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  • TI Thinks Resolved

CCS/ADS7946: ADS7946

Prodigy 20 points

Replies: 3

Views: 106

Part Number: ADS7946

Tool/software: Code Composer Studio

Hello, TI's Engineer,

Problem description reference voltage is 2.048v

Demand: two signal inputs, POS signal range 0-2.048v (VREF); CMD signal range 0-2v: all DC signals.

Problem 1: when ads7946 is used for sampling, when the CMD voltage is VREF / 2, the transcoding value reaches the maximum value of 16384, and VREF / 2 ~ 2V is cycled again. This phenomenon is inconsistent with the introduction of chip manual
See attachment for test record
When the same circuit is replaced by ads7945, the corresponding conversion code value of 0-vref voltage is 0 ~ - 16384, which is not consistent with the ads7945 described in the manual.
Through the test phenomenon, it is felt that the introduction of ads7945 and ads7946 manuals is just opposite to the actual chip model

The software package here is written according to ads7945 / 7946 on the official website, because these two models are universal, but 7945 is differential, and 7946 is single ended. It is always suspected that there is a problem in software programming. Please give your engineering advice. I also attach the software code. Please give your guidance. If the description is not clear enough, please put forward my supplement below

This is the software code

unsigned int getdataADS7945(unsigned char GetCHSEL)
{
unsigned char t;
unsigned long hd;
unsigned long DataReadTemp;

hd = 0;
DataReadTemp = 0;

// GPIO_PinOutSet(gpioPortF, 3); //不掉电...
GPIO_PinOutClear(gpioPortF, 3);

if(GetCHSEL == 1)
{
GPIO_PinOutClear(gpioPortF, 2); //选择CH1...
}
else
{
GPIO_PinOutSet(gpioPortF, 2);
}

GPIO_PinOutClear(gpioPortF, 4); //CS脚拉低...

// GPIO_PinOutClear(gpioPortF, 5);

for(t=0;t<32;t++)
{
GPIO_PinOutSet(gpioPortF, 5);
// Delay(10);
hd<<=1;
GPIO_PinOutClear(gpioPortF, 5);
// Delay(10);

DataReadTemp = GPIO_PinInGet(gpioPortE, 8);

hd|=DataReadTemp;
// Delay(10);
}

hd>>=2;
hd = hd & 0x03fff;


GPIO_PinOutSet(gpioPortF, 4); //CS脚拉高...
// GPIO_PinOutSet(gpioPortF, 5);

return hd;

}

  • 10.24Hello,

    I am not sure I understand the issue. You are reading an incorrect measurement from the ADC compared to the expected output based on the DC input used, is this correct?

    I suggest not trading between the differential and single ended parts. These devices have different methods of formatting the output data as the differential part has a signed bit to show negative and positive measurements.

    Only use one device and use that to fully debug. when using the single ended part (ads7946), with a Vref of 2.048V, then an input voltage of Vref/2 = 1.024V will output a 2000xh. you will need to change this to decimal to use the below formula to solve for the voltage

    The formula is: Vin = Code (decimal) * (Vref / 2^N)

    Please provide a scope shot of the digital lines, SDO, SDA, CS, SCLK. this will help to visually debug, instead of going through code

    Regards

    Cynthia

  • In reply to Cynthia:

    Hello TI engineer, do you have the software programming code for ads7946?

  • In reply to user6215961:

    Hello, apologies for the delay due to holidays

    There is no sample code available.

    Are you still having issues?

    Regards

    Cynthia

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