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ADC121S021 Power on Reset(POR) and Power sequence with SPI

Kuramochi Tadahiko
Guru 28715 points
Other Parts Discussed in Thread: ADC121S021

Hello,

I would like to confirm the power on reset(POR) and power sequence for ADC121S021.

1. Does this device have the POR circuit?

    If it does, please let me know the condition required reset.

2. Is there requiring for the SPI when the power up/down?

    i.e.) the relativity the CS signal and the power sequence

Thanks and Regars,

Kuramochi

  • 0
    TI__Guru 52366 points
    Hello Kuramochi,

    There is a t_POWER-UP spec of 1uS on page 6, and start-up is mentioned in the "Shutdown Mode" (p14) and "Power Management" (p15) sections of the Applications section.

    The /CS is essentially the "power switch". You must wait 1us regardless if you turned on VA or pulled /CS low.

    The VA must be above the minimum supply voltage (2.7V) before /CS is asserted. It is not specified, but I would guess there should be a minimum of 50ns from the time VA crosses 2.7V and when /CS is asserted. Then you must wait the 1us.

    Also note that the first conversion after power-up is invalid and you must take a second conversion.

    Regards,
  • 0 in reply to Paul Grohe
    Guru 28715 points

    Paul-san,

    Thank you for your reply.

    Could you give me the answer for Q1?

    >Does this device have the POR circuit?

    >If it does, please let me know the condition required reset.

    Thanks and Regards,
    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    Guru 28715 points

    Paul-san,

    Thank you for your reply

    Could you give me the answer for Q1?

    >Does this device have the POR circuit?

    >If it does, please let me know the condition required reset.

    Regards,

    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    TI__Genius 16890 points
    Hello,

    The condition to reset is to bring the power low. As Paul mentioned, when power is brought up, the part will start as described in the Timing Specifications. The first conversion will not be useable, the second conversion is usable.

    Mike
  • 0 in reply to Michael Stout
    Guru 28715 points
    Michael-san,

    Thank you for your help.

    I would like to understand the "tPOWER-UP".
    The tPOWER-UP is provided 1us(typ).
    If the power-Up time is shorter more than 1us from Full Power-Down, what problem will be occurred?
    In other words, why is 1us necessary for?

    The problem is occurred by another manufacturer's device.
    The problem is that the POR works when the power supply drops in a moment.
    My customer would like to confirm that the problem is not occurred the ADC121S021.

    Thanks and Regards,
    Kuramochi
  • 0 in reply to Kuramochi Tadahiko
    TI__Genius 16890 points
    Hello,

    The ADC takes time to power-up, either after first applying VA, or after returning to normal mode from shutdown mode. This is called tPOWER-UP. This corresponds to one "dummy" conversion for any SCLK frequency within the specifications in the datasheet. After this first dummy conversion, the ADC will perform conversions properly. Note that the tQUIET time must still be included between the first dummy conversion and the second valid conversion
    So after a power up discard the first conversion and the rest of the conversion should be ok.

    Mike