
INTEGRATED CIRCUITS DIVISION
CPC1465
10 www.ixysic.com R05
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 e xcellent method t o monitor f or 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 fe w 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 ov er- voltage transients, IXYS
Integr ated Circuits recommends t he use of a
crowbar-type surge pr otector that limits the surge
v oltage seen by the CPC1465 to 250 V. The protection
de vice must be able to withstand the sur ge
requirements specified b y the appropriate governing
agency in regions where the product will be deplo y ed.
Littelfuse , I nc. makes suitable surge protectors for
most applications. Devices such as Littelfuse's
P1800SCL or P2000SCL SIDA Ctor devices should
provide suitab le protection.
2.3 Bridge Rectifier
The bridge rectifier in the CPC1465 ensures that the
de vice 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 charact eristics of the
CPC1465 are sho wn 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
Wav eform for Activ at ion Test”, and in Figure 8‚
“Applied Wav eform f or Deact ivation 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 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
appro x imat ely 35 V. With application of sufficient
v olt age 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
activ ation. 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
activ ation will occur within 50 ms of an applied volt age
greater than 43.5 V but not within the first 3 ms.
2.4.2 Deactivation - Off-State
While the CPC1465 activ ation protocol is based on an
initial minimum v oltage level, deactiv ation is based on
a diminished sealing current le vel. Deact ivation occurs
when the nominal sealing current le vel drops below
0.5 mA with guaranteed deactivation occurring for
sealing current levels less t han 0. 1 mA