LP3910 Datasheet, PDF (24/72 Pages) Texas Instruments – Power Management IC for Hard-Drive-Based Portable Media Players

LP3910
SNVS481M – NOVEMBER 2006 – REVISED DECEMBER 2015
8 Detailed Description
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8.1 Overview
The LP3910 incorporates 2 low-dropout LDO voltage regulators, 2 integrated buck DC-DC converters with
dynamic voltage scaling (DVS), one wide load range buck-boost DC-DC converter with programmable output
voltage, a 4-channel 8-bit ADC and a dual source Li-ion or Li-polymer battery charger. The charger has the
capability to charge and maintain a single cell battery by seamlessly switching between regulated wall adapter
and USB power sources. The LP3910 also incorporates advanced battery management functions such as battery
temperature measurement, reverse current blocking for USB, LED charger status indication, thermally regulated
internal power FETs, battery-voltage monitoring, overcurrent protection, and a 10-hour safety timer.
The buck-boost DC-DC converter targets the power management of hard disk drives and maintains a typical
operating voltage of 3.3 V ±5% with a battery voltage below or above this output level. The buck- boost output
voltage can be selected to be as low as 1.8 V.
The 4-channel ADC measures the battery voltage and charge current, which can be used for fuel gauging. Two
undedicated channels can be used to measure other analog parameters such as discharge current, battery
temperature, keyboard resistor scanning and more. The various device parameters are programmable through a
400-kHz I²C-compatible interface.
8.1.1 Two Buck Converters
The LP3910 incorporates two high efficiency synchronous switching buck regulators, Buck1 and Buck2 that
deliver a constant voltage from a wall adapter or a single Li-ion battery to the portable system processors,
memory and I/O. Using a voltage mode architecture with synchronous rectification, both bucks have the ability to
deliver up to 600 mA. Buck1 can output voltages from 0.8 V to 2 V while Buck2 can output voltages from 1.8 V to
3.3 V. Additional features include soft-start, undervoltage lockout, current-overload protection, and thermal-
overload protection.
8.1.2 Buck-Boost Converter
The synchronous buck-boost magnetic DC-DC converter supplies power to a hard drive that has a typical 3.3-V
operating voltage. This voltage is lower than the maximum battery (4.2 V typically for Li-polymer cells) and higher
than the minimum battery (typically 2.8 V). Therefore, in order to provide 3.3 V, regardless of the battery voltage,
the buck-boost converter either steps down the battery voltage or steps up the battery voltage. The buck-boost
automatically switches between PWM and PFM modes depending on the load and automatically switches
between buck and boost modes depending on the battery voltage. The buck-boost converter uses an input
voltage from 2.7 V to 5.7 V and generates an output voltage between 1.8 V and 3.3 V for up to 1-A loads.
8.1.3 LDO Regulators
LDO1 is a regulator that can respond to fast transients and is slated for digital loads and high bandwidth analog
loads. LDO2 is a linear regulator with a similar architecture but has a slower transient response time with a lower
noise performance to supply analog loads. Both regulators can supply up to 150-mA loads and have output
voltages that are register programmable through the I²C interface. The LDO1 output voltage is programmable
from 1.2 V to 3.3 V, and the LDO2 output voltage is programmable in steps of 100 mV from 1.3 V to 3.3 V.
8.1.4 Battery Charger
The LP3910 can safely charge and maintain a single-cell Li-ion or Li-polymer battery operating off a regulated 6-
V automotive adapter, an AC wall adapter, or USB power (VBUS). Input power source selection of USB/adapter
is seamless. If present, the charger uses the adapter power regardless of the presence of USB power. The
connection of either power source is detected by LP3910. The charger module is a linear charger with constant
current pre-qualification, constant current (CC) full-rate charging and constant voltage (CV) charging. CC and CV
regulation is performed using an internal power FET Q2 with reverse current blocking. The power FET Q1 acts
as a switch with programmable current limit for USB operation.
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