July 2005 1 M9999-070105
MIC2287 Micrel, Inc.
MIC2287
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.
Typical Application
10µH
0.22µF
6.3Ω
95mV
1-Cell
Li Ion 1µF
2
3
1
4
5
MIC2287BD5
VIN
EN
SW
FB
GND
CMDSH-3
3-Series White LED Driver in Thin SOT-23
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
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc.
10µH
0.22µF
1µF1-Cell
Li Ion
6.3Ω
MIC2287-34BML
VIN
EN
SW
OVP
FB
GND
95mV
CMDSH-3
6-Series White LED Driver
with Output OVP in 2mm × 2mm MLF™-8
MIC2287 Micrel, Inc.
M9999-070105 2 July 2005
Pin Description
Pin Number Pin Number
TSOT-23-5 2mm ×2mm MLF™ Pin Name Pin Function
1 7 SW Switch node (Input): Internal power BIPOLAR collector.
2 GND Ground (Return): Ground.
3 6 FB Feedback (Input): Output voltage sense node. Connect the cathode of the
LED to this pin. A resistor from this pin to ground sets the LED current.
4 3 EN Enable (Input): Logic high enables regulator. Logic low shuts down regula-
tor.
5 2 VIN Supply (Input): 2.5V to 10V for internal circuitry.
— 1 OVP Overvoltage protection (Input): Connect to the output.
— 4 AGND Analog ground.
— 8 PGND Power ground.
— 5 NC No connect (no internal connection to die).
— EP GND Ground (Return): Exposed backside pad.
Pin Configuration
FB GND
EN VIN
SW
31
5
2
4
TSOT-23-5 (BD5)
OUT
VIN
EN
GND
GND
SW
FB
NC
1
2
3
4
8
7
6
5
EP
8-Pin MLF™ (BML)
(Top View)
Fused Lead Frame
Ordering Information
Marking Overvoltage Junction
Part Number Code Protection Temp. Range Package Lead Finish
MIC2287BD5 SGAA N/A –40°C to 125°C Thin SOT-23-5 Standard
MIC2287YD5 SGAA N/A –40°C to 125°C Thin SOT-23-5 Lead Free
MIC2287-15BML SLA 15V –40°C to 125°C 2mm x 2mm MLF™ Standard
MIC2287-15YML SLA 15V –40°C to 125°C 2mm x 2mm MLF™ Lead Free
MIC2287-24BML SLB 24V –40°C to 125°C 2mm x 2mm MLF™ Standard
MIC2287-24YML SLB 24V –40°C to 125°C 2mm x 2mm MLF™ Lead Free
MIC2287-34BML SLC 34V –40°C to 125°C 2mm x 2mm MLF™ Standard
MIC2287-34YML SLC 34V –40°C to 125°C 2mm x 2mm MLF™ Lead Free
July 2005 3 M9999-070105
MIC2287 Micrel, Inc.
Absolute Maximum Ratings(1)
Supply Voltage (VIN) ..................................................... 12V
Switch Voltage (VSW) ......................................–0.3V to 34V
Enable Pin Voltage (VEN) ................................... –0.3 to VIN
FB Voltage (VFB) ............................................................. 6V
Switch Current (ISW) ........................................................ 2A
Ambient Storage Temperature (TS) .......... –65°C to +150°C
ESD Rating(3) ............................................................... 2kV
Operating Ratings(2)
Supply Voltage (VIN) ..........................................2.5V to 10V
Junction Temperature Range (TJ) ............ –40°C to +125°C
Package Thermal Impedance
2mm × 2mmMLF™ (θJA) ..................................... 93°C/W
Thin SOT-23-5 (θJA) .........................................256°C/W
Electrical Characteristics(4)
TA = 25°C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 10mA, unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤125°C.
Symbol Parameter Condition Min Typ Max Units
VIN Supply Voltage Range 2.5 10 V
VUVLO Under Voltage Lockout 1.8 2.1 2.4 V
IVIN Quiescent Current VFB > 200mV, (not switching) 2.5 5 mA
ISD Shutdown Current VEN = 0V(5) 0.1 1 µA
VFB Feedback Voltage (±5%) 90 95 100 mV
IFB Feedback Input Current VFB = 95mV –450 nA
Line Regulation(6) 3V ≤ VIN ≤ 5V 0.5 1 %
Load Regulation(6) 5mA ≤ IOUT ≤ 20mA 0.5 2 %
DMAX Maximum Duty Cycle 85 90 %
ISW Switch Current Limit 750 mA
VSW Switch Saturation Voltage ISW = 0.5A 450 mV
ISW Switch Leakage Current VEN = 0V, VSW = 10V 0.01 5 µA
VEN Enable Threshold TURN ON 1.5 V
TURN OFF 0.4 V
IEN Enable Pin Current VEN = 10V 20 40 µA
fSW Oscillator Frequency 1.05 1.2 1.35 MHz
VOVP Overvoltage Protection MIC2287BML- 15 only 13 14 16 V
MIC2287BML- 24 only 21 22.5 24 V
MIC2287BML- 34 only 30 32 34 V
TJ Overtemperature 150 °C
Threshold Shutdown Hysteresis 10 °C
Notes:
1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating
the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(max),
the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. The maximum allowable power dissipation will result in excessive
die temperature, and the regulator will go into thermal shutdown.
