TMS320F28377S: power sequence

Emma Wang

hi expert,

we see from datasheet, which has description below.

”The voltage on VDDIO should be greater than VDD or no less than 0.3 V below VDD at all times. VDDIO,
VDD3VFL, VDDOSC, and VDDA should be powered up together and be kept within 0.3 V of each other during
operation. Before powering the device, no voltage larger than 0.3 V above VDDIO should be applied to any
digital pin, and no voltage larger than 0.3 V above VDDA should be applied to any analog pin. The VREFHI
voltage should not exceed VDDA at any time.“

however，my customer use 2 devices providing 3.3V power supply. Is there any issues here？provide the power train wavaform below.

Yellow for VDDA,

Blue for VDDIO, VDDOSC and VDD3VFL,

Red for VDD.

And the board can work normal, only some boards have abnormal performance.

could you kindly check if the design has some crutial error.

does it a must to provide 3.3V power together by 1 LDO?

Emma

over 6 years ago

0 Frank Ankapong over 6 years ago

TI__Mastermind 28275 points

Hi Emma,

A voltage delta between VDDIO and VDDA can open up parasitic current paths within the device. We are currently investigating the full ramifications of this in the background. Once we finalize this, we will update the datasheet to clarify as needed.

For now, our recommendation is to tie all 3.3 rails together and power them up from a single LDO.

0 Emma Wang over 6 years ago in reply to Frank Ankapong

TI__Expert 5370 points

Frank,

thanks.

so the 3.3V is about 4ms after the 1.2V power supply is OK?

BR Emma

0 Frank Ankapong over 5 years ago in reply to Emma Wang

TI__Mastermind 28275 points

Emma,

We have a INTOSC frequency drift advisory in the errata for cases where the 3.3V rail and 1.2V rail are not powered up together. However, this only affects the application if INTOSC is used as the primary clock source. I recommend you take a look at that advisory and let us know if you have any questions on it.

0 Emma Wang over 5 years ago in reply to Frank Ankapong

TI__Expert 5370 points

Frank，

Thanks，I read the errata and understand.

Emma

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TMS320F28377S: power sequence