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LP3878-ADJ
SNVS311D – MAY 2005 – REVISED FEBRUARY 2015
LP3878-ADJ Micropower 800-mA Low-Noise "Ceramic Stable" Adjustable Voltage
Regulator for 1-V to 5-V Applications
1 Features
3 Description
•
•
•
The LP3878-ADJ is an 800-mA, adjustable output,
voltage regulator designed to provide high
performance and low noise in applications requiring
output voltages as low as 1 V.
1
•
•
•
•
•
•
Input Supply Voltage: 2.5 V to 16V
Output Voltage Range: 1 V to 5.5 V
Designed for Use With Low-ESR Ceramic
Capacitors
Very Low Output Noise
8-Lead SO PowerPAD™ and WSON SurfaceMount Packages
< 10-μA Quiescent Current in Shutdown
Low Ground Pin Current at all Loads
Overtemperature and Overcurrent Protection
–40°C to 125°C Operating Junction Temperature
Range
2 Applications
•
•
•
•
Using an optimized VIP (Vertically Integrated PNP)
process,
the
LP3878-ADJ
delivers
superior
performance:
• Ground Pin Current: Typically 5.5 mA at 800-mA
load, and 180 µA at 100-µA load.
• Low Power Shutdown: The LP3878-ADJ draws
less than 10-μA quiescent current when the
SHUTDOWN pin is pulled low.
• Precision Output: Ensured output voltage
accuracy is 1% at room temperature.
• Low Noise: Broadband output noise is only 18 μV
(typical) with a 10-nF bypass capacitor.
ASIC Power Supplies In:
– Desktops, Notebooks, and Graphic Cards
– Set Top Boxes, Printers, and Copiers
DSP and FPGA Power Supplies
SMPS Post-Regulator
Medical Instrumentation
Device Information(1)
PART NUMBER
PACKAGE
LP3878-ADJ
BODY SIZE (NOM)
SO PowerPAD (8)
4.89 mm × 3.90 mm
WSON (8)
4.00 mm × 4.00 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Basic Application Circuit
VIN
IN
R1
LP3878-ADJ
**S/D
*4.7 µF
(Ceramic or
Tantalum
recommended)
VOUT
OUT
S/D
ADJ
BYPASS
*0.01 µF
CFF
*10 µF
(Ceramic
recommended)
GND
R2
*Capacitor values shown are minimum required to assure stability. A larger output capacitor provides improved
dynamic response. Output capacitor must meet ESR requirements (see Application Information).
**The SHUTDOWN (or S/D) pin must be actively terminated (see Device Functional Modes). Tie to IN (pin 4) if not
used.
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.
LP3878-ADJ
SNVS311D – MAY 2005 – REVISED FEBRUARY 2015
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
4
4
4
4
5
6
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Typical Characteristics ..............................................
