ADS7038-Q1: Question about AVDD effect on SPI interface

Jim Brinkhurst1

Part Number: ADS7038-Q1

Hi experts

I have a question about the ADS7038-Q1

If DVDD is applied but AVDD drops out (to 0V or close to), will there be any impact to other SPI devices sharing the same SDI (from the ADS) pin?

What will happen to the GPIO outputs?

Are there any sequencing concerns with power-ups/downs on DVDD/AVDD alone?

I appreciate your quick response.

Best regards,

Jim B

10 months ago

0 Tom Hendrick 10 months ago

TI__Guru**** 173096 points

Hi Jim,

From section 8.4.1 in the ADS7038-Q1, the loss of AVDD will reset the device. The SPI interface will revert to SPI-00 (see table 8-8) and all inputs will be set to analog input channels (see section 8.3.1). I'm not sure what you mean by "any impact to other SPI devices sharing the same SDI", but anything on SDO should be suspect data (i.e. corrupted). There is no special requirement for power sequencing.

0 Jim Brinkhurst1 10 months ago in reply to Tom Hendrick

TI__Mastermind 44530 points

Hi Tom

The concern is if we're using a common bus for SDI to multiple devices, would a drop on the AVDD power bus cause the SDI signal to be pulled low due to an ESD structure, or other mechanism.

Thanks,

Jim B

+1 Tom Hendrick 10 months ago in reply to Jim Brinkhurst1

TI__Guru**** 173096 points

Not seeing anything wonky with the SPI lines, just corrupted data on SDO.

0 Jim Brinkhurst1 10 months ago in reply to Tom Hendrick

TI__Mastermind 44530 points

Hi Tom

I have a couple follow-up items for clarification:

The device without AVDD will go into reset, which is expected. In this condition, clocking SCLK while chip select is low (active) will result in garbage data, which is also expected. If chip select remains high (inactive) and AVDD drops out (chip in reset), is it correct to say that SDO will remain high impedance and not impact other devices being driven on the bus as long as DVDD remains powered?

Thanks for your response.

Jim B

0 Sanel Hirkic 10 months ago in reply to Jim Brinkhurst1

TI__Intellectual 1160 points

Hi Tom,

The engineer would also be willing to hop on a call tomorrow or Monday if that works better for you.

0 Tom Hendrick 10 months ago in reply to Sanel Hirkic

TI__Guru**** 173096 points

Sure thing - my calendar is up to date. I'm available from 7AM us central time.

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ADS7038-Q1: Question about AVDD effect on SPI interface