Cermetek Microelectronics, Inc.
High Speed Internet Modem Family
2005 Cermetek Microelectronics, Inc.
Page 12
Document No. 607-0017-01 Revision A (05/05)
Figure 3. PSTN Line Interface for all iNet Appliance Products.
1. Currently Limiting PSTN Protection Line
Device.
Currently limiting devices are mandatory to meet
UL safety standards. To maintain conveyed FCC
Part 68 approval, the current limiting components
identified as F1 and F2 in dashed Box #1 must
also survive FCC Part 68 surge testing. Refer to
Cermetek Application Note #126, Supplemental
PSTN Line Protection, for more details. Refer to
Application Note # 130, Summary of Recommend
Suppliers, for a list of suppliers and associated
part numbers.
A. A PTC (rated at 0.15 amps) is preferred
because it resets automatically upon removal
of the current flow. Fuse devices are also
acceptable. Refer to Application Note #130
for a complete list of recommended vendors
and associated part numbers.
B. Resistors (10
Ω
carbon film or 1/8 watt
minimum) may be used in Canada, as
Canada has no requirements that PSTN
equipment be operational after a Type B
surge test.
C. Although Industry Canada CS-03 Part 1
(Canada) follows the requirements of FCC
Part 68 (USA), Cermetek recommends
contacting DOT (Canada) and/or a certified
independent lab to verify compliance. For
Canada, use either 10
Ω
resistors (carbon film
or SMD parts 1/8 watt minimum) as described
in paragraph B above.
2. Over Voltage and Lightning Protection.
A. Surge Protection is provided by internal
circuitry (see Figure 3). No additional external
components are required to maintain
conveyed FCC Part 68 approval.
B. In most environments, 2 terminal surge
suppressors are adequate. For severe
environments, use an external 3 terminal
device with an earth ground.
3. EMI/RFI
Suppression.
No external EMI/RFI noise suppression circuitry is
required to maintain conveyed FCC Part 68
approval. However, additional suppression, if
required for other reasons, may be added as
described below in Sections 3A-3B without
adversely affecting FCC Part 68 approval.
A. To provide adequate EMI/RFI suppression,
the capacitor/inductor network contained in
dashed Box #3 should be located as close to
the RJ-11C jack as possible. Further, this
network should be provided with an excellent
ground path to the chassis.
B. Capacitors C1 and C2 should not exceed
0.005
µ
f. They must have a rating of 1.5KV
and typically are 0.001
µ
f ± 20%. Inductors L1
and L2 may be either individual inductors or a
dual inductor. Refer to Application Note #130
for a complete list of recommended vendors
and associated part numbers. For UL
applications, choose capacitors and inductors
that are UL 1950 listed. The actual values of
the components used may vary depending on
the end product design.
