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PDF MIC2245 Data sheet ( Hoja de datos )
| Número de pieza | MIC2245 | |
| Descripción | PWM Synchronous Buck Regulator | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MIC2245 (archivo pdf) en la parte inferior de esta página. Total 14 Páginas | ||
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MIC2245
4MHz PWM Synchronous Buck
Regulator with LDO Standby Mode
General Description
The Micrel MIC2245 is a high efficiency 4MHz pulse
width modulated (PWM) synchronous buck (step-
down) regulator that features a LOWQ™ LDO
standby mode that draws only 18µA of quiescent
current. The MIC2245 allows an ultra-low noise,
small size, and high efficiency solution for portable
power applications.
In PWM mode, the MIC2245 operates with a
constant frequency 4MHz PWM control. Under light
load conditions, such as in system sleep or standby
modes, the PWM switching operation can be
disabled to reduce switching losses. In this light
load LOWQ™ mode, the LDO maintains the output
voltage and draws only 18µA of quiescent current.
The LDO mode of operation saves battery life while
not introducing spurious noise and high ripple as
experienced with pulse skipping or bursting mode
regulators.
The MIC2245 operates from a 2.7V to 5.5V input
voltage and features internal power MOSFETs that
can supply up to 500mA output current in PWM
mode. It can operate with a maximum duty cycle of
100% for use in low-dropout conditions.
The MIC2245 is available in the 10-pin 3mm x 3mm
MLF™ package with a junction operating range from
–40°C to +125°C.
Data sheet and support documentation can be found
on Micrel’s web site at: www.micrel.com.
Features
• 2.7 to 5.5V supply/input voltage
• Light load LOWQ™ LDO mode
20µA quiescent current
Low noise, 75µVrms
• 4MHz PWM mode
Output current to 500mA
>92% efficiency
100% maximum duty cycle
• Adjustable output voltage option down to 1V
Fixed output voltage options available
• Ultra-fast transient response
• Uses a tiny 1µH inductor
• Fully integrated MOSFET switches
• Micropower shutdown operation
• Thermal shutdown and current limit protection
• Pb-free 10-pin 3mm x 3mm MLF™ package
• –40°C to +125°C junction temperature range
Applications
• Cellular phones
• PDAs
• USB peripherals
____________________________________________________________________________________________________
Typical Application
Adjustable Output Buck Regulator with LOWQ™ Mode
100
90
80
70
60
50
40
30
20
10
00
1.8VOUT Efficiency
VIN=3.2V
VIN=3.6V
VIN=4.2V
100 200 300 400 500
OUTPUT CURRENT (mA)
Patent Pending
LOWQ is a trademark of Micrel, Inc
MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc
Micrel, Inc • 2180 Fortune Drive • San Jose, Ca 95131 • USA • tel +1 (408) 944-0800 • fax +1 (408) 474-1000 • http://www.micrel.com
January 2006
M9999-012406
www.micrel.com
1 page  
Micrel, Inc.
