TUSB2077A Crystal not oscillating.

Sam Maedjaja

Other Parts Discussed in Thread: TUSB2077A

I have not been able to get my TUSB2077A crystal to oscillate (using the TI suggested circuitry). Is there any special crystal to use or should I use a 6 Mhz resonator, instead? I am using a generic 6 Mhz Crystal. Mode line is Low.

I am at lost. Please help.

over 11 years ago

0 Joel Jimenez0 over 11 years ago

TI__Mastermind 18655 points

Hi Sam,

It seems the TUSB2077A is going into suspend mode. Can you post the schematics?

An important factor that you should follow is the power-up sequence, It requires a reset pulse of between 100us to 3ms after 3.3-V (Vcc) reaches its 90%. I suggest an external RC circuit. See the figure below.

Regards.

0 Sam Maedjaja over 11 years ago in reply to Joel Jimenez0

Prodigy 60 points

Only what is shown in the schematic are connected to TUSB2077A. I have not connected everything, yet. Thanks for your help.

0 Sam Maedjaja over 11 years ago in reply to Sam Maedjaja

Prodigy 60 points

Hi Joel,

This is the Crystal that is used http://www.mouser.com/ProductDetail/CTS-Electronic-Components/ATS060/?qs=sGAEpiMZZMsBj6bBr9Q9aflThh2f9fXEncWN0ho3ObM%3d.

Is this Crystal suitable to use?

Sam

0 Joel Jimenez0 over 11 years ago in reply to Sam Maedjaja

TI__Mastermind 18655 points

Hi Sam,

Yes, you can use that Crystal.

According to your RC circuit (15K pull-up resistor and .1mF cap) the hub is held in reset for a long time (~3 seconds) . This condition is interfering with USB enumeration. Change the .1mF cap (C19) to .1uF.

Regards.

0 Sam Maedjaja over 11 years ago in reply to Joel Jimenez0

Prodigy 60 points

Hi Joel,

I meant to say that C19 is 0.1 micro F, already. I should be able to see the Crystal oscillation with a standard Scope probe and not killing it, right?

Thanks.

0 Joel Jimenez0 over 11 years ago in reply to Sam Maedjaja

TI__Mastermind 18655 points

Hi Sam,

Yes, it is possible, but keep in mind that the resonator will be stopped at logic low whenever the TUSB2077A goes into SUSPEND mode, this will occur after 3 ms of downstream ports inactivity or enumeration errors.

Can you provide a scope capture showing VCC, RESET, XTAL1 at power up sequence?

Is the TUSB2077A being enumerated at some point?

Check the physical connection of C1 and C2.

Regards.

0 Sam Maedjaja over 11 years ago in reply to Joel Jimenez0

Prodigy 60 points

Hi Joel,

It is difficult to show the VCC, RESET and XTAL1 sequence to you. However, RESET does not reach 50% until about 1 millisecond after 3.3V is fully ON. There is no sign of XTAL1 moving at anytime. SUSPEND line is LOW all the time.

C1 and C2 are not present on my breadboard at the moment, but I don't think that they should not have anything to do with the issue.

I bread-boarded 3 TUSB2077's and all behave the same way. So, there is a fundamental issue. Please share your ideas.

Thanks.

0 Joel Jimenez0 over 11 years ago in reply to Sam Maedjaja

TI__Mastermind 18655 points

Hello Sam,

Please specify the complete testing environment your are using (USB Host). What kind of downstream devices are connected to the hub?

Is the TUSB2077A being enumerated at some point?

In regards to reset sequence the image below shows an example of a 1ms long reset pulse. As you can see, XTAL signal must be active during the last 60 μs of the reset window.

Also, 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.

Regards.

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TUSB2077A Crystal not oscillating.