82B715 Datasheet, PDF (4/10 Pages) NXP Semiconductors – I2C bus extender

Philips Semiconductors
I²C bus extender
Preliminary specification
82B715
FUNCTIONAL DESCRIPTION
The 82B715 bipolar integrated circuit contains two identical buffer
circuits which enable I²C and similar bus systems to be extended
over long distances without degradation of system performance or
requiring the use of special cables.
The buffer has an effective current gain of ten from I²C bus to
Buffered bus. Whatever current is flowing out of the I²C bus side,
ten times that current will be flowing into the Buffered bus side (see
Figure 2).
As a consequence of this amplification the system is able to drive
capacitive loads up to ten times the standard limit on the Buffered
bus side. This current based buffering approach preserves the
bi-directional, open-collector/open-drain characteristic of the I²C
SDA/SCL lines.
To minimize interference and ensure stability, current rise and fall
rates are internally controlled.
V_CC
I_B
I²C BUS
S_X
APPLICATION NOTES
By using two (or more) 82B715 ICs, a sub-system can be built which
retains the interface characteristics of an I²C device so that it may
be included in, or optionally added to, any I²C or related system.
The sub-system features a low impedance or “Buffered” bus,
capable of driving large wiring capacities (see Figure 3).
I²C Systems
As with the standard I²C system, pull-up resistors are required to
aprovide the logic HIGH levels on the Buffered bus. (Standard
open-collector configuration of the I²C bus). The size and number of
these pull-up resistors depends on the system.
If the buffer is to be permanently connected into the system, the
circuit should be configured with only one pull-up resistor on the
Buffered bus and none on the I²C bus.
Alternatively a buffer may be connected to an existing I²C system. In
this case the Buffered bus pull-up will act in parallel with the I²C bus
pull-up.
CURRENT
SENSE
10 (I_B)
BUFFERED BUS
L_X
GND
Figure 2. Equivalent Circuit: One Half 82B715
SU00292
SDA
SCL
82B715
1/2
1/2
V_CC
V_CC
LDA
LONG
CABLE
LCL
82B715
1/2
1/2
SDA
SCL
I²C
DEVICE
STANDARD
I²C
INTERFACE
BUFFERED
INTERFACE
BUFFERED
INTERFACE
STANDARD
I²C
INTERFACE
Figure 3. Minimum Sub-System with 82B715
SU00293
1998 Jan 09
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