Datasheet

7–185
V
O
– Output Voltage – V
– Hold Current – AµI
I(hold)
V
CC
= 3.6 V
V
CC
= 3.3 V
V
CC
= 3 V
V
CC
= 2.7 V
V
I
– Input Voltage – V
– Hold Current – AµI
I(hold)
V
CC
= 5.5 V
V
CC
= 5 V
V
CC
= 4.5 V
300
250
200
150
100
50
0
–50
–100
–150
–200
–250
–300
400
250
100
–50
–200
–350
–500
01234
012345
Figure 13. Bus-Hold Input Characteristics
When multiple devices with bus-hold circuits are driven by a single driver, there may be some concern about the ac switching
capability of the driver becoming weaker. As small drivers, bus-hold circuits require an ac current to switch them. This current
is not significant when using TI CMOS and BiCMOS families. Figure 14 shows a 4-mA buffer driving six LVTH16244
devices. The trace is a 75-Ω transmission line. The receivers are separated by 1cm, with the driver located in the center of the
trace. Figure 15 shows the bus-hold loading effect on the driver when connected to six receivers switching low or high. It also
shows the same system with the bus-hold circuit disconnected from the receivers. Both plots show the effect of bus hold on
the driver’s rise and fall times. Initially, the bus-hold circuit tries to counteract the driver, causing the rise or fall time to increase.
Then, the bus-hold circuit changes states (note the crossover point), which helps the driver switch faster, decreasing the rise
or fall time.