Datasheet

7–142
BTL/FB
0 25 50 75 100 125 150 175 200 225 250 275 300
–90
–70
–50
–30
–10
10
–10123456
V
OL
– V
2.8
2
1.6
0.8
0
2.4
1.2
0.4
Input Characteristic Impedance
T
A
= 25°C,
V
CC
= 5 V,
V
IH
= 3 V,
V
IL
= 0 V
GTL
I
IN
– mA
V
IN
– Input Voltage – V
Output Characteristic Impedance
I
OL
– mA
T
A
= 25°C,
V
CC
= 5 V,
V
IH
= 3 V,
V
IL
= 0 V
0.85-V V
IL
(GTL)
1.47-V V
IL
(GTL/FB)
BTL/FB
GTL
Figure 12. GTL and BTL/FB Input and Output Characteristic Impedance
The BTL input receiver is a differential amplifier, with one side connected to an internal reference voltage. The threshold is
designed with a narrow window (V
IH
= 1.62 V and V
IL
= 1.47 V). Unlike GTL, BTL requires a separate supply voltage for
the threshold circuit. It eliminates any noise generated by the switching outputs. The output driver is an open-collector output
with a termination resistor selected to match the bus impedance. When the device is turned off, the output is pulled up to output
supply voltage (V
TT
= 2.1-V typ). The I/Os work independently of the device’s V
CC
; they communicate with devices designed
for 5-V or 3.3-V V
CC
. The TTL input is a 5-V CMOS inverter and the output is a bipolar output similar to the ABT output
structure. BTL requires three power supplies: the main power supply (V
CC
), the bias generator supply (BG V
CC
), and the bias
supply voltage (BIAS V
CC
) that establishes a voltage between 1.62 V and 2.1 V on the BTL outputs when V
CC
is not connected.
The recommended frequency at which the family runs is in the 30-MHz to 75-MHz range, depending on the application as well
as the board layout. Figure 11 shows a typical BTL input and output circuit and Figure 12 shows their characteristic impedance.
Since BTL has an open-collector output, only the I
OL
/V
OL
curve is displayed.