Detailed Description ............................................ 11
7.1 Overview ................................................................. 11
7.2 Functional Block Diagram ....................................... 11
7.3 Feature Description................................................. 11
7.4 Device Functional Modes........................................ 12
8
Application and Implementation ........................ 13
8.1 Application Information............................................ 13
8.2 Typical Application ................................................. 13
9 Power Supply Recommendations...................... 17
10 Layout................................................................... 17
10.1 Layout Guidelines ................................................. 17
10.2 Layout Example .................................................... 17
10.3 Power Dissipation ................................................. 17
11 Device and Documentation Support ................. 18
11.1
11.2
11.3
11.4
Documentation Support ........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
18
18
18
18
12 Mechanical, Packaging, and Orderable
Information ........................................................... 18
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision C (December 2014) to Revision D
Page
•
Deleted trademark symbol from VIP - no longer trademark; add reference design icon to Top Navigators.......................... 1
•
Deleted soldering info - now in POA ..................................................................................................................................... 4
•
Changed wording of footnote 5 to Ab Max Ratings ............................................................................................................... 4
•
Changed IOUT to IOUT throughout document............................................................................................................................ 5
•
Changed wording of Reverse Input-Output Voltage ............................................................................................................ 11
•
Changed outpin pin to OUT pin ........................................................................................................................................... 15
•
Added new paragraph to Noise Bypass Capacitor subsection ........................................................................................... 15
Changes from Revision B (April 2013) to Revision C
•
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
Changes from Revision A (April 2013) to Revision B
•
2
Page
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 16
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SNVS311D – MAY 2005 – REVISED FEBRUARY 2015
5 Pin Configuration and Functions
SO PowerPAD (DDA) Package
8-Pin
Top View
BYPASS 1
8 SHUTDOWN
N/C 2
7 N/C
Thermal
Pad
GROUND 3
6 ADJ
IN 4
5 OUT
BYPASS
1
N/C
2
GROUND
3
IN
4
Thermal Pad
WSON (NGT) Package
8-Pin
Top View
8
SHUTDOWN
7
N/C
6
ADJ
5
OUT
Pin Functions
PIN
NAME
NUMBER
I/O
DESCRIPTION
ADJ
6
I
Provides feedback to error amplifier from the resistive divider that sets the output voltage.
BYPASS
1
—
The capacitor connected between BYPASS and GROUND lowers output noise voltage level
and is required for loop stability.
GROUND
3
—
Device ground.
IN
4
I
Input source voltage.
N/C
2
DO NOT CONNECT. Device pin 2 is reserved for post packaging test and calibration of the
LP3878-ADJ VADJ accuracy. This pin must be left floating. Do not connect to any potential.
Do not connect to ground. Any attempt to do pin continuity testing on device pin 2 is
discouraged. Continuity test results will be variable depending on the actions of the factory
calibration. Aggressive pin continuity testing (high voltage, or high current) on device pin 2
may activate the trim circuitry forcing VADJ to move out of tolerance.
N/C
7
No internal connection.
OUT
5
O
Regulated output voltage.
SHUTDOWN
8
I
Output is enabled above turnon threshold voltage. Pull down to turn off regulator output.
Thermal Pad
—
—
The exposed thermal pad on the bottom of the package should be connected to a copper
thermal pad on the PCB under the package. The use of thermal vias to remove heat from
the package into the PCB is recommended. Connect the thermal pad to ground potential or
leave floating. Do not connect the thermal pad to any potential other than the same ground
potential seen at device pin 3. For additional information on using TI's Non Pull Back WSON
package, see Application Note AN-1187, SNOA401.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1) (2)
MIN
SHUTDOWN pin
Power dissipation
(3)
MAX
UNIT
1
kV
Internally Limited
Input supply voltage (survival), VIN
−0.3
16
V
ADJ pin
−0.3
6
V
−0.3
6
V
Output voltage (survival), VOUT
(4)
IOUT (survival)
Short-Circuit Protected
Input – output voltage (survival), VIN – VOUT (5)
−0.3
16
V
Storage temperature, Tstg
–65
150
°C
(1)
(2)
(3)
(4)
(5)
Stresses beyond those listed under Absolute Maximum Ratings 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.
If Military- or Aerospace-specified devices are required, please contact the TI Sales Office/Distributors for availability and specifications.
The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal
resistance, RθJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated
using: P(MAX) = (TJ(MAX) – TA) / RθJA. The value of RθJA for the WSON (NGT) and SO PowerPAD (DDA) packages are specifically
dependent on PCB trace area, trace material, and the number of layers and thermal vias. For improved thermal resistance and power
dissipation for the WSON package, see Application Note AN-1187, SNOA401. Exceeding the maximum allowable power dissipation will
cause excessive die temperature, and the regulator will go into thermal shutdown.
If used in a dual-supply system where the regulator load is returned to a negative supply, the LP3878-ADJ output must be diodeclamped to ground.
