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ADS7067: internal clock shut down

Roee Kimchi
Prodigy 120 points
Part Number: ADS7067
Other Parts Discussed in Thread: ADS7951

Hi,

is there an option to shut down the internal clock of ADS7067 and connect with an external clock only?

thanks!

  • 0
    TI__Mastermind 18037 points

    Roee,

    No, the ADS7067 does not have this option.  If you explain why you want this option, I may be able to offer advice on options and considerations.

    Art

  • 0 in reply to Art Kay
    Prodigy 120 points

    Hi,

    I wanted to use only an external clock of 32MHz and eliminate other noise that can be caused by the switching of the internal clock.

    is there other model from TI that has this option? the sample rate is around 500KSPS.

    thank you!

  • 0 in reply to Roee Kimchi
    TI__Mastermind 18037 points

    Roee,

    1. I don’t think using an external clock will minimize noise. Because the internal clock does not need to drive an external bus it draws minimal transient current.  Good decoupling will help contain any noise from switching inside the device.  On the other hand, a clock bus on a PCB needs to drive the capacitance of the bus, so it needs to draw more transient currents which can lead to noise emissions.  Furthermore, the external bus is an antenna that can broadcast emissions.  Generally, when considering noise emissions the clock trace is the signal that people focus a lot of care and effort on because it is prone to noise emissions.  However, if care is taken external clock bus noise can also be minimized.
    2. Since you are looking at SAR converters I will provide a suggestion that is similar in resolution, channel count, and sampling rate to your choice. Generally lower resolution older generation devices allow for external clocks on SAR devices.  The ADS833x can use SCLK as the conversion clock.  For this device it does contain an internal oscillator but the SCLK option will override that feature. The ADS7951 does not have an internal clock and always uses SCLK as the conversion clock.  This device is 12 bit, 8 channel, fs up to 1Msps.  Many delta sigma allow for an external clock, but I don’t see any options with fs >= 500ksps and 8 channel mux integrated.
    3. I think that your criteria of requiring an external clock will lead you to choosing devices that are not optimal for your application. Our highest resolution SAR devices with lowest noise use internal oscillators, and these devices have very low noise. 

    I hope this information is helpful to you.

    Art

  • 0 in reply to Art Kay
    Prodigy 120 points

    Hi, thank you so much for the elaborated  and well explained answer. it sure did help a lot and made to refine some of the requirements for selecting my ADC.

    the thing is, that this ADC would be in use just for a short time for each operation of the entire board, so I thought it would be good if the components would have a shut down mode that turns off the internal switching and waiting in stand by mode.

    is there such a component that is also capable of sampling in a rate of 300KSPS (14-16 bits)?

    thanks you,

    I very appreciate your help!

  • 0 in reply to Roee Kimchi
    TI__Mastermind 18037 points

    Roee,

    The two devices I mentioned (ADS833x and ADS7951) can both run at lower sampling rates.  The ADC128S102 is a good option if you are ok with 12 bits.  In general, you can expect older generation and lower resolution devices to use the SCLK as a conversion clock.  Again, I would suggest that restricting your design to devices in this class is not a good idea.  The modern devices with internal clocks are low noise and low emissions.  Also, any external clock will have much greater emissions than internal clocks.

    Art