TCA9555: Unable to get high output logic at Output port

Kiranjit Kaur

Intellectual 395 points

Part Number: TCA9555

Hello,

We are using TCA9555 to drive Led's (MPN: WP130WCP/2EGW).

And we are getting output voltage 1.6VDC from Port 14 to port 17 instead of 3.2 VDC as per logic.

Please share your valuable feedbacks or suggestions.

Thanks,

Kiranjit

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 316690 points

The schematic does not show any LEDs. What is the current you are trying to draw?

The datasheet specifies V_OH for loads up to 10 mA.

0 Kiranjit Kaur over 2 years ago in reply to Clemens Ladisch

Intellectual 395 points

Hi Clemens,

Below image for LEDs connection which will draw 10 mA max for each connection.

Can you please explain why i am getting output voltage 1.6 VDC which is half of high output voltage logic.

Thanks,

Kiranjit

0 Clemens Ladisch over 2 years ago in reply to Kiranjit Kaur

Guru 316690 points

This should not happen.

Can you check the voltage at V_CC (pin 24), and that this really is a TCA9555 chip?

Half of the supply sounds as if the pins are shorted to another output that is driving low.

0 Kiranjit Kaur over 2 years ago in reply to Clemens Ladisch

Intellectual 395 points

Hi Clemens,

Below is our modified schematic:

We did not find any issues from Hardware side.

P14,P15,P16 and P17 should act as a output where we are getting 1.6VDC and other ports should act as a input.

Please advise modification in below mentioned code:

I am not able to understand COMMANDBYTE value (0x8C) as per datasheet of TCA9555.

Thanks,

Kiranjit

0 Clemens Ladisch over 2 years ago in reply to Kiranjit Kaur

Guru 316690 points

How are these symbols used? What are the actual bytes sent to the device?

+1 BOBBY over 2 years ago in reply to Kiranjit Kaur

TI__Guru 72711 points

This device doesn't have a 0x8C command byte. Are you actively setting the bits to be an output and then setting them to output high/lows?

To me, this looks like you are getting your high level from the internal 10k pull ups which are forming a kind of resistor divider between the LED and the 187 ohm resistor. Giving you a 1.6V level bias. You should be setting the device as an output high to bypass the internal 10ks with a stronger output high impedance.

-Bobby

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TCA9555: Unable to get high output logic at Output port