2. This device is not guaranteed to operate beyond its specified operating ratings.
3. Devices are inherently ESD sensitive. Handling precautions required. Human body model.
4. Specification for packaged product only.
5. ISD = IVIN.
6. Guaranteed by design.
MIC2287 Micrel, Inc.
M9999-070105 4 July 2005
Typical Characteristics
90
91
92
93
94
95
96
97
98
99
100
0246810 12
FB VOLTAGE (mV)
VIN (V)
Feedback Voltage
vs. Input Voltage
0
1
2
3
4
5
0246810 12
SHUTDOWN CURRENT (µA)
VIN (V)
Shutdown Current
vs. Input Voltage
0
1
2
3
4
5
0246810 12
QUIESCENT CURRENT (mA)
VIN (V)
Quiescent Current
vs. Input Voltage
70
72
74
76
78
80
82
84
EFFICIENCY (%)
IOUT (mA)
3 Series LED Efficiency
L = 10µH
COUT = 0.22µF
VIN = 4.2V
VIN = 3.6V
VIN = 3.0V
0510 15 20 25
0
0.2
0.4
0.6
0.8
1
1.2
1.4
-40 0 40 80 120
SWITCHING FREQUENCY (MHz)
TEMPERATURE (°C)
Switch Frequency
vs. Temperature
0
5
10
15
20
25
30
35
40
45
50
-50 0 50 100
IENABLE (µA)
TEMPERATURE (°C)
EN Pin Bias Currency
vs. Temperature
IEN = 4.2V IEN = 3.6V
IEN = 3.0V
IEN = 10V
300
350
400
450
500
550
-40 0 40 80 120
SATURATION VOL
T
AGE (mV)
TEMPERATURE (°C)
Saturation Voltage
vs. Temperature
ISW = 500mA
600
650
700
750
800
850
900
-40 0 40 80 120
CURRENT LIMIT (mA)
TEMPERATURE (°C)
Current Limit
vs. Temperature
V
IN = 2.5V
0
100
200
300
400
500
600
0 100 200 300 400 500
SATURATION VOL
T
AGE (mV)
ISW (mA)
Switch Saturation Voltage
vs. Current
VIN = 2.5V
VIN = 5V
July 2005 5 M9999-070105
MIC2287 Micrel, Inc.
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.
Functional Diagram
GND
VREF
PWM
Generator
Ramp
Generator
1.2MHz
Oscillator
SW
ENFB
OVP*
VIN
95mV
*OVP available on MLFTM package option only
gm
OVP*
S
MIC2287 Block Diagram
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:
ILED =
95mv
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.
MIC2287 Micrel, Inc.
M9999-070105 6 July 2005
External Component Selection
The MIC2287 can be used across a wide rage of applications.
The table below shows recommended inductor and output
capacitor values for various series-LED applications.
Series LEDs L Manufacturer Min COUT Manufacturer
2 22µH LQH32CN220K21 (Murata) 2.2µF 0805ZD225KAT(AVX)
NLC453232T-220K(TDK) GRM40X5R225K10(Murata)
15µH LQH32CN150K21 (Murata) 1µF 0805ZD105KAT(AVX)
NLC453232T-150K(TDK) GRM40X5R105K10(Murata)
10µH LQH32CN100K21 (Murata) 0.22µF 0805ZD224KAT(AVX)
NLC453232T-100K(TDK) GRM40X5R224K10(Murata)
6.8µH LQH32CN6R8K21 (Murata) 0.22µF 0805ZD225KAT(AVX)
NLC453232T-6R8K(TDK) GRM40X5R225K10(Murata)
4.7µH LQH32CN4R7K21 (Murata) 0.22µF 0805ZD224KAT(AVX)
NLC453232T-4R7K(TDK) GRM40X5R224K10(Murata)
3 22µH LQH43MN220K21 (Murata) 2.2µF 0805YD225MAT(AVX)
NLC453232T-220K(TDK) GRM40X5R225K16(Murata)
15µH LQH43MN 150K21 (Murata) 1µF 0805YD105MAT(AVX)
NLC453232T-150K(TDK) GRM40X5R105K16(Murata)
10µH LQH43MN 100K21 (Murata) 0.22µF 0805YD224MAT(AVX)
NLC453232T-100K(TDK) GRM40X5R224K16(Murata)
6.8µH LQH43MN 6R8K21 (Murata) 0.22µF 0805YD224MAT(AVX)
NLC453232T-6R8K(TDK) GRM40X5R224K16(Murata)
4.7µH LQH43MN 4R7K21 (Murata) 0.27µF 0805YD274MAT(AVX)
NLC453232T-4R7K(TDK) GRM40X5R224K16(Murata)
4 22µH LQH43MN220K21 (Murata) 1µF 0805YD105MAT(AVX)
NLC453232T-220K(TDK) GRM40X5R105K25(Murata)
15µH LQH43MN 150K21 (Murata) 1µF 0805YD105MAT(AVX)
NLC453232T-150K(TDK) GRM40X5R105K25(Murata)
10µH LQH43MN 100K21 (Murata) 0.27µF 0805YD274MAT(AVX)
NLC453232T-100K(TDK) GRM40X5R274K25(Murata)
6.8µH LQH43MN 6R8K21 (Murata) 0.27µF 0805YD274MAT(AVX)
NLC453232T-6R8K(TDK) GRM40X5R274K25(Murata)
4.7µH LQH43MN 4R7K21 (Murata) 0.27µF 0805YD274MAT(AVX)
NLC453232T-4R7K(TDK) GRM40X5R274K25(Murata)
