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LP3872
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LP3875
SNVS227H FEBRUARY 2003REVISED JANUARY 2015
LP387x 1.5-A Fast Ultra-Low-Dropout Linear Regulators
1 Features 3 Description
The LP387x series of fast ultra low-dropout linear
1 Input Voltage Range: 2.5 V to 7 V regulators operate from a 2.5-V to 7-V input supply.
Ultra Low-Dropout Voltage Wide range of preset output voltage options are
Low Ground Pin Current available. These ultra low-dropout linear regulators
respond very quickly to step changes in load, which
Load Regulation of 0.06% makes them suitable for low-voltage microprocessor
10-nA Quiescent Current in Shutdown Mode applications. The LP3872 and LP3875 are developed
Ensured Output Current of 1.5-A DC on a CMOS process which allows low quiescent
current operation independent of output load current.
Available in DDPAK/TO-263, TO-220, and This CMOS process also allows the LP3872 and
SOT-223 Packages LP3875 to operate under extremely low dropout
Output Voltage Accuracy ± 1.5% conditions.
ERROR Flag for Output Status Dropout Voltage: Ultra low-dropout voltage; typically
Sense Option Improves Load Regulation 38 mV at 150-mA load current and 380 mV at 1.5-A
Minimum Output Capacitor Requirements load current.
Overtemperature/Overcurrent Protection Ground Pin Current: Typically 6 mA at 1.5-A load
40°C to 125°C Junction Temperature Range current.
Shutdown Mode: Typically 10-nA quiescent current
2 Applications when the SD pin is pulled low.
Microprocessor Power Supplies ERROR Flag: ERROR flag goes low when the output
GTL, GTL+, BTL, and SSTL Bus Terminators voltage drops 10% below nominal value (LP3872
Power Supplies for DSPs only).
SCSI Terminators SENSE: Sense pin improves regulation at remote
Post Regulators loads (LP3875 only).
High Efficiency Linear Regulators Precision Output Voltage: Multiple output voltage
options are available ranging from 1.8 V to 5 V with a
Battery Chargers specified accuracy of ±1.5% at room temperature,
Other Battery-Powered Applications and ±3.0% over all conditions (varying line, load, and
space temperature).
space Device Information(1)
space PART NUMBER PACKAGE BODY SIZE (NOM)
space SOT-223 (5) 6.50 mm × 3.56 mm
space LP3872 TO-263 (5) 10.16 mm × 8.42 mm
LP3872 Typical Application Circuit SOT-223 (5) 6.50 mm × 3.56 mm
LP3875 TO-263 (5) 10.16 mm × 8.42 mm
TO-220 (5) 14.986 mm × 10.16 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
LP3875 Typical Application Circuit
*SD and ERROR pins must be pulled high
through a 10-kpullup resistor. Connect
the ERROR pin to ground if this function is
not used. See the Shutdown Mode and
ERROR Flag Operation sections.
*SD must be pulled high through a 10-k
pullup resistor. See the Shutdown Mode
section.
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
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Table of Contents
7.3 Feature Description................................................... 8
1 Features.................................................................. 17.4 Device Functional Modes.......................................... 9
2 Applications ........................................................... 18 Application and Implementation ........................ 11
3 Description............................................................. 18.1 Application Information............................................ 11
4 Revision History..................................................... 28.2 Typical Application.................................................. 11
5 Pin Configuration and Functions......................... 39 Power Supply Recommendations...................... 16
6 Specifications......................................................... 410 Layout................................................................... 16
6.1 Absolute Maximum Ratings ...................................... 410.1 Layout Guidelines ................................................. 16
6.2 ESD Ratings ............................................................ 410.2 Layout Examples................................................... 17
6.3 Recommended Operating Conditions....................... 411 Device and Documentation Support................. 18
6.4 Thermal Information.................................................. 411.1 Related Links ........................................................ 18
6.5 Electrical Characteristics........................................... 511.2 Trademarks........................................................... 18
6.6 Typical Characteristics.............................................. 611.3 Electrostatic Discharge Caution............................ 18
7 Detailed Description.............................................. 811.4 Glossary................................................................ 18
