AN10145

Voltage Level Shifting The GTL-TVC devices can be used to interface between devices I/Os operating at different voltage levels. Since the GTL-TVC device is open drain on both sides, pull up resistors may be needed depending on the I/O interface type (totem pole or open drain) and the translation direction (High to Low, Low to High, or bi-directional). The GTL-TVC devices allow translations between any voltages from 1.0 V to 5.0 V as long as the voltage difference between the Gate and Source voltages is maintained at about 1 V. The recommended circuit in Figure 1 connects the gate (GREF) and reference drain (DREF) together through a 200 k ? resistor to a voltage, which should be at least 1.5 V above the reference Source (SREF) level. This circuit biases the gate to a threshold above the reference source voltage and compensates for part-to-part threshold variations. Since the gate threshold voltage can vary between 0.6 V and 1 V, if the GREF to SREF voltage is less than 1 V, the low voltage side high level may be degraded below the SREF voltage because it can only pull up to a threshold below the GREF voltage.