TCAL9539-Q1: TCAL9539RTWRQ1

IO Expander Checklist

Check

Status (good, okay, verify?)

Comment

Local Decoupling Capacitors

 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

Good

Sometimes PW and RTW get mixed up

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

Verify

I assume PU resistors are somewhere else in the schematic - please check. 

Unused GPIO pins configured as INPUT’s are biased to either VCC or GND via resistor

 Good - TCAL device

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).

TCAL agile IO expanders also have the ability to enable internal PU or PD resistors.

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

Good

0x74, verify with other devices on the I2C bus

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

 Good

Recommended to have a PU resistor to VCC on this pin. External GPIO works too to keep pin HIGH. 

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

 Good

R183 = 10k to VCC, OD output.