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UCC381-ADJ: Lowering the UCC381 LDO output voltage range to 0V

douglas Sudjian
Prodigy 190 points

Part Number: UCC381-ADJ

Is it possible to lower the output voltage on these LDO's by creating a negative

voltage at the gnd pins? This would be just a common mode negative voltage shift relative

to the internal 1.25 reference voltage.

Tis would be similar to using the LM317 series of adjustable regulators.

  • 0
    TI__Genius 10680 points

    Hi,

    This device is different from the LM317 in that the reference is relative to GND, rather than relative to VOUT - it is more like a standard LDO configuration.  You may be able to lower the output voltage by moving the GND voltage negative on this device, however, the output cap. (which is not required, but PSRR and transient  performance will not be good without it) will have to be referenced to the GND of the device, not the GND of the load.  In this case, the improvement from the output cap. will be compromised.  Overall, it is possible but the device performance will be degraded. 

    Regards,

    Mike

  • 0 in reply to Michael Hartshorne
    Prodigy 190 points

    Hi,

    Thanks for the reply.

    Does anyone offer a Spice model for this part?

    I have a file called UCCx813-5 but look at the pin definition. Its all wrong.

    Doug

    *****************************************************************************
    .SUBCKT UCCx813-5 COMP FB CS CT GND DRV VCC VREF
    XUV VCC uvlout UVLOX2 PARAMS: VON=4.1 VOFF=3.6 ; UVLO Setting
    SX5 ct gnd 52 0 SSWITCH

  • 0 in reply to douglas Sudjian
    TI__Genius 10680 points

    Hi Doug,

    Unfortunately, this being an older device, we don't have a model for it.  

    Regards,

    Mike

  • 0 in reply to Michael Hartshorne
    Prodigy 190 points

    Hi Michael,

    I found another part, LP38798-ADJ

    It simulates well.  It may be perfect for my design!

    I wish TI would provide more models, they may have more sales.

    Because it takes a lot of effort to generate a design and PCB design/build based on incomplete

    simulation work.  I think I got lucky here though.

    Doug

  • 0 in reply to douglas Sudjian
    TI__Genius 10680 points

    Hi Doug,

    I'm glad to hear you found the right device.  We do require models for all of our new device releases, but as you found, there are still several older devices without them.   Thanks for the inputs.

    Regards,

    Mike