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PDF MIC2291-15YML Data sheet ( Hoja de datos )
| Número de pieza | MIC2291-15YML | |
| Descripción | 1.2A PWM Boost Regulator Photo Flash LED Driver | |
| Fabricantes | Micrel Semiconductor | |
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MIC2291
MIC2291
1.2A PWM Boost Regulator
Photo Flash LED Driver
Micrel
General Description
The MIC2291 is a 1.2MHz Pulse Width Modulation (PWM),
boost-switching regulator that is optimized for high-current,
white LED photo flash applications. With a guaranteed switch
current of 1.2A, the MIC2291 easily drives a string of 3 white
LEDs in series at 100mA, ensuring a high level of brightness
and eliminating several ballast resistors.
The MIC2291 implements a constant frequency, 1.2MHz
PWM control scheme. The high frequency PWM operation
saves board space by reducing external component sizes.
The added benefit of the constant frequency PWM scheme,
in contrast to variable frequency topologies, is much lower
noise and input ripple injected back to the battery source.
To optimize efficiency, the feedback voltage is set to only
95mV. This reduces the power dissipation in the current set
resistor, and allows the lowest total output voltage, hence
minimal current draw from the battery.
The MIC2291 is available with 2 levels of over-voltage
protection, 15V, and 34V. This allows designers to choose
the smallest possible external components with the appropri-
ate voltage ratings for their applications.
The MIC2291 is available in low-profile, Thin SOT23 5-lead
and 8-lead 2mm × 2mm MLF™ package options. The MIC2291
has a junction temperature range of –40°C to +125°C.
All support documentation can be found on Micrel’s web
site at www.micrel.com.
Features
• 2.5V to 10V input voltage
• Output voltage up to 34V
• 1.2A switch current
• 1.2MHz PWM operation
• 95mV feedback voltage
• Overvoltage protection (OVP)
– Options for 15V and 34V
• Stable with ceramic capacitors
• <1% line and load regulation
• 1µA shutdown current
• Over temperature protection
• UVLO
• Low-profile Thin SOT23-5 package option
• 2mm × 2mm MLF™ package option
• –40°C to +125°C junction temperature range
Applications
• Photo Flash LED driver
• Cell phones
• PDAs
• GPS systems
• Digital cameras
• IP phones
• LED flashlights
Typical Application
10µH
100mA
1-Cell
Li Ion
3V to 4.2V
MIC2291BD5
5
VIN
1
SW
1µF
4 EN
FB 3
95mV
GND
2
0.95Ω
0.22µF
ceramic
Thin SOT23 Flash LED Driver
1-Cell
Li Ion
3V to 4.2V
10µH
100mA
MIC2291-15BML
VIN SW
1µF EN OVP
FB
GND
95mV
0.95Ω
0.22µF
2mm × 2mm Flash LED Driver with Output OVP
MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc.
PowerPAK is a trademark of Siliconix, Inc.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
August, 2004
1
M9999-081104
1 page  
MIC2291
Functional Diagram
Micrel
VIN FB OVP*
EN
OVP*
VREF
95mV
gm
PWM
Generator
Σ
1.2MHz
Oscillator
Ramp
Generator
*OVP available on MLFTM package option only
Figure 1. MIC2291 Block Diagram
SW
GND
Functional Description
The MIC2291 is a constant frequency, PWM current mode
boost regulator. The block diagram is shown above. The
MIC2291 is composed of an oscillator, slope compensation
ramp generator, current amplifier, gm error amplifier, PWM
generator, and a 500mA bipolar output transistor. The
oscillator generates a 1.2MHz clock. The clock’s two func-
tions are to trigger the PWM generator that turns on the output
transistor and to reset the slope compensation ramp genera-
tor. The current amplifier is used to measure the switch
current by amplifying the voltage signal from the internal
sense resistor. The output of the current amplifier is summed
with the output of the slope compensation ramp generator.
This summed current-loop signal is fed to one of the inputs of
the PWM generator.
The gm error amplifier measures the LED current through the
external sense resistor and amplifies the error between the
detected signal and the 95mV reference voltage. The output
of the gm error amplifier provides the voltage-loop signal that
is fed to the other input of the PWM generator. When the
current-loop signal exceeds the voltage-loop signal, the
PWM generator turns off the bipolar output transistor. The
next clock period initiates the next switching cycle, maintain-
ing the constant frequency current-mode PWM control. The
LED is set by the feedback resistor:
95mv
ILED = RFB
The Enable pin shuts down the output switching and disables
control circuitry to reduce input current-to-leakage levels.
Enable pin input current is zero at zero volts.
August, 2004
5
M9999-081104
5 Page | ||
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| PDF Descargar | [ Datasheet MIC2291-15YML.PDF ] | |
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