PE-65793 Datasheet, PDF (4/7 Pages) Pulse A Technitrol Company – ISDN S-Interface Transformers

ISDN S-Interface Transformers
Surface Mount, Dual, 2000Vrms
TE
Sec : Pri
IC
XMIT
Sec : Pri
RCV
S-INTERFACE
Low High
Freq Freq
Choke Choke
High Low
Freq Freq
Choke Choke
Local
Power
Figure 1. Typical ISDN S-Interface Application Circuit
NT
Pri : Sec
IC
RCV
Pri : Sec
XMIT
DC
Supply
1. General Information - The S-interface is the
standardized four-wire digital telephone access point
defined by the CCITTI I-series recommendations for
the Integrated Services Digital Network. This “basic
rate access” accommodates two 64Kpbs “B-channels”
for information, one 16Kbps “D-channel” intended
for signaling and control, and 48 Kbps for framing
and other purposes, giving a total rate of 192Kbps. The
CCITT physical layer recommends that the user network
interface be transformer coupled. A typical application
circuit is presented in Figure 1.
The transformer provides isolation for the line card
or the terminal from the line. It is also a way to provide
phantom power feeding to the terminal over the S-loop.
Each end requires a transmit and a receive transformer.
Chokes are used in some applications to reduce
common mode noise (see note 5).
The transformers described in this data sheet are
matched to the transceivers offered by the major IC
manufacturers listed. The use of a transformer-chip pair
assures that all requirements of CCITT I.430 are met
with respect to pulse waveform templates, impedance
and longitudinal balance. In addition, the transformers
provide the isolation voltages required by the regulatory
agencies and are capable of passing surge voltage tests.
2. Longitudinal Balance for Transformers - The
longitudinal conversion loss specification in I.430 includes
a test setup that is intended for system evaluation,
whether TE or NT. Such a test is performed with DC
current present. The transformer plays an essential role
in achieving the required balance. However, all other
elements in the circuit should be also designed to provide
the highest possible symmetry. These elements include
the protection circuitry, series resistors, chip transmitter
output and receiver input, as well as the cables used
and the TE cord where applicable. A high level of
transformer balance compensates for some circuit AC-
unbalance, and assures compliances of the system with
I.430 on longitudinal conversion loss (LCL) and signal
balance. This is accomplished by a well AC-balanced
winding configuration whereby the capacitive coupling
between primary and secondary windings is evenly
distributed. Also, both halves of the lineside winding are
well balanced. The transformers meet the following LCL
specifications:
•10kHz to 300kHz: 60dB minimum
•300kHz to 1MHz: Minimum value decreasing
20dB/decade.
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T604.F (05/12)