7.1 Overview................................................................... 812 Mechanical, Packaging, and Orderable
7.2 Functional Block Diagram......................................... 8Information ........................................................... 18
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision G (December 2014) to Revision H Page
Added Input voltage range as first Feature ........................................................................................................................... 1
Added "(LP3872 only)" .......................................................................................................................................................... 1
Added "(LP3875 only)" .......................................................................................................................................................... 1
Changed all VIN and VOUT pin names to IN and OUT in drawings and text........................................................................ 1
Changed footnotes to appear under each table .................................................................................................................... 4
Deleted CDM footnote ........................................................................................................................................................... 4
Deleted last sentence of Short-Circuit Protection subsection ............................................................................................... 9
Changes from Revision F (April 2013) to Revision G Page
Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes,Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section; update
thermal values ....................................................................................................................................................................... 1
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1 2 34
5
SD IN OUT ERROR
/SENSE
GND
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5 Pin Configuration and Functions
5-Pin TO-220 5-Pin DDPAK/TO-263
NDH Package KTT Package
Top View Top View
5-Pin SOT-223
NDC Package
Top View
Pin Functions
PIN
NUMBER I/O DESCRIPTION
LP3872 LP3875
NAME TO-220 TO-220
SOT-223 SOT-223
DDPAK/TO-263 DDPAK/TO-263
SD 1 1 1 1 I Shutdown
IN 2 2 2 2 I Input supply
OUT 4 3 4 3 O Output voltage
ERROR 5 4 O Error flag
SENSE 5 4 I Remote voltage sense
GND 3 5 3 5 Ground
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6 Specifications
6.1 Absolute Maximum Ratings(1)(2)
If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/Distributors for availability
and specifications. MIN MAX UNIT
Lead temperature (soldering, 5 sec.) 260 °C
Power dissipation(3) Internally limited
IN pin to GND pin voltage 0.3 7.5 V
Shutdown (SD) pin to GND pin voltage 0.3 7.5 V
OUT pin to GND pin voltage(4),(5) 0.3 6 V
IOUT Short-circuit protected
ERROR pin to GND pin voltage VIN V
SENSE pin to GND pin voltage VOUT V
Storage temperature, Tstg 65 150 °C
(1) Stresses beyond those listed under Absolute Maximum Ratings(1)(2) may cause permanent damage to the device. These are stress
ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under
Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.
(3) Internal thermal shutdown circuitry protects the device from permanent damage.
(4) If used in a dual-supply system where the regulator load is returned to a negative supply, the output must be diode-clamped to ground.
(5) The output PMOS structure contains a diode between the IN and OUT pins. This diode is normally reverse biased. This diode will get
forward biased if the voltage at the output terminal is forced to be higher than the voltage at the input terminal. This diode can typically
withstand 200 mA of DC current and 1 A of peak current.
6.2 ESD Ratings VALUE UNIT
V(ESD) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions MIN MAX UNIT
VIN supply voltage (1) 2.5 7 V
Shutdown (SD) voltage 0.3 7 V
Maximum operating current (DC) IOUT 1.5 A
Junction temperature –40 125 °C
(1) The minimum operating value for VIN is equal to either [VOUT(NOM) + VDROPOUT] or 2.5 V, whichever is greater.
6.4 Thermal Information LP3872, LP3875 LP3875
THERMAL METRIC(1) NDC (SOT-223) KTT (TO-263) NDH (TO-220) UNIT
5 PINS 5 PINS 5 PINS
RθJA Junction-to-ambient thermal resistance 65.2 40.3 32
RθJC(top) Junction-to-case (top) thermal resistance 47.2 43.4 43.8
RθJB Junction-to-board thermal resistance 9.9 23.1 18.6 °C/W
ψJT Junction-to-top characterization parameter 3.4 11.5 8.8
ψJB Junction-to-board characterization parameter 9.7 22 18
RθJC(bot) Junction-to-case (bottom) thermal resistance n/a 1 1.2
(1) For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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6.5 Electrical Characteristics
Unless otherwise specified: TJ= 25°C, VIN = VO(NOM) + 1 V, IL= 10 mA, COUT = 10 µF, VSD = 2 V.
PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT
Output voltage tolerance (3) VOUT +1 V VIN 7 V, 10 mA IL1.5 A –1.5% 0% 1.5%
VOUT VOUT +1 V VIN 7 V, 10 mA IL1.5 A, –3% 3%
–40°C TJ125°C
Output voltage line regulation (3) VOUT + 1 V VIN 7 V 0.02%
ΔVOL VOUT + 1 V VIN 7 V, –40°C TJ125°C 0.06%
Output voltage load regulation (3) 10 mA IL1.5 A 0.06%
ΔVO/
ΔIOUT 10 mA IL1.5 A, 40°C TJ125°C 0.12%
IL= 150 mA 38 50
IL= 150 mA, –40°C TJ125°C 60
VIN -Dropout voltage (4) mV
VOUT IL= 1.5 A 380 450
IL= 1.5 A, –40°C TJ125°C 550
IL= 150 mA 5 9
IL= 150 mA,–40°C TJ125°C 10
Ground pin current in normal
IGND mA
operation mode IL= 1.5 A 6 14
IL= 1.5 A, –40°C TJ125°C 15
Ground pin current in shutdown VSD 0.3 V 0.01 10 µA
IGND mode –40°C TJ85°C 50
IO(PK) Peak output current VOUT VO(NOM) 4% 1.8 A
SHORT CIRCUIT PROTECTION
ISC Short-circuit current 3.2 A
SHUTDOWN INPUT
Output = High VIN
Output = High, –40°C TJ125°C 2
VSDT Shutdown threshold V
Output = Low 0
Output = Low, –40°C TJ125°C 0.3
TdOFF Turnoff delay IL= 1.5 A 20 µs
TdON Turnon delay IL= 1.5 A 25 µs
ISD SD input current VSD = VIN 1 nA
ERROR FLAG
Threshold See(5) 10%
VTSee(5), –40°C TJ125°C 5% 16%
Threshold hysteresis See(5) 5%
VTH See(5), –40°C TJ125°C 2% 8%
ERROR flag saturation Isink = 100 µA 0.02
VEF(Sat) V
Isink = 100 µA, –40°C TJ125°C 0.1
Td Flag reset delay 1 µs
Ilk ERROR flag pin leakage current 1 nA
Imax ERROR flag pin sink current VError = 0.5 V 1 mA
(1) Limits are specified by testing, design, or statistical correlation.
(2) Typical numbers are at 25°C and represent the most likely parametric norm.
(3) Output voltage line regulation is defined as the change in output voltage from the nominal value due to change in the input line voltage.
Output voltage load regulation is defined as the change in output voltage from the nominal value due to change in load current. The line
and load regulation specification contains only the typical number. However, the limits for line and load regulation are included in the
output voltage tolerance specification.
(4) Dropout voltage is defined as the minimum input to output differential voltage at which the output drops 2% below the nominal value.
Dropout voltage specification applies only to output voltages of 2.5 V and above. For output voltages below 2.5 V, the dropout voltage is
nothing but the input to output differential, because the minimum input voltage is 2.5 V.
(5) ERROR Flag threshold and hysteresis are specified as percentage of regulated output voltage. See ERROR Flag Operation.
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SHUTDOWN IQ (PA)
TEMPERATURE (oC)
-40 -20 0 20 40 60 80 100 125
0.001
0.01
0.1
1
10
ERROR THRESHOLD (% of VOUT)
JUNCTION TEMPERATURE (oC)
-40 -20 0 20 40 60 80 100 125
0
2
4
6
8
10
12
14
1.8 2.3 2.8 3.3 3.8 4.3 5.0
OUTPUT VOLTAGE (V)
0
1
2
3
4
5
6
GROUND PIN CURRENT (mA)
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Electrical Characteristics (continued)
Unless otherwise specified: TJ= 25°C, VIN = VO(NOM) + 1 V, IL= 10 mA, COUT = 10 µF, VSD = 2 V.
PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT
AC PARAMETERS
VIN = VOUT + 1 V, COUT = 10 µF 73
VOUT = 3.3 V, f = 120 Hz
PSRR Ripple rejection dB
VIN = VOUT + 0.5 V, COUT = 10 µF 57
VOUT = 3.3 V, f = 120 Hz
ρn(l/f) Output noise density f = 120 Hz 0.8 µV
BW = 10 Hz 100 kHz, VOUT = 2.5 V 150 µV
enOutput noise voltage (rms)
BW = 300 Hz 300 kH, VOUT = 2.5 V 100
6.6 Typical Characteristics
Unless otherwise specified: TJ= 25°C, COUT = 10 µF, CIN = 10 µF, SD pin is tied to VIN, VOUT = 2.5 V, VIN = VO(NOM) + 1 V, IL=
10 mA
Figure 1. Dropout Voltage vs Output Load Current Figure 2. Ground Current vs Output Voltage
IL= 1.5 A
Figure 4. Errorflag Threshold vs Junction Temperature
Figure 3. Shutdown IQvs Junction Temperature
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FREQUENCY (Hz)
0.000
0.500
1.000
1.500
2.000
2.500
3.000
100 1k 10k 100k
IL = 100mA
CIN = COUT = 10PF
NOISE (PV/ Hz
(
-40 -20 0 20 40 60 80 100 125
JUNCTION TEMPERATURE (oC)
0
0.5
1
1.5
2
2.5
3
DC LOAD REGULATION (mV/A)
-40 -20 0 20 40 60 80 100 125
JUNCTION TEMPERATURE (oC)
0
0.5
1
1.5
2
2.5
3
' VOUT/VOLT CHANGE in VIN (mV)
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Typical Characteristics (continued)
Unless otherwise specified: TJ= 25°C, COUT = 10 µF, CIN = 10 µF, SD pin is tied to VIN, VOUT = 2.5 V, VIN = VO(NOM) + 1 V, IL=
10 mA
Figure 5. DC Load Reg. vs Junction Temperature Figure 6. DC Line Regulation vs Temperature
Figure 7. Noise vs Frequency
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7 Detailed Description
7.1 Overview
The LP387x linear regulators are designed to provide an ultra-low-dropout voltage with excellent transient
response and load/line regulation. For battery-powered always-on type applications, the very low quiescent
current of LP387x in shutdown mode helps reduce battery drain. For applications where load is not placed close
to the regulator, LP3875 incorporates a voltage sense circuit to improve voltage regulation at the point of load.
ERROR output pin of LP3872 can be used in the system to flag a low-voltage condition.
7.2 Functional Block Diagram
Figure 8. LP3872
Figure 9. LP3875
7.3 Feature Description
7.3.1 Shutdown (SD)
The LM387x devices have a shutdown feature that turns the device off and reduces the quiescent current to 10
nA, typical.
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Feature Description (continued)
7.3.2 Load Voltage Sense
In applications where the regulator output is not very close to the load, LP3875 can provide better remote load
regulation using the SENSE pin. Figure 10 depicts the advantage of the SENSE option. LP3872 regulates the
voltage at the OUT pin. Hence, the voltage at the remote load will be the regulator output voltage minus the drop
across the trace resistance. For example, in the case of a 3.3-V output, if the trace resistance is 100 m, the
voltage at the remote load will be 3.15 V with 1.5 A of load current, ILOAD. The LP3875 regulates the voltage at
the sense pin. Connecting the sense pin to the remote load will provide regulation at the remote load, as shown
in Figure 10. If the sense option pin is not required, the SENSE pin must be connected to the OUT pin.
Figure 10. Improving Remote Load Regulation Using LP3875
7.3.3 Short-Circuit Protection
The LP3872 and LP3875 devices are short-circuit protected and in the event of a peak overcurrent condition, the
short-circuit control loop will rapidly drive the output PMOS pass element off. Once the power pass element shuts
down, the control loop will rapidly cycle the output on and off until the average power dissipation causes the
thermal shutdown circuit to respond to servo the on/off cycling to a lower frequency.
7.3.4 Low Dropout Voltage
The LP387x devices feature an ultra-low-dropout voltage, typically 38 mV at 150-mA load current and 380 mV at
1.5-A load current.
7.4 Device Functional Modes
7.4.1 Shutdown Mode
A CMOS Logic low level signal at the shutdown (SD) pin will turn off the regulator. The SD pin must be actively
terminated through a 10-kpullup resistor for a proper operation. If this pin is driven from a source that actively
pulls high and low (such as a CMOS rail to rail comparator), the pullup resistor is not required. This pin must be
tied to VIN if not used.
7.4.2 Active Mode
When voltage at SD pin of the LP387x device is at logic high level, the device is in normal mode of operation.
7.4.3 ERROR Flag Operation
The LP3872 and LP3875 produces a logic low signal at the ERROR Flag pin when the output drops out of
regulation due to low input voltage, current limiting, or thermal limiting. This flag has a built-in hysteresis. The
timing diagram in Figure 11 shows the relationship between the ERROR flag and the output voltage. In this
example, the input voltage is changed to demonstrate the functionality of the ERROR Flag.
