CPC5620_1 Datasheet, PDF (13/17 Pages) Clare, Inc. – LITELINK® III Phone Line Interface IC (DAA)

3.5.1 Setting a Current Limit
LITELINK includes a telephone line current limit
feature that is selectable by choosing the desired
value for R_ZDC (R16) using the following formula:
I_CLAmps
=
----1---^V------ + 0.008A
R_ZDC
Clare recommends using 8.2 Ω for R_ZDC for most
applications, limiting telephone line current to 130 mA.
Whether using the recommended value above or
when setting R_ZDC higher for a lower loop current limit
refer to the guidelines for FET thermal management
provided in AN-146, Guidelines for Effective
LITELINK Designs.
3.6 AC Characteristics
3.6.1 Resistive Termination Applications
North American and Japanese telephone line AC
termination requirements are met with a resistive 600
Ω AC termination. Receive termination is applied to
the LITELINK ZNT pin (pin 29) as a 301 Ω resistor,
R_ZNT (R10).
3.6.2 Reactive Termination Applications
Many countries use a single-pole complex impedance
to model the telephone network transmission line
characteristic impedance as shown in the table below.
Line Impedance Model
Australia
R_S 220 Ω
R_S
R_P 820 Ω
R_P
C_P
C_P 120 nF
China
200 Ω
680 Ω
100 nF
TBR 21
270 Ω
750 Ω
150 nF
Proper gain and termination impedance circuits for a
complex impedance requires the use of complex
network on ZNT as shown in the “Reactive Termination
Application Circuit Schematic” on page 8.
3.6.3 Mode Pin Usage
Assert the MODE pin low to introduce a 7 dB pad into
the transmit path and add 7 dB of gain to the receive
path. These changes compensate for the gain
changes made to the transmit and receive paths in
reactive termination implementations.
CPC5620/CPC5621
Insertion loss with MODE de-asserted and the
resistive termination application circuit is 0 dB.
Insertion loss with the reactive termination application
circuit and MODE asserted is also 0 dB.
4. Regulatory Information
LITELINK III can be used to build products that comply
with the requirements of TIA/EIA/IS-968 (formerly
FCC part 68), FCC part 15B, TBR-21, EN60950,
UL1950, EN55022B, IEC950/IEC60950, CISPR22B,
EN55024, and many other standards. LITELINK
provides supplementary isolation. Metallic surge
requirements are met through the inclusion of a
Sidactor in the application circuit. Longitudinal surge
protection is provided by LITELINK’s optical barrier
technology and the use of high-voltage components in
the application circuit as needed.
The information provided in this document is intended
to inform the equipment designer but it is not sufficient
to assure proper system design or regulatory
compliance. Since it is the equipment manufacturer's
responsibility to have their equipment properly
designed to conform to all relevant regulations,
designers using LITELINK are advised to carefully
verify that their end-product design complies with all
applicable safety, EMC, and other relevant standards
and regulations. Semiconductor components are not
rated to withstand electrical overstress or electro-static
discharges resulting from inadequate protection
measures at the board or system level.
5. LITELINK Design Resources
The Clare, Inc. web site has a wealth of information
useful for designing with LITELINK, including
application notes and reference designs that already
meet all applicable regulatory requirements. See the
following links:
LITELINK datasheets and reference designs
Application note AN-117 Customize Caller ID Gain
and Ring Detect Voltage Threshold
Application note AN-146, Guidelines for Effective
LITELINK Designs
Application note AN-152 LITELINK II to LITELINK III
Design Conversion
Application note AN-155 Understanding LITELINK
Display Feature Signal Routing and Applications
R04
www.clare.com
13