DC306A-A Analog Devices

DC306A Demo Board Quick Start Guide LT1795 and LT1361 ADSL Line Driver / Receiver Tim Regan May 13, 2002 The DC306A demo board contains all of the necessary circuitry to interface an ADSL AFE (Analog Front End) to a telephone line. It utilizes the LT1795 500mA high-speed Dual Driver amplifier in the small TSSOP power package and the LT1361 Low-noise, high-speed Dual Receiver amplifier. Line isolation and coupling is achieved through a 1:1.4 transformer. This demo board has several configuration and control options managed by the position of six jumpers: The board can easily be configured for split +/-12V supplies or single supply operation. AFE interface signals are DC coupled and biased to 0Vdc with split supplies and VCC/2 with single supply operation. The quiescent operating current of the LT1795 line driver can be adjusted from an external control voltage (0V to +3V) or set to a fixed value of approximately 14mA per amplifier. An external ON/OFF logic control signal can be used to enable or disable the line driver or this function can be fixed in the ON state. The LT1361 differential receiver can be configured to provide local transmit echo cancellation or as a simple differential amplifier monitoring the signal appearing at the primary of the line coupling transformer. The connection to the phone line is AC coupled. The LINE(-) connection can be connected to the driver circuit ground potential or can be isolated (floating). As delivered, DC306A has the following default settings: Supply Voltage: +/-12V split supplies Quiescent current control: Fixed to 14mA/amplifier ON/OFF control: Fixed to ON Receiver configuration: Echo cancellation Line interface: Line(-) is connected to the driver circuit ground. The schematic for the system is provided on page 2. An orientation sheet to show where connections are to be made and how to configure the six jumpers on the board is on page 3. Discussion of operation and connecting to the board begins on page 4. Linear Technology Confidential For Customer Use Only. DC306A Page 1 of 5 Linear Technology Confidential For Customer Use Only. DC306A Page 2 of 5 DC306A Schematic