ON/OFF
COUT
2.2 µF
LP2985LV
ON/OFF CBYPASS
0.01 µF
GND
IN
BYPASS
OUT VOUT
VIN
CIN
1 µF
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LP2985LV-N
SNOS510Q NOVEMBER 1999REVISED OCTOBER 2016
LP2985LV-N Micropower 150-mA, Low-Noise, Low-Dropout Regulator in SOT-23 and
DSBGA Packages
1
1 Features
1 Wide Supply Voltage Range: 2.2 V to 16 V
Ensured 150-mA Output Current
Requires Minimum External Components
Stable With Low-ESR Output Capacitor
< 1-µA Quiescent Current When Shut Down
Low Ground Pin Current at all Loads
Output Voltage Accuracy 1% (A Grade)
High Peak Current Capability
Low ZOUT: 0.3-Typical (10 Hz to 1 MHz)
Overtemperature/Overcurrent Protection
40°C to +125°C Junction Temperature Range
2 Applications
Cellular Phone
Palmtop/Laptop Computer
Personal Digital Assistant (PDA)
Camcorder, Personal Stereo, Camera
3 Description
The LP2985LV-N is a 150-mA, fixed-output voltage
regulator designed to provide high performance and
low noise in applications requiring output voltages 2
V.
Using an optimized vertically integrated PNP (VIP)
process, the LP2985LV-N delivers unequaled
performance in all specifications critical to battery-
powered designs:
Ground Pin Current: Typically 825 µA at 150-mA
load, and 75 µA at 1-mA load.
Enhanced Stability: The LP2985LV-N is stable
with output capacitor equivalent series resistance
(ESR) as low as 5 m, which allows the use of
ceramic capacitors on the output.
Sleep Mode: Less than 1-µA quiescent current
when ON/OFF pin is pulled low.
Precision Output: 1% tolerance output voltages
available (A grade).
Low Noise: By adding a 10-nF bypass capacitor,
output noise can be reduced to 30 µV (typical).
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
LP2985LV-N SOT-23 (5) 2.90 mm × 1.60 mm
DSBGA (5) 1.164 mm × 0.987 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Space
Typical Application
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Table of Contents
1 Features.................................................................. 1
2 Applications ........................................................... 1
3 Description............................................................. 1
4 Revision History..................................................... 2
5 Pin Configuration and Functions......................... 3
6 Specifications......................................................... 4
6.1 Absolute Maximum Ratings ...................................... 4
6.2 ESD Ratings.............................................................. 4
6.3 Recommended Operating Conditions....................... 4
6.4 Thermal Information.................................................. 5
6.5 Electrical Characteristics........................................... 5
6.6 Typical Characteristics.............................................. 7
7 Detailed Description............................................ 11
7.1 Overview................................................................. 11
7.2 Functional Block Diagram....................................... 11
7.3 Feature Description................................................. 12
7.4 Device Functional Modes........................................ 13
8 Application and Implementation ........................ 14
8.1 Application Information............................................ 14
8.2 Typical Application.................................................. 14
9 Power Supply Recommendations...................... 22
10 Layout................................................................... 22
10.1 Layout Guidelines ................................................. 22
10.2 Layout Example .................................................... 22
10.3 DSBGA Mounting.................................................. 23
10.4 DSBGA Light Sensitivity ....................................... 23
11 Device and Documentation Support................. 24
11.1 Documentation Support ........................................ 24
11.2 Community Resources.......................................... 24
11.3 Trademarks........................................................... 24
11.4 Electrostatic Discharge Caution............................ 24
11.5 Glossary................................................................ 24
12 Mechanical, Packaging, and Orderable
Information........................................................... 24
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision P (April 2013) to Revision Q Page
Added Device Information and Pin Configuration and Functions sections, ESD Ratings and Thermal Information
tables, Feature Description,Device Functional Modes,Application and Implementation,Power Supply
Recommendations,Layout,Device and Documentation Support, and Mechanical, Packaging, and Orderable
Information sections; change pin names in text and app circuit drawing "VOUT" and "VIN" to "OUT" and "IN" .................. 1
Deleted lead temperature spec per new TI documentation guidelines ................................................................................. 4
Changed value of RθJA for the SOT-23 package is 220°C/W ..." to "...value of RθJA for the SOT-23 package is
175.7°C/W..." in footnote 3 to Abs Max table - see update thermal info for SOT-23 in Thermal Information; add RθJA
values to footnote 3 to Abs Max............................................................................................................................................. 4
Added Power Dissipation and Estimating Junction Temperature subsections ................................................................... 19
Changes from Revision O (April 2013) to Revision P Page
Changed layout of National Semiconductor data sheet to TI format .................................................................................... 1
3
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5 Pin Configuration and Functions
DBV Package
5 Pin SOT-23
Top View
YPB Package
5-Pin DSBGA
Top View
(1) The actual physical placement of the package marking varies from part to part. Package marking contains date code
and lot traceability information and will vary considerably. Package marking does not correlate to device type.
