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CH1840 FCC Registered Data Access Arrangement (DAA) Module

INTRODUCTION

The CH1840 is an ultra small, low profile Data Access Arrangement (DAA).  Its modular construction and single +5 Volt D.C. power requirement simplify your development process.  Designed for both voice and data, the CH1840 allows direct connection of your product to telephone lines.  The CH1840 includes FCC Part 68 registration that is transferrable to your product.  The transferrable registration eliminates the costs and delays associated with Part 68 testing and registration of your equipment. The FCC registration, modular construction, and single +5 Volt D.C. power requirement simplify your product development.

The CH1840 also meets Industry Canada (IC) requirements.  However, you must register your product with the Industry Canada (IC) before it can be used in Canada.

The small size of the CH1840 maximizes design flexibility. CH1840 requires only 1.5 square inches of circuit board space and stands just 0.35 inches high.  It can be mounted directly on a printed circuit board or socketed.  The CH1840 uses 0.025-inch square pins on 0.10-inch centers.  The telephone line connection is made through a user supplied RJ-11 jack. 

The CH1840/D DAA is designed for use with a variety of voice circuitry and with fax and modem chip sets up through V.32bis (19,200 bps).  The CH1840 is pin compatible with the CH1837A.

FEATURES

• Compatible with modem chip sets and discrete analog circuits
• Available varieties provide a range of insertion losses; CH1840D 0 dB, CH1840DM -6.5 dB, and CH1840 –9 dB
• Available in extended temperature operation, -40C to +85C (CH1840 ET)
• Available RoHS compliant versions
• Complete DAA function
• For Voice and Data applications
• FCC Part 68 Registration Conveyed to User
• Hook switch control
• Ring detection
• Single +5V operation
• Pulse dial capability

FUNCTIONAL DESCRIPTION
The operation of the CH1840 can be broken down into the functional blocks shown in Figure 1.

• Phone Line Control
• Billing delay
• Ring Detector
• Level Monitor and XMIT Squelch
• 2- to 4-wire Hybrid
• Bandpass Filter

.

Figure 1.          CH1840 DAA Functional Block Diagram.

PHONE LINE CONTROL 

In the Public Switched Telephone Network (PSTN), the wires from a telephone to the phone company’s central office (CO) are referred to as the local loop. The "Hook Switch" at the heart of the Phone Line Control circuitry makes the electrical connection between the CH1840 and the local loop. The OFFHK input to the CH1840 controls the Hook Switch. A HIGH on OFFHK connects the CH1840 to the local loop; a LOW on OFFHK opens the Hook Switch disconnecting the circuit from the local loop, "hanging up the phone." Pulse dialing can be executed by toggling OFFHK at the appropriate rate.

BILLING DELAY 

FCC Part 68 rules require data calls to maintain 2 seconds of silence on the phone line after completion of a call. This pause allows the central offices to exchange billing information. The CH1840 assures conformance to this Billing Delay be employinga two-second timer on a LOW to HIGH transition of OFFHK and blocking transmitted signals until the timer expires. The CH1840 defeats this function when Voice Mode is slected on the D/V "Data/Voice" Pin.

RING DETECTOR

The central office signals an incoming call by placing a ring signal on the local loop.  The CH1840 monitors the loop for this signal.  The Ring Indication output, RI, is normally HIGH.  The CH1840 presents a square wave on RI at the ring signal frequency while the ring is active. RI then returns HIGH between rings, typically 4.  The ring detection circuit prevents false indications due to noise or pulse dialing on the line.

The RI output of the CH1840 is diode protected so that an external pull-up resister greater than 100 KOhms allows activation ofthe ring detection circuit when no power is applied to the CH1840. This circuit virtually eliminates current draw with no ring signal present, saving power without missing a call.  See Figure 2.

Figure 2: Low Power Ring Detection

LEVEL MONITOR AND XMIT SQUELCH

The outgoing analog signal to be transmitted through the phone line should be applied to the XMIT(+) pin (with respect to GND) or between the XMIT(+) and XMIT(-) on the CH1840D or CH1840DM.

FCC Part 68 rules limit the signal power placed on teh telephone line. When transferring data, teh singal power can be no greater than -9 dBM across Tip and Ring. The CH1840 squelches any data singal greater than -9dBm to prevent a violation The CH1840 monitors the transmitted data signal at XMIT. If the signal level would cause a violation of FCC rules, the CH1840 sets the normally LOW PSQ output HIGH and squelches the transmit signal. PSQ returns LOW when teh transmitted signal drops below the FCC threshold.

The squelch feature is disabled when Voice Mode is selected by setting the Data/Voice pin (D/V) HIGH. PSQ remains inactive wehn the CH1840 is in Voice Mode.

The CH1840 attenuates the transmit signal by 9.5, dB (0dB for the D option applied to XMIT will comply with the FCC Part 68 requirement for data signals of -9dBm across Tip and Ring.  In all cases in the data mode, the CH1840 prevents the signal level from being greater than -9dBm at Tip and Ring.

