Running out of GPIO pins on a microcontroller design can be a challenging situation, often requiring significant changes to the embedded software. However, I2C GPIO extenders offer a practical solution. Nexperia has recently introduced two new chips, the NCA9539PW and NCA9555PW, which come with a range of interesting features to address this issue.

NCA9539PW and NCA9555PW – I2C GPIO extenders with 16 output pins

To compare the NCA9539PW and NCA9555PW, it is helpful to refer to their overview diagrams, as shown in the figure above. The NCA9555PW has three exposed address lines, while the NCA9539PW has two address lines and a RESET pin. Both chips provide 16 GPIO lines that can be configured as input or output.

Interrupt logic, pull up resistors

These GPIO extenders offer more than just additional pins. Nexperia's datasheet highlights their maximum current drive capability of 25mA per pin, making them suitable for powering small to medium-sized LEDs. Additionally, the NCA9555PW includes weak pull-up resistors on each input, reducing the need for external components and simplifying the bill of materials.

To minimize bus congestion and optimize performance, the devices feature an open drain interrupt engine. This engine detects changes on relevant input pins and raises a dedicated GPIO line, eliminating the need for constant polling.

Furthermore, both chips are fully certified for 400 KHz operation, ensuring compatibility with other peripherals on the same bus controller.

The datasheet also mentions the presence of a noise filter on SCL and SDA inputs, making these parts compatible not only with I2C but also with I3C-based buses.

In terms of availability, the NCA9555PWJ is readily available from various distributors, with an average price of around 85 Eurocents for a quantity of 100 pieces. On the other hand, the NCA9539PWJ is currently out of stock, with lead times ranging from seven to twelve weeks. Its price, for a quantity of 100, is expected to be around 1.2 EUR  (Price correct as of the date of publication).

In conclusion, Nexperia's NCA9539PW and NCA9555PW components bring new capabilities to the I2C GPIO market. With their high speed and a range of convenient features, these GPIO extenders offer a powerful and cost-effective solution. Their affordability makes it worth considering these chips as an alternative to long-established part choices.