LP3971 datasheet(17/57 Pages) TI1

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LP3971

www.ti.com

SNVS432U – JANUARY 2006 – REVISED OCTOBER 2008

2C Compatible Serial Interface Electrical Specifications (SDA and SCL)

Unless otherwise noted, VIN = 3.6V. Typical values and limits appearing in normal type apply for TJ = 25°C. Limits appearing

in boldface type apply over the entire junction temperature range for operation,

−40°C to +125°C.

(1) (2) and (3)

Symbol

Parameter

Conditions

Min

Typ

Max

Units

VIL

Low Level Input Voltage

(4)

−0.5

0.3

VRTC

VIH

High Level Input Voltage

(4)

0.7

VRTC

VOL

Low Level Output Voltage

(4)

0.2

VTRC

IOL

Low Level Output Current

VOL = 0.4V

(4)

3.0

FCLK

Clock Frequency

(4)

400

kHz

tBF

Bus-Free Time Between Start and Stop

(4)

1.3

μs

tHOLD

Hold Time Repeated Start Condition

(4)

0.6

μs

tCLKLP

CLK Low Period

(4)

1.3

μs

tCLKHP

CLK High Period

(4)

0.6

μs

tSU

Set Up Time Repeated Start Condition

(4)

0.6

μs

tDATAHLD

Data Hold Time

(4)

μs

tCLKSU

Data Set Up Time

(4)

100

TSU

Set Up Time for Start Condition

(4)

0.6

μs

TTRANS

Maximum Pulse Width of Spikes that Must

(4)

be Suppressed by the Input Filter of Both

DATA & CLK Signals

(1)

All voltages are with respect to the potential at the GND pin.

(2)

All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits

are production tested, guaranteed through statistical analysis or guaranteed by design. All limits at temperature extremes are

guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing

Quality Level (AOQL).

(3)

The I2C signals behave like open-drain outputs and require an external pull-up resistor on the system module in the 2 k

Ω to 20 kΩ

range.

(4)

This electrical specification is guaranteed by design.

BUCK CONVERTER OPERATION

DEVICE INFORMATION

The LP3971 includes three high efficiency step down DC-DC switching buck converters. Using a voltage mode

architecture with synchronous rectification, the buck converters have the ability to deliver up to 1600 mA

depending on the input voltage, output voltage, ambient temperature and the inductor chosen.

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

operates in PWM mode at load currents of approximately 100 mA or higher, having voltage tolerance of ±3%

with 95% efficiency or better. Lighter load currents cause the device to automatically switch into PFM for reduced

current consumption. Shutdown mode turns off the device, offering the lowest current consumption (IQ, SHUTDOWN

= 0.01 µA typ).

Additional features include soft-start, under voltage protection, current overload protection, and thermal shutdown

protection.

The part uses an internal reference voltage of 0.5V. It is recommended to keep the part in shutdown until the

input voltage is 2.7V or higher.

CIRCUIT OPERATION

The buck converter operates as follows. During the first portion of each switching cycle, the control block turns

on the internal PFET switch. This allows current to flow from the input through the inductor to the output filter

capacitor and load. The inductor limits the current to a ramp with a slope of (VIN–VOUT)/L, by storing energy in a

magnetic field.

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