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PDF BA8274F Data sheet ( Hoja de datos )
| Número de pieza | BA8274F | |
| Descripción | I2C Bus Line Buffer IC | |
| Fabricantes | ROHM Semiconductor | |
| Logotipo |  |
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Audio ICs
I2C bus line buffer IC
BA8274 / F
BA8274 / F
BA8274, BA8274F are buffer ICs that can lengthen the bus line retaining all features and operating mode of I2C bus
system. Adoption of this buffer in data and clock line enable to improve the drive capacity and to lengthen the bus line
with using standard wire at a low price.
zApplications
Mini-component stereo, Micro-component stereo and Television.
zFeatures
1) Dual, bi-directional, unity voltage gain buffer.
2) I2C bus compatible.
3) 1:10 impedance transformation.
4) Logic signal levels may include both supply and ground.
5) Power supply voltage range is large.
zAbsolute maximum ratings (Ta=25°C)
Parameter
Power supply voltage
Power dissipation
Operating temperature
Storage temperature
Symbol
VCC
Pd
Topr
Tstg
Limits
13.0
∗∗
800 / 550
−40 to +85
−55 to +125
∗ For Ta=25°C or more it is reduced at 5.5mW/°C(SOP), 8.0mW/°C (DIP).
Unit
V
mW
°C
°C
zRecommended operating conditions (Ta=25°C)
Parameter
Symbol Min.
Power supply voltage VCC
4.5
Typ.
−
Max.
12
Unit
V
∗ I2C bus is a trademark of Philips.
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Audio ICs
BA8274 / F
zAttached components
1. Selection of external components
(1) Pull-up resistance calculation
In practical system the pull-up resistance is determined by the rise time limit for I2C systems. As an approximation this
limit will be satisfied if the time constant (product of the net resistance and net capacitance) of the total system is set to
1 microsecond.
The total time constant may either be set by considering each bus node individually (i.e., the I2C nodes, and the
buffered bus node) and choosing pull-up resistors to give time constants of 1 microsecond for each node; or by
combining the capacitances into an equivalent capacitive loading on the buffered bus, and calculating the buffered
bus
pull-up resistor required by this equivalent capacitance.
For each separate bus the pull-up resistor may be calculated as follows:
R = 1µsec
Cdevice + Cwiring
Where : Cdevice = Sum of device capacitances connected to each bus.
Cwiring = Total wiring and stray capacitance on each bus.
If these capacitances are not know then a good approximation is to assume that each device presents 10pF of load
capacitance and 10pF of wiring capacitance.
The capacitance figures for one or more individual I2C bus nodes should be multiplied by a factor of about 10 times,
and then added to the buffered bus capacitance. Calculation of a new buffered bus pull-up resistor will allow this single
pull-up resistor to act for both the included I2C bus nodes and the buffered bus. Thus it is possible to combine some or
all of these separate pull-up resistors into a signal resistor on the buffered bus (the value of which is calculated from
the sum of the scaled capacitances on the buffered bus.) If the buffer is to be permanently connected into the system
then all the separate pull-up resistors should be combined. But if it is to be connected by adding it onto an existing
system, then only those on the additional I2C bus system can be combined onto to the buffered bus if the original
system is required to be able to still operate on a stand-alone basis.
A further restriction is that the maximum pull-up current, with the bus LOW, should not exceed the I2C bus
specification
maximum of 3mA, or 30mA on buffered bus. The following formula applies:
30mA > VCC-0.4
Rp
Where : Rp = Scaled parallel combination of all pull-up resistors.
If this condition is met, the fall time specifications will also be met.
5/8
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| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet BA8274F.PDF ] | |
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