• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 1208 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.

TPS3890: How to calculate the threshold voltage for the monitored supply?

Vishnu
Prodigy 180 points
Part Number: TPS3890

Q1) Please verify the following calculation

This is the datasheet-section I am dealing with:

Intention is to calculate the maximum positive and negative threshold voltage for R1 = 30k and R2 = 10k.

VIN = 5V.

 

TPS389001, NEGATIVE THRESHOLD (VITN) = 1.15 V, POSITIVE THRESHOLD (VITP) = 1.157 V

From the equations, VITP(MON) = VITP × (1 + R1 ÷ R2 )    =   1.157 * (1+30/10)  = 5.35 V

VITN(MON) = VITN × (1 + R1 ÷ R2 )    =   1.15 * (1+30/10)  = 4.6 V

Q2) What is the potential at VMON ?

Q3) What will be the scenario if VMON connected to VIN ?

Please explain in the contest of following image,

 

 

 

 

  • 0
    Guru 140200 points
    Hi Vishnu,

    I get different monitor voltages: 4.628V and 4.600V.

    If Vmon is rising and exceeds 4.628V, then the /RESET output goes high. If Vmon is decreasing and goes under 4.600V, then the /RESET output goes low. This is also shown in the timing diagram (figure 1 of datasheet).

    The difference of 4.628V - 4.600V = 28mV is called hysteresis and makes that the /RESET output does not oscillate if Vmon is exactly at the threshold voltage.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 180 points

    Hi Kai,

    Thanks a lot for the response.

    I stand corrected, Regarding the equation we used to calculate the thresholds, I found one in the following link: slva450a

    Kindly check equation-4 (Page - 2). I think this will be more accurate as we includes leakage current as well. Make sense?

    Regards,

    Vishnu

  • 0 in reply to Vishnu
    Guru 140200 points
    Hi Vishnu,

    yes, equation 4 is more accurate.

    Another method taking into account Isense is to keep the currents in R1 and R2 more than 100 times bigger than Isense. See also section 8.3.4 of datasheet. This is accomplished if you choose R1=30k and R2=10k, as in your example: 1.15V / 10k = 115µA. And the maximum Isense from datasheet is 100nA. So, 115µA is more than 1000 times bigger than 100nA.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 180 points

    That was informative, thanks a lot for the response.
    - Vishnu