LD3986 SERIES
source used to drive the EN input must be able to
swing above and below the specified turn-on/off
voltage thresholds listed in the Electrical
Characteristics section under Enable Input Logic
Low and Enable Input Logic High.
Proper operation of the Enable function is
guaranteed by driving EN pins with TR and TF = 10
ms.
FAST ON-TIME
The LD3986 outputs are turned on after VREF
voltage reaches its final value (1.23V nominal). To
speed up this process, the noise reduction
capacitor at the bypass pin is charged with an
internal 70µA current source. The current source
is turned off when the bandgap voltage reaches
approximately 95% of its final value. The turn on
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.
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