Pin Functions
PIN TYPE DESCRIPTION
NAME SOT-23 DSBGA
BYPASS 4 B2 I/O Bypass capacitor for low noise operation
GND 2 A1 Common ground (device substrate)
IN 1 C3 I Input voltage
ON/OFF 3 A3 I Logic high enable input
OUT 5 C1 O Regulated output voltage
J_MAX A
MAX JA
T T
PR
T
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(1) 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.
(2) If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(3) 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:
Where the value of RθJA for the SOT-23 package is 175.7°C/W in a typical PC board mounting or 178.8°C/W for YPB-type DSBGA
package.
Exceeding the maximum allowable dissipation causes excessive die temperature, and the regulator goes into thermal shutdown.
(4) If used in a dual-supply system where the regulator load is returned to a negative supply, the LP2985LV-N output must be diode-
clamped to GND.
(5) The output PNP structure contains a diode between the IN to OUT pins that is normally reverse-biased. Reversing the polarity from IN to
OUT turns on this diode.
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)(2)
MIN MAX UNIT
Input supply voltage –0.3 16 V
Shutdown input voltage –0.3 16 V
Power dissipation(3) Internally Limited
Output voltage(4) –0.3 9 V
IOUT Short-circuit protected
Input-output voltage(5) –0.3 16 V
Storage temperature, Tstg –65 150 °C
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
6.2 ESD Ratings VALUE UNIT
V(ESD) Electrostatic discharge Human-body model (HBM), per
ANSI/ESDA/JEDEC JS-001(1)
Pins 3 and 4 (SOT-23)
Pins A3 and B2 (DSBGA) ±1000 V
Pins 1, 2, and 5 (SOT-23)
Pins A1, C1, and C3 (DSBGA) ±2000
(1) Recommended minimum VIN is the greater of 2.2 V or VOUT(MAX) + rated dropout voltage (maximum) for operating load current.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) MIN MAX UNIT
VIN Supply input voltage 2.2(1) 16 V
VON/OFF ON/OFF input voltage 0 VIN V
IOUT Output current 150 mA
TJOperating junction temperature –40 125 °C
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(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
(2) Thermal resistance value RθJA is based on the EIA/JEDEC High-K printed circuit board defined by: JESD51-7 - High Effective Thermal
Conductivity Test Board for Leaded Surface Mount Packages.
6.4 Thermal Information
THERMAL METRIC(1) LP2985LV-N
UNITSOT-23 (DBV) DSBGA (YPB)
5 PINS
RθJA(2) Junction-to-ambient thermal resistance 175.7 178.8 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 78 2.1 °C/W
RθJB Junction-to-board thermal resistance 30.8 146.3 °C/W
ψJT Junction-to-top characterization parameter 2.8 1.9 °C/W
ψJB Junction-to-board characterization parameter 30.3 146.3 °C/W
(1) Exposing the DSBGA device to direct sunlight causes misoperation. See Layout for additional information.