Note: When transmitting recorded or synthesized voice, the signal must be treated as Data per the FCC; thus Data Mode. D/V LOW must be selected on the Data/Voice pin.

For live voice or DTMF, when the CH1840 family products are in voice mode, the output can be 0 dBm.  Hence, by applying a 0dBm signal to the CH1840D and a +9.5 dBm signal to the CH1840, it will achieve the maximum signal output.

Table 1: Insertion Loss by Model

Use Table 1 to select the CH1840 version with the correct signal attenuation for your equipment's output signal level.

2-WIRE TO 4-WIRE HYBRID

This block has two functions: (1) it applies the XMIT signal to the phone line, (2) it subtracts this signal from the total combined signal on the phone to reveal the received signal. 

The signal received off of the telehone line is presented at RCV with respect to GND. Thuis signal must be AC coupled to your systems receive input. The received signal typically has a very low amplitude. The CH1840 does not amplify the received signal. Receveid singal can be as low as -50 dBm.

To extract a usable received signal the 2-wire to 4-wire hybrid subtracts outgoing transmit signal from the combined signal on the telephone line. The accuracy of this subtraction process depends on how closely the impedance of the phone line matches 600 ohms.  A small remnant of the XMIT signal will appear at RCV.  Trans-hybrid loss shows teh level of the original transmit signal. The CH1840 has a high trans-hybrid loss of at least 18dB from 300 Hz to 4 KHz bandwidth.

BANDPASS FILTER

Voice signals are much more complex in nature than data signals.  A voice signal is comprised of numerous frequencies combined at varying intensities.  Whereas a data signal is comprised of no more than a few discreet frequencies.  This difference dictates that voice signals receive more attention before connecting to the telephone lines.

The FCC restricts voice and data signals to between 300 Hz and 3300Hz.  This is because the Telephone Company uses frequencies below 300 Hz for low-speed tele type and frequencies above 3300 Hz for internal signaling and multiplexing.

Data signals easily meet the FCC requirements without additional filtering.  However, bandpass filters are essential for voice communication. 

A bandpass filter is utilized on the transmit line.  This filter ensures that the signal meets FCC requirements.  It also shapes the signal to minimize the phone line distortion.

Table 2: Pin Descriptions

Figure 3:Typical CH1840 Application.

SAMPLE APPLICATION

Figure 3 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 shoud drive the D/V pin high.  This disavles 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

CH1840:  -9 dB XMIT ATTENUATION

The CH1840 has -9 dB of insertion loss with respect to teh input at XMIT(+).  This allows the maximum signal strength of 0 dBm to be input while maintaining FCC compliance.  Ground the XMIT(-) pin through a 0.1uF capacitor.

CH1840D:  0 dB XMIT ATTENUATION

The CH1840D has 0.0 dB insertion loss with respect to a differential input between XMIT (-) and XMIT (+).  This allows the maximum signal strength of –9 dBm to be input while maintaining FCC compliance.  To use the CH1840-D as single end input device, ground the XMIT (-) pin through a 0.1uF capacitor.

CH1840DM:  -6.5 dB XMIT ATTENUATION

The CH1840DM has -6.5 dB insertion loss with respect to a differential input between XMIT (-) and XMIT (+).  This allows the maximum signal strength of –2.5 dBm to be input while maintaining FCC compliance.  To use the CH1840-D as single end input device, ground the XMIT (-) pin through a 0.1uF capacitor.

MOUNTING THE DAA

The DAA can be soldered directly to the host circuit card or installed in sockets.  To avoid the problems of contamination, hand soldering is preferred to wave soldering.  When hand cleaning use only deionized water; when wave soldering use washless flux.

DESIGN CONSIDERATIONS

The CH1840 DAA couples modem signals to the phone line and provides isolation and protection.  To utilize the CH1840 transferrable FCC registration for the host product, your design must follow the guidelines below.

1.  Mount the DAA module on the circuit board so taht it is isolated from any hazardous voltages within the assembly through adequate trace separation and restraint of cables and cords.

2. Use an FCC approved RJ-11C jack for teh telephone line connection.

3. Circuit board traces from the CH1840 DAA’s TIP and RING pins to the RJ-11C Jack must be more than 0.1 inch from all other traces or other conducting materials.  This spacing insures maintenance of 1000 VAC isolation between the phone line and the other traces.  Traces should have a nominal width of 0.020 inches or greater.

4. TIP and RING traces should be as short as possible and oriented to prevent direct or induced coupling with other signals on the host circuit card.

5. The CH1840 should be treated as sensitive integrated component.  Pay special attention to the power supply.  The CH1840 handles signals in the millivolt range.  Even though it is designed to handle noise in the power supply, the noise level should not exceed 50mV peak-peak.

6. Part 68 rules require silence on the phone line for at least 2 seconds after a data call has been completed. This quiet period allows central offices to exchange billing information. FCC rules also specify a transmit level no greater than -9 dBm.  The FCC rules also regulate Out-of Band Energy and DTMF Transmit Levels.  Because the CH1840 already meets FCC requirements for Part 68 registration for High Voltage isolation and Surge Protection.

