LP3906 datasheet(18/47 Pages) TI

18 / 47 page

VIN

ENLDO

VLDO

GND

Vref

LDO

controlled

LP3906

SNVS456M – AUGUST 2006 – REVISED MAY 2013

www.ti.com

Table 2. SUPPLY SPECIFICATION

Output

Supply

Load

IMAX

VOUT Range(V)

Resolution (mV)

Maximum Output Current (mA)

LDO1

analog

1.0 to 3.5

100

300

LDO2

analog

1.0 to 3.5

100

300

SW1

digital

0.8 to 2.0

1500

SW2

digital

1.0 to 3.5

100

1500

LINEAR LOW DROP-OUT REGULATORS (LDOS)

LDO1 and LDO2 are identical linear regulators targeting analog loads characterized by low noise requirements.

LDO1 and LDO2 are enabled through the ENLDO pin or through the corresponding LDO1 or LDO2 control

programmed during Final Test, which can be tailored to the specific needs of the system designer.

NO-LOAD STABILITY

The LDOs will remain stable and in regulation with no external load. This is an important consideration in some

circuits, for example CMOS RAM keep-alive applications.

LDO1 AND LDO2 CONTROL REGISTERS

LDO1 and LDO2 can be configured by means of the LDO1 and LDO2 control registers. The output voltage is

programmable in steps of 100mV from 1.0V to 3.5V by programming bits D4-0 in the LDO Control registers. Both

LDO1 and LDO2 are enabled by applying a logic 1 to the ENLDO1 and ENLDO2 pin. Enable/disable control is

also provided through enable bit of the LDO1 and LDO2 control registers. The value of the enable LDO bit in the

SW1, SW2: Synchronous Step Down Magnetic DC/DC Converters

FUNCTIONAL DESCRIPTION

The LP3906 incorporates two high efficiency synchronous switching buck regulators, SW1 and SW2 that deliver

a constant voltage from a single Li-Ion battery to the portable system processors. Using a voltage mode

architecture with synchronous rectification, both bucks have the ability to deliver up to 1500mA depending on the

input voltage and output voltage (voltage head room), and the inductor chosen (maximum current capability).

There are three modes of operation depending on the current required - PWM, PFM, and shutdown. PWM mode

handles current loads of approximately 70mA or higher, delivering voltage precision of +/-3% with 90% efficiency

or better. Lighter output current loads cause the device to automatically switch into PFM for reduced current

consumption (IQ = 15 µA typ.) and a longer battery life. The Standby operating mode turns off the device, offering

the lowest current consumption. PWM or PFM mode is selected automatically or PWM mode can be forced

through the setting of the buck control register.

Both SW1 and SW2 can operate up to a 100% duty cycle (PMOS switch always on) for low drop out control of

the output voltage. In this way the output voltage will be controlled down to the lowest possible input voltage.

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