CRMET CH1817LM, CH1817LET, CH1817L, CH1817ET, CH1817DM Datasheet

CH1817

Family of Low Profile DAA Modules

INTRODUCTION FEATURES

The CH1817 is a Family of Low Profile Data Access
Arrangement (DAA) Modules. They are compatible
with all modem chip sets. These devices have been
tested to meet or exceed FCC Part 68 requirements
and are Canadian DOC approvable. They are also
recognized by Underwriters Laboratories to UL 1459
Specifications.

The CH1817 modules are ultra small (1.0” x 1.0”
x0.35”) affording an easy integration into space­sensitive designs, including laptop and hand-held
computer based products. The CH1817 family of
products may be socketed or mounted directly onto a
Printed Circuit Board (PCB). The telephone line
connection is made through TIP and RING to an RJ-11
jack or equivalent.

The CH1817 is intended for use with FAX/modem chip
sets that have a data throughput of up through
V.32bis. For High Speed Applications, Cermetek
recommends the CH1837A.

FUNCTIONAL DESCRIPTION

Ring Detection. Referring to the block diagram in

Figure 1, incoming ring detection is performed by the
CH1817 and the RI pin is set Low during the 2 second
(typical) ring period and is restored to High for the 4
seconds (typical) between rings. During incoming ring
signal activity, the RI output is pulsed at the same
frequency as the ringing signal, typically 20Hz. Figure
2 contains additional external circuitry which may be
used to provide an envelope indication of the ring
signal. The internal ring detection circuit is designed
to deter false indications due to pulse dialing or noise
on the line.

The RI output of the CH1817 is diode protected.
Therefore, an external pull-up resistor (R>100Kohm)
to +5V may be utilized to activate the ring detection
circuit when the CH1817 is not connected to power.
This can be handy in designs where power
consumption is of concern. When circuited in this
manner, there is virtually no current draw until a ring
signal is present.

• Low Profile, Ultra small size: 1.0” x 1.0” x 0.35”

• Complete DAA function

• Ring detection

• Built-in 2-wire to 4-wire conversion

• Lightweight

• Multimedia compatible

• +5V operation

• 1000 VAC isolation

• 800 Volt surge protection

• V.32bis/14,400bps, applications

• UL1459 recognized

• CH1817-L: Low power consumption and Common

mode noise rejection filter

• CH1817-LM (special order): Reduced transmit
attenuation

• CH1817-D: Differential transmission input and 0dB
transmission insertion loss.

ISOLATION

XMIT

RCV

RI

OFFHK

CONVERTER

VCC

HYBRID

2W/4W

GND

SURGE

AND

PROTECTION

CIRCUITRY

OFF-HOOK

SWITCH

RING DET.

TIP

RING

RI

Output: Active low
Opto coupler, 30KΩ pull-up
Square wave: 15-68Hz (Typ. 20Hz)
Sensitivity: 38Vrms across Tip & Ring

Figure 1. CH1817 DAA Functional Block Diagram.

2002 Cermetek Microelectronics, Inc. Page 1 Document No. 607-0007 Revision B (01/02)

Cermetek Microelectronics, Inc. CH1817 Family of Low Profile DAA Modules

Hook Switch. The OFFHK input is used to control the
on-hook and off-hook status of the CH1817. When
OFFHK is low, the CH1817 is in the On-Hook State.
This indicates to the CO that the CH1817 is ready to
receive calls. When OFFHK is high, the CH1817
allows the CO supplied loop current to flow, indicating
either it is answering a call or preparing to place a call.

OFFHK

Input: Active High
Active Current: 4mA

2-Wire To 4-Wire Hybrid Converter. This block has

TRANSMIT SIGNAL

The outgoing analog signal to be transmitted through
the phone line should be applied to the XMIT pin (with
respect to GND) and must be AC coupled as shown in
Figure 2. For the CH1817-D a XMIT (+) and XMIT (-)
pins provide a differential input. The CH1817-L
attenuates the transmit signal by 9.5dB, 0dB for the –D
option. Therefore, a transmit signal of 0dBm for the –L
option (-9.5 dB for –D) applied to XMIT will comply
with the FCC Part 68 requirement for data signals of –
9dBm across TIP and RING.

two functions: RECEIVE SIGNAL

1. It applies the XMIT signal to the phone line.

2. It subtracts the desired signal from the total
outgoing signal on the phone line to derive the
RCV signal.

The accuracy of this derivation depends on how
closely the impedance of the phone line matches 600
Ohms. Generally, a small amount of the XMIT signal
will appear at RCV. The ratio of the applied XMIT
signal to the received XMIT signal is called Trans­Hybrid Rejection, or Trans-Hybrid Loss. On a 600Ω
phone line, the CH1817 DAAs have very high trans­hybrid rejection, typically 23 dB.

NOTE
The FCC requires that the DTMF tone not exceed
0dBm.

The incoming analog signal appearing between TIP
and RING is presented at RCV with respect to GND
and must be AC coupled to the user equipment
receive input. The CH1817 does not gain the receive
signal. Receive signals can vary from a maximum
strength of –9dBm to below –50dBm.

RCV

Gain: 0dB
Out impedance: 100Ω
Typical Output Signal:

-9dBm to –50dBm

2.5Vrms to 0.27mVrms
Signal referenced to GND
AC coupling required

XMIT CH1817-D CH1817-L CH1817-DM CH1817-LM Attenuation 0dBm 9.5dBm 6.5dBm 6.5dBm Input Impedance

150KΩ 150KΩ 150KΩ 150KΩ

Figure 2. Typical CH1817 Application.

2002 Cermetek Microelectronics, Inc. Page 2 Document No. 607-0007 Revision B (01/02)

Cermetek Microelectronics, Inc. CH1817 Family of Low Profile DAA Modules

Table 1. CH1817 Family Pin Description.

Pin Name I/O Function

1

TIP

I/O TIP. Direct telephone line connection.

2

3

4

5

6

7

RING

OFFHK

RI

RCV

XMIT(-)

or

N/C

VCC

I/O RING. Direct telephone line connection.

I

OFF HOOK. When set LOW, the CH1817 is placed On-Hook. When set HIGH, the
CH1817 is placed Off-Hook to answer or place a call. This input can also be used
for pulse dialing. NOTE: When answering incoming calls in response to a ring
indication on RI, internal relay contact degradation may occur if OFFHK is set HIGH
before RI returns to its HIGH state.

O

RING INDICATION. It is asserted LOW by the CH1817 during the 2 second ON
portion of the incoming AC Ring Signal and is asserted HIGH during the 4 second
idle period between rings. An envelope of the AC ring signal may be created using
the application circuit shown in Figure 2.

O

RECEIVE. This provides the signal or audio output with respect to ground and must
be AC coupled with a 0.1µF capacitor to eliminate DC offset.

I

TRANSMIT SIGNAL (-). Input a differential AC coupled audio signal with respect to

or

XMIT(+), CH1817-D versions only. All others, No Connection. For single ended

-

operation of CH1817-D, connect this pin to ground through a 0.1µF capacitor.

I

POWER SUPPLY. +5V ± 5%

8

XMIT(+)

I

TRANSMIT SIGNAL (+). Input an AC coupled audio signal with respect to ground.
Input a differential signal with respect to XMIT(-) for the CH1817-D versions only.

9

GND

I

Ground. Must be connected to signal ground. Note: Noise should be less than
25mV peak-to-peak.

2002 Cermetek Microelectronics, Inc. Page 3 Document No. 607-0007 Revision B (01/02)