I2C repeaters/hubs/extenders

New bus buffers from NXP Semiconductors overcome the previous system capacitance limitation of 400pF. These new bus buffers allow designers more freedom in their design to expand the use of the I2C or SMBus:

• More I2C devices than the 400pF maximum allowed by the I2C specification
• Long bus wiring in point-to-point or multi-point applications
• Different operating supply voltages or logic voltage levels within one system
• Opto-isolation for safety or due to difference in ground plane
• Isolating a section of a system that has lost its power supply
• Insertion of unpowered cards into an active I2C bus on multi-point backplanes like those found in CompactPCI, VME, or AdvancedTCA systems

These devices can be used in a wide variety of applications:

All bus buffer devices isolate the system capacitance and, at least, double the number of devices allowed in the same I2C or SMBus system. Typically 20 to 30 devices are the limit for the 400pF maximum capacitance specified by the I2C protocol. By using these bus buffers, the designer can extend the use of the I2C or SMBus in systems with many more devices.

The P82B715 and P82B96 are specifically designed to extend the reach of the I2C or SMBus over long distances, in the range of kilometers, depending on the maximum bus speed. This allows the designer to use I2C to interconnect equipment cabinets or for large area systems such as warehouse pick and place systems.

Most devices have an enable/disable feature that can be used to electrically isolate an I2C or SMBus segment. In addition, all devices except the P82B715 release their I/O pins should their supply voltage fail.

Examples where this enable/disable feature could be useful include:

• Allow mixed operation of 100kHz and 400kHz devices on a combined bus by isolating the segment with 100kHz devices from the rest of the 400kHz system so that the 400kHz devices can operate at their maximum speed
• Supporting the PCI management bus with 8 or more PCI slots
• Isolating the I2C or SMBus to support hot-plug PCI slots
• Allowing the main I2C or SMBus to drive multiple system boards
• Addressing selected devices if there are multiple devices in the system with the same I2C address

PCA954X devices (Application Note AN262 PCA954X Family of I2C/SMBus Multiplexers and Switches) provide a variety of lower cost 2-, 4-, and 8-channel I2C controlled multiplexers for applications that don't require bus buffering and can also be used for voltage level translation. PCA954X devices operate at 400kHz with voltage supply range of 2.3V to 5.5V.

CBTXXXX devices offer the lowest cost manually controlled multiplexers and voltage level translators at 5V operation in non bus buffering application.

The bus buffers isolate the system capacitance and also allow translation of the I2C or SMBus voltage levels if required.

The PCA9515/16/18 operate at 3.3V V_CC but, since they have 5V-tolerant I/Os, they support different I2C or SMBus segments at 3.3V and 5V. This extends the life of older 5V circuit blocks while allowing use of newer 3.3V devices for improved system performance. The PCA9515A/16A/18A operate at 2.5V and 3.3V V_CC with 5V-tolerance.

The PCA9517 operates between 2.7V and 3.6V V_CC with 5V-tolerant I/O. The second V_CC on this new device adjusts between 0.9V and 5.5V allowing voltage level translation with optimum noise margin between 0.9V to 5V levels. The low voltage SDA/SCL pins also pull to ground providing excellent V_IL margins even at lower voltages and allowing connections to other static or dynamic level shifting bus buffers.

The PCA9510(A)/11(A)/12(A)/13(A)/14(A) operate between 2.7V to 5.5V V_CC and provide voltage level translation capability with the PCA9512(A) featuring two V_CCs for optimum noise margin in 3.3V-to-5V level translation applications.

The P82B96 operates at 3.3V or at 5V logic levels on the Sx side that is independent of the V_cc. The logic levels on the higher drive Rx/Tx side are half-rail CMOS switching levels related to the V_cc that can range from 2V to 15V. The P82B715 does NOT support logic level translations.

GTL20XX devices (Application Note AN10145 Bi-Directional Low Voltage Translators GTL2000, GTL2002, GTL2010) and the new PCA9306 offer lower-cost voltage level translations at any voltage between the range of 1V and 5V for applications that don't also require bus buffering.

The I2C bus is very effective at communicating amongst equipment in a multi-point arrangement. The I2C bus is increasingly being used to interconnect multiple backplane cards such as those in Intel IPMI (Intelligent Platform Management Interface), VME, PICMG (PCI Industrial Computer Manufacturers Group), CompactPCI^©, and AdvancedTCA^TM architectures using the PCA9510/11/12/13/14. We have more information on IPMI, VME, and PICMG architectures.

