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LT1166 Current Limit Function

Kazu

Hi All,

Here is a question about the current limit if the LT1166. My circuit is almost the same as Figure 9. in the datasheet

and I have attached it. I'd like the current limit to work more than 1A so I selected the 1.3 ohm Rsense.

However the output current clamped about 3.6A peak as attached LTSpice simulation result [V(n012)=Vin, V(n009)=Vout, I(R9)=Iout].  Why is not the output current clamped about 1A? Is my understanding about the current limit function wrong?

Regards,

Kazu

attachments.zip
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    •  Analog Employees 
    on Mar 1, 2018 10:42 PM

    The current limit function is not a smooth function, but rather a hysteretic trip point (and not very precise) that shuts down the output stage for a period of time set by capacitances in the circuit (was only intended to minimize FET stress in a fault condition). If you have a specific current limit in mind, it isn’t too hard to add a transistor to each FET that will form a fast limiter function (the sense resistor could turn on a Vbe and the transistor collector could shunt away gate current from the FET).

    If fairly accurate and/or variable current control is of interest, one might consider an LT1970-based circuit.

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  • 0
    •  Analog Employees 
    on Mar 1, 2018 10:42 PM

    The current limit function is not a smooth function, but rather a hysteretic trip point (and not very precise) that shuts down the output stage for a period of time set by capacitances in the circuit (was only intended to minimize FET stress in a fault condition). If you have a specific current limit in mind, it isn’t too hard to add a transistor to each FET that will form a fast limiter function (the sense resistor could turn on a Vbe and the transistor collector could shunt away gate current from the FET).

    If fairly accurate and/or variable current control is of interest, one might consider an LT1970-based circuit.

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