Datasheet LT1794 (Analog Devices) - 7
| Fabricante | Analog Devices |
| Descripción | Dual 500mA, 200MHz xDSL Line Driver Amplifier |
| Páginas / Página | 20 / 7 — TEST CIRCUIT. SUPPLY BYPASSING. APPLICATIO S I FOR ATIO. Setting the … |
| Formato / tamaño de archivo | PDF / 287 Kb |
| Idioma del documento | Inglés |
TEST CIRCUIT. SUPPLY BYPASSING. APPLICATIO S I FOR ATIO. Setting the Quiescent Operating Current
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LT1794
TEST CIRCUIT SUPPLY BYPASSING
12V 12V + 0.1µF 4.7µF + RSHDN 0.1µF 2 + 4.7µF 9 19 + 0.1µF 4.7µF 10 (SHDN) 3 VOUT(P-P) –12V A 8 7 – 6 5 4 12.7Ω 10k –12V 1k 1:2* 110 OUT (+) Ω RL ≈ 50Ω EIN SPLITTER 100 LINE LOAD 0.01µF OUT (–) 49.9Ω 110Ω 1k MINICIRCUITS ZSC5-2-2 10k 13 12.7Ω – 18 1794 TC B 12 17 11 (SHDNREF) + 16 15 14 *COILCRAFT X8390-A OR EQUIVALENT VOUTP-P AMPLITUDE SET AT EACH AMPLIFIER OUTPUT –12V DISTORTION MEASURED ACROSS LINE LOAD
U U W U APPLICATIO S I FOR ATIO
The LT1794 is a high speed, 200MHz gain bandwidth
Setting the Quiescent Operating Current
product, dual voltage feedback amplifier with high output Power consumption and dissipation are critical concerns current drive capability, 500mA source and sink. The in multiport xDSL applications. Two pins, Shutdown LT1794 is ideal for use as a line driver in xDSL data (SHDN) and Shutdown Reference (SHDNREF), are pro- communication applications. The output voltage swing vided to control quiescent power consumption and allow has been optimized to provide sufficient headroom when for the complete shutdown of the driver. The quiescent operating from ±12V power supplies in full-rate ADSL current should be set high enough to prevent distortion applications. The LT1794 also allows for an adjustment of induced errors in a particular application, but not so high the operating current to minimize power consumption. In that power is wasted in the driver unnecessarily. A good addition, the LT1794 is available in small footprint surface starting point to evaluate the LT1794 is to set the quiescent mount packages to minimize PCB area in multiport central current to 10mA per amplifier. office DSL cards. The internal biasing circuitry is shown in Figure 1. Ground- To minimize signal distortion, the LT1794 amplifiers are ing the SHDNREF pin and directly driving the SHDN pin with decompensated to provide very high open-loop gain at a voltage can control the operating current as seen in the high frequency. As a result each amplifier is frequency Typical Performance Characteristics. When the SHDN pin stable with a closed-loop gain of 10 or more. If a closed- is less than SHDNREF + 0.4V, the driver is shut down and loop gain of less than 10 is desired, external frequency consumes typically only 100µA of supply current and the compensating components can be used. 7
TEST CIRCUIT SUPPLY BYPASSING
12V 12V + 0.1µF 4.7µF + RSHDN 0.1µF 2 + 4.7µF 9 19 + 0.1µF 4.7µF 10 (SHDN) 3 VOUT(P-P) –12V A 8 7 – 6 5 4 12.7Ω 10k –12V 1k 1:2* 110 OUT (+) Ω RL ≈ 50Ω EIN SPLITTER 100 LINE LOAD 0.01µF OUT (–) 49.9Ω 110Ω 1k MINICIRCUITS ZSC5-2-2 10k 13 12.7Ω – 18 1794 TC B 12 17 11 (SHDNREF) + 16 15 14 *COILCRAFT X8390-A OR EQUIVALENT VOUTP-P AMPLITUDE SET AT EACH AMPLIFIER OUTPUT –12V DISTORTION MEASURED ACROSS LINE LOAD
U U W U APPLICATIO S I FOR ATIO
The LT1794 is a high speed, 200MHz gain bandwidth
Setting the Quiescent Operating Current
product, dual voltage feedback amplifier with high output Power consumption and dissipation are critical concerns current drive capability, 500mA source and sink. The in multiport xDSL applications. Two pins, Shutdown LT1794 is ideal for use as a line driver in xDSL data (SHDN) and Shutdown Reference (SHDNREF), are pro- communication applications. The output voltage swing vided to control quiescent power consumption and allow has been optimized to provide sufficient headroom when for the complete shutdown of the driver. The quiescent operating from ±12V power supplies in full-rate ADSL current should be set high enough to prevent distortion applications. The LT1794 also allows for an adjustment of induced errors in a particular application, but not so high the operating current to minimize power consumption. In that power is wasted in the driver unnecessarily. A good addition, the LT1794 is available in small footprint surface starting point to evaluate the LT1794 is to set the quiescent mount packages to minimize PCB area in multiport central current to 10mA per amplifier. office DSL cards. The internal biasing circuitry is shown in Figure 1. Ground- To minimize signal distortion, the LT1794 amplifiers are ing the SHDNREF pin and directly driving the SHDN pin with decompensated to provide very high open-loop gain at a voltage can control the operating current as seen in the high frequency. As a result each amplifier is frequency Typical Performance Characteristics. When the SHDN pin stable with a closed-loop gain of 10 or more. If a closed- is less than SHDNREF + 0.4V, the driver is shut down and loop gain of less than 10 is desired, external frequency consumes typically only 100µA of supply current and the compensating components can be used. 7