LP3985

SNVS087AE – OCTOBER 2000 – REVISED MAY 2015

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Feature Description (continued)

7.3.3 Fast On-Time

The LP3985 output is turned on after VREF voltage reaches its final value (1.23 V, nominal). To speed up this

process, the noise reduction capacitor at the BYPASS pin is charged with an internal 70-µA current source. The

current source is turned off when the bandgap voltage reaches approximately 95% of its final value. The turnon

time is determined by the time constant of the bypass capacitor. The smaller the capacitor value, the shorter the

turn on time, but less noise gets reduced. As a result, turn on time and noise reduction need to be taken into

design consideration when choosing the value of the bypass capacitor.

7.4 Device Functional Modes

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.

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