4

dc1851af

DEMO MANUAL DC1851A

The LTC2872 may be made to self-oscillate as a ring

oscillator by connecting the drivers and receivers in one

all-encompassing loop, and adding one inversion. The

inversion may be introduced with a logic inverter, or by

cross-connecting the RS485 driver and receiver in full-

duplex mode (connect Y to B and Z to A). The connection

arrangement shown in Figure 2 forms a ring oscillator

when used with the default jumper conditions. With VCC =

VL = 3.3V, the frequency of oscillation is typically 260kHz.

QUICK START PROCEDURE

LOGIC SUPPLY, VL

1.7V TO VCC

–

+

MAIN SUPPLY, VCC

3.0V TO 5.5V

–

+

dc1851 F01

LOGIC

SIGNALS

I/O

SIGNALS

CONTROL LINES

Figure 1. Basic Test Setup. As Shown, Channel 1 is Configured for Full-Duplex RS485, While Channel 2 Is Configured for 2 + 2 RS232.