Cermetek Microelectronics, Inc.
High Speed Modem and FAX Family
2003 Cermetek Microelectronics, Inc.
Page 16
Document No. 607-0003 Revision K3 (09/03)
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 Polyfuse (rated at 0.15 amps) is preferred
because it resets automatically upon removal
of the current flow. Non-resettable 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 CSA 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 contained within all HS Modems
except the CH1799LL (see Figure 6). No
additional external components are required to
maintain conveyed FCC Part 68 approval for
all HS Modems (excluding the CH1799LL).
B. For CH1799LL, the required surge protection
(identified as D1 in dashed Box 2) must be
supplied externally. The purchaser must
include some form of surge protection as
described herein to maintain conveyed FCC
Part 68 approval. Refer to Application Note #
130 for a list of recommended suppliers.
C. In most environments, 2 terminal surge
suppressors (300V sidactor or equivalent) are
adequate. For severe environments, use an
external 3 terminal device with an earth
ground. DO NOT USE MOUs or transorbs
this purpose.
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 RJ11 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.
Figure 6. PSTN Line Interface for all HS Modems.
