FB2031

The FB2031 is a 9-bit latched/registered transceiver featuring a latched, registered or pass-thru mode in either the A-to-B or B-to-A direction. The FB2031 is intended to provide the electrical interface to a high performance wired-OR bus.

The FB2031 TTL-level side (A port) has a common I/O. The common I/O, open collector B port operates at BTL signal levels. The logic element for data flow in each direction is controlled by two mode select inputs (SEL0 and SEL1). A "00" configures latches in both directions. A "10" configures thru mode in both directions. A "01" configures register mode in both directions. A "11" configures register mode in the A-to-B direction and latch mode in the B-to-A direction.

When configured in the buffer mode, the FB2031 inverse of the input data appears at the output port. In the register mode, data is stored on the rising edge of the appropriate clock input (LCAB or LCBA). In the latch mode, clock pins serve as transparent-Low latch enables. Regardless of the mode, data is inverted from input to output.

The FB2031 3-State A port is enabled by asserting a High level on OEA. The B port has two output enables, OEB0 and OEB1. Only when OEB0 is High and OEB1 is Low is the output enabled.
When either OEB0 is Low or OEB1 is High, the B port is inactive and is pulled to the level of the pullup voltage. New data can be entered in the register and latched modes or can be retained while the associated outputs are in 3-State (A port) or inactive (B port).

The FB2031 B-port drivers are Low-capacitance open collectors with controlled ramp and are designed to sink 100mA. Precision band gap references on the B-port insure very good noise margins by limiting the switching threshold to a narrow region centered at 1.55V.

The FB2031 B-port interfaces to "Backplane Transceiver Logic" (see the IEEE 1194.1 BTL standard). BTL features low power consumption by reducing voltage swing (1V p-p, between 1V and 2V) and reduced capacitive loading by placing an internal series diode on the drivers. BTL also provides incident wave switching, a necessity for high performance backplanes.

FB2031 Output clamps are provided on the BTL outputs to further reduce switching noise. The "V_OH" clamp reduces inductive ringing effects during a Low-to-High transition. The "V_OH" clamp is always active. The other clamp, the "trapped reflection" clamp, clamps out ringing below the BTL 0.5V V_OL level. This clamp remains active for approximately 100ns after a High-to-Low transition.

To support live insertion, FB2031 OEB0 is held Low during power on/off cycles to insure glitchfree B port drivers. Proper bias for B port drivers during live insertion is provided by the BIAS V pin when at a 5V level while V_CC is Low. The BIAS V pin is a low current input which will reverse-bias the BTL driver series Schottky diode, and also bias the B port output pins to a voltage between 1.62V and 2.1V. This bias function is in accordance with IEEE BTL Standard 1194.1. If live insertion is not a requirement, the BIAS V pin should be tied to a V_CC pin.

The FB2031 LOGIC GND and BUS GND pins are isolated inside the package to minimize noise coupling between the BTL and TTL sides. These pins should be tied to a common ground external to the package.

Each FB2031 BTL driver has an associated BUS GND pin that acts as a signal return path and these BUS GND pins are internally isolated from each other. In the event of a ground return fault, a "hard" signal failure occurs instead of a pattern dependent error that may be infrequent and impossible to troubleshoot.

As with any high power device, thermal considerations are critical. It is recommended that airflow (300Ifpm) and/or thermal mounting be used to ensure proper junction temperature.