LP3905 datasheet(7/15 Pages) NSC

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Typical Application Circuit

Functional Description

POWER UP/DOWN PROCEDURE

The LP3905 Bucks and LDOs are powered UP/DOWN with

2 control pins, EN1 and EN2. In order for the enable pins to

operate, V

IN1 and VIN2 should be set to a voltage level higher

than V

UVLO_R (specified in electrical characteristic). Once

enabled, EN1 will turn on Buck1, LDO1 and LDO2. EN2 can

independently be used to enable Buck2. Figure 6 illustrates

the power UP/DOWN timing sequence of the LP3905 blocks

for V

≥ V

IH (min) (enable) and VEN

≤V

IL (max) (disable).

Both linear regulators have active pulldowns when the out-

puts are disabled.

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FIGURE 5. Typical Application Circuit For Adjustable Device

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EN1 and EN2 can be controlled fully independently.

LDOs will be turned on only after Buck1 is powered up. LDOs are powered on simultaneously.

In case EN1 and EN2 are enabled at the same time, power up of Buck2 is delayed by 50µs in order to minimize the inrush current

from the battery.

When EN1 and EN2 are disabled, the relevant output voltages are turned off.

FIGURE 6. LP3905 Power UP/DOWN Timing Sequence

LP3905 Arkusz danych(PDF) 7 Page - National Semiconductor (TI)