The ISO1176T is an isolated half-duplex differential line transceiver that meets the requirements of EN 50170 and TIA/EIA 485/422 applications. It has integrated transformer driver for convenient secondary power supply design. The device is rated to provide galvanic isolation of up to 4242 V_PK per VDE and 2500 V_RMS per UL 1577. The device has active-high driver enable and active-low receiver enable functions to control the data flow. It has maximum data transmission speed of 40 Mbps.

When the driver enable pin, DE, is logic high, the differential outputs A and B follow the logic states at data input D. A logic high at D causes A to turn high and B to turn low. In this case, the differential output voltage defined as V_OD = V_(A) – V_(B) is positive. When D is low, the output states reverse, B turns high, A becomes low, and V_OD is negative. When DE is low, both outputs turn high-impedance. In this condition, the logic state at D is irrelevant. The DE pin has an internal pulldown resistor to ground, thus when left open the driver is disabled (high-impedance) by default. The D pin has an internal pullup resistor to V_CC, thus, when left open while the driver is enabled, output A turns high and B turns low.

When the receiver enable pin, RE, is logic low, the receiver is enabled. When the differential input voltage defined as V_ID = V_(A) – V_(B) is positive and higher than the positive input threshold, V_IT+, the receiver output, R, turns high. When V_ID is negative and lower than the negative input threshold, V_IT– , the receiver output, R, turns low. If V_ID is between V_IT+ and V_IT– the output is indeterminate. When RE is logic high or left open, the receiver output is high-impedance and the magnitude and polarity of V_ID are irrelevant. Internal biasing of the receiver inputs causes the output to go failsafe-high when the transceiver is disconnected from the bus (open-circuit), the bus lines are shorted (short-circuit), or the bus is not actively driven (idle bus).