8.3 Feature Description

The DS92LV040A differential line driver is a balanced current mode design. A current mode driver, generally speaking has a high output impedance (100 Ω) and supplies a reasonably constant current for a range of loads (a voltage mode driver on the other hand supplies a constant voltage for a range of loads). The current is switched through the load in one direction to produce a logic state and in the other direction to produce the other logic state.

The current mode driver provides substantial benefits over voltage mode drivers, such as an RS-422 driver. Its quiescent current remains relatively flat versus switching frequency. Whereas the RS-422 voltage mode driver increases exponentially in most case between 20 MHz–50 MHz. This is due to the overlap current that flows between the rails of the device when the internal gates switch. Whereas the current mode driver switches a fixed current between its output without any substantial overlap current. This is similar to some ECL and PECL devices, but without the heavy static ICC requirements of the ECL/PECL designs. LVDS requires 80% less current than similar PECL devices. AC specifications for the driver are a tenfold improvement over other existing RS-422 drivers. The TRI-STATE function allows the driver outputs to be disabled, thus obtaining an even lower power state when the transmission of data is not required.