ZHCSNJ5E October 2005 – March 2021 PCA9545A
PRODUCTION DATA
The pull-up resistors on the INT3- INT0 terminals in the application schematic are not required in all applications. If the device generating the interrupt has an open-drain output structure or can be tri-stated, a pull-up resistor is required. If the device generating the interrupt has a push-pull output structure and cannot be tri-stated, a pull-up resistor is not required. The interrupt inputs should not be left floating in the application.
The A0 and A1 terminals are hardware selectable to control the slave address of the PCA9545A. These terminals may be tied directly to GND or VCC in the application.
If multiple slave channels will be activated simultaneously in the application, then the total IOL from SCL/SDA to GND on the master side will be the sum of the currents through all pull-up resistors, Rp.
The pass-gate transistors of the PCA9545A are constructed such that the VCC voltage can be used to limit the maximum voltage that is passed from one I2C bus to another.
Figure 9-2 shows the voltage characteristics of the pass-gate transistors (note that the graph was generated using data specified in the Electrical Characteristics section of this data sheet). In order for the PCA9545A to act as a voltage translator, the Vpass voltage must be equal to or lower than the lowest bus voltage. For example, if the main bus is running at 5 V and the downstream buses are 3.3 V and 2.7 V, Vpass must be equal to or below 2.7 V to effectively clamp the downstream bus voltages. As shown in Figure 9-2, Vpass(max) is 2.7 V when the PCA9545A supply voltage is 4 V or lower, so the PCA9545A supply voltage could be set to 3.3 V. Pull-up resistors then can be used to bring the bus voltages to their appropriate levels (see Figure 9-1).