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PDF LP3991 Data sheet ( Hoja de datos )
| Número de pieza | LP3991 | |
| Descripción | 300mA Linear Voltage Regulator | |
| Fabricantes | National Semiconductor | |
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www.DataSheet4U.com
January 2007
LP3991
300mA Linear Voltage Regulator for Digital Applications
General Description
Operating from a minimum input voltage of 1.65V, the LP3991
regulator has been designed to provide fixed stable output
voltages for load currents up to 300mA. This device is suitable
where accurate, low voltages are required from low input volt-
age sources and is therefore suitable for post regulation of
switched mode regulators. In such applications, significant
improvements in performance and EMI can be realized, with
little reduction in overall efficiency. The LP3991 will provide
fixed outputs as low as 1.2V from a wide input range of 1.65V
to 3.6V Using the enable pin, the device may be controlled to
provide a shutdown state, in which negligible supply current
is drawn.
The LP3991 is designed to be stable with space saving ce-
ramic capacitors as small as 0402 case size.
Performance is specified for a -40°C to 125°C junction tem-
perature range.
For output voltage options please contact your local NSC
sales office.
Features
■ Operation from 1.65V to 3.6V Input
■ 1% accuracy at room temperature
■ Output Voltage from 1.2V to 2.8V
■ 125mV Dropout at 300mA load
■ 50µA Quiescent Current at 1mA Load
■ Inrush Current controlled to 600mA
■ PSRR 65dB at 1kHz
■ 100µs Start-Up time for 1.5V VOUT
■ Stable with Ceramic Capacitors as small as 0402
■ Thermal-Overload and Short-Circuit Protection
Package
4 pin micro SMD (0.963mm x 1.446mm)
For other package options contact your NSC sales office.
Applications
■ Post DC/DC Regulator
■ Battery Operated Devices
■ Hand-Held Information Appliances
Typical Application Circuit
© 2007 National Semiconductor Corporation 201100
20110002
www.national.com
1 page  
Electrical Characteristics con't.
Unless otherwise noted, VEN =950mV, VIN = VOUT + 0.5V, or 1.8V, whichever is higher. CIN = 1µF, IOUT = 1.0mA, COUT =4.7µF.
Typical values and limits appearing in normal type apply for TA = 25°C. Limits appearing in boldface type apply over the full junction
temperature range for operation, −40 to +125°C. (Note 9)
Symbol
Parameter
Conditions
Limit
Typ Units
Min Max
Enable Control Characteristics
IEN
(Note 15)
Maximum Input Current at
VEN Input
VIL Low Input Threshold
VIH High Input Threshold
Timing Characteristics
VEN = 0V, VIN = 3.6V
VEN = VIN = 3.6V
VIN = 1.65V to 3.6V
VIN = 1.65V to 3.6V
0.001
3
0.95
5.5
0.4
µA
V
V
TON
Transient
Response
Turn On Time (Note 14)
To 95% Level VOUT ≤ 2.0V
VIN(MIN) to 3.6V VOUT > 2.0V
Line Transient Response |δVOUT| Trise = Tfall = 30µs (Note 14)
δVIN = 600mV
Load Transient Response |δVOUT| Trise = Tfall = 1µs IOUT = 0 mA to 300mA
(Note 14)
IOUT = 1mA to 300mA
IOUT = 300mA to 1mA
IOUT = 0mA to 200mA
IOUT = 1mA to 200mA
IOUT = 200mA to 1mA
IOUT = 0mA to 150mA
IOUT = 1mA to 150mA
IOUT = 150mA to 1mA
Overshoot on Start-up
100
140
6
140
110
80
110
80
60
100
70
50
0
µs
mV
(pk - pk)
mV
2%
IIR In-Rush Current (Note 14)
600
1000
mA
Note 1: Absolute Maximum Ratings are limits beyond which damage can occur. Operating Ratings are conditions under which operation of the device is
guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical
Characteristics tables.
Note 2: All Voltages are with respect to the potential at the GND pin.
Note 3: For further information on these packages please refer to the following application notes,AN-1112 Micro SMD Wafer Level Chip Scale Package.
Note 4: Internal thermal shutdown circuitry protects the device from permanent damage.
