LTC2845 datasheet(14/20 Pages) LINER

14 / 20 page

LTC2845

sn2845 2845fs

DTE vs DCE Operation

The DCE/DTE pin acts as an enable for Driver 3/Receiver 1

in the LTC2846, and Driver 3/Receiver 1 in the LTC2845.

The LTC2846/LTC2845 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 LTC2846/LTC2845

using a dedicated DTE cable or dedicated DCE cable.

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

shown in Figure 23. The interface mode is selected by logic

outputs from the controller or from jumpers to either VIN

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

using a DB-25 female connector is shown in Figure 24.

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

either DTE or DCE operation is shown in Figure 25. 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 LTC2846. In DCE mode, Driver 1 now routes the RXD

signal to Pins 2 and 14.

Compliance Testing

The LTC2846/LTC2845 chipset has been tested by TUV

Rheinland of North America Inc. and passed the NET1,

NET2 and TBR2 requirements. Copies of the test report are

available from LTC or TUV Rheinland of North America Inc.

The title of the report is Test Report No.TBR2/050101/02

The address of TUV Rheinland of North America Inc. is:

TUV Rheinland of North America Inc.

1775, Old Highway 8 NW, Suite 107

St. Paul, MN 55112

Tel. (651) 639-0775

Fax (651) 639-0873

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 bias circuitry, drivers and receiv-

ers are turned off, the driver outputs are forced into a high

impedance state, and the supply current drops to less than

700

µA.

LTC2846 and LTC2847 Supplies

The LTC2846 and LTC2847 use 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. Three 1µF

surface mounted tantalum or ceramic capacitors are re-

quired for C1, C2 and C3. The VEE capacitor C4 should be

a minimum of 3.3

µF. All capacitors are 16V and should be

placed as close as possible to the LTC2846 to reduce EMI.

The LTC2846 has an internal boost switching regulator

which generates a 5V output from the 3.3V supply as

shown in Figure 22. The 5V VCC supplies its internal charge

pump and transceivers as well as its companion chip. The

LTC2847 requires an external 5V supply.

Receiver Fail-Safe

All LTC2846/LTC2845 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.

APPLICATIONS INFORMATION

2845 F21

µF

3.3

µF

LTC2846

LTC2847

VDD

C1+

C1–

VCC

C2+

C2–

VEE

GND

Figure 21. Charge Pump

Figure 22. LTC2846 Boost Switching Regulator

GND

VIN

SHDN

VIN

3.3V

2845 F22

5.6

µH

13k

BOOST

SWITCHING

REGULATOR

µF

4.3k

VCC

480mA

C1,C2: TAIYO YUDEN X5R JMK316BJ106ML

D1: ON SEMICONDUCTOR MBR0520

L1: SUMIDA CR43-5R6

SHDN

Figure 20. V.35 Driver

V.35 DRIVER

51.5

Ω

2845 F20

51.5

Ω

LTC2846

124

Ω

LTC2845 Datasheet(PDF) 14 Page - Linear Technology

LTC2845 Datasheet(HTML) 14 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL