ADS1298: Low VCAP1 Voltage and not working SPI

Hi,

Do you happen to have/use an evaluation kit/board(EVM)? Or Are you using your own board?

It's highly recommended to use the EVM as an experiment/test control reference to compare, validate and/or do A/B test with customer board so that developers/designers could track what have been changed appropriate or not.

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Please make sure all the power supplies comply/follow the data sheet spec, and, yes, it may take some time for VAP1 to reach 1.1V, please refer to datasheet page 96 11.1 Power-Up Sequencing

Thanks

Hi,

thank you very much for your response.
First: I don't use the EVM but I did use the schematic of the EVM.
As AVDDs I use 5V and as DVDD I use 3.3V. Furthermore, I encountered that Voltage at VCAP3 is not AVDD+1.9V but only 4.4V... Maybe this helps as well resolving this.
In the DS it is mentioned that all Digital INs have to be low at powering up. How is this ensured at the EVM? Furthermore, how is it ensured on a usual PCB where the powersupply for all components is switched on together, that the Reset pin voltage is defined and not floating at this point?
In my opinion it would make sense to use pull downs on these pins (at least RSTN and PWDN), but these are not mentioned in the DS.

Thank you all for your help.

Best regards

Gerad

Hi Gerad,

How many customer board do you have? Do you want to measure on a different one?

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May I ask what might be your AVSS supply?

What might be your power source(s) for AVDD? Do the power source(s) capable of providing sufficient power?

Make sure all the power to ADS1298 is not shared/distributed by any other devices.

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If you checked above are all good, Please check if there is any short(s) on the customer board. 

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I may suggest you compare your design with the EVM schematic carefully or get an EVM for reference. 

Or, Could it be possible at some moment/or point either the customer board and/or the IC may have been shorted/damaged?

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On the EVM, the VCAP1 pin H5 from the chip is connected to C9(22uF), and VCAP1 can be measured 1.1~1.2V with respect to AVSS.

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Thanks

Hi ChienChun,
At the moment I only have a single board.
AVSS is 0V.
The supply is done by an LDO tha delivers sufficient current. if this would not be the case, the output voltage of the LDO would drop, doesn't it?

I will compare again and check for shorts!
I already checked the CapValues on the VCAP pins. THey are all as recommended.

Thank you!

Best regards
Gerad

Hi,

Yes, please double check the power sources voltages, any pay attention if any shorts, or if possible to get a 2nd board and EVM to co-validate.

Thanks.

Hello chienchun,

Solved it finally by using a new IC. All VCAPs are now what they are supposed to be.

Thank you a lot again! 

Best regards

Gerad