The PNP pass element contains a parasitic diode between the IN pin and the OUT pin that is normally reverse-biased. Forcing the OUT
pin voltage above the IN pin voltage will turn on this diode and may induce a latch-up mode which can damage the part (see Application
and Implementation).
6.2 ESD Ratings
V(ESD)
(1)
Electrostatic discharge
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins
(1)
VALUE
UNIT
±2000
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
2.5
16
UNIT
VIN
Supply input voltage
VSD
SHUTDOWN input voltage
VIN
V
IOUT
Output current
800
mA
TJ
Operating junction temperature
125
°C
−40
V
6.4 Thermal Information
LP3878-ADJ
THERMAL METRIC (1)
DDA
NGT
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
42.5
38.1
RθJC(top)
Junction-to-case (top) thermal resistance
54.0
27.9
RθJB
Junction-to-board thermal resistance
26.5
15.2
ψJT
Junction-to-top characterization parameter
8.0
0.2
ψJB
Junction-to-board characterization parameter
26.4
15.3
RθJC(bot)
Junction-to-case (bottom) thermal resistance
3.6
4.5
(1)
4
°C/W
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
Limits are specified through design, testing, or correlation. The limits are used to calculate TI's Average Outgoing Quality
Level (AOQL). Unless otherwise specified: TJ = 25°C, VIN = 3 V, VOUT = 1 V, IOUT = 1 mA, COUT = 10 µF, CIN = 4.7 µF, VSD = 2
VVSD, CBYPASS = 10 nF.
PARAMETER
VADJ
ΔVOUT/ΔVIN
TEST CONDITIONS
Adjust pin voltage
Output voltage line regulation
MIN
TYP
MAX
0.99
1.00
1.01
1 mA ≤ IOUT ≤ 800 mA, 3 V ≤ VIN ≤ 6 V
0.98
1.00
1.02
1 mA ≤ IOUT ≤ 800 mA, 3 V ≤ VIN ≤ 6 V
–40°C ≤ TJ ≤ 125°C
0.97
3 V ≤ VIN ≤ 16 V
0.007
VIN(MIN)
3.1
IOUT = 800 mA, VOUT ≥ VOUT(NOM) – 1%
0 ≤ TJ ≤ 125°C
2.5
V
IOUT = 800 mA, VOUT ≥ VOUT(NOM) – 1%
0 ≤ TJ ≤ 125°C, –40°C ≤ TJ ≤ 125°C
2.8
2.5
IOUT = 750 mA, VOUT ≥ VOUT(NOM) – 1%
–40°C ≤ TJ ≤ 125°C
3.0
IOUT = 100 µA
1
2
150
200
IOUT = 100 µA, –40°C ≤ TJ ≤ 125°C
VDOUT
Dropout voltage
VOUT = 3.8 V
3
IOUT = 200 mA
IOUT = 200 mA, –40°C ≤ TJ ≤ 125°C
475
IOUT = 800 mA, –40°C ≤ TJ ≤ 125°C
600
1100
IOUT = 100 µA
180
IOUT = 100 µA, –40°C ≤ TJ ≤ 125°C
Ground pin current
mV
300
IOUT = 800 mA
IGND
%/V
2.5
IOUT = 750 mA, VOUT ≥ VOUT(NOM) – 1%
(1)
0.014
0.032
IOUT = 800 mA, VOUT ≥ VOUT(NOM) – 1%
–40°C ≤ TJ ≤ 125°C
Minimum input voltage
required to maintain output
regulation
V
1.03
3 V ≤ VIN ≤ 16 V, –40°C ≤ TJ ≤ 125°C
IOUT = 800 mA, VOUT ≥ VOUT(NOM) – 1%
UNIT
200
µA
225
IOUT = 200 mA
1.5
IOUT = 200 mA, –40°C ≤ TJ ≤ 125°C
2
3.5
IOUT = 800 mA
5.5
IOUT = 800 mA, –40°C ≤ TJ ≤ 125°C
mA
8.5
15
IOUT(PK)
Peak output current
VOUT ≥ VOUT(NOM) − 5%
1200
IOUT(MAX)
