75Ω to ground) to absorb unwanted en- ergy. The best performance can be obtained by double termination (75Ω in series with the output of the amplifier, 0V V and 75Ω to ground at the other end of the cable). This SHDN – 5V termination is preferred because reflected energy is ab- sorbed at each end of the cable. When using the double termination technique it is important to note that the signal VOUT is attenuated by a factor of 2, or 6dB. This can be compen- sated for by taking a gain of 2, or 6dB in the amplifier. The cable driver has a – 3dB bandwidth in excess of 30MHz while driving the 150Ω load. LT1190 • TA10 1MHz SINE WAVE GATED OFF WITH SHUTDOWN PIN, AV = 1, RL = 1kΩ 9
