• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 64 subscribers
  • Views 571 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TPS7B63-Q1: Side effects for R_ROSC 2k...10kOhm as watchdog

Konrad Schmid
Prodigy 50 points
Part Number: TPS7B63-Q1

Hi all,

my customer wants to use the watchdog function of TPS7B6333-Q1 with the following parameters (see, datasheet p. 15):

FSEL = Low

R_ROSC = 2 k .. 10 kOhm (twd = 1 .. 5 ms), lower value is better from customer’s systems perspective.

 

In the overview / specification R_ROSC is used as a parameter (not limited) with values >= 20 kOhm

 

Does/What kind of side effect(s) does the customer introduce if they choose R_ROSC in the range 2k .. 10 kOhm?

 

What disadvantages besides of higher power dissipation will occur?

Thanks,

Konrad

  • 0
    Guru 140200 points
    Hi Konrad,

    figure 26 of datasheet shows R_ROSC = 10...20k in a typical apllication.

    Kai
  • 0 in reply to kai klaas69
    TI__Prodigy 50 points
    Hi Kai,

    thanks for letting me know about figure 26. The customer is specifically asking for the range 2k...10kOhm. What kind of effects could be introduced by a value in this particular range?

    Regards,
    Konrad
  • 0 in reply to Konrad Schmid
    TI__Guru 55940 points
    Hi Konrad,

    TPS7B63-Q1 was designed, tested, and characterized for an Rrosc of 20 k to 100 k. found a typo where the second 0 was left off of figure 26 by mistake. If Rrosc is outside of the 20 k to 100 k range, the watchdog timing and functionality may or may not be within the described performance.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Prodigy 50 points

    Hi Ryan,

    what kind of side effects will occur in case Rrosc is 2k...10kOhm? It's understood that it can't behave as it performes with higher Rrosc but what will happen indeed? Blow up or TPS7B63-Q1 will break over a longer period of time? I would appreciate it if you have concrete indication what type of side effects will occur since my customer is highly interested what side effects could happen.

    Best Regards,

    Konrad

  • 0 in reply to Konrad Schmid
    TI__Guru 55940 points

    Hi Konrad,

    The oscillator frequency is set by changing the current through Rrosc.  While a resistor 2k to 10k should not cause enough current to damage the LDO, the current will be outside the expected range.  As a result, the accuracy may be outside of 10% or WDO may remain low, indicating a fault status.  Resistors smaller than 10 k begin to be detected as a short to GND.  Resistors bigger than 200 k begin to be detected as an open.

    I used an EVM to bench an Rrosc of 2k and WDO remained low, indicating a fault status.

    Very Respectfully,

    Ryan