Dual Supply Level translating I2C-bus/SMBus repeater

The PCA9509 is a level translating I²C-bus/SMBus repeater that enables processor low

voltage 2-wire serial bus to interface with standard I²C-bus or SMBus I/O. While retaining

all the operating modes and features of the I²C-bus system during the level shifts, it also

permits extension of the I²C-bus by providing bidirectional buffering for both the data

(SDA) and the clock (SCL) lines, thus enabling the I²C-bus or SMBus maximum

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

1.35 V to VCC(B) ‑ 1.0 V and requires no external pull-up 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.

For applications where Port A VCC(A) is less than 1.35 V or Port B VCC(B) is less than 3.0 V,

use drop-in replacement PCA9509A.

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 hard LOW and the input level is set at 0.3 of SMBus or I²C-bus voltage level

which enables port B to connect to any other I²C-bus devices or buffer.

The PCA9509 drivers are not enabled unless VCC(A) is above 0.8 V and VCC(B) is above

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

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

the bus is idle.