Cermetek Microelectronics, Inc.
CH1837A/7F/8A Data Access Arrangement Module
2002 Cermetek Microelectronics, Inc.
Page 7
Document No. 607-0014 Revision C2 (12/02)
Figure 5. PSTN Line Interface.
1. Currently Limiting PSTN Protection Line
Device.
Currently limiting devices are mandatory to meet
UL safety standards. For 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. The required UL1950 and FCC Part 68 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 obtain FCC Part 68
approval and to maintain UL1950 Edition 3
listing.
B. In most environments, 2 terminal surge
suppressors are adequate.
For severe
environments, use an external 3 terminal
device (as indicated in Figure 5) with an earth
ground.
3. EMI/RFI Suppression.
Additional suppression, if required, may be added
as described below in Sections 3A-3B without
adversely affecting FCC Part 68 approval or
UL1950 listing.
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
µf. They must have a rating of 1.5KV
and typically are 0.001
µf ± 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.
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
