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TUSB2077A: unused pin left floating behavior

Vincenzo Pizzolante

Mastermind 25486 points

Part Number: TUSB2077A

hi,

we are working on a design with TUSB2077A

as we won't need all the 7 ports, we were considering left the unused pins (/OVRCURx, DPx, DMx and /PWRONx) open.
is there any drawback or we need to bias them (pull up or down)?
thansk a lot in advance
KR

Vincenzo

PS:

we tried to leave them unconnected, but as it seems the floating lines cause problems.
The host tries to enumerate "phantom" devices, and lots of errors are logged in the Linux system.

over 4 years ago

0 Malik Barton57 over 4 years ago

TI__Guru 64326 points

Hi,

The DP and DM signals of the unused port should be tied to ground with 15K resistors like the pull-downs used on the active ports.

The OVRCUR/ input of the unused port can be left tied to the other OVRCUR/ inputs if the hub is configured as GANGED.

Also ensure that the reset signal at power-up is 1ms to 3ms long after the power supplies reached its 90%.

FYI, The link below contains some frequent asked questions:

0 Vincenzo Pizzolante over 4 years ago in reply to Malik Barton57

TI__Mastermind 25486 points

thanks a lot Malik.

as space is extermely tight, can we shunt DP/DM togher and use 1 pull-down resistor?

if so, shoud that be 7.5K or still 15K?

thansk a lot

KR

Vincenzo

0 Malik Barton57 over 4 years ago in reply to Vincenzo Pizzolante

TI__Guru 64326 points

Hi Vincenzo,

This is allowed and I would recommend using a 7.5k resistor.