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LT3040 shutdown behavior

Dear All,

I have a doubt concerning the shutdown behavior of the LT3040.

On page 21, in the power supply sequencing paragraph the datasheet says:

If the VIN pin is powered high while LT3040 is in shutdown, the DC current flowing through the internal VINto VFB clamp may pull output above ground

On the next page, in the ENABLE/UVLO paraghraps is written:

The EN/UV pin is used to put the buffer into a micro-power shutdown state.

Is there a risk to have the output above the ground when Vin and V+ are biased but ENABLE is grounded?

Rationally should not be the case. I am going to use several LT3040 togheter with an LTC2937 for power sequencig to supply a very sensitive decive, so I should be sure that in any condition the power sequence is respected and when a supply if off, the output is really off.

Thank you for any advice

  • Hello Alex,

      If VIN is powered while the LT3040 is shutdown, there is a possibility that the Absolute Maximum rating for the voltage differential from VIN to VFB or the current rating (max 20mA) on the VIN and VFB pins or both may be exceeded; damaging the part.  You may notice that in the application circuit drawings, the device providing the input to VIN receives its input from the same signal tied to V+ and EN/UV.

    Best regards,

    Brad

  • Hi Blovell,

    Thank you for your message.

    What happen when Vin and V+ are both powered but the shutdown mode is induced by keeping low the EN pin?

    In case the part may still be damaged, I do not see the purpose of an Enable pin

    Thank you,

    Alessandro