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INx of TPS3700

Masami Michino
Genius 5070 points
Other Parts Discussed in Thread: TPS3700, TPS3702


Dear, All

A customer would like to make a highly precise OV/UL detection circuit using TPS3700.
They have 2 questions.

Question 1:
A customer is considering the precision of the detecting voltage.
I'd like to know whether leakage current of INA+/INB- influences detecting voltage.
Before and after the voltage of INA+/IN- is a threshold, is there a change in leakage current?
When having that, how does it change?

Question 2:
The min value of Vhys isn't indicated on the datasheet.
Please tell me the min value.

Thanks, Masami M.

  • 0
    TI__Guru 55940 points
    Hi Masami,

    Please allow until the next US business day for a reply.

    Very respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    TI__Guru 55940 points

    Hi Masami,

    1: The accuracy of the thresholds is defined in the Electrical Characteristic table:

    As mentioned on page 11 of the datasheet in describing how to select the resistor divider, the total resistance in the divider should be chosen so that the divider current is 100x higher than the input current.

    2: Figure 5 demonstrates how hysteresis behaves over temperature and Vdd.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Genius 5070 points

    Hi, Ryan-san,

    Thank you for your reply.
    But,

    Question 1:
    When input voltage changed near the threshold, the customer would like to know whether the hysteresis of the threshold changes or doesn't change.
    For example when the input current when being less than 400 mV, is 15nA for input voltage, and more than 400 mV of input current is -15nA, its difference will be 30nA.
    When setting the electric current which flows to division resistance as 1.5uA, it has about 2% of influence on detecting voltage.
    How does actual condition change?

    Question 2:
    It's the minimum value of
    "hys = Vit+ - Vit-"
    that the customer wants to know.
    The minimum value isn't indicated on "7.5 Electrical Characteristics".

    Thanks, Masami M.

  • 0 in reply to Masami Michino
    TI__Guru 55940 points

    Masami-san,

    The current through the resistor divider should be sized so that at the threshold, the current is 100x or greater than the sense pin current (INA, INB).  Higher divider current will not adversely affect the accuracy of the device.  As a result, the customer could choose to increase the divider current to ensure the highest accuracy.

    As accuracy seems to be the key concern for your customer, have you considered TPS3702 for their application?  This device is more accurate than TPS3700 and has the resistor divider internal so the customer does not need to worry about setting the divider current and they can reduce their Bill of Materials count.

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Genius 5070 points


    Hi, Ryan-san,

    Thank you for your reply.
    The setting voltage of OV and UL, the customer would like to have the lead more than 1 digit.
    Therefore they are thinking in TPS3700.
    The purpose of a question is 2.
    * I'd like to choose the most suitable resistance value about the setting voltage.
    * I'd like to confirm whether hysteretic charactanstics won't be value of the negative by the change in leakage current of INx.
    Therefore question 1 and question 2 were inquired.

    Thanks, Masami M.

  • 0 in reply to Masami Michino
    TI__Guru 55940 points
    Masami-san,

    In order to ensure accuracy, the divider current needs to be 100x or greater the sense pin current. This is detailed in Section 9.2.2.1 of the datasheet.

    We also have an application note ( www.ti.com/.../slva450a.pdf ) that describes this process for selecting resistor dividers.

    You will not get a negative hysteresis if you set the resistor divider to be 100x or greater than the sense pin current.

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Genius 5070 points


    Hi, Ryan-san,

    Thank you for your reply.
    I'll answer to a customer.

    Thanks, Masami M.