Datasheet

7
LTC1345
Review of CCITT Recommendation V.35
Electrical Specifications
V.35 is a CCITT recommendation for synchronous data
transmission via modems. Appendix 2 of the recommen-
dation describes the electrical specifications which are
summarized below:
1. The interface cable is balanced twisted-pair with 80Ω to
120Ω impedance.
2. The transmitter’s source impedance is between 50Ω and
150Ω.
3. The transmitter’s resistance between shorted terminals
and ground is 150Ω ±15Ω.
4. When terminated by a 100Ω resistive load, the terminal-
to-terminal voltage should be 0.55V ±20%.
5. The transmitter’s rise time should be less than 1% of the
signal pulse or 40ns, whichever is greater.
6. The common-mode voltage at the transmitter output
should not exceed 0.6V.
7. The receiver impedance is 100Ω ±10Ω.
8. The receiver impedance to ground is 150Ω ±15Ω.
9. The transmitter or receiver should not be damaged by
connection to earth ground, short-circuiting, or cross
connection to other lines.
10. No data errors should occur with ±2V common-mode
change at either the transmitter or receiver, or ±4V ground
potential difference between transmitter and receiver.
Cable Termination
Each end of the cable connected to an LTC1345 must be
terminated by either one of two electrically equivalent
external Y or ∆ resistor networks for proper operation. The
Y-termination has two series connected 50Ω resistors and
a 125Ω resistor connected between ground and the center
tap of the two 50Ω resistors as shown in Figure 6A.
Figure 6. Y and ∆ Termination Networks
50Ω
50Ω
125Ω
A
LTC1345 • F06
300Ω
300Ω
120Ω
B
The alternative ∆-termination has a 120Ω resistor across
the twisted wires and two 300Ω resistors between each
wire and ground as shown in Figure 6B. Standard 1/8W,
5% surface mount resistors can be used for the termination
network. To maintain the proper differential output swing,
the resistor tolerance must be 5% or less. A termination
network that combines all the resistors into an SO-14
package is available from:
BI Technologies (Formerly Beckman Industrial)
Resistor Networks
4200 Bonita Place
Fullerton, CA 92635
Phone: [phone]
FAX: [phone]
Part #: BI Technologies 627T500/1250 (SOIC)
899TR50/125 (DIP)
APPLICATIO S I FOR ATIO
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