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CPC1466M Datasheet(PDF) 10 Page - Clare, Inc. |
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CPC1466M Datasheet(HTML) 10 Page - Clare, Inc. |
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10 / 15 page  CPC1466 10 www.clare.com R00B 2. Functional Description 2.1 Introduction The CPC1466 can be used for a number of DSL designs requiring a dc hold circuit such as ADSL modem applications. Typical ADSL applications will use a filter circuit design similar to the one shown in Figure 9‚ “Typical ADSL/VDSL Application Diagram” on page 9. The DC Termination IC performs two fundamental functions in an ADSL modem application; as an electronic inductor providing a low impedance dc termination with a high impedance ac termination and second as part of the sealing current detection system for automated line sensing. This function provides an excellent method to monitor for the presence of sealing current. Generally, loss of sealing current indicates loop loss. As can be seen in the application circuit in Figure 9 on page 9, CPC1466 designs require few external components. For the CPC1466, all that is needed is a circuit protector, two resistors and a capacitor. To ensure DSL signal integrity over a wide variety of conditions a POTS splitter type filter is recommended to isolate the DSL traffic from the termination. 2.2 Surge Protection Although the CPC1466 self protects via current limiting, it requires over-voltage surge protection to protect against destructive over-voltage transients. Clare recommends the use of a crowbar-type surge protector to limit the surge voltage seen by the CPC1466 to less than 250 V. The protection device must be able to withstand the surge requirements specified by the appropriate governing agency in regions where the product will be deployed. Teccor, Inc. and Bourns, Inc. make suitable surge protectors for most applications. Devices such as Teccor’s P1800SD or P2000SD Sidactors and Bourns’ TISP4220H3BJ or TISP4240H3BJ thyristors should provide suitable protection. 2.3 Bridge Rectifier The bridge rectifier in the CPC1466 ensures that the device is polarity insensitive and provides consistent operational characteristics if the tip to ring polarity is reversed. 2.4 State Transitions The dc tip to ring voltage-current characteristics of the CPC1466 are shown in Figure 2‚ “I-V Requirements Template, 0 V to 50 V”, and in Figure 3‚ “I-V Requirements Template, 0 V to 250 V” on page 5. Transition timings are illustrated in Figure 6‚ “Applied Waveform for Activation Test”, and in Figure 7‚ “Applied Waveform for Deactivation Test”. The test configuration for these timings is given in Figure 5‚ “Test Circuit for Activate and Deactivate Times”. All timing figures are located on page 7. State transition timings are set by the 1 µF capacitor connected between the TC and COM pins. 2.4.1 Activation - On-State Application of battery voltage to the loop causes the CPC1466 to conduct whenever the voltage exceeds approximately 35 V. With application of sufficient voltage applied across the tip and ring terminals, the CPC1466 will initially conduct a nominal 150 µA of sealing current for approximately 20 ms prior to activation. Once activated, the CPC1466 will remain in the on state for as long as the loop current exceeds a nominal 0.5 mA. The CPC1466 turn-on timing circuit assures device activation will occur within 50 ms of an applied voltage greater than 43.5 V but not within the first 3 ms. 2.4.2 Deactivation - Off-State While the CPC1466 activation protocol is based on an initial minimum voltage level, deactivation is based on a diminished sealing current level. Deactivation occurs when the nominal sealing current level drops below 0.5 mA with guaranteed deactivation occurring for sealing current levels less than 0.1 mA The turn-off timing circuit deactivates the sealing current hold circuit when 1 mA of sealing current has been removed for 100 ms but ignores periods of loss up to 3 ms. 2.5 Photo-Diode (PD) Output Behavior Output from the PD pin provides a minimum of 0.2 mA of photodiode drive current for an optocoupler’s LED anytime sealing current exceeds 1 mA. Because LED current is interrupted whenever loop current is interrupted, the optocoupler provides an |
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