Datasheet LT6300 (Analog Devices) - 9
| Manufacturer | Analog Devices |
| Description | 500mA, 200MHz xDSL Line Driver in 16-Lead SSOP Package |
| Pages / Page | 16 / 9 — APPLICATIO S I FOR ATIO. Power Dissipation and Heat Management. Shutdown … |
| File Format / Size | PDF / 240 Kb |
| Document Language | English |
APPLICATIO S I FOR ATIO. Power Dissipation and Heat Management. Shutdown and Recovery
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LT6300
U U W U APPLICATIO S I FOR ATIO
modes. These modes can be useful for overall system
Power Dissipation and Heat Management
power management when full power transmissions are xDSL applications require the line driver to dissipate a not necessary. significant amount of power and heat compared to other components in the system. The large peak to RMS varia-
Shutdown and Recovery
tions of DMT and CAP ADSL signals require high supply The ultimate power saving action on a completely idle port voltages to prevent clipping, and the use of a step-up is to fully shut down the line driver by pulling the SHDN pin transformer to couple the signal to the telephone line can to within 0.4V of the SHDNREF potential. As shown in require high peak current levels. These requirements Figure 5 complete shutdown occurs in less than 10µs and, result in the driver package having to dissipate significant more importantly, complete recovery from the shut down amounts of power. Several multiport cards inserted into state to full operation occurs in less than 2µs. The biasing a rack in an enclosed central office box can add up to circuitry in the LT6300 reacts very quickly to bring the many, many watts of power dissipation in an elevated amplifiers back to normal operation. ambient temperature environment. The LT6300 has built- in thermal shutdown circuitry that will protect the ampli- fiers if operated at excessive temperatures, however data VSHDN SHDNREF = 0V transmissions will be seriously impaired. It is important in the design of the PCB and card enclosure to take measures to spread the heat developed in the driver away to the ambient environment to prevent thermal shutdown (which AMPLIFIER OUTPUT occurs when the junction temperature of the LT6300 exceeds 165°C).
Estimating Line Driver Power Dissipation
6300 F05 Figure 6 is a typical ADSL application shown for the
Figure 5. Shutdown and Recovery Timing
purpose of estimating the power dissipation in the line driver. Due to the complex nature of the DMT signal, 12V 20mA DC 24.9k – SETS IQ PER AMPLIFIER = 10mA 2V +IN + RMS SHDN 17.4Ω A – 1k 1:1.7 110Ω • • ILOAD = 57mARMS 100Ω 3.16VRMS 1000pF 110Ω 1k – 17.4Ω 6300 F06 B SHDNREF –IN + –12V –2VRMS
Figure 6. Estimating Line Driver Power Dissipation
9
U U W U APPLICATIO S I FOR ATIO
modes. These modes can be useful for overall system
Power Dissipation and Heat Management
power management when full power transmissions are xDSL applications require the line driver to dissipate a not necessary. significant amount of power and heat compared to other components in the system. The large peak to RMS varia-
Shutdown and Recovery
tions of DMT and CAP ADSL signals require high supply The ultimate power saving action on a completely idle port voltages to prevent clipping, and the use of a step-up is to fully shut down the line driver by pulling the SHDN pin transformer to couple the signal to the telephone line can to within 0.4V of the SHDNREF potential. As shown in require high peak current levels. These requirements Figure 5 complete shutdown occurs in less than 10µs and, result in the driver package having to dissipate significant more importantly, complete recovery from the shut down amounts of power. Several multiport cards inserted into state to full operation occurs in less than 2µs. The biasing a rack in an enclosed central office box can add up to circuitry in the LT6300 reacts very quickly to bring the many, many watts of power dissipation in an elevated amplifiers back to normal operation. ambient temperature environment. The LT6300 has built- in thermal shutdown circuitry that will protect the ampli- fiers if operated at excessive temperatures, however data VSHDN SHDNREF = 0V transmissions will be seriously impaired. It is important in the design of the PCB and card enclosure to take measures to spread the heat developed in the driver away to the ambient environment to prevent thermal shutdown (which AMPLIFIER OUTPUT occurs when the junction temperature of the LT6300 exceeds 165°C).
Estimating Line Driver Power Dissipation
6300 F05 Figure 6 is a typical ADSL application shown for the
Figure 5. Shutdown and Recovery Timing
purpose of estimating the power dissipation in the line driver. Due to the complex nature of the DMT signal, 12V 20mA DC 24.9k – SETS IQ PER AMPLIFIER = 10mA 2V +IN + RMS SHDN 17.4Ω A – 1k 1:1.7 110Ω • • ILOAD = 57mARMS 100Ω 3.16VRMS 1000pF 110Ω 1k – 17.4Ω 6300 F06 B SHDNREF –IN + –12V –2VRMS
Figure 6. Estimating Line Driver Power Dissipation
9
