NSC LP2978 Micropower sot, 50 ma low-noise ultra low-dropout regulator designed for use with very low esr output capacitor Datasheet

April 23, 2009
LP2978
Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout
Regulator
Designed for Use with Very Low ESR Output Capacitors
General Description
Features
The LP2978 is a 50 mA, fixed-output voltage regulator designed to provide ultra low-dropout and low noise in battery
powered applications.
Using an optimized VIP® (Vertically Integrated PNP) process,
the LP2978 delivers unequalled performance in all specifications critical to battery-powered designs:
Dropout Voltage: Typically 120 mV @ 50 mA load, and
7 mV @ 1 mA load.
Ground Pin Current: Typically 350 µA @ 50 mA load, and
75 µA @ 1 mA load.
Enhanced Stability: The LP2978 is stable with output capacitor ESR as low as 5 mΩ, 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.
Smallest Possible Size: SOT-23 package uses absolute
minimum board space.
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).
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■
■
■
■
■
■
■
■
■
■
Ultra low dropout voltage
Smallest possible size (SOT-23 Package)
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
Wide supply voltage range (16V max)
Low ZOUT: 0.3Ω typical (10 Hz to 1 MHz)
Overtemperature/overcurrent protection
−40°C to +125°C junction temperature range
Custom voltages available
Applications
■
■
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Cellular Phone
Palmtop/Laptop Computer
Personal Digital Assistant (PDA)
Camcorder, Personal Stereo, Camera
Block Diagram
10093501
VIP® is a registered trademark of National Semiconductor Corporation.
© 2009 National Semiconductor Corporation
100935
100935 Version 6 Revision 2
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Print Date/Time: 2009/04/23 16:08:18
LP2978 Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout Regulator
OBSOLETE
LP2978
Basic Application Circuit
10093502
*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 Application Hints).
***Reduces output noise (may be omitted if application is not noise critical). Use ceramic or film type with very low leakage current (see Application Hints).
Connection Diagram
10093503
See NS Package Number MF05A
Ordering Information
TABLE 1. Package Marking and Ordering Information
Output Voltage (V)
Grade
Order Information
Package Marking
3.8
A
LP2978AIM5X-3.8
LØLA
3000 Units on Tape and Reel
3.8
A
LP2978AIM5-3.8
LØLA
1000 Units on Tape and Reel
3.8
STD
LP2978IM5X-3.8
LØLB
3000 Units on Tape and Reel
3.8
STD
LP2978IM5-3.8
LØLB
1000 Units on Tape and Reel
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Supplied As:
2
100935 Version 6 Revision 2
Print Date/Time: 2009/04/23 16:08:18
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Storage Temperature Range
Operating Junction Temperature
Range
Lead Temp. (Soldering, 5 sec.)
ESD Rating (Note 2)
−65°C to +150°C
−40°C to +125°C
260°C
2 kV
Internally Limited
−0.3V to +16V
2.5V to +16V
−0.3V to +16V
−0.3V to +9V
Short Circuit
Protected
−0.3V to +16V
Input-Output Voltage (Survival,
(Note 5))
Electrical Characteristics
Limits in standard typeface are for TJ = 25°C. and limits in boldface type apply over the full operating temperature range. Unless
otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, CIN = 1 µF, COUT = 4.7 µF, VON/OFF = 2V.
Symbol
ΔVO
Parameter
Conditions
Typ
LP2978AI-X.X
(Note 6)
LP2978I-X.X
(Note 6)
Min
Max
Min
Max
Output Voltage
Tolerance
IL = 1 mA
−1.0
1.0
−1.5
1.5
1 mA ≤ IL ≤ 50 mA
−1.5
1.5
−2.5
2.5
2.5
−3.5
Output Voltage
VO(NOM)+1V ≤ VIN ≤ 16V
−2.5
0.007
Line Regulation
VIN–VO
Dropout Voltage
(Note 7)
IL = 0
1
IL = 1 mA
IGND
Ground Pin Current
7
VON/OFF
ION/OFF
en
0.014
0.032
0.032
3
3
5
5
10
10
15
15
60
40
60
90
90
IL = 50 mA
120
150
150
225
225
IL = 0
65
95
95
125
125
IL = 1 mA
75
110
110
170
170
220
220
400
400
600
600
120
%VNOM
3.5
0.014
IL = 10 mA
IL = 10 mA
Units
IL = 50 mA
350
1000
1000
VON/OFF < 0.3V
0.01
0.8
0.8
VON/OFF < 0.15V
0.05
2
2
%/V
mV
µA
ON/OFF Input Voltage
(Note 8)
High = O/P ON
1.4
Low = O/P OFF
0.55
0.15
0.15
ON/OFF Input Current
VON/OFF = 0
0.01
−2
−2
VON/OFF = 5V
5
15
15
BW = 300 Hz to 50 kHz,
COUT = 10 µF
30
µV
45
dB
Output Noise
Voltage (RMS)
1.6
1.6
V
µA
CBYPASS = 10 nF
Ripple Rejection
f = 1 kHz, CBYPASS = 10 nF
COUT = 10 µF
IO(SC)
Short Circuit Current
RL = 0 (Steady State)
400
mA
IO(PK)
Peak Output Current
VOUT ≥ Vo(NOM) −5%
350
mA
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100935 Version 6 Revision 2
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LP2978
Power Dissipation (Note 3)
Input Supply Voltage (Survival)
Input Supply Voltage (Operating)
Shutdown Input Voltage (Survival)
Output Voltage (Survival, (Note 4))
IOUT (Survival)
Absolute Maximum Ratings (Note 1)
LP2978
Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating
the device outside of its rated operating conditions.