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Device Functional Modes (continued)
The internal ERROR flag comparator has an open-drain output stage. Hence, the ERROR pin should be pulled
high through a pullup resistor. Although the ERROR flag pin can sink current of 1 mA, this current is energy drain
from the input supply. Hence, the value of the pullup resistor should be in the range of 10 kto 1 M.The
ERROR pin must be connected to ground if this function is not used. It should also be noted that when the SD
pin is pulled low, the ERROR pin is forced to be invalid for reasons of saving power in shutdown mode.
Figure 11. ERROR Flag Operation
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LP387x devices are linear regulators designed to provide high load current of up to 1.5 A, low dropout
voltage, and low quiescent current in shutdown mode. Figure 12 and Figure 13 show the typical application
circuit for these devices.
8.1.1 Dropout Voltage
The dropout voltage of a regulator is defined as the minimum input-to-output differential required to stay within
2% of the nominal output voltage. For CMOS LDOs, the dropout voltage is the product of the load current and
the Rds(on) of the internal MOSFET.
8.1.2 Reverse Current Path
The internal MOSFET in LP3872 and LP3875 has an inherent parasitic diode. During normal operation, the input
voltage is higher than the output voltage and the parasitic diode is reverse biased. However, if the output is
pulled above the input in an application, then current flows from the output to the input as the parasitic diode gets
forward biased. The output can be pulled above the input as long as the current in the parasitic diode is limited to
200-mA continuous and 1-A peak.
8.2 Typical Application
*SD and ERROR pins must be pulled high through a 10-kpullup resistor. Connect the ERROR pin to ground if this
function is not used. See the Shutdown Mode and ERROR Flag Operation sections.
Figure 12. LP3872 Typical Application Circuit
*SD must be pulled high through a 10-kpullup resistor. See the Shutdown Mode section.
Figure 13. LP3875 Typical Application Circuit
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Typical Application (continued)
8.2.1 Design Requirements
Table 1. Design Parameters
DESIGN PARAMETER EXAMPLE VALUE
Input voltage range 2.5 V to 7 V
Output voltage 1.8 V
Output current 1.5 A
Output capacitor 10 µF
Input capacitor 10 µF
Output capacitor ESR range 100 mΩto 4 Ω
8.2.2 Detailed Design Procedure
8.2.2.1 Power Dissipation and Device Operation
The permissible power dissipation for any package is a measure of the capability of the device to pass heat from
the power source, the junctions of the IC, to the ultimate heat sink, the ambient environment. Thus, the power
dissipation depends on the ambient temperature and the thermal resistance across the various interfaces
between the die junction and ambient air.
The maximum allowable power dissipation for the device in a given package can be calculated using Equation 1:
PD-MAX = ((TJ-MAX TA) / RθJA) (1)
The actual power being dissipated in the device can be represented by Equation 2:
PD= (VIN VOUT)×IOUT (2)
Equation 1 and Equation 2 establish the relationship between the maximum power dissipation allowed due to
thermal consideration, the voltage drop across the device, and the continuous current capability of the device.
These two equations should be used to determine the optimum operating conditions for the device in the
application.
In applications where lower power dissipation (PD) and/or excellent package thermal resistance (RθJA) is present,
the maximum ambient temperature (TA-MAX) may be increased.
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum
ambient temperature (TA-MAX) may have to be derated. TA-MAX is dependent on the maximum operating junction
temperature (TJ-MAX-OP = 125°C), the maximum allowable power dissipation in the device package in the
application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (RθJA),
as given by Equation 3:
TA-MAX = (TJ-MAX-OP (RθJA × PD-MAX)) (3)
Alternately, if TA-MAX can not be derated, the PDvalue must be reduced. This can be accomplished by reducing
VIN in the VIN VOUT term as long as the minimum VIN is met, or by reducing the IOUT term, or by some
combination of the two.
8.2.2.2 External Capacitors
Like any low-dropout regulator, external capacitors are required to assure stability. These capacitors must be
correctly selected for proper performance.
Input Capacitor: An input capacitor of at least 10 µF is required. Ceramic, tantalum, or Electrolytic capacitors
may be used, and capacitance may be increased without limit.
Output Capacitor: An output capacitor is required for loop stability. It must be located less than 1 cm from the
device and connected directly to the output and ground pins using traces which have no other currents
flowing through them (see Layout section).
