Question: What action must be taken to use a CY8C201xx device either with external pull-ups or with a master operating at different VDD?
The CY8C201xx devices support internal pull-up resistors on I2C lines. Table 1 shows the factory default settings for internal pull-up resistors.
Table 1: Factory Default Values for Internal Pull-Up Setting
Internal Pull-Up (factory default)
The setting for the internal pull-up resistors must match the requirements of the overall design. When the setting is incorrect, the following problems can occur:
- Pull-ups should be sized correctly to meet rise time and IOL requirements in an I2C design. Use of internal pull-ups enabled in combination with external pull-ups in a CapSense® device reduces the effective resistance. Proper bus operation is not guaranteed.
- Consider the scenario in which the CapSense device operates at 3.3 V with internal pull-ups enabled while the master operates at 1.8 V and external pull-ups pull the bus to 1.8 V. Bus voltage (VIH) seen by the master is between 1.8 V and 3.3 V due to the voltage divider formed by internal and external pull-ups. This condition can damage the master device.