(2) Limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation using statistical
quality control (SQC) methods. The limits are used to calculate average outgoing quality level (AOQL).
(3) VIN must be the greater of 2.2 V or VOUT(NOM) + dropout voltage to maintain output regulation. Dropout voltage is defined as the input to
output differential at which the output voltage drops 2% below the value measured with a 1-V differential.
6.5 Electrical Characteristics
Unless otherwise specified: VIN = VO(NOM) + 1 V, IL= 1 mA, CIN = 1 µF, COUT = 4.7 µF, VON/OFF = 2 V, TJ= 25°C.(1)
PARAMETER TEST CONDITIONS LP2985AI-XX(2) LP2985I-XX(2) UNIT
MIN TYP MAX MIN TYP MAX
ΔVOOutput voltage
tolerance
IL= 1 mA 1 1 1.5 1.5
%VNOM
1 mA < IL< 50 mA 1.5 1.5 2.5 2.5
1 mA < IL< 50 mA
–40°C TJ125°C 2.5 2.5 3.5 3.5
1 mA < IL< 150 mA 2.5 2.5 3 3
1 mA < IL< 150 mA
–40°C TJ125°C 3.5 3.5 4 4
ΔVO/ΔVIN Output voltage line
regulation
VO(NOM) + 1 V VIN 16 V 0.007 0.014 0.007 0.014 %/V
VO(NOM) + 1 V VIN 16 V
–40°C TJ125°C 0.032 0.032
VIN(MIN) Minimum input voltage
required to maintain
output regulation(3)
2.05 2.05 V
–40°C TJ125°C 2.2 2.2
VIN
VOUT Dropout voltage(3)
IL= 50 mA 120 150 120 150
mV
IL= 50 mA, –40°C TJ125°C 250 250
IL= 150 mA 280 350 280 350
IL= 150 mA, –40°C TJ125°C 600 600
IGND Ground pin current
IL= 0 mA 65 95 65 95
μA
IL= 0 mA, –40°C TJ125°C 125 125
IL= 1 mA 75 110 75 110
IL= 1 mA, –40°C TJ125°C 170 170
IL= 10 mA 120 220 120 220
IL= 10 mA, –40°C TJ125°C 400 400
IL= 50 mA 300 500 300 500
IL= 50 mA, –40°C TJ125°C 900 900
IL= 150 mA 825 1200 825 1200
IL= 150 mA, –40°C TJ125°C 2000 2000
VON/OFF < 0.3 V 0.01 0.8 0.01 0.8
VON/OFF < 0.15 V
–40°C TJ125°C 0.05 2 0.05 2
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Electrical Characteristics (continued)
Unless otherwise specified: VIN = VO(NOM) + 1 V, IL= 1 mA, CIN = 1 µF, COUT = 4.7 µF, VON/OFF = 2 V, TJ= 25°C.(1)
PARAMETER TEST CONDITIONS LP2985AI-XX(2) LP2985I-XX(2) UNIT
MIN TYP MAX MIN TYP MAX
(4) The ON/OFF inputs must be properly driven to prevent misoperation. For details, see Operation With ON/OFF Control.
(5) The LP2985LV-N has foldback current limiting, which allows a high peak current when VOUT > 0.5 V and then reduces the maximum
output current as VOUT is forced to ground (see related curve(s) in Typical Characteristics).
