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TPL5111: Can a resistor be inserted between EN/ONE_SHOT and GND?

Kazuya Nakai59
Guru 21595 points
Part Number: TPL5111

Hello guys,

One of my customers is going to evaluate TPL5111 for their new products.
At this moment, the customer has the following question.
Could you please give me your reply for them?

Q. They want to insert a resistor between EN/ONE_SHOT terminal (No. 6) and GND as a pull down resistor
      like the circuit in the following blog.
      https://www.instructables.com/Solar-and-Battery-Powered-Timed-Shed-LED-Light/
      They have already confirmed that TPL5111 worked correctly when the resistor range was 0ohm ~ 820kohm. 

      Is it no problem to insert the pull down resistor?

Your reply would be much appreciated.

Best regards,

Kazuya.

  • 0
    TI__Guru** 107830 points

    Hi Nakai-san,

    This pin can be pull-low directly or via a resistor, however 820kΩ does not make sense to me, a few kΩ is more reasonable. 

  • 0 in reply to Noel Fung
    Guru 21595 points

    Hello Noel,

    Thank you very much for your prompt reply.
    Could I ask an additional question as the follow?

    Q. I found TPL5111 datasheet said that the EN/ONE_SHOT pin must be hard wired to GND or VDD according to the required mode of operation.

    I think hard wire means direct connection. Is my understanding correct?
    Is it no problem to use a pull up or pull down resistor for setting EN/ONE_SHOT to H or L level?

    Thank you again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru** 107830 points

    Hi Nakai-san,

    Hard wired means either pull-up or pull-down, but not floating.

    EN/ONE_SHOT is an input pin, it won't draw current, we can pull it up or down directly or via a resistor. 

  • 0 in reply to Noel Fung
    Guru 21595 points

    Hi Noel,

    Thank you very much for your reply.

    I have a question about EN/ONE_SHOT terminal.
    The customer checked EN/ONE_SHOT voltage when the terminal was pulled up to VDD with 10kohm resistor.
    The terminal voltage changed VDD to GND side when the interval time set by a external resistor was lapsed.
    So we thought that EN/ONE_SHOT terminal sank a few current and the terminal was I/O terminal.

    Q1. Is EN/ONE_SHOT terminal input only? Is it not Input/output terminal?
    Q2. Can EN/ONE_SHOT terminal be pulled up to VCC with 10kohm resistor? Is it no problem?

    Thank you again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru** 107830 points

    Hi Nakai-san,

    Alright, let me check the history, it may take some time, I will try to give you an update no later than tomorrow.

  • 0 in reply to Noel Fung
    Guru 21595 points

    Hi Noel,

    Thank you very much for your strong supports.
    I'm looking forward to receiving your update.

    Thank you again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    Guru 21595 points

    Hi Noel,

    Do you have any update for Q1 and Q2?

    Thank you and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Guru** 107830 points

    Hi Nakai-san

    sorry to keep you waiting. Unfortunately I cannot find any specific information on this pin, I am asking help from the design team, hopefully they can give me the answer. Designer may takes a few days to review the chip design, I expect I should have the answer in next week. Meanwhile, I suggest the customer reserves the pull-up resistor, we can put a 0Ω resistor in case later on we find out that this pin has to be tied to VDD directly.

  • 0 in reply to Noel Fung
    Guru 21595 points

    Hi Noel,

    Thank you very much for the updating.
    I understood the situation and to prepare the resistor land pattern.
    I'm looking forward to receiving your reply next week.

    And could I ask you the following additional questions?
    Q. When EN/ONE_SHOT terminal is pulled down to GND, can the terminal be pulled down with a resistor?

    Thank you again and best regards,

    Kazuya.  

  • 0 in reply to Kazuya Nakai59
    TI__Guru** 107830 points

    Hi Nakai-san,

    I think the question is, "can we pull-up/down via a resistor?". I hope to find this out soon. Since all the original designers of this device are no longer with TI, it will take longer time for the existing designer to review the design. Thank you for your patience. 