Note 2: The ESD rating of pins 3 and 4 is 1 kV.
Note 3: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperture is calculated using:
Where the value of θJ-A for the SOT-23 package is 220°C/W in a typical PC board mounting. Exceeding the maximum allowable dissipation will cause excessive
die temperature, and the regulator will go into thermal shutdown.
Note 4: If used in a dual-supply system where the regulator load is returned to a negative supply, the LP2978 output must be diode-clamped to ground.
Note 5: The output PNP structure contains a diode between the VIN to VOUT terminals that is normally reverse-biased. Reversing the polarity from VIN to VOUT
will turn on this diode.
Note 6: Limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality
Control (SQC) methods. The limits are used to calculate National's Average Outgoing Quality Level (AOQL).
Note 7: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below the value measured with a 1V differential.
Note 8: The ON/OFF input must be properly driven to prevent possible misoperation. For details, refer to Application Hints.
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EXTERNAL CAPACITORS
Like any low-dropout regulator, the LP2978 requires external
capacitors for regulator stability. These capacitors must be
correctly selected for good performance.
Noise Bypass Capacitor
Connecting a 10 nF capacitor to the Bypass pin significantly
reduces noise on the regulator output. It should be noted that
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 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 polypropolene and polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low leakage current.
Input Capacitor
An input capacitor whose capacitance is ≥ 1 µF is required
between the LP2978 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.
Important: 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 guaranteed
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 will
be ≥ 1 µF over the entire operating temperature range.
CAPACITOR CHARACTERISTICS
The LP2978 was 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
(which makes them best for eliminating high-frequency
noise). The ESR of a typical 2.2 µF ceramic capacitor is in the
range of 10 mΩ to 20 mΩ, which easily meets the ESR limits
required for stability by the LP2978.
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.
This could cause problems if a 2.2 µF capacitor were used on
the output since it will drop down to approximately 1 µF at high
ambient temperatures (which could cause the LP2978 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.
Output Capacitor
The LP2978 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 next section Capacitor Characteristics).
The output capacitor must meet the requirement for minimum
amount of capacitance and also have an ESR (equivalent series resistance) value which is within the stable range. Curves
are provided which show the stable ESR range as a function
of load current (see ESR graph below).
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.
Another 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.
It should also be noted that the ESR of a typical Tantalum will
increase about 2:1 as the temperature goes from 25°C down
to −40°C, so some guard band must be allowed.
10093507
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 LP2978 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
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100935 Version 6 Revision 2
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LP2978
amount of output capacitance is provided over the full operating temperature range. It should be noted that ceramic
capacitors can exhibit large changes in capacitance with temperature (see next section, Capacitor Characteristics).
The output capacitor must be located not more than 1 cm from
the output pin and returned to a clean analog ground.
Application Hints
LP2978
ON/OFF INPUT OPERATION
The LP2978 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 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 ON/OFF input must be able to swing above and below the
specified turn-on/turn-off voltage thresholds listed in the Electrical Characteristics section under VON/OFF. To prevent misoperation, the turn-on (and turn-off) voltage signals applied to
the ON/OFF input must have a slew rate which is
≥ 40 mV/µs.
Caution: the regulator output voltage can not be guaranteed
if a slow-moving AC (or DC) signal is applied that is in the
range between the specified turn-on and turn-off voltages listed under the electrical specification VON/OFF (see Electrical
Characteristics).
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REVERSE INPUT-OUTPUT VOLTAGE
The PNP power transistor used as the pass element in the
LP2978 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 reversebiased.
However, if the output is pulled above the input, this diode will
turn ON and current will flow into the regulator output. In such
cases, a parasitic SCR can latch which will allow 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 LP2978 to 0.3V (see Absolute Maximum Ratings).
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100935 Version 6 Revision 2
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LP2978
Physical Dimensions inches (millimeters) unless otherwise noted
5-Lead Small Outline Package (M5)
NS Package Number MF05A
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100935 Version 6 Revision 2
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LP2978 Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout Regulator
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