1.

General description

capacitance of 400 pF on the higher voltage side. Port A allows a voltage range from

resistors due to the internal current source. Port B allows a voltage range from 3.0 V to

5.5 V and is overvoltage tolerant. Both port A and port B SDA and SCL pins are

high-impedance when the PCA9509 is unpowered.

The bus port B drivers are compliant with SMBus I/O levels, while port A uses a current

sensing mechanism to detect the input or output LOW signal which prevents bus lock-up.

Port A uses a 1 mA current source for pull-up and a 200

Ω pull-down driver. This results in

a LOW on the port A accommodating smaller voltage swings. The output pull-down on the

port A internal buffer LOW is set for approximately 0.2 V, while the input threshold of the

internal buffer is set about 50 mV lower than that of the output voltage LOW. When the

port A I/O is driven LOW internally, the LOW is not recognized as a LOW by the input. This

prevents a lock-up condition from occurring. The output pull-down on the port B drives a

2.5 V. The enable (EN) pin can also be used to turn the drivers on and off under system

control. Caution should be observed to only change the state of the EN pin when the bus

is idle.

2.

Features

port B (3.0 V to 5.5 V)

PCA9509

Rev. 05 — 10 July 2009

Product data sheet