VON/OFF ON/OFF input
voltage(4)
High = O/P ON 1.4 1.4
V
High = O/P ON
–40°C TJ125°C 1.6 1.6
Low = O/P OFF 0.55 0.55
Low = O/P OFF
–40°C TJ125°C 0.15 0.15
ION/OFF ON/OFF input current
VON/OFF = 0 V 0.01 0.01
μA
VON/OFF = 0 V
–40°C TJ125°C –2 –2
VON/OFF = 5 V 5 5
VON/OFF = 5 V
–40°C TJ125°C 15 15
IO(PK) Peak output current VOUT VO(NOM) 5% 350 350 mA
enOutput noise voltage BW = 300 Hz to 50 kHz
COUT = 10 μF
CBYPASS = 10 nF, VOUT = 1.8 V 30 30 μV(RMS)
ΔVO/ΔVIN Ripple rejection ƒ = 1 kHz, COUT = 10 μF
CBYPASS = 10 nF 45 45 dB
IO(SC) Short-circuit current RL= 0 Ω(steady state)(5) 400 400 mA
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6.6 Typical Characteristics
Unless otherwise specified: CIN = 1 µF, COUT = 4. 7µF, VIN = VOUT(NOM) + 1, VOUT = 1.8 V, TA= 25°C, ON/OFF pin is tied to
VIN.
Figure 1. VOUT vs Temperature Figure 2. Short-Circuit Current
Figure 3. Short-Circuit Current Figure 4. Short-Circuit Current vs Output Voltage
COUT = 4.7 µF Bypass = 10 nF
Figure 5. Ripple Rejection
COUT = 4.7 µF No Bypass
Figure 6. Ripple Rejection
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Typical Characteristics (continued)
Unless otherwise specified: CIN = 1 µF, COUT = 4. 7µF, VIN = VOUT(NOM) + 1, VOUT = 1.8 V, TA= 25°C, ON/OFF pin is tied to
VIN.
Figure 7. Output Impedance vs Frequency Figure 8. Output Impedance vs Frequency
Figure 9. Noise Density Figure 10. Noise Density
Figure 11. Ground Pin vs Load Current Figure 12. Minimum Input Voltage vs Temperature
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Typical Characteristics (continued)
Unless otherwise specified: CIN = 1 µF, COUT = 4. 7µF, VIN = VOUT(NOM) + 1, VOUT = 1.8 V, TA= 25°C, ON/OFF pin is tied to
VIN.
Figure 13. Minimum Input Voltage vs Temperature Figure 14. Input Current vs VIN
Figure 15. Input Current vs VIN Figure 16. Input Current vs VIN
Figure 17. Ground Pin Current vs Temperature Figure 18. Instantaneous Short Circuit Current
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Typical Characteristics (continued)
Unless otherwise specified: CIN = 1 µF, COUT = 4. 7µF, VIN = VOUT(NOM) + 1, VOUT = 1.8 V, TA= 25°C, ON/OFF pin is tied to
VIN.
Figure 19. Output Characteristics
11
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7 Detailed Description
7.1 Overview
The LP2985LV-N family of fixed-output, ultra-low-dropout and low-noise regulators offers exceptional, cost-
effective performance for battery-powered applications. Available in output voltages from 1.5 V to 2 V, the family
has an output voltage tolerance of 1% for the A version (1.5% for the non-A version) and is capable of delivering
150-mA continuous load current. Standard regulator features, such as overcurrent and overtemperature
protection, are also included.
Using an optimized vertically integrated PNP (VIP) process, the LP2985LV-N contains several features to
facilitate battery-powered designs:
Multiple voltage options
Low dropout voltage, typical dropout of 280 mV at 150-mA load current and 120 mV at 50-mA load current.
Low quiescent current and low ground current, typically 825-μA at 150-mA load, and 75 μA at 1-mA load.
A shutdown feature is available, allowing the regulator to consume only 0.01 µA typically when the ON/OFF
pin is pulled low.
Overtemperature protection and overcurrent protection circuitry is designed to safeguard the device during
unexpected conditions
Enhanced stability: The LP2985LV-N is stable with output capacitor ESR as low as 5 mΩ, which allows the
use of ceramic capacitors on the output.
Low noise: A BYPASS pin allows for low-noise operation, with a typical output noise of 30 µVRMS, with the
use of a 10-nF bypass capacitor.
