ADC128S102-SEP: Power Down VA > VD+0.3V

Martin Beakes

Prodigy 50 points

Part Number: ADC128S102-SEP

Hi,

I'm planning to use the ADC128S102-SEP with the following:

- VA = 5V (provided by a LDO). There are only few small circuit connected to this power rail. So not much capacity

- VD = 3.3V (provided by a DC/DC). This rail is used to power many devices and have much higher capacitive load.

Based on datasheet Absolute maximum rating, VD is specified as VA+0.3V.

For power-up, there is no issue, this specification will be followed.

Considering that there is much more capacity on the VA power rail (3.3V), it's hard to guarantee that VA will fall before VD when the input power of the board is turned OFF.

Is there an internal diode between VA and VD that will prevent guarantee VD >= VA + 0.3V during power down ?

If VA falls after VD is this could cause an issue (damage to the component or reliability issue)

Thanks

over 1 year ago

0 Samiha Sharif over 1 year ago

TI__Expert 6731 points

Hi Martin,

Thanks for your question! This FAQ may be helpful.

Best,

Samiha

0 Martin Beakes over 1 year ago in reply to Samiha Sharif

Prodigy 50 points

Hi,

thanks for the quick reply. I will look into this in more details and see how it applies to my use case.

0 Samiha Sharif over 1 year ago in reply to Martin Beakes

TI__Expert 6731 points

Hi Martin,

For sure. The FAQ has a diagram showing the internal diode structure. We recommend adding an external Zener/TVS diode on the VA supply.

Best,

Samiha

0 Martin Beakes 11 months ago

Prodigy 50 points

Hi,

The FAQ Item 1.c mentioned that the ADC does not have know brown-out issue other than not allowing VD to be lower than VA at any time.

Based on on datasheet, VD is specified as VA + 0.3V.

This means that VD should not exceed VA which is the opposite of what mentioned in FAQ 1.c.

0 Samiha Sharif 11 months ago in reply to Martin Beakes

TI__Expert 6731 points

Hi Martin,

Thanks for pointing that out, it may be a typo. Please follow the datasheet recommendations.

Best,

Samiha

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ADC128S102-SEP: Power Down VA > VD+0.3V