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PDF LP3905 Data sheet ( Hoja de datos )
| Número de pieza | LP3905 | |
| Descripción | Power Management Unit For Low Power Handheld Applications | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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www.DataSheet4U.com
August 2006
LP3905
Power Management Unit For Low Power Handheld
Applications
General Description
LP3905 is a multi-functional Power Management Unit,
optimized for low power handheld applications. This device
integrates two 600mA DC/DC buck regulators and two
150mA linear regulators. Fixed and adjustable buck output
versions are available. The LP3905 additionally features two
enable pins for the device output control and is offered in an
LLP package.
Features
n Two buck regulators for powering high current processor
functions or peripheral devices
n Two linear regulators for powering internal processor
functions and I/Os
n One enable pin for Buck1 and Linear Regulators 1 & 2
n Separate enable pin for Buck2
n Thermal and current overload protection
n Small 14–Pin LLP package (4mm x 4mm x 0.8mm)
Applications
n Baseband Processors
n Peripheral Processor (Video, Audio)
n I/O Power
n FPGA Power
Key Specifications
Buck Regulators
n Fixed and adjustable voltage options, range 1.0V to
3.3V *
n Up to 90% Efficiency
n Auto-switching PFM-PWM mode and fixed PWM mode
n 2MHz PWM fixed switching frequency (Typ)
n 600mA output current
n ±4% output voltage accuracy over temp.
n Internal softstart
n 2.2µH inductor, 10µF Input and 10µF output Caps
Linear Regulators
n Output options in the range 1.5V to 3.3V *
n 13.5µVrms output voltage noise
n PSRR - 70dB @ 1kHz
n ±3% output voltage accuracy over full line and load
regulation
n 0mA to 150mA output current
n Cin = 1.0µF, Cout = 0.47µF for 100mA O/P
Cin = 1.0µF, Cout = 1.0µF for 150mA O/P
80mV Dropout voltage
* Fixed output voltage devices can be customized to fit
system requirements. Please contact National Semiconduc-
tor Sales Office.
Typical Application Circuit
FIGURE 1. Typical Application Circuit – 14 Pin LLP Package
20152901
© 2006 National Semiconductor Corporation DS201529
www.national.com
1 page  
General Electrical Characteristics (Notes 2, 8, 9) (Continued)
Buck Regulator Electrical Characteristics
Buck 1 & 2 have a current rating of Imax= 600mA. Unless otherwise specified, limits are set with VIN = VEN1/2 = 3.8V, VOUT-
(Buck1)= Vnom1 , VOUT(Buck2)= Vnom2 and CIN= COUT=10µF. Limits in standard typeface are for TJ = 25˚C. Limits in boldface
type apply over the full junction temperature range (−40˚C ≤ TJ ≤ +125˚C). Unless otherwise noted, specifications apply to the
LP3905 Typical Application Circuit (Figure. 1) (Notes 2, 8)
Symbol
Parameter
Condition
Min Typ Max Units
VFB
VOUT
Feedback Voltage
Line Regulation
RDSON (P)
RDSON (N)
ILIM
FOSC
η
Load Regulation
Pin-Pin Resistance for PFET
Pin-Pin Resistance for NFET
Switch Peak Current Limit
Internal Oscillator Frequency
Efficiency
(Note 16)
3.0V ≤ VIN ≤ 5.5V
IO = 1mA
100 mA ≤ IO ≤ 600mA
VIN= VGS= 3.6V
VIN= VGS= 3.6V (Note 15)
Open Loop
PWM Mode
IOUT = 5mA, PFM mode (Note 15)
-4 +4
0.045
%
%/V
0.002
%/mA
380 500
mΩ
250 400
mΩ
650 1000 1220
mA
2 MHz
88 %
IOUT = 300mA, PWM mode (Note 15) 90
LDO Regulator Electrical Characteristics
The linear regulators have a current rating of Imax= 150mA with COUT = 1.0µF. A 100mA rating applies with COUT = 0.47µF.
