AMC7812B: ADC updating speed through SPI

David Park

Expert 6640 points

Part Number: AMC7812B
Other Parts Discussed in Thread: AMC7812

Hi,

Customer would like to adopt 2 AMC7812 for their application.

There is updating speed issue in each ADC results for the sensing.

There is daisy-chain method for reducing SPI line.

When customer read 32ch(2 devices) ADC, which is faster of daisy-chain and other?

If daisy-chain method is slower than normal connection, is there any method for increasing updating speed?

Thanks.

over 7 years ago

0 Uttam Sahu over 7 years ago

TI__Genius 14220 points

Hi David,

Thank you for your query. The engineer responsible for this part is currently unavailable due to the Thanks Giving holidays. He will pick up the thread once he returns.

Regards,
Uttam Sahu
Applications Engineer, Precision DACs

0 David Park over 7 years ago in reply to Uttam Sahu

TI__Expert 6640 points

Hi Uttam,

Customer would like to use daisy-chain.

CS triggering and delay time is longer than expected one.

Could you guide for daisy-chain connection of SPI?

pin treatment, CNVT, DAV, etc...

Thanks.

0 Uttam Sahu over 7 years ago in reply to David Park

TI__Genius 14220 points

Hi David,

I am not an expert on this part. Appreciate if you could wait till Monday for the responsible engineer to jump in.

Regards,
Uttam

0 Paul_Frost over 7 years ago in reply to Uttam Sahu

TI__Guru 53773 points

Hi David,

What do you mean when you say "CS triggering and delay time is longer than expected one"? Can you share a scope shot of what you are seeing?

Thanks!
Paul

0 David Park over 7 years ago in reply to Paul_Frost

TI__Expert 6640 points

Hi Paul,

I mean below time.

Thanks.

0 Paul_Frost over 7 years ago in reply to David Park

TI__Guru 53773 points

Hi David,

Figure 108 describes the connection scheme for the SPI signals.

The other pins are as follows:
RESET, CNVT, DAC-CLR-0, DAC-CLR-1 are all inputs and can be shared across the multiple devices, assuming that is the customer's desire.
DAV should be monitored separately, or some kind of OR gate can be implemented to share resources.
ALARM is an active low open drain output - a 10kΩ pullup is recommended, but this signal can also be shared across all the drives.

Please let me know if you have more questions.
Paul

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AMC7812B: ADC updating speed through SPI