82B715 Datasheet, PDF (7/10 Pages) NXP Semiconductors – I2C bus extender

Philips Semiconductors
I²C bus extender
Preliminary specification
82B715
V_CC
EXISTING
R1
I²C ^SDA
I²C
SDA
GND
PROPOSED BUS EXPANSION
5V
R2
LDA
3nF
R3
SDA
I²C
0V
EFFECTIVE CAPACITANCE
NEAR I²C DEVICES
2 × I²C Devices
Strays
82B715 Buffer
TOTAL CAP.
20pF
20pF
10pF
–––––
50pF
I²C pull-up
R1
+
1m sec
50pF
+
20KW
EFFECTIVE CAPACITANCE
BUFFERED LINE
Wiring Cap.
TOTAL CAP.
3000pF
–––––
3000pF
Buffered Bus pull-up
R2
+
1m sec
3000pF
+
333W
EFFECTIVE CAPACITANCE
REMOTE I²C DEVICES
1 × I²C Devices
Strays
82B715 Buffer
TOTAL CAP.
10pF
10pF
10pF
–––––
30pF
I²C pull-up
R3
+
1m sec
30pF
+
33KW
AS AN ADDITION TO AN EXISTING SYSTEM * :
R1 = 20KΩ
R2Ȁ
+
R2
R2
)
0.1R3
0.1R3
+
300W
R3 not required since
buffer always connected
FOR A PERMANENT SYSTEM * :
R1 not required since
buffer always connected
R2Ȁ
+
1
0.1R1
)
1
1
0.1R2
)
1
0.1R3
+
262W
R3 not required since
buffer always connected
* NOTE:
R1, R2 and R3 are calculated from the capacitive loading and a 1µsec time constant on each bus node. For an addition to an existing
system, R2’ (the new value for R2) is shown as being calculated from the parallel combination of R2 and the scaled value of R3;
while for a permanent system R2, and scaled values of R1 and R3 have been used. Note that this example has used scaled resistor
values and combined the node and cable capacitances.
CHECK FOR MAXIMUM PULL-UP CURRENT:
(5
* 0.4)V
260W
+
17.6mA
t
30mA
Figure 4. Typical Loading Calculation: I²C Bus with 82B715
SU00294
1998 Jan 09
7