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LP3985 Functional Modes?

Michael Raleigh
Expert 3245 points
Other Parts Discussed in Thread: LP3985

Hello,

The LP3985 datasheet refers to two functional modes in section 7.4:

7.4.1 Operation with VOUT(TARGET) + 0.3 V ≤ VIN ≤ 6 V The device operates if the input voltage is equal to, or exceeds, VOUT(TARGET) + 0.3 V. At input voltages below the minimum VIN requirement, the devices does not operate correctly, and output voltage may not reach target value.

7.4.2 Operation Using the EN Pin If the voltage on the EN pin is less than 0.4 V, the device is disabled, and in this state shutdown current does not exceed 1.5 μA. Raising VEN above 1.4 V initiates the start-up sequence of the device.

If I understand correctly this is an either or situation, where you either use the enable pin and then the standard Vdo applies or this other mode where the Vdo is 300mV? Can you please elaborate on what 7.4.1 is functionally implying from an application perspective?

Thanks,

-Michael

  • 0
    TI__Mastermind 22610 points

    Both apply.

    Section 7.4.1 is for the minimum operating input voltage relative to Vout. This is stating  the typical minimum input voltage where you would have any expectation of reasonably functional device behavior, not the same as the ensured behavior in the Electrical Characteristics table.

    The Recommended Operating Vin range is defined in Section 6.3 .

    Section 7.4.2 is for the Enable pin on/off thresholds only. When the Enable pin voltage is between 0.4V and 1.4V the output status is undefined.

    If your actual Vout option is 2.5V, I would recommend a Vin of absolutely no less than 2.8V based on device behavior showing in the ' Ground Current vs Vin ' charts (Figs 6, 7, and 8)