LP28400 datasheet(16/17 Pages) POWER

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Preliminary Datasheet

LP28400

LP28400-00 Version 1.0 May.-2013

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Page 16 of 17

plugs in and the voltage is above the battery voltage, the IC

exits SLEEP mode. The battery is disconnected from the

system and the adapter is connected to the system after exiting

SLEEP. An automatic break-before-make logic prevents

shoot-through currents when the selectors switch. The ACDRV

is used to drive a pair of back-to-back n-channel power

MOSFETs between adapter and ACP with sources connected

together to CMS. The n-channel FET with the drain connected

to the ACP (Q2, RBFET) provides reverse battery discharge

protection, and minimizes system power dissipation with its

low-RDSON. The other n-channel FET with drain connected to

adapter input (Q1, ACFET) separates battery from adapter, and

provides a limited dI/dt when connecting the adapter to the

system by controlling the FET turn-on time. The /BATDRV

controls a p-channel power MOSFET (Q3, BATFET) placed

between battery and system with drain connected to battery.

Before the adapter is detected, the ACDRV is pulled to CMS to

keep ACFET off, disconnecting the adapter from system.

/BATDRV stays at ACN-5V (clamp to ground) to connect

battery to system.

After the device comes out of SLEEP mode, the system begins

to switch from battery to adapter.

When the adapter is removed, the IC turns off ACFET and

enters SLEEP mode to turn on p-channel BATFET, connecting

the battery to the system

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