TUSB8042A: Questions about pull down resistor on pin 49 (TEST).

Phil Salisbury

Part Number: TUSB8042A
Other Parts Discussed in Thread: TUSB8041,

Hello,

I have a hub board vendor that has replaced TUSB8041 with TUSB8042A on an existing PCB design. They did not make provisions for 10K PD on Pin 49 (TEST). The HUB works and I measure about 6K pull down resistince inside the TUSB42A when power is not applied and nothing is connected. Questions:

1. Why did TI make the change to require 10K or less pull-down, when 8041,8041A, and 8042 did not require it?

2. Perhaps the 8042A data sheet is wrong and there is an internal PD in 8042A?

3. Would a PCBA manufacurer need to drive the pin 49 (TEST) to test a manufactured board?

4. Can external PD be 0-Ohms to GND?

Thanks

Phil

over 4 years ago

+1 JMMN over 4 years ago

TI__Guru 60870 points

Hi Phil,

There was a concern that came up with the TUSB8042A/43A/44A devices about a corner case where the hub could unexpectedly enter test mode.

There is still an internal PD on the TEST pin but under these corner conditions, it could get disabled.

The TEST pin is for TI functional test only, not PCB test.

Yes, the pin can be shorted to ground.

Regards,

JMMN

0 Phil Salisbury over 4 years ago in reply to JMMN

Prodigy 240 points

Thanks for the info and quick replay.

Phil

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TUSB8042A: Questions about pull down resistor on pin 49 (TEST).