ADSP-21489 Power Sequence Schematic

Hi All,
I want to know how to design the ADSP-21489 Power Circuit simply,
and I want to know why the Time Delay device(ADM1085) is needed in the VDDINT circuit.

The DSP has a specific power-up sequence like as below.
- Power Up Sequencing Timing Requirements
  . VDDINT = VDDEXT +/- 200ms
  .
- ADSP-21489 Power Circuit
  . VDDEXT(3.3V@2A) -> Time.Delay(ADM1085) -> ADP1864(DCDC) -> VDDINT(1.1V@2A)
  . I think Time.Delay(ADM1085) doesn't need in the VDDINT power circuit, because VDDINT is VDDEXT +/- 200ms.
  . Can I remove the Time Delay Device(ADM1085)?
  . Why is the Time Delay device(ADM1085) needed in the VDDINT circuit?
  . Please share the simple VDDINT Power Circuit to be recommended if you have.
  . VDDINT Circuit
    :

Best Regards,
Eric.


  • Hi
    I would also like to hear the answer to this question.
    That I can say in my PCB specifically did not install the ADM1085 and nothing bad happens. I'm working with my PCB from the beginning of January, turn on it several times a day. Every time it properly starts from HOST processor.

    I still don't  what to do: install it or not ?
    Regards
    Grzegorz

  • Hi Grzegorz,

    I'm making the schematic using ASDP-21489.
    But I couldn't decide whether I have to insert Time.Delay(ADM1085) device or not.
    I'll decide that after confirming the method.

    Please tell me if anyone knows it.

  • 0
    •  Analog Employees 
    on Mar 17, 2017 10:07 AM

    Hi Eric,

    According to the schematics, the CEXT pin of the ADM1085 is floating and hence the typical delay (VIN to ENOUT/ENOUT Delay VIN Rising) is 35us as per its datasheet.  As per the ADSP-21489 datasheet, there is no specific power-up sequencing is required between VDD_EXT and VDD_INT. However, note that no power supply should be powered up for an extended period of time (> 200 ms) before another supply starts to ramp up. 

    There are some other considerations that system designs should take into account which is given below, it is described in the page#: 23 of ADSP-2148x datasheet. 

    .

    • No power supply should be powered up for an extended period of time (> 200 ms) before another supply starts to ramp up. • If the VDD_INT power supply comes up after VDD_EXT, any pin, such as RESETOUT and RESET, may actually drive momentarily until the VDD_INT rail has powered up. Systems sharing these signals on the board must determine if there are any issues that need to be addressed based on this behavior. Note that during power-up, when the VDD_INT power supply comes up after VDD_EXT, a leakage current of the order of threestate leakage current pull-up, pull-down may be observed on any pin, even if that is an input only (for example the RESET pin) until the VDD_INT rail has powered up.

    Thanks,

    Jithul

  • Hi Jithul,
    Thanks for your response.

    But I couldn't understand the below items exactly.
    Could you tell the meaning easily? (Sorry~)

    - I have to insert the ADM1085 for 35us delay or NOT.
    - What's the reason if I have to insert the ADM1085?
    - I don't know the exact meaning of the below contents.
      . Note that no power supply should be powered up for an extended period of time (> 200 ms) before another supply starts to ramp up.

    Best Regards,
    Eric.

  • 0
    •  Analog Employees 
    on Mar 29, 2017 7:20 AM

    Sorry for the delay in getting back on this.

    Eric_Kang wrote:
      Note that no power supply should be powered up for an extended period of time (> 200 ms) before another supply

    It means that the time delay between VDD_INT and VDD_EXT applies to the processor should be not exceed 200 ms. In other words, if the VDD_INT  is powered up then VDD_EXT should be powered up with in 200ms (it can be vice versa as well, VDD_EXT can be powered up first then VDD_EXT)

    Best Regards,

    Jithul