ADS8319

imran sayeed

Other Parts Discussed in Thread: ADS8319

Hello,

Am using this ADS8319 with 3wire with busy indicator, the schematic am attaching.

Am able to get the proper response for input analog voltage till 2.5 volts for which am getting ADC value of 32767, but if I increase the input analog voltage above 2.5V it is still giving the same value 32767.

can't able to measure voltages above 2.5V.

Vref am giving is 4.98V

please suggest the solution.

over 8 years ago

0 RahulVK over 8 years ago

TI__Expert 3785 points

Hi Imran,

The device has a unipolar range of 0V to +Vref, In your case, full scale output code 65535 should be seen at Vin = Vref = 4.98V.
Could you please share oscilloscope plots of SCLK and DOUT when Vin > 2.5V?

Regards,
Rahul

0 imran sayeed over 8 years ago in reply to RahulVK

Prodigy 60 points

Hello Rahul,
Thanks for the reply,
I have noticed that the SCLK pulses are coming if Vin < 2.48V, once I increase the Vin above 2.48V, SCLK pulses are not coming.

0 RahulVK over 8 years ago in reply to imran sayeed

TI__Expert 3785 points

Hi Imran,

If I understood the problem correctly, the host controller does not provide SCLKs to read data when Vin > 2.48V?

Regards,
Rahul

0 imran sayeed over 8 years ago in reply to RahulVK

Prodigy 60 points

Hello Rahul,

No its not the host controller, ADC itself is making SCKL pin low(0V) when the input is above 2.48V.

0 imran sayeed over 8 years ago in reply to imran sayeed

Prodigy 60 points

here is the simple code for SCKL from host controller
for(i = 0; i < 16; i++)
{
SCLK = 1;
delay_us(200);
SCLK = 0;
delay_us(200);
}
if the input is less than 2.48V, SCLK are coming, and once input rises above 2.48, ADC is making its SCKL pin to 0V.

0 RahulVK over 8 years ago in reply to imran sayeed

TI__Expert 3785 points

Hi Imran,

The SCLK pin is an input logic for the ADC. It has no driver on it and hence it cannot drive it to 0V.
However, this pin does have internal protection diodes to +VBD and GND. If voltage on SCLK is more than (+VBD + 0.3V), it will get clamped.

Could you please confirm the following when Vin > 2.5V
1) Voltage on +VBD pin
2) Disconnect SCLK of host from ADC and probe SCLK output from host

Regards,
Rahul

0 imran sayeed over 8 years ago in reply to RahulVK

Prodigy 60 points

I understood the problem,
As am using 3wire with busy indicator am checking for SDO pin to go low after conversion, if SDO goes low after conversion am sending the SCLK to read the ADC value, but for some reason after 2.48V SDO is not going low hence host controller was not sending SCKL.
kindly let me know how to check the busy indicator...
if i remove the condition of checking SDO and sending SCK without checking SDO its working.

0 RahulVK over 8 years ago in reply to imran sayeed

TI__Expert 3785 points

Hi Imran,

Please refer to section 8.3.1.2 of the data-sheet. It covers the details required for 3-wire interface with Busy indicator including template schematic.

I hope this helps.

Regards,
Rahul

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