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TCA9554: LEDs flash momentarily upon power-up

switch

Genius 3750 points

Part Number: TCA9554
Other Parts Discussed in Thread: TCA9534

Tool/software:

Hi TI team，

When using the TCA9554PWR to control LED indicators, all LEDs flash momentarily upon power-up. What is the reason for this? Below are the schematic and video.

0 Tyler Townsend 5 months ago

TI__Mastermind 47328 points

Hi Switch,

I can't view the video, but I understand what you are describing.

Not sure what the scope capture is attempting to depict. may I have some clarification there?

The TCA9554 has internal 100k PU resistors. Powering on the supply might have an initial surge of current and therefore the LED's flash. After the surge, the supply settles and LED's turn OFF.

Regards,

Tyler

0 switch 5 months ago in reply to Tyler Townsend

Genius 3750 points

Hi Tyler，

Thanks for your reply! If so, is there a solution?

0 Clemens Ladisch 5 months ago in reply to switch

Guru 316690 points

Use the TCA9534 without pullups. Or change the circuit to drive the LEDs by their cathodes (on = low).

0 switch 5 months ago in reply to Clemens Ladisch

Genius 3750 points

Hi Clemens，

The waveform below appears at the output at the moment of power-on. Is this normal?

0 Tyler Townsend 5 months ago in reply to switch

TI__Mastermind 47328 points

Hi Switch,

Where is the leakage coming from before VCC is powered ON?

It looks like the device powers up from a non-0V state.

Regards,

Tyler