  • 0 in reply to Noel Fung
    Guru 21595 points

    Hi Noel,

    Yes, My question is "can we pull-up/down via a resistor?" as you wrote.
    I'm looking forward to receiving your reply.

    Thank you and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    Guru 21595 points

    Hi Noel,

    Could you please give me your reply?

    Thank you and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 28550 points

    Hello Nakai-san,

    Kazuya Nakai59 said:
    Q1. Is EN/ONE_SHOT terminal input only? Is it not Input/output terminal?
    Q2. Can EN/ONE_SHOT terminal be pulled up to VCC with 10kohm resistor? Is it no problem?

    Q1) Datasheet shows EN/ONE_SHOT as an input pin:

    HIGH = EN (enable) timer functionality.
    LOW = ONE_SHOT functionality.

    Q2) Datasheet shows VIH/VIL for "DONE" pin.  I expect these levels are same/similar to EN/ONE_SHOT but cannot confirm.  Also, it does not list the max input leakage current which would define the maximum allowed resistance to still meet VIL. (or VIH).

    • Given that you tested with 820 kohm pull-down, this suggest any voltage drop caused by some leakage current is still <= VIL requirement.
      • So it *probably* would work...
    • As for pull-high with 10 kohm, it would *probably* also work and keep VIH level > 0.7 * VDD.  But again, I don't see any leakage data and...

    As you point out, the datasheet guideline and schematics use a direct connect by it's schematic.

    • So why wouldn't the customer simply use as datasheet describes?
    • I can understand, if they would like to have a pad for debug, or to isolate the pin... if so, then a 0 ohm resistor can be used.  (However, according to datasheet, this pin should never be left floating).
    • Not knowing any details - my concern (especially when pulling high) is that perhaps there is some decision the device makes to switch modes.  If you have a resistor to Vcc, then perhaps the voltage doesn't arrive at the right level internally to make the proper decision.  I don't know.

    My recommendation is to follow the datasheet and eval board design which is to tie direct to Vcc or GND.  Again, if you want the option to switch between GND or VCC on PIN6 (EN/ONE_SHOT) use a 0 ohm resistor to switch.  (Or a switch as done in the EVM.  Note they did not use a jumper on EVM which could have been removed and left this pin floating.

    73,
    Timothy

  • 0 in reply to Timothy T
    Guru 21595 points

    Hello Timothy,

    Thank you very much for your reply.

    The reason the customer didn't connect directly to the power supply was because he wanted to switch EN/ONE_SHOT pin settings to H or L level by a short pin.

    Do you think which is better, EN/ONE_SHOT is pulled up to VDD for H level setting and low level setting by short pin
    or EN/ONE_SHOT is pulled down to GND for L level setting and high level setting by short pin?

    Your reply would be much appreciated.

    Thank you again and best regards,

    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 28550 points

    Hello Nakai-san,

    The customer should tie EN/ONE_SHOT high or low based on the functionality they want.  From the pin function table:

    When EN/ONE_SHOT = HIGH, the TPL5111 works as a TIMER.

    When EN/ONE_SHOT = LOW, the TPL5111 asserts DRVn one time for the programmed time interval. In this mode, the DRVn signal may be manually asserted by applying a logic HIGH to the DELAY/M_DRV pin.

    --

    In either case, simply use a 0 ohm resistor to make the switch between HIGH or LOW.  This will match the EVM which is using a switch to connect the pin to HIGH (Vcc) or LOW (GND).

    73,
    Timothy

  • 0 in reply to Timothy T
    Guru 21595 points

    Hi, Timothy and Noel,

    I discussed the customer about EN/ONE_SHOT pin connection using your replies and they decided to use direct connection to VDD or GND for H/L level setting.

    Thank you very much for your strong supports.

    Thank you again and best regards,

    Kazuya.