PCA9509A: Low-Power Level Translating I²C-bus/SMBus Repeater

The PCA9509A is a level translating I²C-bus/SMBus repeater with two voltage supplies 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 0.8 V to 1.5 V and requires no external pull-up resistors due to the internal current source. Port B allows a voltage range from 2.3 V to 5.5 V and is overvoltage tolerant. Both port A and port B SDA and SCL pins are high-impedance when the PCA9509A is unpowered.

The bus port B drivers are compliant with SMBus I/O levels, while port A uses an offset LOW which prevents bus lock-up and allows the bidirectional nature of the device. Port A uses a current source for pull-up and an offset 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_CC(A), 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 30 % of SMBus or I²C-bus voltage level which enables port B to connect to any other I²C-bus devices or buffer.

The PCA9509A drivers are not enabled unless V_CC(A) is above 0.7 V and V_CC(B) is above 1.7 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.

The PCA9509A is similar to the PCA9509 but offers lower A port voltage range to 0.8 V to accommodate lower voltage processors and disables the current mirrors when disabled to reduce standby power.

Selection recommendations

The PCA9509A is recommended for all applications except in the following cases:

• PCA9509P should be used if an external A-port pull-up resistor is required to adjust current for noise margin considerations or to reduce operating current consumption even more.
• The PCA9509 should be used if instant on from disable is required with A Port voltage greater than 1.0 V and larger standby current is not a concern.

[1] The PCA9509 current mirrors do not shut down when the device is disabled allowing instant turn-on, but at the cost of the higher standby current. The PCA9509A and PCA9509P current mirrors are turned off when disabled for lowest standby power consumption, but sufficient delay (10 μs) after enable is needed before resuming operation.

[2] Operating currents do not include the current consumed by the external pull-ups on B-port or the external pull-ups on the A-port of the PCA9509P.