PCA9617A

http://onsemi.com

4

FUNCTIONAL DESCRIPTION

system performance. The PCA9617A contains two

bidirectional open−drain buffers specifically designed to

support up−translation/down−translation between the low

or SMBus. All inputs and I/Os are overvoltage tolerant to

2.2 V and until after the internal reference circuits have

settled in ~400

power−up and with the enable (EN) HIGH, a LOW level on

driver (either SDA or SCL) on and drives port B down to

B pull−down driver is turned off and the external pull−up

resistor pulls the pin HIGH. When port B falls first and goes

below 0.4 V, the port A driver is turned on and port A pulls

down to ~0 V. The port A pull−down is not enabled unless

the port B voltage goes below 0.4 V. If the port B low voltage

goes below 0.4 V, the port B pull−down driver is enabled and

port B will only be able to rise to 0.55 V until port A rises

comparators and for the power good detect circuit. The

pin.

Enable Pin (EN)

The EN pin is active HIGH with thresholds referenced to

device active unless the user selects to disable the repeater

to isolate a badly behaved slave on power−up until after the

system power−up reset. It should never change state during

operation will hang the bus and enabling part way through

The enable does not switch the internal reference circuits so

the ~400

The enable pin should only change state when the global

bus and the repeater port are in an idle state to prevent system

failures.

required to provide the logic HIGH levels on the buffered

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,

devices only specify 3 mA output drive; this limits the

where Standard−mode devices, Fast−mode devices and

multiple masters are possible. When only Fast−mode Plus

devices are used with 30 mA at 5 V drive strength, then

lower value pull−up resistors can be used. The B−side RC

should not be less than 67.5 ns because shorter RCs increase

the turnaround bounce when the B−side transitions from

being externally driven to pulled down by its offset buffer.