The minimum value of output capacitance that can be used for stable full-load operation is 10 µF, but it may be
increased without limit. The output capacitor must have an equivalent series resistance (ESR) value as shown in
Figure 14. Tantalum capacitors are recommended for the output capacitor.
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COUT ESR (:)
LOAD CURRENT (A)
STABLE REGION
COUT > 10 PF
012
.001
.01
0.1
1.0
10
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Figure 14. ESR Curve
8.2.2.3 Selecting a Capacitor
Capacitance tolerance and variation with temperature must be considered when selecting a capacitor so that the
minimum required amount of capacitance is provided over the full operating temperature range. In general, a
good tantalum capacitor will show very little capacitance variation with temperature, but a ceramic may not be as
good (depending on dielectric type). Aluminum electrolytics also typically have large temperature variation of
capacitance value.
Equally important to consider is how ESR of a capacitor changes with temperature: this is not an issue with
ceramics, as their ESR is extremely low. However, it is very important in tantalum and aluminum electrolytic
capacitors. Both show increasing ESR at colder temperatures, but the increase in aluminum electrolytic
capacitors is so severe they may not be feasible for some applications (see Capacitor Characteristics).
8.2.2.4 Capacitor Characteristics
8.2.2.4.1 Ceramic
For values of capacitance in the 10-µF to 100-µF range, ceramics are usually larger and more costly than
tantalums but give superior AC performance for bypassing high frequency noise because of very low ESR
(typically less than 10 m). However, some dielectric types do not have good capacitance characteristics as a
function of voltage and temperature.
Z5U and Y5V dielectric ceramics have capacitance that drops severely with applied voltage. A typical Z5U or
Y5V capacitor can lose 60% of its rated capacitance with half of the rated voltage applied to it. The Z5U and Y5V
also exhibit a severe temperature effect, losing more than 50% of nominal capacitance at high and low limits of
the temperature range.
X7R and X5R dielectric ceramic capacitors are strongly recommended if ceramics are used, as they typically
maintain a capacitance range within ±20% of nominal over full operating ratings of temperature and voltage. Of
course, they are typically larger and more costly than Z5U/Y5U types for a given voltage and capacitance.
8.2.2.4.2 Tantalum
Solid tantalum capacitors are recommended for use on the output because their typical ESR is very close to the
ideal value required for loop compensation. They also work well as input capacitors if selected to meet the ESR
requirements previously listed.
Tantalums also have good temperature stability: a good quality tantalum will typically show a capacitance value
that varies less than 10-15% across the full temperature range of 40°C to 125°C. ESR will vary only about 2X
going from the high to low temperature limits.
The increasing ESR at lower temperatures can cause oscillations when marginal quality capacitors are used (if
the ESR of the capacitor is near the upper limit of the stability range at room temperature).
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8.2.2.4.3 Aluminum
This capacitor type offers the most capacitance for the money. The disadvantages are that they are larger in
physical size, not widely available in surface mount, and have poor AC performance (especially at higher
frequencies) due to higher ESR and equivalent series inductance (ESL).
Compared by size, the ESR of an aluminum electrolytic is higher than either tantalum or ceramic, and it also
varies greatly with temperature. A typical aluminum electrolytic can exhibit an ESR increase of as much as 50X
when going from 25°C down to 40°C.
It should also be noted that many aluminum electrolytics only specify impedance at a frequency of 120 Hz, which
indicates they have poor high-frequency performance. Only aluminum electrolytics that have an impedance
specified at a higher frequency (from 20 kHz to 100 kHz) should be used for the LP387x. Derating must be
applied to the manufacturer's ESR specification, because it is typically only valid at room temperature.
Any applications using aluminum electrolytics should be thoroughly tested at the lowest ambient operating
temperature where ESR is maximum.
8.2.2.5 Turnon Characteristics for Output Voltages Programmed to 2 V or Less
As VIN increases during start-up, the regulator output will track the input until Vin reaches the minimum operating
voltage (typically about 2.2 V). For output voltages programmed to 2 V or less, the regulator output may
momentarily exceed its programmed output voltage during start-up. Outputs programmed to voltages above 2 V
are not affected by this behavior.
8.2.2.6 RFI/EMI Susceptibility
Radio frequency interference (RFI) and electromagnetic interference (EMI) can degrade the performance of any
IC because of the small dimensions of the geometries inside the device. In applications where circuit sources are
present which generate signals with significant high frequency energy content (> 1 MHz), care must be taken to
ensure that this does not affect the IC regulator.