7.2 Functional Block Diagram
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7.3 Feature Description
7.3.1 Multiple Voltage Options
In order to meet different application requirement, the LP2985LV-N family provide multiple fixed output options
from 1.5 V to 2 V. Contact your regional TI sales team for custom voltage options.
7.3.2 Output Voltage Accuracy
Output voltage accuracy specifies minimum and maximum output voltage error, relative to the expected nominal
output voltage stated as a percent. This accuracy error includes the errors introduced by the internal reference
and the load and line regulation across the full range of rated load and line operating conditions over
temperature, unless otherwise specified by the Electrical Characteristics. Output voltage accuracy also accounts
for all variations between manufacturing lots.
7.3.3 Ultra-Low-Dropout Voltage
Generally speaking, the dropout voltage often refers to the voltage difference between the input and output
voltage (VDO = VIN VOUT), where the current pass transistor loses its voltage-controlled current capability and
the collector (VOUT) to emitter (VIN) voltage becomes constant for a given current and is characterized by the
classic VCE(SAT) of the PNP transistor. VDO indirectly specifies a minimum input voltage above the nominal
programmed output voltage at which the output voltage is expected to remain within its accuracy boundary. If the
input falls below this VDO limit (VIN < VOUT + VDO), then active regulation of the output voltage is no longer
possible, and the output voltage decreases as the input voltage falls.
7.3.4 Low Ground Current
The LP2985LV-N device uses a vertical PNP process which allows for quiescent currents that are considerably
lower than those associated with traditional lateral PNP regulators, typically 825 μA at 150-mA load.
7.3.5 Sleep Mode
When the ON/OFF pin is pulled to a low level the LP2985LV-N enters sleep mode, and less than 2-μA quiescent
current is consumed. This function is designed for the application which needs a sleep mode to effectively
enhance battery life cycle.
7.3.6 Internal Protection Circuitry
7.3.6.1 Short Circuit Protection (Current Limit)
The internal current limit circuit is used to protect the LDO against high-load current faults or shorting events. The
LDO is not designed to operate in a steady-state current limit. During a current-limit event, the LDO sources
constant current. Therefore, the output voltage falls when load impedance decreases. Note also that if a current
limit occurs and the resulting output voltage is low, excessive power may be dissipated across the LDO, resulting
in a thermal shutdown of the output.
A foldback feature limits the short-circuit current to protect the regulator from damage under all load conditions. If
VOUT is forced below 0 V before EN goes high and the load current required exceeds the foldback current limit,
the device may not start up correctly.
7.3.6.2 Thermal Protection
The LP2985LV-N contains a thermal shutdown protection circuit to turn off the output current when excessive
heat is dissipated in the LDO. The thermal time-constant of the semiconductor die is fairly short, and thus the
output cycles on and off at a high rate when thermal shutdown is reached until the power dissipation is reduced.
The internal protection circuitry of the LP2985LV-N is designed to protect against thermal overload conditions.
The circuitry is not intended to replace proper heat sinking. Continuously running the device into thermal
shutdown degrades its reliability.
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Feature Description (continued)
7.3.7 Enhanced Stability
The LP2985LV-N 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 output capacitor whose ESR is as low
as 5 mΩ. For output capacitor requirement, refer to Output Capacitor.
7.3.8 Low Noise
The LP2985LV-N includes a low-noise reference ensuring minimal noise during operation because the internal
reference is normally the dominant term in noise analysis. Further noise reduction can be achieved by adding an
external bypass bapacitor between the BYPASS pin and the GND pin.
7.4 Device Functional Modes
7.4.1 Operation with VOUT(TARGET) + 0.6 V VIN > 16 V
The device operate if the input voltage is equal to, or exceeds VOUT(TARGET) + 0.6 V. At input voltages below the
minimum VIN requirement, the devices do not operate correctly and output voltage may not reach target value.
