CH1840 Datasheet, PDF (4/7 Pages) List of Unclassifed Manufacturers – Low Profile Data Access Arrangement (DAA) Modules

SAMPLE APPLICATION
Figure 2 illustrates a typical application of the CH1840. When
transmitting data the controller must assert the D/V pin low to
provide the two second billing delay required by the FCC. When
transmitting voice signals, the controller should drive the D/V pin
high. This disables the billing delay, and power squelch.
One of the requirements of an FCC approved DAA is that the
signal transmitted to Tip and Ring does not exceed -9.0 dBm.
The CH1840 incorporates an automatic squelch. If the signal
exceeds -9.5 dBm, the DAA will discontinue transmission until the
signal returns to acceptable levels. The PSQ output indicates
when the squelch circuit has been activated. By utilizing PSQ to
drive the illustrated LED circuit, a visual indication of the squelch
activation can be attained.
DESIGN CONSIDERATIONS
The following guidelines for your product desgin must be fol-
lowed to meet the requirements of FCC Part 68 rules.
1) The mounting of the DAA in the final assembly must be
made so that it is isolated from exposure to any hazard-
ous voltages within the assembly. Adequate separation
and restraint of cables and cords must be provided.
2) The circuitry from the registered unit to the telephone line
must be provided in wiring that carries no other circuitry
than that specifically allowed in the rules ( such as A and
A1 leads).
3) See Section “For Your User’s Manual” for information that
must appear in your User’s Manual.
4) Connection to the phone line should be made through a
standard RJ-11C jack or equivalent.
5) Circuit board traces from the CH1840’s TIP and RING
pins must exceed 0.1 inch spacing to one another and
0.2 inches spacing from all other traces or other conduct-
ing material. Traces should have a nominal width of 0.020
inches or greater.
6) TIP and RING traces should be as short as possible and
should be oriented to prevent direct or induced coupling with other
signals on the host circuit card.
7) No additional application circuitry should be connected be-
tween the CH1840 and the phone line RJ-11C jack, except as
described in note 10 below.
8) The registration label included with the product must be affixed
to the outside of your product where it is easily visible to your end
user.
9) The CH1840 Module is a sensitive subsystem that should be
treated as any other integrated component. Pay special attention
to the power supply to the DAA. The device handles signals in the
millivolt range. Although it is designed to handle noise in the
power supply, steps should be taken to assure the noise level
does not exceed 50 mV peak-to-peak. Failure to provide such
operating conditions could cause the CH1840 to malfunction.
10) The CH1840 DAA meets or exceeds the hazardous voltage,
surge and leakage requirements of the FCC. For applications that
connect to Canadian phone lines, governed by the DOC (Depart-
ment of Communications) and to further protect the CH1840 from
field failure due to poor lines, a higher level of transient protection
is required, thereby making mandatory the circuit consisting of two
fuses and one varistor as shown in Figure 4. Adding these three
devices will not affect FCC or U.L. registration.
Components L1, L2, C1, C2 are optional and serve two
purposes. First, they restrict high frequency signals from
reaching the phone line and thereby add EMI protection.
Second, they protect against externally generated RFI
from degrading the modem’s ability to operate on proper
carrier signals. Adding these devices will not affect
FCC, DOC, or U.L. registration.
Figure 4. Telephone Line Interfaces
© 2000 Cermetek Microelectronics, Inc.
Page 4
Document No. 607-0011 Rev. A (5/00)