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BA8274 / F
Audio ICs
I2C bus line buffer IC
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.
Applications Mini-component stereo, Micro-component stereo and Television.
Features 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.
Absolute maximum ratings (Ta=25C)
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

Unit V mW C C
For Ta=25C or more it is reduced at 5.5mW/C(SOP), 8.0mW/C (DIP).
Recommended operating conditions (Ta=25C)
Parameter Power supply voltage Symbol VCC Min. 4.5 Typ. - Max. 12 Unit V
I C bus is a trademark of Philips.
2
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BA8274 / F
Audio ICs
Block diagram
VCC 8
LY 7
SY 6
N.C. 5
Buffer
Buffer
1 N.C.
2 LX
3 SX
4 GND
Pin descriptions and input output circuits
Pin No. Pin Name
VCC
Equivalent circuit
Pin description
2 7
LX LY
35.7 GND
A pin for outputting a buffer.
VCC
3 6
SX SY
35.7
A pin for inputting a buffer.
GND
4 8
GND VCC
- -
A ground pin. Power supply pin.
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BA8274 / F
Audio ICs
Electrical characteristics (unless otherwise noted, Ta=25C, VCC=5V)
Parameter Supply current 1 Supply current 2 Supply current 3 Drive current 1 Drive current 2 Input current 1 Input current 2 Leakage current Input/Output impedance Symbol IQ1 IQ2 IQ3 ISX, ISY ILX, ILY ISX, ISY ILX, ILY ILX, ILY ZIN / ZOUT Min. - - - 2.0 20 - - - 8 Typ. 16 17 30 2.7 27 2.8 3.0 - 10 Max. 30 30 40 - - 3.5 3.3 200 13 Unit mA mA mA mA mA mA mA A - VCC=12V Both I2C inputs LOW, both buffered outputs sinking 30mA. ISX, ISY LOW=0.4V VLX, VLY LOW on buffered bus=0.3V. ILX, ISY LOW=0.4V VSX, VSY LOW on I2C bus=0.3V. ILX, ILY sink on buffered bus=30mA. ISX, ISY sink on I2C bus=3mA. VLX, VLY=VCC and VSX, VSY=VCC. Conditions
Measurement circuit
VCC N.C. F I4 E4 150 VCC N.C. I3 D2 E3 150 VCC
A
0 1
A
A2 2 3
V
B2
V
C2 0 1
A
2 3
SW4
SW3
8 VCC LY
7
6 SY
5 N.C.
N.C. 1
SW1
LX 2 3
SX
GND 4
SW2
0
1
2 A1
3 B1 C1
0
1
2
3
A
I2 N.C. E2 VCC 150
V
V
I1 N.C. D1
A
150 E1 VCC
Fig.1
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BA8274 / F
Audio ICs
Circuit operation BA8274/F 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 about 10 from I2C bus to buffered bus. When current is flowing out of the I2C bus side, about 10 times that current will be flowing into the buffered bus side (See Fig.2). As a consequence of this amplification the system is able to drive capacitive load up to about 6 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.
VCC
I I2C BUS SX
CURRENT SENSE
10xI
BUFFERED BUS LX
GND
Fig.2
Application circuit
VCC 150 -COM
8
7
6
5
Buffer
Buffer
1
2
3
4
150
-COM
Fig.3
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BA8274 / F
Audio ICs
Attached 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=
1sec 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.
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BA8274 / F
Audio ICs
2. Loading calculations for the expanded I2C bus.
EXISTING VCC PROPOSED BUS EXPANSION 5V
R1
R2
R3
BA8274/F IC
2
BA8274/F LDA SDA IC
2
SDA
3000pF
GND
0V
Fig.4
Effective capacitance Near I2C devices
Effective capacitance Buffered line
Effective capacitance Remote I2C devices
2 x I2C Devices Strays BA8274 Buffer Total Cap.
20pF 20pF 10pF 50pF Wiring Cap. Total Cap. 3000pF 3000pF
1 x I2C Devices Strays BA8274 Buffer Total Cap.
