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PCA9515D

I2C-bus repeater

NXP Semiconductors. 

NXP Semiconductors

PCA9515

I2C-bus repeater

6. Functional description

The PCA9515 BiCMOS integrated circuit contains two identical buffer circuits which

enable I2C-bus and similar bus systems to be extended without degradation of system

performance. (Refer to Figure 1 “Block diagram of PCA9515”.)

The PCA9515 BiCMOS integrated circuit contains two bidirectional open-drain buffers

specifically designed to support the standard low-level-contention arbitration of the

I2C-bus. Except during arbitration or clock stretching, the PCA9515 acts like a pair of

non-inverting, open-drain buffers, one for SDA and one for SCL.

6.1 Enable

The EN pin is active HIGH with an internal pull-up and allows the user to select when the

repeater is active. This can be used to isolate a badly behaved slave on power-up until

after the system power-up reset. It should never change state during an I2C-bus operation

because disabling during a bus operation will hang the bus and enabling part way through

a bus cycle could confuse the I2C-bus parts being enabled.

The enable pin (EN) should only change state when the global bus and the repeater port

are in an idle state to prevent system failures.

6.2 I2C-bus systems

As with the standard I2C-bus system, pull-up resistors are required to provide the logic

HIGH levels on the buffered bus. (Standard open-collector configuration of the I2C-bus.)

The size of these pull-up resistors depends on the system, but each side of the repeater

must have a pull-up resistor. This part is designed to work with Standard-mode and

Fast-mode I2C-bus devices in addition to SMBus devices. Standard-mode I2C-bus devices

only specify 3 mA output drive; this limits the termination current to 3 mA in a generic

I2C-bus system where Standard-mode devices and multiple masters are possible. Under

certain conditions, higher termination currents can be used. Please see application note

AN255, “I2C/SMBus Repeaters, Hubs and Expanders” for additional information on sizing

resistors and precautions when using more than one PCA9515 in a system or using the

PCA9515 in conjunction with the P82B96.

PCA9515_9

Product data sheet

Rev. 09 — 23 April 2009

© NXP B.V. 2009. All rights reserved.

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