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CPC1465M Datasheet(PDF) 10 Page - Clare, Inc. |
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CPC1465M Datasheet(HTML) 10 Page - Clare, Inc. |
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10 / 15 page  CPC1465 10 www.clare.com R02 2. Functional Description 2.1 Introduction The CPC1465 can be used for a number of designs requiring a dc hold circuit such as SHDSL modem and ISDN NT1 terminal applications. Typical SHDSL applications will use a circuit design similar to the one shown in Figure 10‚ “Typical ISDN NT1 Application Diagram” on page 9 while the typical ISDN NT1 circuit design will be similar to the one shown in Figure 10‚ “Typical ISDN NT1 Application Diagram” on page 9. The DC Termination IC performs two functions in an ISDN NT1 terminal; as an electronic inductor providing a low impedance dc termination with a high impedance ac termination, and second as part of the dc signalling system for automated line testing capability. The CPC1465 meets or exceeds the requirements for an NT1 dc termination as described in ANSI T1.601-1991. Whereas the SHDSL modem application does not have a signalling requirement, the signaling function provides an excellent method to monitor for the loss of sealing current. Generally, loss of sealing current in an SHDSL application indicates loop loss. As can be seen in the application circuit in Figure 1 on page 1, CPC1465 designs require few external components. For the most basic design, all that is needed is a circuit protector, two resistors and a capacitor. 2.2 Surge Protection Although the CPC1465 is current limited, it is not an over-voltage surge protector. To protect the CPC1465 against destructive over-voltage transients, Clare recommends the use of a crowbar-type surge protector that limits the surge voltage seen by the CPC1465 to 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 P1800SC or P2000SC Sidactors and Bourns’ TISP4220H3 or TISP4240H3 thyristors should provide suitable protection. 2.3 Bridge Rectifier The bridge rectifier in the CPC1465 ensures that the device is polarity insensitive and provides consistent operational characteristics if the tip and ring leads are reversed. 2.4 State Transitions The dc tip to ring voltage-current characteristics of the CPC1465 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 7‚ “Applied Waveform for Activation Test”, and in Figure 8‚ “Applied Waveform for Deactivation Test”. The test configuration for these timings is given in Figure 6‚ “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 CPC1465 to conduct whenever the voltage exceeds approximately 35 V. With application of sufficient voltage applied across the tip and ring terminals, the CPC1465 will initially conduct a nominal 150 μA of sealing current for approximately 20 ms prior to activation. Once activated, the CPC1465 will remain in the on state for as long as the loop current exceeds a nominal 0.5 mA. The CPC1465 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 CPC1465 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. |
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