CH1837F ETC1 [List of Unclassifed Manufacturers], CH1837F Datasheet - Page 3

• Manufacturer Part Number: CH1837F
• Description: CH1837A/7F/8A Data Access Arrangement Module V.34bis High Speed DAA Module
• Manufacturer: ETC1 [List of Unclassifed Manufacturers]

2002 Cermetek Microelectronics, Inc.
Cermetek Microelectronics, Inc.
TRANSMIT SIGNALS
The CH1837A/7F/8A does not attenuate the transmit
signal before it applies the signal across tip and ring.
Therefore, a transmit signal of –9dBm applied to XMIT
will comply with the FCC Part 68 requirement for data
signals across Tip and Ring.
CH1837A/F. The user presents all outgoing transmit
signals to the XMIT(-) pin with respect to GND for
single
XMIT (+) for differential operation. This signal must be
AC coupled through a 0.1µF capacitor present on both
the XMIT(-) and XMIT(+) pins as shown in Figure 3.
For single-ended operation, the outgoing analog signal
is applied to the XMIT(-) pin with respect to GND. This
signal must be AC coupled using a 0.1µF capacitor as
shown in Figure 3. In single ended signal operation,
the XMIT(+) pin must be connected to GND through a
0.1µF capacitor.
CH1838A.
presented between T1 and T2. The user must provide
an external hybrid conversion circuit and/or control the
flow of the transmit and receive signals into/from the
CH1838A.
RECEIVE SIGNALS
The incoming analog signal appears across TIP and
RING.
receive signal.
maximum strength of -9dBm to below -50dBm.
CH1837A/F.
signal and presents it at RCV with respect to GND.
The user must AC couple RCV through a 0.1µF
capacitor as indicated in Figure 3.
CH1838A.
signal between T1 and T2. The user must provide an
external hybrid conversion circuit and/or control the
flow of the transmit and receive signals into/from the
CH1838A.
Attenuation:
Input Impedance:
Typical Input Signal:
UL RECOGNITION
To further protect the end product containing the
CH1837A/7F/8A from field failures caused by large
transients present on poor quality PSTN lines and to
maintain UL recognition, an additional level of external
ended
The CH1837A/7F/8A does not amplify the
All incoming and outgoing signals are
The CH1838A presents the incoming
The CH1837A/F derives the incoming
operation or between XMIT(-) and
Receive signals can vary from a
0.0dN
150KΩ
0dBm or 0.775Vrms with the
Signal referenced to GND and
AC coupled
Page 3
transient protection is required. Refer to Figure 5 for
mandatory additional protection circuitry.
DESIGN CONSIDERATIONS
The CH1837A/7F/8A DAA includes circuitry that
couples the modem signals to the PSTN line and
provides the FCC required voltage isolation and surge
protection when circuited per Figure 5 herein.
Cermetek offers the following end product design
guidelines as suggestions only. These guidelines are
intended to facilitate the usage of Cermetek DAA
modules and to assist the user with FCC certification
of their end product.
1. Mount the DAA in the final assembly so that it is
2. Connect to the PSTN line through a standard FCC
3. All PCB traces from the CH1837A/7F/8A TIP and
4. TIP and RING PCB traces should be as short as
5. The CH1837A/7F/8A processes signals in the
6. For data calls, FCC Part 68 rules require silence
7. For voice calls, the FCC rules require that the end
isolated from exposure to any hazardous voltages
within the assembly.
restraint of cables and cords must be provided.
approved RJ-11C jack or equivalent. For RJ-11,
use the two center pins.
RING pins must be at least 0.1 inch spacing from
all other traces or other conducting material. The
purpose for this spacing is to maintain 1500 VC
isolation between the incoming PSTN line and the
other traces. PSTN related PCB Traces should
have a width of 0.020 inches or greater.
possible and should be oriented to prevent direct
or induced coupling with other signals present on
the PCB.
millivolt range. Even though the CH1837A/7F/8A
is designed to handle noise in the power supply,
steps should be taken to assure that the noise
level does not exceed 50 mV peak-to-peak.
Particular attention should be paid to both the
power supply and the ground line PCB traces.
on the PSTN line for at least 2 seconds after a
data call has been completed to allow central
offices to exchange billing information.
Part 68 specifies that the transmit level must not
exceed -9dBm.
product must meet the requirements of Part 68 for
Out-of-Band Energy, and DTMF Transmit Levels.
CH1837A/7F/8A Data Access Arrangement Module
Document No. 607-0014 Revision C2 (12/02)
Adequate separation and
Further,