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LM5060-Q1: LM5060 design methodology for OVP protection (typeA)

Jeff Wang29
Prodigy 90 points
Part Number: LM5060-Q1
Other Parts Discussed in Thread: LM5060

Hello TI experts,

We’re reviewing the OVP calculations of LM5060-Q1 and have some questions as below. Could you please help check and reply to us?

Thank you.

 

  • The R3 resistor calculation formula might have problem in the datasheet, it seems comes a negative value by calculation. Could you please help take a look?

<<Pict in reply pdf file>> 

  • Can we use the below formula VINmax in datasheet for calculating the OVP limit? Also can we exclude the UVLObias parameter in the calculation?

<<Pict in reply pdf file>> 

  • There is a hysteresis of 240mV for OVP, how does the OVP work with this hysteresis?
    • The behavior, for example a 17V OVP setting, when the input over 17V, the OVP is active to turn off output, and while the input voltage fall down below 16.76V(17V-240mV), then the output will come back, right?

 

  • Have you ever met or had any lesson learn that the practical OVP active point below the OVP calculation point?

 

  • What’s the difference between OVPbias and UVLObias? From the datasheet block diagram, I do not find where is OVPbias current, what’s it’s function and effect?
    • When we design OVP, shall we consider both of them or only UVLObias current as spec formula is enough?
    • In the TI calculation tool, it only considers UVLObias without OVPbias. Why OVPbias is not considered?

 (TI LM5060 datasheet) 

<<Pict in reply pdf file>>

 

(TI design calculator kit)

 <<Pict in reply pdf file>>

  • 0
    Prodigy 90 points

    Problem posting the picts, so I attach pdf file here for questions with picts. thank you.

    LM5060 TI Forums Q with picts.pdf

  • 0 in reply to Jeff Wang29
    TI__Guru* 95891 points

    Hi Jeff,

    Thanks for reaching out!

    I suggest to use design calculator for calculations. 

    What is your target UVLO, OVLO cut-off ?

    3. There is a hysteresis of 240mV for OVP, how does the OVP work with this hysteresis? The behavior, for example a 17V OVP setting, when the input over 17V, the OVP is active to turn off output, and while the input voltage fall down below 16.76V(17V-240mV), then the output will come back, right?

    Right

    4. Have you ever met or had any lesson learn that the practical OVP active point below the OVP calculation point?

    UVLO, OVLO cut-off voltages can vary as the OVP, UVLO thresholds has variation with temperature, process.

    5. What’s the difference between OVPbias and UVLObias? From the datasheet block diagram, I do not find where is OVPbias current, what’s it’s function and effect? When we design OVP, shall we consider both of them or only UVLObias current as spec formula is enough? In the calculation tool you provided, it only considers UVLObias without OVPbias. Why OVPbias is not considered?

    Typical value of OVPbias is 0 V and hence not considered.

    BR, Rakesh

  • 0 in reply to Rakesh
    Prodigy 90 points

    Thank you Rakesh and TI team,

    1. The design target of UVLO is 7V, and OVLO is 17V.

    Had used TI calculation tool. We are using type A (UV/OV protections) with R1 = 200k, R2 = 28.7k and R3  = 30.1k ohms.

    Exclude the hysteresis effect, the min OV is 16.92V, typical is 18.30V and Max is 19.67V.

    2.  Understand OVPbias can be waived. However, when we design OVP, shall we STILL consider UVLObias current as spec formula guided?

    VINmax (OVP) formula is in TI LM5060 spec datasheet page 22 formula #(11).

  • 0 in reply to Jeff Wang29
    TI__Guru* 95891 points

    Hi Jeff,

    Yes, UVLObias current comes in to calculation wherever R1 appears, this is to account the UVLObias current * R1 drop in the calculation.

    I have attached unlocked design calculator to refer the background calculations for UVLO, OVLO.

    LM5060 Design_Calculator_REV_C.xlsx

    BR Rakesh

  • 0 in reply to Rakesh
    Prodigy 90 points

    Thank you, Rakesh, for great support.