Short-circuit current
RL = 0 Ω (steady state)
1300
en
Output noise voltage (RMS)
Bandwidth = 100 Hz to 100 kHz, CBYPASS = 10
nF
18
µV(RMS)
ΔVOUT/ΔVIN
Ripple rejection
f = 1 kHz
60
dB
IADJ
ADJ pin bias current
(sourcing)
IOUT = 800 mA
200
nA
VH = Output ON
1.4
mA
SHUTDOWN Input
VH = Output ON, –40°C ≤ TJ ≤ 125°C
VSD
SHUTDOWN input voltage
1.6
VL = Output OFF, IIN ≤ 10 µA
VL = Output OFF, IIN ≤ 10 µA
–40°C ≤ TJ ≤ 125°C
0.20
VOUT ≤ 10 mV, IIN ≤ 50 µA
0.6
VSD = 0 V
ISD
SHUTDOWN input current
0.02
VSD = 0 V, –40°C ≤ TJ ≤ 125°C
−1
VSD = 5 V
5
VSD = 5 V, –40°C ≤ TJ ≤ 125°C
(1)
V
0.04
µA
15
Dropout voltage specification applies only if VIN is sufficient so that it does not limit regulator operation.
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6.6 Typical Characteristics
Unless otherwise specified: VIN = 3.3 V, VOUT = 1 V, IOUT = 1 mA, CIN = 4.7 µF, COUT = 10 µF, VSD = 2 V, CBYP = 10 nF, TJ =
25°C.
10.0
9.0
8.0
IGND (mA)
7.0
IL = 800 mA
6.0
5.0
4.0
3.0
IL = 240 mA
2.0
1.0
IL = 1 mA
0
-60 -40 -20 0 20 40 60 80 100 120 140
TEMPERATURE (°C)
Figure 2. Minimum VIN Over Temperature
Figure 1. IGND vs Temperature
1.020
1.015
VOUT (V)
1.010
1.005
1.000
0.995
0.990
0.985
0.980
-50
-25
0
25
50
75
100
125
o
TEMPERATURE ( C)
Figure 3. IGND vs ILoad
Figure 4. VOUT vs Temperature
4.5
4.0
TJ = 125oC
TJ = 0°C
4.0
3.5
IL = 800 mA
400 mA
IL = 400 mA
3.5
800 mA
VIN (V)
VIN (V)
3.0
2.5
3.0
2.5
2.0
2.0
100 mA
IL = 100 mA
1.5
1.0
1.0
1,5
1.5
2.0
2.5
3.0
3.5
1.0
1.0
2.0
2.5
3.0
3.5
VOUT (V)
VOUT (V)
Figure 5. Minimum VIN vs VOUT
6
1.5
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Figure 6. Minimum VIN vs VOUT
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Typical Characteristics (continued)
Unless otherwise specified: VIN = 3.3 V, VOUT = 1 V, IOUT = 1 mA, CIN = 4.7 µF, COUT = 10 µF, VSD = 2 V, CBYP = 10 nF, TJ =
25°C.
4.0
100
TJ = -40°C
90
IL = 400 mA
3.5
80
RIPPLE REJECTION (dB)
IL = 800 mA
VIN (V)
3.0
2.5
2.0
IL = 100 mA
70
60
50
40
30
20
1.5
10
1.0
1.0
1.5
2.0
2.5
3.0
3.5
0
10
VOUT (V)
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 7. Minimum VIN vs VOUT
Figure 8. Ripple Rejection
100
90
IL= 800 mA
RIPPLE REJECTION (dB)
80
70
60
50
40
30
20
10
0
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 9. Ripple Rejection
Figure 10. Output Noise Spectral Density
Figure 11. Output Noise Spectral Density
Figure 12. Line Transient Response
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Typical Characteristics (continued)
Unless otherwise specified: VIN = 3.3 V, VOUT = 1 V, IOUT = 1 mA, CIN = 4.7 µF, COUT = 10 µF, VSD = 2 V, CBYP = 10 nF, TJ =
25°C.