Unless otherwise specified, limits are set with VIN = 3.8V, VEN1/2 = 3.8V, CIN = 1µF, COUT = 0.47µF, IOUT = 1.0mA. Limits in
standard typeface are for TJ = 25˚C. Limits in boldface type apply over the full junction temperature range (−40˚C ≤ TJ ≤
+125˚C). Unless otherwise noted, specifications apply to the LP3905 Typical Application Circuit (Figure. 1)(Notes 2, 8)
Symbol
Parameter
Conditions
Min Typ Max Units
∆VOUT
ILOAD
VDO
ISC
IOUT
PSRR
Output Voltage Tolerance
Line Regulation Error
Load Regulation Error
Load Current
Dropout Voltage
Short Circuit Current Limit
Maximum Output Current
Power Supply Rejection Ratio
(Note 15)
en Output Noise Voltage
(Note 15)
Over Full Line and Load Regulation
−3
3%
VIN = 3.8V to 5.5V,
IOUT = 1mA
IOUT = 1 mA to 100mA
(Notes 11, 15)
0.05
0.003
0
%/V
%/mA
mA
IOUT = 100mA
(Note 13)
80 150 mV
300 500 mA
COUT = 1.0µF
f = 100Hz, IOUT = 100mA
f = 1kHz, IOUT = 100mA
f = 10kHz, IOUT = 100mA
f = 50kHz, IOUT = 100mA
f = 100kHz, IOUT = 100mA
BW = 10Hz to
IOUT = 1mA
100kHz, VIN = 4.2V
Buck1 Turned ON
with ILOAD= 0mA,
IOUT = 100mA
Buck2 Turned OFF
150
90
90
60
35
25
13.5
15.5
mA
dB
µVRMS
5 www.national.com
5 Page 
Application Information
DC/DC CONVERTORS
Adjustable Buck - Output Voltage Selection
The buck converter output voltage of the adjustable version
device can be set via the selection of the external feedback
resistor network forming the output feedback between the
output voltage side of the Inductor and the FB pin and the FB
Pin and GND.
around 200kΩ to keep the current drawn through the resistor
network well below the 16µA quiescent current level (PFM
mode) but large enough that it is not susceptible to noise. If
R2 is 200kΩ and with VFB at 0.5V, the current through the
resistor feedback network will be 2.5µA.
The formula for output voltage selection is
VOUT - output voltage (Volts)
VFB - feedback voltage (0.5V)
R1FB - feedback resistor from VOUT to FB
R2FB - feedback resistor from FB to GND
For any out voltage greater than or equal to 1.0V a zero
should be added around 45 kHz by the addition of a capaci-
tor C1. The formula for the calculation of C1 is:
20152958
Adjustable Buck Converter Components
VOUT will be adjusted to make the voltage at FB equal to
0.5V. The resistor from FB to ground (RFB2) should be
For recommended component values see Table 1
TABLE 1. Buck Component Configurations for Various Output Voltage Values
VOUT (V)
1.0
1.2
1.4
1.5
1.6
1.85
2.5
2.8
3.3
RFB1 (kΩ)
200
280
360
360
442
540
402
464
562
RFB2 (kΩ)
200
200
200
180
200
200
100
100
100
C1 (pF)
18
12
10
10
8.2
6.8
8.2
8.2
6.8
C2 (pF)
none
none
none
none
none
none
none
33
33
L (µH)
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
2.2
COUT (µF)
10
10
10
10
10
10
10
10
10
Buck Inductor Selection
There are two main considerations when choosing an induc-
tor; the inductor should not saturate, and the inductor current
ripple is small enough to achieve the desired output voltage
ripple. Different saturation current rating specs are followed
by different manufacturers so attention must be given to
details. Saturation current ratings are typically specified at
25˚C so ratings at max ambient temperature of application
should be requested from manufacturer.
There are two methods to choose the inductor saturation
current rating.
Method 1:
The saturation current is greater than the sum of the maxi-
mum load current and the worst case average to peak
inductor current. This can be written as
• IOUTMAX: maximum load current (600mA)
• VIN: maximum input voltage in application
• L : min inductor value including worst case tolerances
(30% drop can be considered for method 1)
• f : minimum switching frequency (1.6Mhz)
• VOUT: output voltage
Method 2:
A more conservative and recommended approach is to
choose an inductor that has saturation current rating greater
than the max current limit of 1220mA.
A 2.2µH inductor with a saturation current rating of at least
1250mA is recommended for most applications.The induc-
tor’s resistance should be less than 0.3Ω for good efficiency.
For low-cost applications, an unshielded bobbin inductor
could be considered. For noise critical applications, a toroi-
dal or shielded-bobbin inductor should be used. A good
practice is to lay out the board with overlapping footprints of
both types for design flexibility. This allows substitution of a
low-noise shielded inductor, in the event that noise from
low-cost bobbin models is unacceptable.
• IRIPPLE: average to peak inductor current
11
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet LP3905.PDF ] | |
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