LP3971 Datasheet, PDF (17/57 Pages) National Semiconductor (TI) – POWER MANAGEMENT UNIT FOR ADVANCED APPLICATION PROCESSORS

LP3971
www.ti.com
SNVS432U – JANUARY 2006 – REVISED OCTOBER 2008
I²C Compatible Serial Interface Electrical Specifications (SDA and SCL)
Unless otherwise noted, V_IN = 3.6V. Typical values and limits appearing in normal type apply for T_J = 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
V_IL
V_IH
V_OL
I_OL
F_CLK
t_BF
t_HOLD
t_CLKLP
t_CLKHP
t_SU
t_DATAHLD
t_CLKSU
T_SU
T_TRANS
Parameter
Low Level Input Voltage
High Level Input Voltage
Low Level Output Voltage
Low Level Output Current
Clock Frequency
Bus-Free Time Between Start and Stop
Hold Time Repeated Start Condition
CLK Low Period
CLK High Period
Set Up Time Repeated Start Condition
Data Hold Time
Data Set Up Time
Set Up Time for Start Condition
Maximum Pulse Width of Spikes that Must
be Suppressed by the Input Filter of Both
DATA & CLK Signals
Conditions
(4)
(4)
(4)
V_OL = 0.4V ⁽⁴⁾
(4)
(4)
(4)
(4)
(4)
(4)
(4)
(4)
(4)
(4)
Min
Typ
Max Units
−0.5
0.7
V_RTC
0
3.0
0.3
V
V_RTC
V_RTC
0.2
V_TRC
mA
400
kHz
1.3
μs
0.6
μs
1.3
μs
0.6
μs
0.6
μs
0
μs
100
ns
0.6
μs
50
ns
(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 kΩ 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 (I_{Q, 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 (V_IN–V_OUT)/L, by storing energy in a
magnetic field.
Copyright © 2006–2008, Texas Instruments Incorporated
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