The FB2041 is a 7-bit bidirectional BTL transceiver and is intended
to provide the electrical interface to a high performance wired-OR
bus. The FB2041 is an inverting transceiver.
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 .
FEA TURES
•7-bit BTL transceiver
•Separate I/O on TTL A-port
•Inverting
•Three separate pairs of driver enables in a 1 bit, 3 bit, 3 bit
arrangement
•Drives heavily loaded backplanes with equivalent load
impedances down to 10Ω.
•Allows incident wave switching in heavily loaded backplane buses
•Reduced BTL voltage swing produces less noise and reduces
power consumption
•Built-in precision band-gap reference provides accurate receiver
thresholds and improved noise immunity
•Compatible with IEEE Futurebus+ or proprietary BTL backplanes
•Controlled output ramp and multiple GND pins minimize ground
bounce
•Each BTL driver has a dedicated Bus GND for a signal return
•Glitch-free power up/power down operation
•Low I
current
CC
•Tight output skew
•Supports live insertion
•Pins for the optional JTAG boundary scan function are provided
•High density packaging in plastic Quad Flatpack
•High drive 100mA BTL open collector drivers on B-port
QUICK REFERENCE DATA
SYMBOLPARAMETERTYPICALUNIT
t
PLH
t
PHL
t
PLH
t
PHL
C
I
OB
OL
CC
Propagation delay3.7
AIn to Bn2.7
Propagation delay3.4
Bn to AOn3.2
Output capacitance (B0 - B6 only)6pF
Output current (B0 - B6 only)100mA
Standby19
pp
AIn to Bn (outputs Low or High)40
Bn to AOn (outputs Low)22
Bn to AOn (outputs High)19
The B-port interfaces to “Backplane Transceiver Logic” (See the
IEEE 1194.1 BTL standard). BTL features low power consumption
by reducing voltage swing (1Vp-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.
There are three separate pairs of driver enables in a 1 bit, 3 bit, 3 bit
arrangement. The TTL/BTL output drivers for bit 0 are enabled with
OEA1/OEB1
OEA2/OEB2
OEA3/OEB3
, output drivers for bits 1–2–3 are enabled with
and output drivers for bits 4–5–6 are enabled with
.
The A-port operates at TTL levels with separate I/O. The 3-state
A-port drivers are enabled when OEAn goes High after an extra 6ns
delay which is built in to provide a break-before-make function.
When OEAn goes Low, A-port drivers become High impedance
without any extra delay. During power on/of f cycles, the A-port
drivers are held in a High impedance state when V
is below 2.5V.
CC
The B-port has an output enable, OEB0, which affects all seven
drivers. When OEB0 is High and OEBn
be enabled. When OEB0 is Low or if OEBn
is Low the output driver will
is High, the B-port
drivers will be inactive and at the level of the backplane signal.
CC
B0
TMS (option)
OEB0
OEB1
OEA2
TDO (option)
TCK (option)
BUS V
CC
OEA3
BUS V
TDI (option)
BUS GND
39
38
37
36
35
34
33
32
31
30
29
28
27
OEB2
OEB3
BUS GND
B1
BUS GND
B2
BUS GND
B3
BUS GND
B4
BUS GND
B5
BUS GND
B6
BUS GND
BIAS V
OEA1
FB2041
AI6
LOGIC GND
To support live insertion, OEB0 is held Low during power on/off
cycles to insure glitch free 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
BIAS V pin should be tied to a V
is Low. If live insertion is not a requirement, the
CC
CC
pin.
The LOGIC GND and BUS GND pins are isolated in 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 very
infrequent and impossible to trouble-shoot.
The LOGIC V
and BUS VCC pins are also isolated internally to
CC
minimize noise and may be externally decoupled separately or
simply tied together.
JTAG boundary scan functionality is provided as an option with
signals TMS, TCK, TDI and TDO. When this option is not present,
TMS and TCK are no-connects (no bond wires) and TDI and TDO
are shorted together internally.
B0 – B640, 38, 36, 34, 32, 30, 28I/OData inputs/Open Collector outputs, High current drive (BTL)
OEB046InputEnables the Bn outputs when High
OEB145InputEnables the B0 output when Low
OEB225InputEnables the B1 – B3 outputs when Low
OEB326InputEnables the B4 – B6 outputs when Low
OEA147InputEnables the A0 outputs when High
OEA220InputEnables the A1 – A3 outputs when High
OEA324InputEnables the A4 – A6 outputs when High
23, 43PowerPositive supply voltage
17, 49PowerPositive supply voltage
ABSOLUTE MAXIMUM RATINGS
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
CC
IN
I
IN
V
OUT
OUT
T
STG
Supply voltage-0.5 to +7.0V
p
Input current-18 to +5.0mA
Voltage applied to output in High output state-0.5 to +V
Current applied to output inAO0 – AO648mA
Low output stateB0 – B6200
Storage temperature-65 to +150°C
H=High voltage level
L=Low voltage level
X=Don’t care
Z=High-impedance (OFF) state
— =Input not externally driven
H** =Goes to level of pull-up voltage
B* =Precaution should be taken to ensure B inputs do not float.
If they do, they are equal to Low state.
Z=High-impedance (OFF) state
— =Input not externally driven
H** =Goes to level of pull-up voltage
B* =Precaution should be taken to ensure B inputs do not float.
If they do, they are equal to Low state.
1995 May 25
5
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