7.4.2 Operation With ON/OFF Control
If the voltage on the ON/OFF pin is less than 0.15 V, the device is disabled, and in this state shutdown current
does not exceed 2 μA. Raising ON/OFF above 1.6 V initiates the start-up sequence of the device.
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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 LP2985LV-N is a linear voltage regulator operating from 2.2 V to 16 V on the input and regulating voltages
from 1.5 V to 2 V with 1% accuracy (A-grade) and 150-mA maximum output current. Efficiency is defined by the
ratio of output voltage to input voltage because the LP2985LV-N is a linear voltage regulator. To achieve high
efficiency, the dropout voltage (VIN VOUT) must be as small as possible, thus requiring a very-low-dropout LDO.
Successfully implementing an LDO in an application depends on the application requirements. If the
requirements are simply input voltage and output voltage, compliance specifications (such as internal power
dissipation or stability) must be verified to ensure a solid design. If timing, start-up, noise, power supply rejection
ratio (PSRR), or any other transient specification is required, then the design becomes more challenging.
8.2 Typical Application
*ON/OFF input must be actively terminated. Tie to VIN if this function is not to be used.
**Minimum capacitance is shown to ensure stability (may be increased without limit). Ceramic capacitor required for
output (see Output Capacitor).
***Reduces output noise (may be omitted if application is not noise critical). Use ceramic or film type with very low
leakage current (see Noise Bypass Capacitor).
Figure 20. Typical Application Schematic
8.2.1 Design Requirements
For typical design parameters, see Table 1.
Table 1. Design Parameters
DESIGN PARAMETERS VALUE
Input voltage 2.8 V ±10%
Output voltage 1.8 V ±4%
Output current 150 mA (maximum)
PSRR at 1 kHz > 50 dB
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8.2.2 Detailed Design Procedure
At 150-mA loading, the dropout of the LP2985LV-N has 600-mV maximum dropout over temperature, thus an
1000-mV headroom is sufficient for operation over both input and output voltage accuracy. The efficiency of the
LP2985LV-N in this configuration is VOUT / VIN = 64%. To achieve the smallest form factor, the DSBGA package
is selected.
Input and output capacitors are selected in accordance with the Capacitor Characteristics section. Ceramic
capacitances of 1 μF for the input and one 2.2-μF capacitor for the output are selected. With a VIN of 2.8 V, a
VOUT of 1.8 V, and an output current of 150 mA Equation 1 shows the power dissipation to be 150 mW. With an
RθJA rating of 178.8°C/W for the DSBGA YPB package, and a maximum operating ambient temperature of 85°C,
Equation 2 shows the maximum junction temperature to be approximately 111.8°C.
8.2.2.1 External Capacitors
Like any low-dropout regulator, the LP2985LV-N requires external capacitors for regulator stability. These
capacitors must be correctly selected for good performance.
8.2.2.1.1 Input Capacitor
An input capacitor whose capacitance is 1 µF is required between the LP2985LV-N input and ground (the
amount of capacitance may be increased without limit).
This capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean
analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.
NOTE
Tantalum capacitors can suffer catastrophic failure due to surge current when connected
to a low-impedance source of power (like a battery or very large capacitor). If a Tantalum
capacitor is used at the input, it must be ensured by the manufacturer to have a surge
current rating sufficient for the application.
There are no requirements for ESR on the input capacitor, but tolerance and temperature coefficient must be
considered when selecting the capacitor to ensure the capacitance is 1 µF over the entire operating
temperature range.
8.2.2.1.2 Output Capacitor
The LP2985LV-N 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 output capacitor whose ESR is as low
as 5 mΩ. It may also be possible to use tantalum or film capacitors at the output, but these are not as attractive
for reasons of size and cost (see Capacitor Characteristics).
The output capacitor must meet the requirement for minimum amount of capacitance and also have an ESR
value which is within the stable range. Curves are provided showing the stable ESR range as a function of load
current (see Figure 21 and Figure 22).
