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PDF MIC2287 Data sheet ( Hoja de datos )
| Número de pieza | MIC2287 | |
| Descripción | 1.2MHz PWM White LED Driver | |
| Fabricantes | Micrel Semiconductor | |
| Logotipo |  |
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MIC2287
MIC2287
Micrel, Inc.
1.2MHz PWM White LED Driver with OVP in
2mm × 2mm MLF™ and Thin SOT-23
General Description
The MIC2287 is a 1.2MHz pulse width modulated (PWM),
boost-switching regulator that is optimized for constant-
current, white LED driver applications. With a maximum
output voltage of 34V and a switch current of over 500mA,
the MIC2287 easily drives a string of up to 8 white LEDs in
series, ensuring uniform brightness and eliminating several
ballast resistors.
The MIC2287 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
as opposed 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 MIC2287 is available with 3 levels of overvoltage protec-
tion, 15V, 24V, and 34V. This allows designers to choose the
smallest possible external components with the appropriate
voltage ratings for their applications.
The MIC2287 is available in low profile Thin SOT-23 5-lead and
an 8-lead 2mm × 2mm MLF™ package options. The MIC2287
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
• Over 500mA switch current
• 1.2 MHz PWM operation
• 95mV feedback voltage
• Output Overvoltage Protection (OVP)
• Options for 15V, 24V, and 34V OVP
• <1% line and load regulation
• <1µA shutdown current
• Over-temperature protection
• UVLO
• Low profile Thin SOT-23-5 package option
• 8-lead 2mm × 2mm MLF™ package option
• –40°C to +125°C junction temperature range
Applications
• White LED driver for backlighting:
- Cell phones
- PDAs
- GPS systems
- Digital cameras
- MP3 players
- IP phones
• Photo flash LED driver
• LED flashlights
• Constant current power supplies
Typical Application
10µH
CMDSH-3
1-Cell
Li Ion
MIC2287BD5
5 VIN
SW 1
1µF
4 EN
FB 3
95mV
GND
2
6.3Ω
0.22µF
1-Cell
Li Ion
10µH
CMDSH-3
MIC2287-34BML
VIN SW
1µF EN OVP
FB
GND
95mV
6.3Ω
0.22µF
3-Series White LED Driver in Thin SOT-23
6-Series White LED Driver
with Output OVP in 2mm × 2mm MLF™-8
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
July 2005
1 M9999-070105
1 page  
MIC2287
Functional Diagram
VIN FB OVP*
EN
OVP*
VREF 95mV
gm
PWM
Generator
S
1.2MHz
Oscillator
Ramp
Generator
*OVP available on MLFTM package option only
MIC2287 Block Diagram
Micrel, Inc.
SW
GND
Functional Description
The MIC2287 is a constant frequency, PWM current mode
boost regulator. The block diagram is shown above. The
MIC2287 is composed of an oscillator, slope compensation
ramp generator, current amplifier, gm error amplifier, PWM
generator, and a 500mA bipolar output transistor. The oscil-
lator generates a 1.2MHz clock. The clock’s two functions
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 cur-
rent 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.
July 2005
5 M9999-070105
5 Page | ||
| Páginas | Total 10 Páginas | |
| PDF Descargar | [ Datasheet MIC2287.PDF ] | |
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