ISO742x provide galvanic isolation up to 2500 VRMS for 1 minute per UL and 4242 VPK per VDE. These devices have two isolated channels. Each channel has a logic input and output buffer separated by a silicon dioxide (SiO2) insulation barrier. Used in conjunction with isolated power supplies, these devices prevent noise currents on a data bus or other circuit from entering the local ground and interfering with or damaging sensitive circuitry. ISO7420 has both channels in the same direction while ISO7421 has the two channels in opposite direction. In case of input power or signal loss, default output is 'low' for devices with suffix 'F' and 'high' for devices without suffix 'F'. ISO742x have no integrated noise filter and thus have fast propagation delays. These devices have TTL input thresholds and operate from 3-V to 5.5-V supplies. All inputs are 5-V tolerant when supplied from a 3.3-V supply.