LTC1545CG View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC1545CG

Software-Selectable Multiprotocol Transceiver

Linear Technology 

LTC1545

APPLICATIONS INFORMATION

Any mismatch in the driver rise and fall times or skew in

the driver propagation delays will force current through

the center termination resistor to ground, causing a high

frequency common mode spike on the A and B terminals.

The common mode spike can cause EMI problems that are

reduced by capacitor C1 which shunts much of the com-

mon mode energy to ground rather than down the cable.

No-Cable Mode

The no-cable mode (M0=M1=M2=D4ENB=1, R4EN = 0)

is intended for the case when the cable is disconnected

from the connector. The charge pump, bias circuitry,

drivers and receivers are turned off, the driver outputs are

forced into a high impedance state, and the supply current

drops to less than 200µA.

Charge Pump

The LTC1543 uses an internal capacitive charge pump to

generate VDD and VEE as shown in Figure 21. A voltage

doubler generates about 8V on VDD and a voltage inverter

generates about – 7.5V for VEE. Four 1µF surface mounted

tantalum or ceramic capacitors are required for C1, C2, C3

and C4. The VEE capacitor C5 should be a minimum of

3.3µF. All capacitors are 16V and should be placed as close

as possible to the LTC1543 to reduce EMI. The turn-on

time for the charge pump is 60ms.

C3

1µF

5V

3

VDD

C2+ 28

2 C1+

C1

1µF 1 C1–

LTC1543

C2– 27

26

VEE

4

VCC

C4

1µF

25

GND

C2

1µF

C5

+ 3.3µF

1545 F21

Figure 21. Charge Pump

Receiver Fail-Safe

All LTC1543/LTC1545 receivers feature fail-safe opera-

tion in all modes. If the receiver inputs are left floating or

shorted together by a termination resistor, the receiver

output will always be forced to a logic high.

DTE vs DCE Operation

The DCE/DTE pin acts as an enable for Driver 3/Receiver

1 in the LTC1543, and Driver 3/Receiver 1 in the LTC1545.

The LTC1543/LTC1545 can be configured for either DTE

or DCE operation in one of two ways: a dedicated DTE or

DCE port with a connector of appropriate gender, or a port

with one connector that can be configured for DTE or DCE

operation by rerouting the signals to the LTC1543/LTC1545

using a dedicated DTE cable or dedicated DCE cable.

A dedicated DTE port using a DB-25 male connector is

shown in Figure 22. The interface mode is selected by logic

outputs from the controller or from jumpers to either VCC

or GND on the mode select pins. A dedicated DCE port

using a DB-25 female connector is shown in Figure 23.

A port with one DB-25 connector, can be configured for

either DTE or DCE operation is shown in Figure 24. The

configuration requires separate cables for proper signal

routing in DTE or DCE operation. For example, in DTE

mode, the TXD signal is routed to Pins 2 and 14 via Driver

1 in the LTC1543. In DCE mode, Driver 1 now routes the

RXD signal to Pins 2 and 14.

Compliance Testing

A European standard EN 45001 test report is available for

the LTC1343/LTC1545/LTC1344A chipset. A copy of the

test report is available from LTC or TUV Telecom Services

Inc. (formerly Detecon Inc.)

The title of the report is:

Test Report No. NET2/071601/98.

The address of TUV Telecom Services Inc. is:

TUV Telecom Services Inc.

Suite 107

1775 Old Highway 8

St. Paul, MN 55112 USA

Tel. +1 (612) 639-0775

Fax. +1 (612) 639-0873

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