TCA9539: schematic review

U1 / U2 / U3 / U4

Check

Status (good, bad, okay, ?)

Comment

Local Decoupling Capacitors

U1: 100 nF, Good

U2: 100 nF, Good

U3: 100 nF, Good

U4: 100 nF, Good

Generally, a 0.1-uF capacitor is placed on VCC, as close to the device as possible

Verify the schematic pinout matches the data sheet pinout

U1: Good

U2: Good

U3: Good

U4: Good

Check that the pullup resistors are present on the SDA and SCL net within the schematic.

U1: Verify

U2: Verify

U3: Verify

U4: Verify

I can't find them on the schematic, probably on another page. 

Unused GPIO pins are biased to either VCC or GND via resistor

U1: Verify

U2: Verify

U3: Verify

U4: Verify

Most of TI's IO expander portfolio do not include internal pull-up resistors on the p-port pins; the exceptions are PCF8575, PCF8574, PCF8574A, TCA9555|PCA9555, PCA9554|TCA9554, and TCA9554A|PCA9554A and therefore can be left floating.

An alternative approach is after powering up the device, any unused p-port pins can be set as an output (does not matter if set high or low).

Need to verify what is the purpose of each GPIO. Follow the above description if the pin is going to be left as a floating input. 

Device address is unique on the bus unless using an I2C switch or I2C MUX to resolve conflicts

U1: Good

U2: Good

U3: Good

U4: Good

 All I2C addresses are unique between all TCA9539's

If the device has a /RESET pin, bias the pin high (preferably with a pull-up resistor) after powering up.

U1: Good

U2: Good

U3: Good

U4: Good

 All pulled high through 0 ohm resistor

If the device has a /INT pin and the /INT pin is used, tie this pin to a pull-up resistor.

U1: Verify

U2: Verify

U3: Verify

U4: Verify

 Need to verify if a pull-up resistor is provided on /INT. This is an open-drain output.