10pF 10pF 10pF 30pF
I2C pull-up R1 = 1sec 50pF = 20k
Buffered bus pull-up R2 = 1sec 3000pF = 333k
I2C pull-up R3 = 1sec 30pF = 33k
As an addition to an existing system:
R2 x 0.1R3 R2 + 0.1R3
R1 = 20k
R2 =
= 300
R3 not required since buffer always connected.
For a permanent system:
R2 = 1 1 1 1 + + 0.1R1 0.1R2 0.1R3 R1 and R3 not required since buffer always connected. = 262
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BA8274 / F
Audio ICs
Note): R1, R2 and R3 are calculated from the capacitive loading and a 1sec 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 260
= 17.6mA < 30mA
Operation notes 1. About operation voltage supply range Within operation voltage supply range, basic circuit function operation is guaranteed within operation ambient temp. But please confirm set up of constant and element, voltage set up and temp set up on use. 2. About operation temp range If it within recommended operation voltage range, circuit function operation is guaranteed within operation temp. It corralled to conditions of power dissipation to temp. Please watch out except condition stipulated by electrical characteristics within the range, it cannot guarantee standard value of electrical characteristics. But it retains original function. 3. SX, SY, I2C BUS, SDA or SCL Because the two buffer circuits in the BA8274/F are identical either input pin can be used as the I2C BUS SDA data line, or the SCL clock line. 4. LX, LY, Buffered bus, LDA or LCL On the buffered low impedance line side, the corresponding output becomes LDA and LCL.
Electrical characteristic curves
0.1 0.09
: (A)
0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 : (V) 0.4 S PIN VOLTAGE VSX,
DRIVE CURRENT ILX,
ILY
VSY
Fig.5 S pin voltage-drive current ILX, ILY
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BA8274 / F
Audio ICs
External dimensions (Unit: mm)
BA8274
9.30.3 8 5
BA8274F
5.00.2
6.50.3
8 5
1
4 7.62
6.20.3 4.40.2
1
4
1.50.1 0.11
0.51Min.
0.150.1 0.1
3.40.3
1.27 0.40.1
3.20.2
0.30.1
2.54 0.50.1 0 ~ 15
DIP8
SOP8
0.3Min.
8/8
Appendix
Notes
No technical content pages of this document may be reproduced in any form or transmitted by any means without prior permission of ROHM CO.,LTD. The contents described herein are subject to change without notice. The specifications for the product described in this document are for reference only. Upon actual use, therefore, please request that specifications to be separately delivered. Application circuit diagrams and circuit constants contained herein are shown as examples of standard use and operation. Please pay careful attention to the peripheral conditions when designing circuits and deciding upon circuit constants in the set. Any data, including, but not limited to application circuit diagrams information, described herein are intended only as illustrations of such devices and not as the specifications for such devices. ROHM CO.,LTD. disclaims any warranty that any use of such devices shall be free from infringement of any third party's intellectual property rights or other proprietary rights, and further, assumes no liability of whatsoever nature in the event of any such infringement, or arising from or connected with or related to the use of such devices. Upon the sale of any such devices, other than for buyer's right to use such devices itself, resell or otherwise dispose of the same, no express or implied right or license to practice or commercially exploit any intellectual property rights or other proprietary rights owned or controlled by ROHM CO., LTD. is granted to any such buyer. Products listed in this document use silicon as a basic material. Products listed in this document are no antiradiation design.
The products listed in this document are designed to be used with ordinary electronic equipment or devices (such as audio visual equipment, office-automation equipment, communications devices, electrical appliances and electronic toys). Should you intend to use these products with equipment or devices which require an extremely high level of reliability and the malfunction of with would directly endanger human life (such as medical instruments, transportation equipment, aerospace machinery, nuclear-reactor controllers, fuel controllers and other safety devices), please be sure to consult with our sales representative in advance. About Export Control Order in Japan Products described herein are the objects of controlled goods in Annex 1 (Item 16) of Export Trade Control Order in Japan. In case of export from Japan, please confirm if it applies to "objective" criteria or an "informed" (by MITI clause) on the basis of "catch all controls for Non-Proliferation of Weapons of Mass Destruction.
Appendix1-Rev1.0

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