Adding soft-start for LDO LT3080

Hi,

I have a question about the below circuit of LT3080, what is the purpose of D1?

Is that for discharge C2 when the Vin disappeared? 

Because D1 will affect the accuracy of Vout, I do not want to add D1。

Best Regards,

Leo

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    •  Analog Employees 
    on Oct 28, 2020 3:59 PM 4 months ago

    Thanks for the post.  Yes, the diode D1 you show will affect accuracy.  I show how much a silicon diode can leak in the image below.  As far as I know, the purpose of D1 is to prevent SET from being held up if IN=VCONTROL is forced low.   Actually, if IN=VCONTROL is forced low, OUT will also be forced low because there is a parasitic diode from OUT to IN on the LT3080, similar to the parasitic diode I discuss in this post titled "Disable LT3083".

    1N4148 leakage_1.png

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  • 0
    •  Analog Employees 
    on Oct 28, 2020 3:59 PM 4 months ago

    Thanks for the post.  Yes, the diode D1 you show will affect accuracy.  I show how much a silicon diode can leak in the image below.  As far as I know, the purpose of D1 is to prevent SET from being held up if IN=VCONTROL is forced low.   Actually, if IN=VCONTROL is forced low, OUT will also be forced low because there is a parasitic diode from OUT to IN on the LT3080, similar to the parasitic diode I discuss in this post titled "Disable LT3083".

    1N4148 leakage_1.png

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