Drift Down of 3.3V Rail in Power-off Sequence

Tsutomu Furuse

Other Parts Discussed in Thread: OMAPL138

Hi.

One of my customers found drift down of the 3.3V rail in the power-off sequence of C6746. It seems that it is pulled down by the 1.8V rail. Would you please tell me if this is a normal behavior as well as the drift up in the power-up sequence described in Advisory 2.3.18? Or does the power circuit need to be fixed?

Best regards,
Tsutomu Furuse

over 8 years ago

0 Titusrathinaraj Stalin over 8 years ago

TI__Guru** 116100 points

Hi Tsutomu,
Did you see the same behavior in OMAPL138 EVM boards (LogicPD and DA850 EVM) ?

0 Senthilkumar Srinivasan over 8 years ago

TI__Mastermind 43660 points

Hello Tsutomu,

As Titus suggested, Are you seeing the same drift on EVM board ?

Are you seeing this behavior in all of the custom boards ?

Is there any drift in power up sequence ?

During the DVDD18 ramp there will be some minor drift up in the undriven DVDD3318_x supplies. This is normal and is not a problem. So i guess the drift in power down also being normal and could not be a problem.

Regards,
Senthil

0 Tsutomu Furuse over 8 years ago in reply to Senthilkumar Srinivasan

Expert 1435 points

Titus,
Senthil,

Thank you for your advices.

I just done quick check for the 3.3V pin of the C6748 LCDK J15 expansion header. Then I saw a small drift down in it as the attached. I have not probe the 1.8V of LCDK yet.

The customer card shows 3.3V drift up in the power-up sequence.

Best regards,
Tsutomu Furuse

0 Senthilkumar Srinivasan over 8 years ago in reply to Tsutomu Furuse

TI__Mastermind 43660 points

Hello Tsutomu,

As i mentioned in the earlier post, this is normal and is not a problem. A small drift appears on the 3.3V supply during normal power up sequence in Figure 5 in the device errata.

Regards,
Senthil

0 Tsutomu Furuse over 8 years ago in reply to Senthilkumar Srinivasan

Expert 1435 points

Thank you!

Best regards,
Tsutomu Furuse

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Drift Down of 3.3V Rail in Power-off Sequence