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Figure 21. LP2985LV-N 2.2-µF Stable ESR Range
Figure 22. LP2985LV-N 4.7-µF Stable ESR Range
NOTE
The output capacitor must maintain its ESR within the stable region over the full operating
temperature range of the application to assure stability.
The LP2985LV-N requires a minimum of 2.2 µF on the output (output capacitor size can be increased without
limit).
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. Ceramic capacitors can exhibit large changes in capacitance
with temperature (see Capacitor Characteristics). The output capacitor must be located not more than 1 cm from
the output pin and returned to a clean analog ground.
8.2.2.1.3 Noise Bypass Capacitor
Connecting a 10-nF capacitor to the BYPASS pin significantly reduces noise on the regulator output. The
capacitor is connected directly to a high-impedance circuit in the bandgap reference.
Because this circuit has only a few microamperes flowing in it, any significant loading on this node causes a
change in the regulated output voltage. For this reason, DC leakage current through the noise bypass capacitor
must never exceed 100 nA and must be kept as low as possible for best output voltage accuracy.
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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 polypropolene and
polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low
leakage current.
8.2.2.2 Capacitor Characteristics
The LP2985LV-N is designed to work with ceramic capacitors on the output to take advantage of the benefits
they offer: for capacitance values in the 2.2-µF to 4.7-µF range, ceramics are the least expensive and also have
the lowest ESR values (making them best for eliminating high-frequency noise). The ESR of a typical 2.2-µF
ceramic capacitor is in the range of 10 mΩto 20 mΩ, which easily meets the ESR limits required for stability by
the device.
One disadvantage of ceramic capacitors is that their capacitance can vary with temperature. Most 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.
Problems may ensue if a 2.2-µF capacitor is used on the output because it drops down to approximately 1 µF at
high ambient temperatures (which could cause the LM2985 to oscillate). If Z5U or Y5V capacitors are used on
the output, a minimum capacitance value of 4.7 µF must be observed.
A better choice for temperature coefficient in ceramic capacitors is X7R, which holds the capacitance within
±15%. Unfortunately, the larger values of capacitance are not offered by all manufacturers in the X7R dielectric.
8.2.2.2.1 Tantalum
Tantalum capacitors are less desirable than ceramics for use as output capacitors because they are more
expensive when comparing equivalent capacitance and voltage ratings in the 1 µF to 4.7 µF range.
An additional important consideration is that tantalum capacitors have higher ESR values than equivalent size
ceramics. This means that while it may be possible to find a tantalum capacitor with an ESR value within the
stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic
capacitor with the same ESR value.
Note that the ESR of a typical tantalum increases about 2:1 as the temperature goes from 25°C down to 40°C,
so some guard band must be allowed.
8.2.2.3 On/OFF Input Operation
The LP2985LV-N is shut off by driving the ON/OFF input low, and turned on by pulling it high. If this feature is
not to be used, the ON/OFF input must be tied to VIN to keep the regulator output on at all times.
To assure proper operation, the signal source used to drive the ON/OFF input must be able to swing above and
below the specified turnon/turnoff voltage thresholds listed inElectrical Characteristics under VON/OFF. To prevent
mis-operation, the turnon (and turnoff) voltage signals applied to the ON/OFF input must have a slew rate which
is 40 mV/µs.
CAUTION
The regulator output voltage cannot be ensured if a slow-moving AC (or DC) signal is
applied that is in the range between the specified turnon and turnoff voltages listed
under the electrical specification VON/OFF (see Electrical Characteristics).
8.2.2.4 Reverse Input-Output Voltage
The PNP power transistor used as the pass element in the LP2985LV-N has an inherent diode connected
between the regulator output and input. During normal operation (where the input voltage is higher than the
output) this diode is reverse-biased.
VIN VOUT
PNP
GND
SCHOTTKY DIODE
VIN VOUT
PNP
GND
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Figure 23. Normal Operation
However, if the output is pulled above the input, this diode turns ON, and current flows into the regulator output.