8
Figure 13. Line Transient Response
Figure 14. Line Transient Response
Figure 15. Line Transient Response
Figure 16. Line Transient Response
Figure 17. Line Transient Response
Figure 18. Line Transient Response
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Typical Characteristics (continued)
Unless otherwise specified: VIN = 3.3 V, VOUT = 1 V, IOUT = 1 mA, CIN = 4.7 µF, COUT = 10 µF, VSD = 2 V, CBYP = 10 nF, TJ =
25°C.
Figure 19. Line Transient Response
Figure 20. Line Transient Response
Figure 21. Line Transient Response
Figure 22. Line Transient Response
Figure 23. Load Transient Response
Figure 24. Load Transient Response
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Typical Characteristics (continued)
Unless otherwise specified: VIN = 3.3 V, VOUT = 1 V, IOUT = 1 mA, CIN = 4.7 µF, COUT = 10 µF, VSD = 2 V, CBYP = 10 nF, TJ =
25°C.
1.2
1.2
1
1
0.6
0.8
VOUT (V)
VOUT (V)
25oC
0o C
0.8
25oC
0.4
0.6
0.4
125oC
0.2
0o C
0.2
0
0
0
0.5
1
1.5
2
0
0.5
1
1.5
2
VS/D
VS/D
Figure 25. Turnon Characteristics
10
125oC
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Figure 26. Turnoff Characteristics
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7 Detailed Description
7.1 Overview
The LP3878-ADJ is an adjustable regulator; the output voltage can be set from 1 V to 5.5 V. The device can
deliver 800-mA continuous load current. Standard regulator features, such as overcurrent and overtemperature
protection, are also included.
The LP3878-ADJ contains other features:
• Low power shutdown current and low ground pin current
• Very low output noise
• 8-lead SO PowerPAD or WSON surface-mount packages to allow for increased power dissipation.
7.2 Functional Block Diagram
ADJ
6
BYPASS
1
IN
4
OUT
5
Error
Amp
2 N/C
+
8 SHUTDOWN
+
1V
VREF
LP3878ADJ
7 N/C
GROUND 3
7.3 Feature Description
7.3.1 Shutdown Input Operation
The LP3878-ADJ is shut off by pulling the SHUTDOWN input low, and turned on by pulling it high. If this feature
is not to be used, the SHUTDOWN input should be tied to VIN to keep the regulator output on at all times.
To assure proper operation, the signal source used to drive the SHUTDOWN input must be able to swing above
and below the specified turnon or turnoff voltage thresholds listed in the Electrical Characteristics under VON/OFF.
7.3.2 Reverse Input-Output Voltage
The PNP power transistor used as the pass element in the LP3878-ADJ contains a parasitic diode between the
IN pin and the OUT pin. During normal operation (where the IN pin voltage is higher than the OUT pin voltage)
this parasitic diode is reverse-biased. However, if the OUT pin voltage is pulled above the IN pin voltage this
diode will turn ON, and current will flow into the LP3878-ADJ OUT pin.
In such cases, a parasitic SCR between the IN pin and the GND pin can latch ON which will allow a high current
to flow from the VIN supply, into the IN pin to ground, which can damage the part. In any application where the
OUT pin voltage may be higher than the IN pin voltage, even momentarily, an external Schottky diode must be
connected from the IN pin to the OUT pin (cathode to IN pin, anode to OUT pin), to limit the reverse voltage
across the LP3878-ADJ to 0.3 V (see Absolute Maximum Ratings).
