Datasheet

Product data sheet Rev. 09 — 23 April 2009 4 of 16

NXP Semiconductors

PCA9515

C-bus repeater

6. Functional description

The PCA9515 BiCMOS integrated circuit contains two identical buffer circuits which

enable I

C-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

C-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 I

C-bus operation

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

a bus cycle could confuse the I

C-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 I

C-bus systems

As with the standard I

C-bus system, pull-up resistors are required to provide the logic

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

C-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 I

C-bus devices in addition to SMBus devices. Standard-mode I

C-bus devices

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

C-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, “I

C/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.