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ADS131E08 External clock

Mladen Rikic
Prodigy 40 points
Other Parts Discussed in Thread: ADS131E08

Hello,

I have the question about the ADS131E08.

Is it posible for the AD converter to work on external 2.4576 Mhz clock (60/50 * 2.048 MHz )?

We intend to use it for 50 Hz (internal 2.048 Mhz clock, Sample Rate 16 kSPS ) and 60Hz power systems (external 2.4576 Mhz clock,  Sample Rate 19.2 kSPS).


Best Regards,
Mladen

  • 0
    Expert 2585 points

    Hi, Mladen,

    According to the datasheet maximum external clock input frequency is 2.25MHz.(p.4 of the  ADS131E08 data sheet)

  • 0 in reply to Oleksiy Pazyuk
    Prodigy 40 points

    Hello Oleksiy,
    Thank you for your reply.

    I have performed the test with ADS131E08EVM development board:
    1. on the external clock input frequency 2.048MHz, sample rate is 16kSPS.
    2. when increase the external clock input frequency to 2.4576MHz (6/5*2.048MHz), sample rate is 19.2kSPS (6/5*16kSPS). AD converter works well.

    I need to know whether the increase of the external clock to 2.4576MHz cause unstable operation of the AD converter (or damage ADC). As you say 'According to the datasheet maximum external clock input frequency is 2.25MHz.'.

    Best Regards,
    Mladen

  • 0 in reply to Mladen Rikic
    Expert 2585 points
    Hello Mladen,

    As I understand you check functionality with ADS131E08EVM at room temperature.
    I guess you could have the issue in temperature range when you need to guarantee minimum master clock period 444ns (equivalent to the 2.25MHz ). This mean that in some case converter could work unstable with higher clock.
  • 0 in reply to Oleksiy Pazyuk
    Prodigy 40 points
    Hello Oleksiy.

    Thanks for the quick response.
    I still hope that the manufacturer has left some space for overclocking...

    Best regards
    Mladen
  • 0 in reply to Mladen Rikic
    TI__Mastermind 23235 points
    The ADS131E08 has a datasheet max spec of 2.25MHz for all supply voltages. Based on your description, it sounds like you want to sample at 128x the line frequency (which equals 2.4576MHz for 60Hz). Unfortunately, we cannot recommend operation outside of the specified limits. While the device may appear to work fine at the mentioned frequency, this may be only under certain conditions. Other conditions – input short, full-scale signal, across temp – could result in degradation of performance to level unacceptable by the customer.

    We would recommend dropping the oversample by half, to 64x, and then you can run the external clock at 1.2288MHz. This is within the specified range for 5V operation only.
  • 0 in reply to Greg Hupp
    Prodigy 40 points

    Dear Greg,

    Thanks for response. If I understood well, this is idea:

    50 Hz => 2.048   Mhz => (DR{2:0] = 010) => 16    kHz, 24-bit
    60 Hz => 2.4576 Mhz => (DR{2:0] = 010) => 19.2 kHz, 24-bit   => No good!
    60 Hz => 1.2288 Mhz => (DR{2:0] = 001) => 19.2 kHz, 16-bit!

    Gud idea, but 16-bit resolution is below our desire...