7.3.3 Low Output Noise
With a 10-nF capacitor on the BYPASS pin, the output noise is only 18 µV.
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7.4 Device Functional Modes
7.4.1 Operation With VOUT(TARGET) + 2 V ≤ VIN ≤ 16 V
The device operates if the input voltage is equal to, or exceeds VOUT(TARGET) + 2 V. At input voltages below the
minimum VIN requirement, the device does not operate correctly and output voltage may not reach target value.
7.4.2 Operation With SHUTDOWN Pin Control
LP3878-ADJ is turned off by pulling the SHUTDOWN pin low, and turned on by pulling it high. If this feature is
not used, the SHUTDOWN pin should be tied to VIN to keep the regulator output on at all times. To assure
proper operation, the signal source used to drive the SHUTDOWN input must be able to swing above and below
the specified turnon and turnoff voltage thresholds listed in the Electrical Characteristics under VL and VH.
12
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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 LP3878-ADJ can provide 800-mA output current with 2.5-V to 6-V output voltage. A minimum 10-µF output
capacitor is required for loop stability. An input capacitor of at least 4.7-µF is required also. The SHUTDOWN pin
must be tied to input if not used. A 10-nF bypass capacitor is required to improve loop stability, it also can reduce
noise on the regulator output significantly. A capacitor, CFF, is required to increase phase margin and assure loop
stability. Output voltage can be set by two resistors R1 and R2 (see Figure 27), and R2 must be less than 5 kΩ
to ensure loop stability.
8.2 Typical Application
VIN
IN
VOUT
OUT
R1
LP3878-ADJ
S/D
**S/D
ADJ
BYPASS
*4.7 µF
(Ceramic or
Tantalum
recommended)
CFF
*10 µF
(Ceramic
recommended)
GND
R2
*0.01 µF
*Capacitor values shown are minimum required to assure stability. Larger output capacitor provides improved
dynamic response. Output capacitor must meet ESR requirements (see Application Information).
**The SHUTDOWN (or S/D) pin must be actively terminated (see Device Functional Modes). Tie to IN (pin 4) if not
used.
Figure 27. Basic Application Circuit
8.2.1 Design Requirements
DESIGN PARAMETER
VALUE
Input voltage
3.8 V ±10%
Output voltage
1.8 V ±3%
Output current
800 mA (maximum)
Input capacitor
4.7 µF (minimum)
Output capacitor
10 µF (minimum)
Bypass capacitor
10 nF
External resistor R2
1 kΩ (less than 5 kΩ)
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8.2.2 Detailed Design Procedure
8.2.2.1 External Capacitors
Like any low-dropout regulator, the LP3878-ADJ requires external capacitors for regulator stability. These
capacitors must be correctly selected for good performance.
8.2.2.1.1 Input Capacitor
A capacitor whose value is at least 4.7 µF (±20%) is required between the LP3878-ADJ input and ground. A
good quality X5R or X7R ceramic capacitor should be used.
Capacitor tolerance and temperature variation must be considered when selecting a capacitor (see Capacitor
Characteristics) to assure the minimum requirement of input capacitance is met over all operating conditions.
The input capacitor must be located not more than 0.5 inches from the input pin and returned to a clean analog
ground. Any good quality ceramic or tantalum capacitor may be used, assuming the minimum input capacitance
requirement is met.
8.2.2.1.2 Output Capacitor
The LP3878-ADJ requires a ceramic output capacitor whose size is at least 10 µF (±20%). A good quality X5R or
X7R ceramic capacitor should be used. Capacitance tolerance and temperature characteristics must be
considered when selecting an output capacitor.
The LP3878-ADJ is designed specifically to work with ceramic output capacitors, utilizing circuitry which allows
the regulator to be stable across the entire range of output current with an ultra-low equivalent series resistance
(ESR) output capacitor.
The output capacitor selected must meet the requirement for minimum amount of capacitance and also have an
ESR value which is within the stable range. A curve is provided which shows the stable ESR range as a function
of load current (see Figure 28).
