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TPS16630-32EVM: Formula for calculating R(IMON) of TPS26600

Conor
Guru 12165 points
Part Number: TPS16630-32EVM
Other Parts Discussed in Thread: TPS26600-02EVM

Tool/software:

Hi,

Q1
The TPS26600-02EVM documentation states "Load current monitor output with 1.5 V / A" and uses R(IMON) of 20 [kΩ]. Is it correct that the IMON output range "1.5 V/A" changes depending on the design value of R(IMON)?

Previously, E2E answered, "The following two formulas have the same meaning, but if the input voltage is 5.5 V or higher, use the simplified second formula when calculating R(IMON)."

Does the input voltage mean V(IN)? Or V(IMONmax)? Also, why is the input voltage 5.5 V or higher? Is V(IMONmax) the maximum input voltage of the ADC? What does "75 × 10^(−6)" in formula 2 mean?

Q2
The following circuit is used to provide a time delay before asserting PGOOD, which is used to enable the DCDC placed after the eFuse.

Is it correct that the time delay is tPGOOD(degl)=(875 + 20 × C(dVdT))?

Is it correct that it can be used as a Power Good indicator for the DCDC placed after the eFuse?

What converters are referred to as "downstream converters"?

Does the logic within the dotted line only function in Latch mode? Also, how does it work in other modes?

Thanks,

Conor

  • 0
    TI__Mastermind 32451 points

    Hello Conor,

    Q1: Yes, EVM calculation is correct

    Input voltage means VIN. 75 × 10^(−6) is obtained multiplying gain with 1.8 . Please use the formula having 75 × 10^(−6).

    Q2: Yes,It;s correct 

    Yes, downstream converter means DC-DC converter connected after E-Fuse in circuit.

    For auto-retry mode you can check waveforms in datasheet how /FLT works.

    Thanks 
    Amrit 

  • 0 in reply to Amrit Jit
    Guru 12165 points

    Hi Amrit, 

    Amrit Jit said:
    Input voltage means VIN. 75 × 10^(−6) is obtained multiplying gain with 1.8 . Please use the formula having 75 × 10^(−6).

    Q1.
    Please tell me how to calculate the above.
    If I use the above as a reference, I get 78.4u x 1.8 = 141.4u, which is not 75u.

    Q2.
    The typical value of GAIN(IMON) in the data sheet is 78.4[uA/A] and 78.28[uA/A]. Which one is correct?

    Q3.
    The TPS26600-02EVM documentation states "Load current monitor output with 1.5 V / A," and R(IMON) is set to 20 kΩ. Is it correct that the IMON output range of "1.5 V/A" changes depending on the design value of R(IMON)?

    Q4.
    It says that "FLT asserts after a delay of 875 us after the current limit is reached." Does the delay value of 875 us refer to the calculated value of tPGOOD(degl)=(875 + 20 × C(dVdT)) (875 us for 0.022 uF)? Is it correct that tPGOOD repeats a cycle of being high for tPGOOD(degl)=(875 + 20 × C(dVdT)) and low for 875 us?

    Thanks,

    Conor

  • 0 in reply to Amrit Jit
    Guru 12165 points

    Hi Amrit,

    I'd like some kind of answer by the end of the day.

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Mastermind 32451 points

    Hello Conor,

    Extremely sorry for the delay in response.

    Conor said:
    Please tell me how to calculate the above.
    If I use the above as a reference, I get 78.4u x 1.8 = 141.4u, which is not 75u.

    VIMON(max) is the maximum voltage supported by ADC. All of our design calculator uses the first formula. I am attaching the design calculator below.

    dr-download.ti.com/.../slvc668.zip

    Conor said:
    The typical value of GAIN(IMON) in the data sheet is 78.4[uA/A] and 78.28[uA/A]. Which one is correct?

    Datasheet typical value is 78.28. But you can check figure 18 wrt temp.

    Conor said:
    The TPS26600-02EVM documentation states "Load current monitor output with 1.5 V / A," and R(IMON) is set to 20 kΩ. Is it correct that the IMON output range of "1.5 V/A" changes depending on the design value of R(IMON)?

    You can check design calculator to verify this.

    Conor said:
    It says that "FLT asserts after a delay of 875 us after the current limit is reached." Does the delay value of 875 us refer to the calculated value of tPGOOD(degl)=(875 + 20 × C(dVdT)) (875 us for 0.022 uF)? Is it correct that tPGOOD repeats a cycle of being high for tPGOOD(degl)=(875 + 20 × C(dVdT)) and low for 875 us?

    Yes, you are correct. That's the deglitch time provided.

    Thanks 

    Amrit