• State TI Thinks Resolved
  • Locked Locked
  • Replies 13 replies
  • Answers 4 answers
  • Subscribers 63 subscribers
  • Views 3824 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMR23630-Q1: input External Clock

tateo yamashiro
Guru 10890 points
Part Number: LMR23630-Q1

Hi,

We got a question from customer about LMR23630-Q1.
Could you help us?

[Question]
Our customer considers to input external clock on the EN/SYNC pin directly.

- Is there any consern about this usage?
- Is there any requirement to the device be enabled? If they input external clock on EN/SYNC pin, will the device be enabled and synchronized to external clock immediately?

Best Regards,
tateo

  • 0
    TI__Mastermind 23815 points

    Hi Yamashiro san,

    I tested this in the lab and yes there is a concern for connecting the clock directly to EN pin. The part will not reliably enabled if you do this connection. 

    You can have a pull up resistor of 100k to VIN and put a AC coupling capacitor in series as shown on figure 16 of the datasheet. You need at least the RENT for synchronization to work properly

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    Guru 10890 points

    Thank you for your reply.
    They need ON/OFF control during Vin exist. But If EN/SYNC should be pulled up to Vin, I think the design is a little bit complicated.
    Is there the recommended circuit for their requirement?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    Guru 10890 points
    Hi, Sorry for rush, but could you give us your feedback by next Tuesday?
  • 0 in reply to tateo yamashiro
    TI__Expert 4100 points

    Hello Tateo-san,

    As mentioned in previous post it is required to have Rent between Vin and EN pin. The other resistor Renb could be left out if UVLO functionality is not required. External clock should be fed through small capacitor (suggested 1nF) into EN/SYNC pin. The requirements for this external clock are described in the data sheet (section 7.3.3). We understand that this may be somewhat more involved, but this is a trade off for combined pin functionality.

    Best regards

    Brani

  • 0 in reply to Brani Dubocanin
    Guru 10890 points

    Hi, We have additional question.
    To control the device by external ON/OFF signal for EN/SYNC pin, I think we can design by EN/SYNC pin is pulled down.

    - When the VIN voltage exist, can the EN/SYNC pin be pulled low by pull-down resistor?


    - I evaluated start-up at the EN/SYNC pin be pulled low by pull-down resistor. There is delay time approximately 1msec from EN/SYNC is high to start switching.
      Is this behavior correct?


    - If the EN/SYNC pin can be pulled low, I think external signal can be input directly. And I think we can design ON/OFF control and frequency synchronization to external clock.

       ON/OFF: the device will start switching after approximately 1 msec from EN/SYNC is high.
       frequency sync: after the device start switching, external clock can be inputed.

      Is there any concern about this usage?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    Guru 10890 points

    Hi, Sorry for rush, but could you give us some feedback on our question?

    Best Regards,

    tateo

  • 0 in reply to tateo yamashiro
    TI__Expert 4100 points
    Hello Tateo-san,
    If EN pin is pulled low, this will disable the device. For that reason it is recommended to have Rent populated between Vin and EN pin.
    As far as observed behavior is concerned (1ms delay between EN going high and SW active), this is normal behavior and it is documented in datasheet (see plots 26 & 27 on page 22).
    The concern with your proposal below
    :::: ON/OFF: the device will start switching after approximately 1 msec from EN/SYNC is high.
    :::: frequency sync: after the device start switching, external clock can be inputed.
    is that if EN pin is toggled device will potentially toggle between ON/OFF states. It could potentially cause device to turn on/off with the SYNC signal applied on this pin. For that reason it is recommended that there is DC pull up signal present on this pin (through Rent resistor).

    I hope this helps clarify the issue.
    Regards
    Brani
  • 0 in reply to Brani Dubocanin
    Guru 10890 points

    Hi, Is there any sequence requirement between VIN and EN/SYNC? Our customer considers ON/OFF control by EN/SYNC pin. In their condition, it is occured that EN is high and VIN is not applied the voltage. Is there any concerns this usage?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    Guru 10890 points

    Hi, I saw absolute rating in datasheet. EN maximum rating is Vin+0.3V. So their conditon is not acceptable?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Guru**** 191445 points
    Did this ever get resolved?
  • 0 in reply to tateo yamashiro
    TI__Expert 4100 points

    Hello Tateo-san,

    I hope this issue has been resolved.

    In order to clarify question above an EVM board was used.

    Voltage to EN pin was applied from external source before Vin is applied to LM23630.

    Device is starting up reliably with this power up sequence, with and without load being applied.

    However it should be mentioned that there is an ESD diode on the EN pin and it is recommended to add resistor to limit current into EN pin.

    As far as “VIN+0.3” voltage range on EN pin is concerned this number specifies maximum allowable voltage that can be applied to EN pin. It does not mean that VIN voltage must be applied first and then voltage to the EN pin. It is clear that EN pin can be driven from different source other than VIN (it could be microcontroller or separate DC rail)

    This voltage is referenced to AGND pin.

    It should be also mentioned that customer should not ignore Abs max specs for any pin.

    Best regrads

    Brani

  • 0 in reply to Brani Dubocanin
    Guru 10890 points

    Hi, Thank you for your support. Let me confrim your answer. If VIN is not supplied and EN is supplied the voltage (e.g. 5V), the voltage of EN is VIN + 5V. I think this condition is over obsolute input voltage rating(VIN + 0.3V).
    Is this opinion right? If it is not problem, could you tell us the example that the condtion of over absolute input voltage rating?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Expert 4100 points

    Hello Tateo-san,

    You are correct that if EN is supplied from a separate source the device will be fully functional.

    Maximum allowed voltage on EN pin should not exceed 36V (as specified in "recommended operating conditions" table).

    Best regards

    Brani