If RFI/EMI noise is present on the input side of the regulator (such as applications where the input source comes
from the output of a switching regulator), good ceramic bypass capacitors must be used at the input pin of the IC.
If a load is connected to the IC output which switches at high speed (such as a clock), the high-frequency current
pulses required by the load must be supplied by the capacitors on the IC output. Because the bandwidth of the
regulator loop is less than 100 kHz, the control circuitry cannot respond to load changes above that frequency.
This means the effective output impedance of the IC at frequencies above 100 kHz is determined only by the
output capacitors.
In applications where the load is switching at high speed, the output of the IC may need RF isolation from the
load. It is recommended that some inductance be placed between the output capacitor and the load, and good
RF bypass capacitors be placed directly across the load.
PCB layout is also critical in high noise environments, because RFI/EMI is easily radiated directly into PC traces.
Noisy circuitry should be isolated from "clean" circuits where possible, and grounded through a separate path. At
MHz frequencies, ground planes begin to look inductive and RFI/EMI can cause ground bounce across the
ground plane.
In multilayer PCB applications, care should be taken in layout so that noisy power and ground planes do not
radiate directly into adjacent layers which carry analog power and ground.
8.2.2.7 Output Noise
Noise is specified in two ways:
Spot Noise (or Output Noise Density): the RMS sum of all noise sources, measured at the regulator output, at
a specific frequency (measured with a 1-Hz bandwidth). This type of noise is usually plotted on a curve as a
function of frequency.
Total Output Noise (or Broad-Band Noise): the RMS sum of spot noise over a specified bandwidth, usually
several decades of frequencies.
Attention should be paid to the units of measurement. Spot noise is measured in units µV/Hz or nV/Hz and
total output noise is measured in µV(rms).
14 Submit Documentation Feedback Copyright © 2003–2015, Texas Instruments Incorporated
Product Folder Links: LP3872 LP3875
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (50Ps/DIV)
MAGNITUDE
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (50Ps/DIV)
MAGNITUDE
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (50Ps/DIV)
MAGNITUDE
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (50Ps/DIV)
MAGNITUDE
VOUT
100mV/DIV
ILOAD
1A/DIV
TIME (50Ps/DIV)
MAGNITUDE
LP3872
,
LP3875
www.ti.com
SNVS227H FEBRUARY 2003REVISED JANUARY 2015
The primary source of noise in low-dropout regulators is the internal reference. In CMOS regulators, noise has a
low frequency component and a high frequency component, which depend strongly on the silicon area and
quiescent current. Noise can be reduced in two ways: by increasing the transistor area or by increasing the
current drawn by the internal reference. Increasing the area will decrease the chance of fitting the die into a
smaller package. Increasing the current drawn by the internal reference increases the total supply current
(ground pin current). Using an optimized trade-off of ground pin current and die size, LP3872 and LP3875
achieves low noise performance and low quiescent current operation.
The total output noise specification for LP3872 and LP3875 is presented in Electrical Characteristics. The Output
noise density at different frequencies is represented by a curve under typical performance characteristics.
8.2.3 Application Curves
CIN = COUT = 100 µF, OSCON
CIN = COUT = 10 µF, OSCON Figure 16. Load Transient Response
Figure 15. Load Transient Response
CIN = COUT = 100 µF, POSCAP CIN = COUT = 10 µF, Tantalum
Figure 17. Load Transient Response Figure 18. Load Transient Response
CIN = COUT = 100 µF, Tantalum Figure 19. Load Transient Response
Copyright © 2003–2015, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Links: LP3872 LP3875
LP3872
,
LP3875
SNVS227H FEBRUARY 2003REVISED JANUARY 2015
www.ti.com
9 Power Supply Recommendations
The LP397x devices are designed to operate from an input supply voltage range of 2.5 V to 7 V. The input
supply should be well regulated and free of spurious noise. To ensure that the LP387x output voltage is well
regulated, the input supply should be at least VOUT + 0.5 V, or 2.5 V, whichever is higher. A minimum capacitor
value of 10 μF is required to be within 1 cm of the IN pin.
10 Layout
10.1 Layout Guidelines
Good PC layout practices must be used or instability can be induced because of ground loops and voltage drops.
The input and output capacitors must be directly connected to the input, output, and ground pins of the regulator
using traces which do not have other currents flowing in them (Kelvin connect).