10
ESR (:)
1
0.1
STABLE REGION
0.01
0.001
0
200
400
600
800
LOAD CURRENT (mA)
Figure 28. Stable Region for Output Capacitor ESR
14
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NOTE
Important: The output capacitor must maintain its ESR within the stable region over the
full operating temperature range of the application to assure stability.
The output capacitor ESR forms a zero which is required to add phase lead near the loop gain crossover
frequency, typically in the range of 50 kHz to 200 kHz. The ESR at lower frequencies is of no importance. Some
capacitor manufacturers list ESR at low frequencies only, and some give a formula for Dissipation Factor (DF)
which can be used to calculate a value for a term referred to as ESR. However, because the DF formula is
usually at a much lower frequency than the range listed above, it will give an unrealistically high value. If good
quality X5R or X7R ceramic capacitors are used, the actual ESR in the 50-kHz to 200-kHz range will not exceed
25 mΩ. If these are used as output capacitors for the LP3878-ADJ, the regulator stability requirements are
satisfied.
It is important to remember that capacitor tolerance and variation with temperature must be taken into
consideration when selecting an output capacitor so that the minimum required amount of output capacitance is
provided over the full operating temperature range (see Capacitor Characteristics).
The output capacitor must be located not more than 0.5 inches from the OUT pin and returned to a clean analog
ground.
8.2.2.1.3 Noise Bypass Capacitor
The 10-nF capacitor on the BYPASS pin significantly reduces noise on the regulator output and is required for
loop stability. However, the capacitor is connected directly to a high-impedance circuit in the bandgap reference.
Because this circuit has only a few µA flowing in it, any significant loading on this node will cause a change in the
regulated output voltage. For this reason, dc leakage current through the noise bypass capacitor must never
exceed 100 nA, and should be kept as low as possible for best output voltage accuracy.
The types of capacitors best suited for the noise bypass capacitor are ceramic and film. High-quality ceramic
capacitors with either NPO or COG dielectric typically have very low leakage. 10-nF polypropylene and
polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low
leakage current.
While the capacitor value on the BYPASS will affect start-up time, this is not intended to be used as a soft-start
circuit. There is no dedicated discharge circuitry for this capacitor, and it can be pre-biased if the IN pin, or the
SHUTDOWN pin are not at 0 V at start-up.
8.2.2.2 Feedforward Capacitor
The feedforward capacitor designated CFF in Figure 27 is required to increase phase margin and assure loop
stability. Improved phase margin also gives better transient response to changes in load or input voltage, and
faster settling time on the output voltage when transients occur. CFF forms both a pole and zero in the loop gain,
the zero providing beneficial phase lead (which increases phase margin) and the pole adding undesirable phase
lag (which should be minimized). The zero frequency is determined both by the value of CFF and R1:
fZ = 1 / (2πCFF × R1)
(1)
The pole frequency resulting from CFF is determined by the value of CFF and the parallel combination of R1 and
R2:
fP = 1 / (2πCFF × (R1 // R2))
(2)
At higher output voltages where R1 is much greater than R2, the value of R2 primarily determines the value of
the parallel combination of R1 // R2. This puts the pole at a much higher frequency than the zero. As the
regulated output voltage is reduced (and the value of R1 decreases), the parallel effect of R2 diminishes and the
two equations become equal (at which point the pole and zero cancel out). Because the pole frequency gets
closer to the zero at lower output voltages, the beneficial effects of CFF are increased if the frequency range of
the zero is shifted slightly higher for applications with low VOUT (because then the pole adds less phase lag at the
loop crossover frequency).
CFF should be selected to place the pole-zero pair at a frequency where the net phase lead added to the loop at
the crossover frequency is maximized. The following design guidelines were obtained from bench testing to
optimize phase margin, transient response, and settling time:
• For VOUT ≤ 2.5 V: CFF should be selected to set the zero frequency in the range of about 50 kHz to 200 kHz.
