TCAL9539-Q1: nRESET characteristics?

Max Luc Balen

Part Number: TCAL9539-Q1
Other Parts Discussed in Thread: TCAL9539

Tool/software:

Hi team,

During the hardware bring-up, we encountered an issue with an unexpected voltage level on a specific signal. After removing some zero-ohm jumpers for debugging, we isolated the signal and found that it is only connected to the nRESET pin of the IO expander TCAL9539-Q1.

However, it's unclear whether this pin is open-drain and has an internal pull-up resistor in the IO expander.

Could you please help confirm the characteristics of the nRESET pin?

Thanks,
Max DFAE

3 months ago

0 Tyler Townsend 3 months ago

TI__Guru 51378 points

Hi Max,

TCAL9539-Q1 nRESET is an input and requires a PU resistor to VCC if unused or some type of constant signal output that can always drive the nRESET HIGH or LOW.

No internal PU resistor on this pin.

Regards,

Tyler

0 Max Luc Balen 3 months ago in reply to Tyler Townsend

TI__Prodigy 610 points

Hi Tyler,

What should the voltage be if it's lower than 3.3?
The DS lists it as 3.3V

0 Clemens Ladisch 3 months ago in reply to Max Luc Balen

Guru 318050 points

Where does the datasheet list 3.3 V for this pin? It should be connected to V_CC.

+1 Tyler Townsend 3 months ago in reply to Max Luc Balen

TI__Guru 51378 points

HI Max,

The VIH and VIL levels of nRESET follow the TCAL9539. These logics levels were incorrectly not ported over to the Q1 datasheet.

^^^ from the TCAL9539 datasheet.

70% is a valid HIGH logic for nRESET. Suggest that voltage stay above 70% of VCC for a nRESET to not occur.

Regards,

Tyler

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TCAL9539-Q1: nRESET characteristics?