The higher drives on the special side of the P82B96 and P82B715 provide reliable, very-long distance, multi-point communications at higher voltages for better noise margin.

The PCA9510(A)/11(A)/12(A)/13(A)/14(A) have been specifically designed for multi-point system implementations and include features like SDA/SCL precharge, idle detection, ready hardware pin, and rise-time accelerators to provide optimum protection of active I2C bus data in hot swap backplane applications.

The I2C bus may need to be electrically isolated due to safety reasons such as in heath care or where high voltages are involved or in cases where the ground plane is at different potentials such as in power supplies. The P82B96, with split input and output pins on its high-voltage, high-drive side, is optimized for interconnection with optical isolators and, depending on the opto-isolator used, speeds up to 400kHz are achievable.

Product	Usage
P82B715	3000pF
P82B96	4000pF
PCA9510(A)	800pF
PCA9511(A)	800pF
PCA9512(A)	800pF
PCA9513(A)	800pF
PCA9514(A)	800pF
PCA9515(A)	800pF
PCA9516(A)	2000pF
PCA9517	800pF
PCA9518(A)	2000pF x n
GTL20XX	400pF
PCA9306	400pF
PCA954X	400pF
CBTXXXX	400pF

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	P82B96		Dual Bi-Directional I2C Bus Buffer
	P82B715		I2C Bus Extender
	PCA9306		Dual bidirectional I2C-bus and SMBus voltage-level translator
	PCA9507		2-wire serial bus extender for HDMI DDC I2C-bus and SMBus
	PCA9508		Hot swappable level translating I2C-bus repeater
	PCA9509		Level translating I2C-bus/SMBus repeater
	PCA9510		See PCA9510A replacement
	PCA9510A		Hot swappable I2C and SMBus buffer with higher series resistance
	PCA9511		See PCA9511A replacement
	PCA9511A		Hot swappable I2C and SMBus buffer with higher series resistance
	PCA9512		See PCA9512A replacement
	PCA9512A		Level shifting hot swappable I2C and SMBus buffer with higher series resistance
	PCA9513		See PCA9513A replacement
	PCA9513A		Hot swappable I2C and SMBus buffer with higher series resistance
	PCA9514		See PCA9514A replacement
	PCA9514A		Hot swappable I2C and SMBus buffer with higher series resistance
	PCA9515		3.3V I2C bus repeater; BiCMOS process
	PCA9515A		2.5V and 3.3V I2C bus repeater; CMOS process
	PCA9516		3.3V 5-channel I2C hub; BiCMOS process
	PCA9516A		2.5V and 3.3V 5-channel I2C hub; CMOS process
	Datasheet (Sep 29, 2004) PCA9516AD SO-16 Production SOT109-1 Pb-Free MSL=1 PCA9516APW TSSOP-16 Production SOT403-1 Pb-Free MSL=1 Device Family Functions Literature Models Support Docs Price Buy Online More...
	PCA9517		Level translating I2C-bus repeater; See PCA9517A replacement
	PCA9517A		Level translating I2C-bus repeater, improved ESD protection
	PCA9518		Expandable 5-channel I2C hub; See PCA9518A replacement
	PCA9518A		Expandable 5-channel I2C hub
	PCA9519		4-channel level translating I2C-bus/SMBus repeater
	PCA9600		Bidirectional Fm+ I2C-bus buffer, dual channel

• Only New I2C Repeaters/Hubs/Extenders

• P82B96 and P82B715 Device Highlight
• PCA9510(A), PCA9511(A), PCA9512(A), PCA9513(A), and PCA9514(A) Device Highlight
• PCA9515(A), PCA9516(A), PCA9517, and PCA9518 Device Highlight

• Electronic Design Bus Repeaters Expand Use of Popular Inter-IC Bus Article

• AN255-02 I²C/SMBus Repeaters, Hubs, and Expanders (Dec 19, 2002)

AN255 covers useage in a generic, multiple-master environment. Discusses pull-up resistor sizing in detail. Information on the permitted interfaces and bus propagation delays between P82B715/96 Buffers and the PCA9515/16/18 is also included.

• More I2C Support Documents

• Intelligent Platform Management Interface (IPMI) Explained