MOUNTING THE CH1840

The CH1840 can be soldered directly to the host circuit card or installed in sockets.  Direct soldering provides the most sound connection.  To avoid the problems of flux contamination, hand soldering is preferred to wave soldering. This part is not hermetically sealed; water or chemical intrusion into the case can cause malfunction and void the warranty. 

Many socket manufacturers offer socket strips that accept the 0.025 inch square pins on 0.10 inch centers.  When using sockets mechanical restraint of the CH1840 should be provided to keep it seated during shipment.  Plastic cable wraps are secure yet easily removed.

The CH1840 contains static sensitive devices and should be handled by personnel and in areas that are properly protected against static discharge.

FCC REGISTRATION INFORMATION

• FCC Registration Number: B46-USA-68641-DP-E
• Ringer Equivalence (REN): 0.2A

FOR YOUR USER’S MANUAL

The Part 68 rules require the following or the equivalent information be provided to the end user of equipment containing the CH1840.

FCC NOTICE TO THE USERS

1)   UPON REQUEST ONLY, you must provide the following data to your telephone service provider (telco):

a)   Notice of intention to install or permanently remove an FCC Part 68 registered device or system, and the FCC Registration Number.

b)   The Ringer Equivalence Number (REN).  Note that if several devices are connected to the same line, the RENs must not add up to more than 5.0 (A or B).  This REN figure is important to your telco.

c)   The (USOC) jack type to be provided by telco.  Typically this will be RJ-11C/W for single lines.

2)   This device may not be used on telco-operated coin phone lines.  Party lines and privately owned coin-phones are subject to local State regulatory policies, and possible additional State special requirements.

3)   The telco has the right to make changes to their network which may affect the operation of your equipment, provided you are given adequate advance written notice to permit correct operation.

4)   In telephone line problems occur, remove the modular plug from the telco jack.  If other equipment on the line wiorks after disconnecting your product, your has a problem and must remain disconnected and (officially) serviced or returned for repairs.  If telephone line problems persist after your equipment is disconnected, there may be a telephone system problem. Notify your Telco to request service of your line.

5)   Unless otherwise noted in the User’s Manual (eg: fuses, etc.), user may not under any circumstances (in or out of warranty) attempt any service, adjustments or repairs on this unit.  It must be returned to the factory or authorized U.S. service agency for all such work.  Locations (or phone numbers) of factory or authorized U.S. service points are listed in this user’s manual.

6) Special FCC rules apply to equipment connected behind PBX or KTS.

7) Changes in Attestation Procedure for Plugs and Jacks; (Name of Applicant) attests that the network interface plugs or jacks used on this equipment comply with and will continue to comply with the mechanical requirements specified in Part 68. Subpart F. Specifically the dimensions, tolerances and metallic plating requirements.  The compliance of these connectors will be assured by purchase specifications and incoming inspections.  Documentation of such specifications and/or inspections will be provided the FCC within 30 days of their request for same.

Figure 4     Telephone Line Interface.

1. RJ-11 Jacks must be provided by one of the vendors on the list.  Refer to Application Note #130, Summary of Recommended Suppliers.

2.   Current Line Device: F1 and F2 – 1.25amp.

A. UL60950 must use a current limit device.  A Poly Fuse is recommended as this device resets automatically after each power surge.

B. Resistors (10 ohm  carbon film or SMD 1/8W minimum) may be used for non UL applications.

3.   Over Voltage and Lightning Protection.

A. DOC (Canada) may require external current limiting devices.  Use 1 ohm resistors (carbon film or SMD parts 1/8W minimum) in each lead (TIP and RING).  You may substitute fuses or the Poly Fuse described in Section 2.

B. For lightning prone areas provide an earth ground connection and use a three terminal sidactor or similar device that provides metallic and longitudinal protection.  This must also include the current protection in Section 2.

EMI/RFI Suppression.

The capacitor/ inductor network should be located as close to the RJ-11 Jack as possible with an excellent ground path to the chassis.  Capacitors C1 and C2 should not exceed 0.005mF.  They must have a rating of 1.5KV and typically have a value of 0.001mF ± 20%.  Inductors L1 and L2 are ferrite cylinders and provide attenuation to high frequencies from system level components external to the CH1840.  The required values must be empirically determined for each product design

Model Numbers

Table 4: CH1840 Model Numbers

Figure 6: Pin Connections.

Figure 7: Mechanical Specifications.

Cermetek reserves the right to make changes in specifications at any time and without notice.  The information furnished by Cermetek in this publication is believed to be accurate and reliable.  However, Cermetek assumes no responsibility for its use, or for any infringements of patents or other rights of third parties resulting from its use.  No license is granted under any patents or patent rights of Cermetek.

Cermetek provides the user with a FCC (USA) and IC (Canada) Approved or device.  However, Cermetek does not have influence over nor knowledge of the specific user application environment.  Therefore, for FCC and IC Approved or Approvable devices, the user assumes all risk for maintaining compliance to registration.

Printed in U.S.A

Copyright 2018 Cermetek Microelectronics, Inc.                

Document No. 607-0011 Revision D (04/018)