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ADS8671: How is the the read data to be intterpreted

Daniel Zinner
Prodigy 20 points
Part Number: ADS8671

Hello Ti Team,

I am working with the ADS8671 ADC and I couldn't find anything on how the data should be interpreted or what is needed to set up the ADC.

So I have two questions.

1. If I do not write anything to the ADC and just pull CS low, wait t_conv_max, hold SDI low for 32 Clocks on SPI, (basically sending NOP) will I receive a valid read from the ADC? If not what is required for me to get a valid read? Do any commands need to be written in order for me to get a valid read?

2. If I send a NOP and read the most recent conversion from ADC, how are these 14 bits to be interpreted? I couldn't find this anywhere in the data sheet. Is it signed or unsigned?

For example if I do not set up the ADC, the range should be +-12.288V. What will be the value when the ADC's input Voltage is at 0V, +12V and -12V. Is it 0b00000000000000 for -12.288V and 0b11111111111111 for +12.288V and 0b10000000000000 for 0V?

Kind Regards

Daniel

  • 0
    TI__Mastermind 35550 points

    Hi Daniel,

    Please see my answers below:

    1. The /CS is executed as CONVST signal too which activates a data conversion at the rising edge, so you need to send a low-high-low pulse to the ADC on this pin. By doing this, you should be able to get a conversion result from your ADC. The default configuration includes SPI configuration 00 (CPOL = 0 and CPHA=0), Internal voltage reference, +/-3Vref input range.

    2. Please check transfer function in the Figure 7-15 and the Table 7-4 in the data sheet. The code is straight-binary format and MSB is shifted first. When the input range of ADC is +/-3Vref (+/-12.288V), the code 0000h corresponds to -12.288V and the code 3FFFh corresponds to +12.288V. When the input range of ADC is 0~3Vref (0~12.288V), the code 0000h corresponds to 0V and the code 3FFFh corresponds to +12.288V.

    Best regards,

    Dale