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 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
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 3-State A port is enabled by asserting a
High level on OEA. The B port has two output
enables, OEB0 and OEB1
is High and OEB1
enabled.
. Only when OEB0
is Low is the output
When either OEB0 is Low or OEB1
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 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 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.
Output clamps are provided on the BTL
outputs to further reduce switching noise.
The “V
effects during a Low-to-High transition. The
“V
clamp, the “trapped reflection” clamp, clamps
out ringing below the BTL 0.5V V
This clamp remains active for approximately
100ns after a High-to-Low transition.
” clamp reduces inductive ringing
OH
” clamp is always active. The other
OH
is High,
level.
OL
To support live insertion, 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
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
The 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 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.
CC
pin.
CC
is
P ACKAGE THERMAL CHARACTERISTICS
PARAMETERCONDITION52-PIN PLASTIC QFP
θjaStill air80°C/W
θja300 Linear feet per minute air flow58°C/W
θjcThermally mounted on one side to heat sink20°C/W
BG GND19GNDBand Gap threshold voltage reference ground
SEL020InputMode select
SEL115InputMode select
LCAB18InputA to B clock/latch enable (transparent latch when Low)
LCBA16InputB to A clock/latch enable (transparent latch when Low)
TMS42InputTest Mode Select (optional, if not implemented then no connect)
TCK44InputTest Clock (optional, if not implemented then no connect)
TDI22InputTest Data In (optional, if not implemented then no connect)
TDO21OutputTest Data Out (optional, if not implemented then shorted to TDI)
40, 38, 36, 34, 32,
30, 28, 26, 24
25, 27, 29, 31, 33,
35, 37, 39, 41
23, 43, 49PowerPositive supply voltage
17PowerBand Gap threshold voltage reference
I/OData inputs/Open Collector outputs, High current drive (BTL)
H=High voltage level
L=Low voltage level
l=Low voltage level one set-up time
prior to the Low-to-High LCXX transition
h=High voltage level one set-up time
prior to the Low-to-High LCXX transition
1995 May 25
MODE SELECTEDSEL0SEL1
Thru modeHL
Register mode (An to Bn)XH
Latch mode (An to Bn)LL
Register mode (Bn to An)LH
LL
HH
X=Don’t care
Z=High-impedance (OFF) state
— =Input not externally driven
↑=Low-to-High transition
H** =Goes to level of pull-up voltage
4
Bn
* =Precaution should be taken to
ensure B inputs do not float. If they do, they
are equal to Low state.
Disable = OEB0 is Low or OEB1
Operation beyond the limits set forth in this table may impair the useful life of the device.
Unless otherwise noted these limits are over the operating free-air temperature range.
SYMBOL
V
T
V
V
I
OUT
I
OUT
STG
CC
IN
IN
Supply voltage-0.5 to +7.0V
Input voltageAll inputs except B0 – B8-1.2 to +7.0V
Input current-40 to +5.0mA
Voltage applied to output in High output state-0.5 to +V
Current applied to output in Low output stateA0 – A848mA