Note 5: The human body model is 100pF discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly into
each pin.
Note 6: The maximum ambient temperature (TA(max)) is dependant on the maximum operating junction temperature (TJ(max-op) = 125°C), the maximum power
dissipation of the device in the application (PD(max)), and the junction to ambient thermal resistance of the part / package in the application (θJA), as given by the
following equation: TA(max) = TJ(max-op) - (θJA × PD(max)).
Note 7: Junction to ambient thermal resistance is dependant on the application and board layout. In applications where high maximum power dissipation is
possible, special care must be paid to thermal dissipation issues in board design.
Note 8: Full details can be found in JESD61-7
Note 9: All limits are guaranteed. All electrical characteristics having room-temperature limits are tested during production at TJ = 25°C or correlated using
Statistical Quality Control methods. Operation over the temperature specification is guaranteed by correlating the electrical characteristics to process and
temperature variations and applying statistical process control.
Note 10: VIN(MIN) = VOUT(NOM) + 0.5V or 1.65V, whichever is greater. (See post DC/DC convertor example in application information section).
Note 11: Dropout voltage is voltage difference between input and output at which the output voltage drops to 100mV below its nominal value. This parameter is
only specified for output voltages above 1.8V.
Note 12: The device maintains the regulated output voltage without a load.
Note 13: Short circuit current is measured with VOUT pulled to 0V.
Note 14: This electrical specification is guaranteed by design.
Note 15: Enable Pin has an internal 1.2MΩ typical, resistor connected to GND.
5 www.national.com
5 Page 
1µF to 4.7µF 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.
ENABLE CONTROL
The LP3991 features an active high Enable pin, VEN, which
turns the device on when pulled high. When not enabled the
regulator output is off and the device typically consumes 2nA.
If the application does not require the Enable switching fea-
ture, the VEN pin should be tied to VIN to keep the regulator
output permanently on.
To ensure proper operation, the signal source used to drive
the VEN input must be able to swing above and below the
specified turn-on/off voltage thresholds listed in the Electrical
Characteristics section under VIL and VIH.
micro SMD MOUNTING
The micro SMD package requires specific mounting tech-
niques which are detailed in the National Semiconductor
Application Note (AN-1112). Referring to the section Surface
Mount Technology (SMT) Assenbly Considerations, it should
be noted that the pad style which must be used with the 4 pin
package is NSMD (non-solder mask defined) type.
For best results during assembly, alignment ordinals on the
PCB may be used to facilitate placement of the micro SMD
device.
micro SMD LIGHT SENSITIVITY
Exposing the micro SMD device to direct sunlight may cause
mis-operation of the device. Light sources such as halogen
lamps can affect the electrical performance if brought near to
the device.
The wavelengths which have most detrimental effect are reds
and infra-reds, which means that fluorescent lighting, used
inside most buildings will have little effect on performance.
FIGURE 2. LP3991 Used as a Post DC/DC regulator
20110036
POST-BUCK REGULATOr
Linear Post-Regulation can be an effective way to reduce rip-
ple and switching noise from DC/DC convertors while still
maintaining a reasonably high overall efficiency.
The LP3991 is particularly suitable for this role due to its low
input voltage requirements. In addition, there is often no need
for a separate input capacitor for the LP3991 as it can share
the output cap of the DC/DC convertor.
Care of PCB layouts involving switching regulators is
paramount. In particular, the ground paths for the LDO should
be routed separately from the switcher ground and star con-
nected close to the battery. Routing of the switch pin of the
DC/DC convertor must be kept short to minimize radiated
EMI. A low pass filter such as a ferrite bead or common mode
choke on the battery input leads can further reduce radiated
EMI.
Figure 2 shows a typical example using an LM3673, 350mA
DC/DC buck regulator with a nominal output of 1.8V and a
1.5V LP3991. The overall efficiency will be greater than 70%
over the full Li-Ion battery voltage range. Maximum efficiency
is achieved by minimizing the difference between VIN and
VOUT of the LP3991. The LP3991-1.5 will remain in regulation
down to an input voltage of 1.65V, so, in this case, a 1.8V
buck with 5% tolerance is adequate for all conditions of tem-
perature and load.
11 www.national.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LP3991.PDF ] | |
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