In such cases, a parasitic SCR can latch, allowing a high current to flow into VIN (and out the ground pin), which
can damage the part.
In any application where the output may be pulled above the input, an external Schottky diode must be
connected from VIN to VOUT (cathode on VIN, anode on VOUT), to limit the reverse voltage across the LP2985LV-N
to 0.3V (see Absolute Maximum Ratings).
Figure 24. Operation With Schottky Diode
8.2.2.5 Power Dissipation
Knowing the device power dissipation and proper sizing of the thermal plane connected to the tab or pad is
critical to ensuring reliable operation. Device power dissipation depends on input voltage, output voltage, and
load conditions and can be calculated with Equation 1.
PD(MAX) = (VIN(MAX) VOUT)×IOUT(MAX) (1)
Power dissipation can be minimized, and greater efficiency can be achieved, by using the lowest available
voltage drop option that would still be greater than the dropout voltage (VDO). However, keep in mind that higher
voltage drops result in better dynamic (that is, PSRR and transient) performance.
On the DSBGA (YPB) package, the primary conduction path for heat is through the four bumps to the PCB.
On the SOT-23 (DBV) package, the primary conduction path for heat is through the device leads to the PCB,
predominately device lead 2 (GND). It is recommended that the trace from lead 2 be extended under the
package body and connected to an internal ground plane with thermal vias.
The maximum allowable junction temperature (TJ(MAX)) determines maximum power dissipation allowed (PD(MAX))
for the device package.
Power dissipation and junction temperature are most often related by the junction-to-ambient thermal resistance
(RθJA) of the combined PCB and device package and the temperature of the ambient air (TA), according to
Equation 2 or Equation 3:
TJ(MAX) = TA(MAX) + (RθJA × PD(MAX)) (2)
PD(MAX) = (TJ(MAX) TA(MAX)) / RθJA (3)
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Unfortunately, this RθJA is highly dependent on the heat-spreading capability of the particular PCB design, and
therefore varies according to the total copper area, copper weight, and location of the planes. The RθJA recorded
in Thermal Information is determined by the specific EIA/JEDEC JESD51-7 standard for PCB and copper-
spreading area, and is to be used only as a relative measure of package thermal performance. For a well-
designed thermal layout, RθJA is actually the sum of the package junction-to-case (bottom) thermal resistance
(RθJCbot) plus the thermal resistance contribution by the PCB copper area acting as a heat sink.
8.2.2.6 Estimating Junction Temperature
The EIA/JEDEC standard recommends the use of psi (Ψ) thermal characteristics to estimate the junction
temperatures of surface mount devices on a typical PCB board application. These characteristics are not true
thermal resistance values, but rather package specific thermal characteristics that offer practical and relative
means of estimating junction temperatures. These psi metrics are determined to be significantly independent of
copper-spreading area. The key thermal characteristics (ΨJT and ΨJB) are given in Thermal Information and are
used in accordance with Equation 4 or Equation 5.
TJ(MAX) = TTOP + (ΨJT × PD(MAX))
where
PD(MAX) is explained in Equation 1.
TTOP is the temperature measured at the center-top of the device package. (4)
TJ(MAX) = TBOARD + (ΨJB × PD(MAX))
where
PD(MAX) is explained in Equation 1.
TBOARD is the PCB surface temperature measured 1-mm from the device package and centered on the
package edge. (5)
For more information about the thermal characteristics ΨJT and ΨJB, see Semiconductor and IC Package Thermal
Metrics, available for download at www.ti.com.
For more information about measuring TTOP and TBOARD, see Using New Thermal Metrics, available for download
at www.ti.com.
For more information about the EIA/JEDEC JESD51 PCB used for validating RθJA, see Thermal Characteristics
of Linear and Logic Packages Using JEDEC PCB Designs, available for download at www.ti.com.