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For VOUT > 2.5 V: CFF should be selected to set the zero frequency in the range of about 20 kHz to 100 kHz.
8.2.2.3 Capacitor Characteristics
8.2.2.3.1 Ceramic
The LP3878-ADJ was designed to work with ceramic capacitors on the output to take advantage of the benefits
they offer: for capacitance values in the 10-µF range, ceramics are the least expensive and also have the lowest
ESR values (which makes them best for eliminating high-frequency noise). The ESR of a typical 10-µF ceramic
capacitor is in the range of 5 mΩ to 10 mΩ, which meets the ESR limits required for stability by the LP3878-ADJ.
One disadvantage of ceramic capacitors is that their capacitance can vary with temperature. Many large value
ceramic capacitors (≥ 2.2 µF) are manufactured with the Z5U or Y5V temperature characteristic, which results in
the capacitance dropping by more than 50% as the temperature goes from 25°C to 85°C.
Another significant problem with Z5U and Y5V dielectric devices is that the capacitance 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.
For these reasons, X7R and X5R type ceramic capacitors must be used on the input and output of the LP3878ADJ.
8.2.2.4 Setting the Output Voltage
The output voltage is set using resistors R1 and R2 (see Figure 27).
The formula for output voltage is:
VOUT = VADJ × (1 + (R1 / R2))
(3)
R2 must be less than 5 kΩ to ensure loop stability.
To prevent voltage errors, R1 and R2 must be located near the LP3878-ADJ and connected via traces with no
other currents flowing in them (Kelvin connect). The bottom of the R1/R2 divider must be connected directly to
the LP3878-ADJ ground pin.
8.2.3 Application Curves
Figure 29. Load Transient Response
16
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Figure 30. Load Transient Response
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9 Power Supply Recommendations
The LP3878-ADJ is designed to operate from an input voltage supply range between 2.5 V and 16 V. The input
voltage range provides adequate headroom in order for the device to have a regulated output. This input supply
must be well regulated. An input capacitor of at least 4.7 μF is required.
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 ground
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 its capacitors fixed the problem.
Because high current flows through the traces going into IN and coming from OUT, Kelvin connect the capacitor
leads to these pins so there is no voltage drop in series with the input and output capacitors.
10.2 Layout Example
BYP
S/D
N/C
N/C
Bypass
Capacitor
R2
CFF
GND
ADJ
IN
OUT
Input
Capacitor
R1
Output
Capacitor
10.3 Power Dissipation
The LP3878-ADJ is offered in the 8-lead SO PowerPAD or WSON surface-mount packages to allow for
increased power dissipation compared to the SO-8 and Mini SO-8. For details on thermal performance as well as
mounting and soldering specifications, refer to Application Note AN-1187, SNOA401.
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11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
For related documentation see the following:
Application Note AN-1187, SNOA401
11.2 Trademarks
PowerPAD is a trademark of Texas Instruments.
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.
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PACKAGE OPTION ADDENDUM
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30-Sep-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LP3878MR-ADJ
NRND
SO PowerPAD
DDA
8
95
Non-RoHS
& Green
Call TI
Level-3-260C-168 HR
-40 to 125
3878
MRADJ
LP3878MR-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
95
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
3878
MRADJ
LP3878MRX-ADJ/NOPB
ACTIVE SO PowerPAD
DDA
8
2500
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 125
3878
MRADJ
LP3878SD-ADJ/NOPB
ACTIVE
WSON
NGT
8
1000
RoHS & Green
NIPDAU | SN
Level-1-260C-UNLIM
-40 to 125
3878ADJ
LP3878SDX-ADJ/NOPB
ACTIVE
WSON
NGT
8
4500
RoHS & Green
NIPDAU | SN
Level-1-260C-UNLIM
-40 to 125
3878ADJ
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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