The SN65ELT21 is a differential PECL-to-TTL translator. It operates on +5-V supply and ground only. The device includes circuitry to maintain Q to a low logic level when inputs are in an open condition or < 1.3 V.
The VBB pin is a reference voltage output for the device. When the device is used in single-ended mode, the unused input should be tied to VBB. This reference voltage can also be used to bias the input when it is ac coupled. When it is used, place a 0.01µF decoupling capacitor between VCC and VBB. Also limit the sink/source current to < 0.5 mA to VBB. Leave VBB open when it is not used.
The SN65ELT21 is housed in an industry standard SOIC-8 package and is also available in an optional TSSOP-8 package.