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About the time until the conversion result output of AD7172-2

Let me ask you about the time it takes for the AD7172-2 to get results in single conversion mode (the time it takes for the / RDY pin to go down).

All used with default settings (250Ksps, CH0 only ON, SIN5 + 1,SING_CYC = 1).

Reg: 0x01
DATA: 0xA11C

As a result of writing and starting conversion, the time until the / RDY pin goes down is 354 μS.
I thought that the result would be obtained with 32μS + 161μ (1/250Ksps × 5), but I needed another 161μS.

Q1: Is this correct?

(Virtual Eval Tool --In the BETA tool, the conversion mode is "continuous" and the condition is a little different, but the first conversion seems to be 32 μS + 1 / ODR × 5 and the result is obtained.)
Q2: Is it possible to eliminate the additional 161 μS?

I look forward to your advice.

  • Hi, 

    Q1. Since in single conversion mode, the part is placed in standby mode after the conversion is complete. So it needs to come out of standby to power up and settle. Thus, the timing for the very first conversion will take longer than that in continuous conversion mode, approximately 128 modulator clocks so it should somehow be less than 161us. May I know how are you measuring the time of the first conversion, are you using the SYNC pin to control the start of conversion or are you just measuring it from the last bit of data written to the ADC mode register? 

    Q2. You can only remove the delay when you operate in continuous conversion mode or when not using the SYNC pin. Please take note that the extra delay time at the very first conversion is the setup time for the signal chain before the first conversion is available when the ADC is power up, coming up from standby mode or when using a /SYNC pin. 



  • thank you for your reply.
    The SYNC pin is not used, and the time since the register was written is measured.

  • There was an evaluation board for AD7176-2, so I also checked it.
    As with the AD7172, it took five times as long as the Virtual Eval Tool to get the first conversion result.
    (Confirmed in continuous conversion mode)
    Is it correct with the following idea?
    This is because the value of the tool is not adjusted enough, and I think that it can not be shortened any more in the setting,

    From the MCU using the AD7176-2 evaluation board
    After turning on the power, only the following was written to the register

    Adress0x01 0x8020

    Adress0x20 0x0020

    Adress0x28 0x0000
    ↓ ↓
    Adress0x01 0x8000

  • Hi, 

    I'm sorry I am not sure if I follow/understand this concern correctly. 

    However, the virtual eval timing is only applicable for continuous conversion mode. That is why the delay when operating in single conversion mode is not included in the timing. 

    Please take note that the very first conversion even at continuous conversion mode has an extra delay, the VE tool calculated it and that is why you are seeing the extra 32us or 4 us as the very first conversion. The settling time for subsequent channel conversion is slightly lower than this approximately 33 modulator clock cycles. So in your above table the measurement result column is correct if it is pertaining to the very fist conversion.