CH1840D ET Cermetek Microelectronics, CH1840D ET Datasheet - Page 2

• Manufacturer Part Number: CH1840D ET
• Manufacturer: Cermetek Microelectronics

Specifications of CH1840D ET

• Operating Temperature Classification: Industrial
• Pin Count: 12
• Lead Free Status / RoHS Status: Supplier Unconfirmed

Cermetek Microelectronics, Inc.
Phone Line Control.
Telephone Network (PSTN), the wires from a
telephone to the phone company’s central office (CO)
are referred to as the local loop.
2-Wire To 4-Wire Hybrid Converter. This block has
two functions:
Drawing current from the local loop signals the central
office that the telephone is Off Hook, that is, either
answering a call or preparing to place a call. In the
CH1840, this function is controlled by the OFFHK
signal. When this input is LOW, the CH1840 is On-
Hook, indicating to the central office that it is not using
the line.
OFFHK input
For data calls, FCC Part 68 rules require silence on
the phone line for at least 2 seconds after the call has
been completed to allow central office to exchange
billing information. The CH1840 assures conformance
to this requirement by stating a two-second timer on
the LOW to HIGHT transition to OFFHK and
squelching transmitted signals until the time expires.
The CH1840 defeats this function when Voice Mode is
selected on the Data/Voice pin.
Figure 2.
©2004 Cermetek Microelectronics, Inc.
CH1840 can pulse dial by togging the
Typical CH1840 Application.
In the Public Switched
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RING DETECTION
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. When ringing appears, RI is set
LOW during the typically 2 second ring period and is
restored to HIGH for the typically 4 seconds between
rings. The ring detection circuit is designed to prevent
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(R> 100Kohm) to +5V may
be utilized to activate the ring detection circuit when
the DAA is not connected to power.
handy with designs in which power consumption is of
concern.
virtually no current draw until a ring signal is present.
See Figure 3.
TRANSMIT SIGNAL
The outgoing analog signal to be transmitted through
the phone line should be applied to the XMIT pin (with
respect to GND
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.
When circuited in this manner, there is
CH1840 Family of Low Profile DAA Modules
Document No. 607-0011 Revision C (09/09)
This can be