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Original question:

LP2998 Vref Source Sink 500uA

LP2998: Schematic review

Lumina Gui
Genius 3315 points
Part Number: LP2998

Tool/software:

Dear TI Engineer,

Can you help to review the design of LP2998? The schematic is as below:

We have doubts about the level of the /SD pin, when we pull down this pin, there will be no output from the VTT pin, but when we pull it up to high, the VTT pin will have output. The pin on the datasheet should be at a low level to enable.

By the way, we also need to using the VREF pin to connected to the GPIO and the current is about 3mA. I have noticed that the current capability of VREF pin is only 30uA. So does it feasible for us to directly connect the output of VTT to GPIO through a diode?

Thanks,

Kind regards

  • 0
    TI__Mastermind 20265 points

    Hi Lumina,

    • For VREF, I recommend adding a 10nF capacitor (CREF). Based on the datasheet application examples, VREF usually has a decoupling capacitor.
    • For the VTT output, consider adding another 47uF capacitor to match the datasheet recommendation shown below:

    For /SD, this pin is active low which means the IC will shutdown when the pin is pulled LOW. Pulling the pin HIGH should cause the VTT output to activate again. The behavior you are describing is the normal operation.

    For you GPIO connection, I would not use VREF. VTT will have some slight voltage variation depending on the transient conditions but if you're just using VTT as a pull-up source through a diode, I don't see an issue with that. I haven't seen VTT used for anything other than termination so I don't have an example to reference.

    Regards,

    James