The best way to do this is to lay out CIN and COUT near the device with short traces to the IN, OUT, and GND
pins. The regulator ground pin should be connected to the external circuit ground so that the regulator and its
capacitors have a single-point ground.
It should be noted that stability problems have been seen in applications where vias to an internal ground plane
were used at the ground points of the IC and the input and output capacitors. This was caused by varying ground
potentials at these nodes resulting from current flowing through the ground plane. Using a single-point ground
technique for the regulator and it's capacitors fixed the problem.
Because high current flows through the traces going into VIN and coming from VOUT, Kelvin connect the capacitor
leads to these pins so there is no voltage drop in series with the input and output capacitors.
16 Submit Documentation Feedback Copyright © 2003–2015, Texas Instruments Incorporated
Product Folder Links: LP3872 LP3875
CIN
VOUT
VIN IN
OUT
ERROR/SENSE
GND
COUT
SD
SD
IN
GND
OUT
ERROR/SENSE
VIN
VOUT
COUT
CIN
Layout Example for SOT-223 Package
Layout Example for TO-263 Package
LP3872
,
LP3875
www.ti.com
SNVS227H FEBRUARY 2003REVISED JANUARY 2015
10.2 Layout Examples
Copyright © 2003–2015, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: LP3872 LP3875
LP3872
,
LP3875
SNVS227H FEBRUARY 2003REVISED JANUARY 2015
www.ti.com
11 Device and Documentation Support
11.1 Related Links
Table 2 below lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 2. Related Links
TECHNICAL TOOLS & SUPPORT &
PARTS PRODUCT FOLDER SAMPLE & BUY DOCUMENTS SOFTWARE COMMUNITY
LP3872 Click here Click here Click here Click here Click here
LP3875 Click here Click here Click here Click here Click here
11.2 Trademarks
All trademarks are the property of their respective owners.
11.3 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.4 Glossary
SLYZ022 TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
18 Submit Documentation Feedback Copyright © 2003–2015, Texas Instruments Incorporated
Product Folder Links: LP3872 LP3875
PACKAGE OPTION ADDENDUM
www.ti.com 14-Oct-2017
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LP3872EMP-1.8/NOPB ACTIVE SOT-223 NDC 5 1000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LHAB
LP3872EMP-2.5/NOPB ACTIVE SOT-223 NDC 5 1000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LHBB
LP3872EMP-3.3/NOPB ACTIVE SOT-223 NDC 5 1000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LHCB
LP3872EMP-5.0 NRND SOT-223 NDC 5 1000 TBD Call TI Call TI -40 to 125 LHDB
LP3872EMP-5.0/NOPB ACTIVE SOT-223 NDC 5 1000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LHDB
LP3872EMPX-2.5/NOPB ACTIVE SOT-223 NDC 5 2000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LHBB
LP3872EMPX-3.3/NOPB ACTIVE SOT-223 NDC 5 2000 Green (RoHS
& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LHCB
LP3872ES-1.8 NRND DDPAK/
TO-263 KTT 5 45 TBD Call TI Call TI -40 to 125 LP3872ES
-1.8
LP3872ES-1.8/NOPB ACTIVE DDPAK/
TO-263 KTT 5 45 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP3872ES
-1.8
LP3872ES-2.5 NRND DDPAK/
TO-263 KTT 5 45 TBD Call TI Call TI -40 to 125 LP3872ES
-2.5
LP3872ES-2.5/NOPB ACTIVE DDPAK/
TO-263 KTT 5 45 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP3872ES
-2.5
LP3872ES-3.3/NOPB ACTIVE DDPAK/
TO-263 KTT 5 45 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP3872ES
-3.3
LP3872ES-5.0 NRND DDPAK/
TO-263 KTT 5 45 TBD Call TI Call TI -40 to 125 LP3872ES
-5.0
LP3872ES-5.0/NOPB ACTIVE DDPAK/
TO-263 KTT 5 45 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP3872ES
-5.0
LP3872ESX-1.8/NOPB ACTIVE DDPAK/
TO-263 KTT 5 500 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP3872ES
-1.8
LP3872ESX-2.5/NOPB ACTIVE DDPAK/
TO-263 KTT 5 500 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP3872ES
-2.5
LP3872ESX-3.3/NOPB ACTIVE DDPAK/
TO-263 KTT 5 500 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP3872ES
-3.3