INTEGRATED CIRCUITS DIVISION
CPC1465
10
www.ixysic.com
R04
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
design will be similar to the one shown in
Figure 10The 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 onpage 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, IXYS
Integrated Circuits Division 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
configuration for these timings is given in
Figure 6timing figures are located on
page 7.State transition timings are set by the 1
F 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
A 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