AM2612: Terminating Resister on D+ and D- lines of USB

Hideaki Matsumoto

Genius 9290 points

Part Number: AM2612
Other Parts Discussed in Thread: TUSB2036

Tool/software:

Hi,

My customer is now designing their own board with AM2612.

Are the terminating resistors needed on D+ and D- lines of USB ?

Or don't need them ? Does AM261x have on-chip terminating resistors ?

Thanks and regards,

Hideaki

3 months ago

0 Brennan Hartigan 3 months ago

TI__Genius 11172 points

Hideaki,

You do not need terminating resistors on the D+ and D- nets of USB. A common mode choke is highly recommended to have at the USB connector.

Please see all USB design requirements in section 8 of the AM26x Hardware Design Guidelines application note.

Regards,

Brennan

0 Hideaki Matsumoto 3 months ago in reply to Brennan Hartigan

TI__Genius 9290 points

Hi Brennan,

Thank you for your answer. We understood that the terminating resistors are not needed. Let us confirm a little more.

Does AM261x have these resistors inside of device ?

The reason why the customer is asking this question is that TI recommends to add 27 ohm resistors on D+ and D- lines for TUSB2036 like below.

Thanks and regards,

Hideaki

0 Brennan Hartigan 3 months ago in reply to Hideaki Matsumoto

TI__Genius 11172 points

Hideaki,

AM261x does not have these resistors inside the device. For specific USB hub, such as the TUSB2036 you are using, you should always follow the HW design guidelines in the data sheet.

Regards,

Brennan

0 Hideaki Matsumoto 3 months ago in reply to Brennan Hartigan

TI__Genius 9290 points

Hi Brennan,

Thank you for your answer. Let me confirm.

AM261x doesn't have terminating resistors inside the device, but terminating resistors are not needed ?

Brennan Hartigan said:
You do not need terminating resistors on the D+ and D- nets of USB.

Regards,

Hideaki

0 Brennan Hartigan 3 months ago in reply to Hideaki Matsumoto

TI__Genius 11172 points

Hideaki,

Let me double check with the digital design team.

Regards,

Brennan

0 Hideaki Matsumoto 3 months ago in reply to Brennan Hartigan

TI__Genius 9290 points

Hi Brennan,

Thanks. We're waiting for the result of double check. Since they have to fix the design of their board, it would be appreciated if we can receive it as soon as possible..

Regards,

Hideaki

0 Brennan Hartigan 3 months ago in reply to Hideaki Matsumoto

TI__Genius 11172 points

Hideaki,

The design team is still looking into this, but they told me that there are likely no internal termination resistors. They suggest using external termination resistors.

Regards,

Brennan

+1 Hideaki Matsumoto 3 months ago in reply to Brennan Hartigan

TI__Genius 9290 points

We got confirmed from the team.

We have looked at the Specs and also got confirmed from the CharTeam that we have existing termination resistor of 45ohms.

So, no need of external termination resistor.

D+ and D- lines have terminating resistors (45 ohms) inside the device itself and hence customer don’t have to add them externally

Regards,

Hideaki

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AM2612: Terminating Resister on D+ and D- lines of USB