The PCA9509DP is a level translating I²C-bus/SMBus repeater that enables processor lowvoltage 2-wire serial bus to interface with standard I²C-bus or SMBus I/O. While retainingall the operating modes and features of the I²C-bus system during the level shifts, it alsopermits 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 maximumcapacitance of 400 pF on the higher voltage side. Port A allows a voltage range from1.35 V to VCC(B) ‑ 1.0 V and requires no external pull-up resistors due to the internalcurrent source. Port B allows a voltage range from 3.0 V to 5.5 V and is overvoltagetolerant. Both port A and port B SDA and SCL pins are high-impedance when thePCA9509DP 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 currentsensing 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 ina LOW on the port A accommodating smaller voltage swings. The output pull-down on theport A internal buffer LOW is set for approximately 0.2 V, while the input threshold of theinternal buffer is set about 50 mV lower than that of the output voltage LOW. When theport 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 Bdrives a hard LOW and the input level is set at 0.3 of SMBus or I²C-bus voltage levelwhich enables port B to connect to any other I²C-bus devices or buffer.

The PCA9509DP drivers are not enabled unless VCC(A) is above 0.8 V and VCC(B) is above2.5 V. The enable (EN) pin can also be used to turn on and turn off the drivers undersystem control. Caution should be observed to change only the state of the EN pin whenthe bus is idle.

Feature