Datasheet

LTC4315
17
4315f
APPLICATIONS INFORMATION
example, there are three LTC4300As, one LTC4307 and
one LTC4315. The SCL1 bus is driven by an I
2
C master
(master not shown). When the SCL2 voltage crosses
0.6V and 0.8V, the RTAs on the LTC4300A and LTC4307
turn on respectively and source current into SCL2. The
LTC4315 detects this and turns off its buffers, releasing
SCL1 and SCL2 high. Contention between the LTC4315
buffers and the LTC4300A and LTC4307 RTAs is prevented
and the SCL1, SCL2 and SCL3 waveforms in Figure 11 are
monotonic. The logic low noise margin is reduced because
the LTC4315 buffers turn off when the SCL1 voltage is
approximately 0.6V.
Generally, noise margin will be reduced if other RTAs
turn on at a voltage less than 0.3 • V
MIN
. The reduction
in noise margin is a function of the number of LTC4315s
and the number and turn-on voltage of other RTAs, whose
current must be sunk by the LTC4315 buffers. The same
arguments apply for non-LTC buffer products whose RTA
turn-on voltage is less than 0.3 • V
MIN
.
I n t e r o p e r a b i l i t y i s i m p r o v e d b y r e d u c i n g t h e i n t e r a c t i o n t i m e
between the LTC4315 buffers and other RTAs by reducing
R1 and CB1. The following guidelines are recommended
for single supply systems,
a. For 5V systems choose R1 < 20k and CB1 < 1nF. There
are no other constraints.
b. For 3.3V systems, refer to Figures 12 and 13 for opera-
tion with LTC4300As and LTC4307s. In the figures:
M =
Number of LTC4300As or LTC4307s
Number of LTC4315s
R1 and CB1 must be chosen to be below the curves for a
specific value of M. For M greater than the values shown
in the figures, non-idealities do not result. R1 < 20k and
CB1 <1nF are still recommended.
Figure 12. Recommended Maximum R1 and CB1 Values for the
LTC4315 Operating with Multiple LTC4300As in a 3.3V System.
Figure 13. Recommended Maximum R1 and CB1 Values for the
LTC4315 Operating with Multiple LTC4307s in a 3.3V System.
R
BUS
(k)
02
C
BUS
(pF)
1000
100
10
4
4315 F12
1068
M = 1
M = 2
M = 3
R
BUS
(k)
02
C
BUS
(pF)
10000
1000
100
4
4315 F13
1068
M = 1