Typical Characteristics – PWM Mode
100
90
80
70
60
50
40
30
20
10
00
2.5VOUT Efficiency
VIN=3.2V
VIN=3.6V
VIN=4.2V
100 200 300 400 500
OUTPUT CURRENT (mA)
100
90
80
70
60
50
40
30
20
10
00
1.8VOUT Efficiency
VIN=3.2V
VIN=3.6V
VIN=4.2V
100 200 300 400 500
OUTPUT CURRENT (mA)
1.2VOUT Efficiency
100
90 VIN=3.2V
80
70 VIN=3.6V
60
50
VIN=4.2V
40
30
20
10
00 100 200 300 400 500
OUTPUT CURRENT (mA)
1.0VOUT Efficiency
100
90 VIN=3.2V
80
70
60
VIN=3.6V
50 VIN=4.2V
40
30
20
10
00 100 200 300 400 500
OUTPUT CURRENT (mA)
Quiescent Current
vs. Input Voltage
900
850
800
750
700
650
6020.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
INPUT VOLTAGE (V)
Frequency
vs. Input Voltage
4.5
4.3
4.1
3.9
3.27.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
INPUT VOLTAGE (V)
Enable Threshold
vs. Supply Voltage
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6 L
0.52.7
owQ = VIN
3.4
4.1
4.8
SUPPLY VOLTAGE (V)
5.5
January 2006
5
MIC2245
1.5VOUT Efficiency
100
90 VIN=3.2V
80
70 VIN=3.6V
60 VIN=4.2V
50
40
30
20
10
00 100 200 300 400 500
OUTPUT CURRENT (mA)
Load Regulation
1.004
1.002
1.000
0.998
0.996
0.994
VIN=3.6V
LowQ=VIN
0.992
0.9900
100 200 300 400 500
OUTPUT CURRENT (mA)
Peak Current Limit
vs. Supply Voltage
1200
1000
800
600
400
200
L
02.7
owQ = VIN
3.4
4.1
4.8
SUPPLY VOLTAGE (V)
5.5
M9999-012406
www.micrel.com
5 Page 
Micrel, Inc.
Applications Information
The MIC2245 is a 500mA PWM power supply that
utilizes a LOWQ™ light load mode to maximize
battery efficiency in light load conditions. This is
achieved with a LOWQ control pin that when pulled
low, shuts down all the biasing and drive current for
the PWM regulator, drawing only 20µA of operating
current. This allows the output to be regulated
through the LDO output, capable of providing 60mA
of output current. This method has the advantage of
producing a clean, low current, ultra-low noise
output in LOWQ™ mode. During LOWQ™ mode,
the SW node becomes high impedance, blocking
current flow. Other methods of reducing quiescent
current, such as pulse frequency modulation (PFM),
or bursting techniques, create large amplitude, low
frequency ripple voltages that can be detrimental to
system operation.
When more than 60mA is required, the LOWQ pin
can be forced high, causing the MIC2245 to enter
PWM mode. In this case, the LDO output makes a
"hand-off" to the PWM regulator with virtually no
variation in output voltage. The LDO output then
turns off allowing up to 500mA of current to be
efficiently supplied through the PWM output to the
load.
Input Capacitor
A minimum 1µF ceramic is recommended on the
VIN pin for bypassing. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V
dielectrics lose most of their capacitance over
temperature and are therefore, not recommended.
A minimum 1µF is recommended close to the VIN
and PGND pins for high frequency filtering. Smaller
case size capacitors are recommended due to their
lower ESR and ESL. Please refer to layout
recommendation section of data sheet for proper
layout of the input capacitor.
MIC2245
Output Capacitor
The MIC2245 is optimized for a 4.7µF output
capacitor. The MIC2245 utilizes type III internal
compensation and utilizes an internal high frequency
zero to compensate for the double pole roll off of the
LC filter. For this reason, larger output capacitors
can create instabilities. X5R or X7R dielectrics are
recommended for the output capacitor. Y5V
dielectrics lose most of their capacitance over
temperature and are therefore, not recommended.
In addition to a 4.7µF, a small 10nF is recommended
close to the load for high frequency filtering. Smaller
case size capacitors are recommended due to there
lower ESR and ESL.
Inductor Selection
The MIC2245 is designed for use with a 1.0µH
inductor. Proper selection should ensure the
inductor can handle the maximum average and peak
currents required by the load. Maximum current
ratings of the inductor are generally given in two
methods; permissible DC current and saturation
current. Permissible DC current can be rated either
for a 40°C temperature rise or a 10% to 20% loss in
inductance. Ensure that the inductor selected can
handle the maximum operating current. When
saturation current is specified, make sure that there
is enough margin that the peak current will not
saturate the inductor. Peak inductor current can be
calculated as follows:
IPK
= IOUT
+
VOUT ⎜⎜⎝⎛1−
VOUT
VIN
2×f ×L
⎟⎟⎠⎞
January 2006
11 M9999-012406
www.micrel.com
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet MIC2245.PDF ] | |
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