lt1711ims8-trpbf Linear Technology Corporation, lt1711ims8-trpbf Datasheet - Page 9

• Manufacturer Part Number: lt1711ims8-trpbf
• Description: Single/dual 4.5ns, 3v/5v/?5v, Rail-to-rail Comparators
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
TYPICAL APPLICATIO S
Simultaneous Full Duplex 75Mbaud Interface
with Only Two Wires
The circuit of Figure 3 shows a simple, fully bidirectional,
differential 2-wire interface that gives good results to
75Mbaud, using the LT1712. Eye diagrams under condi-
tions of unidirectional and bidirectional communication
are shown in Figures 4 and 5. Although not as pristine as
the unidirectional performance of Figure 4, the perfor-
mance under simultaneous bidirectional operation is still
excellent. Because the LT1712 input voltage range ex-
tends 100mV beyond both supply rails, the circuit works
RxD
TxD
13
49.9
49.9
750k
750k
V
IN
14
16
LE
50
4
3
3V
LT1712
7
8
1/2
15
50k
+
–
+
–
LT1711
LT1712
+
–
U
9
LE
1/2
3V
2
1
5
6
100k
100k
10
11
U
12
Q
Q
Figure 2. Various Configurations for Introducing Hysteresis
U
Figure 3. 75Mbaud Full Duplex Interface on Two Wires
W
V
V
V
(ALL 3 CASES)
R2A
2.55k
R3A
124
R3B
124
R2B
2.55k
HYST
+
–
= 5V
= –5V
= 5mV
V
IN
499
R
140
R1B
499
R1A
OA
50
V
U
REF
3V
50k
+
–
DIODES: BAV99
LT1711
TWISTED PAIR
Z
O
6-FEET
120
with a full 3V (one whole V
potential difference.
The circuit works well with the resistor values shown, but
other sets of values can be used. The starting point is the
characteristic impedance, Z
The input impedance of the resistive network should
match the characteristic impedance and is given by:
4
R
IN
Q
Q
2
3V
•
140
499
499
R
R1D
R1C
R
O
OB
V
V
•
IN
IN
R
+
–
O
2.55k
124
124
2.55k
R2C
R3C
R3D
R2D
50
50
R
2
1
•
||(
R
R
O
1
100k
100k
2
, of the twisted-pair cable.
||(
+
–
LT1711/LT1712
12 6
S
LT1711
100k
100k
11
R
up or down) of ground
R
2
3
10
LT1712
5
)
3V
2
1
1/2
R
LE
+
–
LT1712
9
3
+
1/2
–
)
3
3V
171112 F02
7
8
15
4
LE
Q
Q
171112 F03
750k
750k
16 13
49.9
49.9
14
RxD
TxD
9