5, 6 22µH LQH43MN220K21 (Murata) 0.22µF 08053D224MAT(AVX)
NLC453232T-220K(TDK) GRM40X5R224K25(Murata)
15µH LQH43MN 150K21 (Murata) 0.22µF 08053D224MAT(AVX)
NLC453232T-150K(TDK) GRM40X5R224K25(Murata)
10µH LQH43MN 100K21 (Murata) 0.27µF 08053D274MAT(AVX)
NLC453232T-100K(TDK) GRM40X5R274K25(Murata)
6.8µH LQH43MN 6R8K21 (Murata) 0.27µF 08053D274MAT(AVX)
NLC453232T-6R8K(TDK) GRM40X5R274K25(Murata)
4.7µH LQH43MN 4R7K21 (Murata) 0.27µF 08053D274MAT(AVX)
NLC453232T-4R7K(TDK) GRM40X5R274K25(Murata)
7, 8 22µH LQH43MN220K21 (Murata) 0.22µF 08053D224MAT(AVX)
NLC453232T-220K(TDK) GRM40X5R224K25(Murata)
15µH LQH43MN 150K21 (Murata) 0.22µF 08053D224MAT(AVX)
NLC453232T-150K(TDK) GRM40X5R224K25(Murata)
10µH LQH43MN 100K21 (Murata) 0.27µF 08053D274MAT(AVX)
NLC453232T-100K(TDK) GRM40X5R274K25(Murata)
6.8µH LQH43MN 6R8K21 (Murata) 0.27µF 08053D274MAT(AVX)
NLC453232T-6R8K(TDK) GRM40X5R274K25(Murata)
4.7µH LQH43MN 4R7K21 (Murata) 0.27µF 08053D274MAT(AVX)
NLC453232T-4R7K(TDK) GRM40X5R274K25(Murata)
July 2005 7 M9999-070105
MIC2287 Micrel, Inc.
Dimming Control
There are two techniques for dimming control. One is PWM
dimming, and the other is continuous dimming.
1. PWM dimming control is implemented by applying
a PWM signal on EN pin as shown in Figure 1. The
MIC2287 is turned on and off by the PWM signal.
With this method, the LEDs operate with either zero
or full current. The average LED current is increased
proportionally to the duty-cycle of the PWM signal.
This technique has high-efficiency because the IC
and the LEDs consume no current during the off
cycle of the PWM signal. Typical PWM frequency
should be between 100Hz and 10kHz.
2. Continuous dimming control is implemented by
applying a DC control voltage to the FB pin of the
MIC2287 through a series resistor as shown in
Figure 2. The LED intensity (current) can be dy-
namically varied applying a DC voltage to the FB
pin. The DC voltage can come from a DAC signal,
or a filtered PWM signal. The advantage of this ap-
proach is a high frequency PWM signal (>10kHz)
that can be used to control LED intensity.
PWM
VIN
EN
SW
FB
GND
VIN
Figure 1. PWM Dimming Method
VIN
EN
SW
FB 5.11k
49.9k
GND
DC
VIN
Equivalent
Figure 2. Continuous Dimming
Open-Circuit Protection
If the LEDs are disconnected from the circuit, or in case
an LED fails open, the sense resistor will pull the FB pin to
ground. This will cause the MIC2287 to switch with a high
duty-cycle, resulting in output overvoltage. This may cause
the SW pin voltage to exceed its maximum voltage rating,
possibly damaging the IC and the external components. To
ensure the highest level of protection, the MIC2287 has 3
product options in the 8-lead 2mm × 2mm MLF™ with over-
voltage protection (OVP). The extra pins of the 8-lead 2mm
× 2mm MLF™ package allow a dedicated OVP monitor with
options for 15V, 24V, or 34V (see Figure 3). The reason for
the three OVP levels is to let users choose the suitable level
of OVP for their application. For example, a 3-LED application
would typically see an output voltage of no more than 12V, so
a 15V OVP option would offer a suitable level of protection.
This allows the user to select the output diode and capacitor
with the lowest voltage ratings, as well as smallest size and
lowest cost. The OVP will clamp the output voltage to within
the specified limits. For the Thin SOT-23-5 package, an OVP
pin is not available. An external zener diode can be connected
from the output of the converter to FB pin as shown in Figure
4. to implement similar protection.
VIN
EN
GND
SW
FB
OVP
VIN
Figure 3. MLF™ Package OVP Circuit
VIN
EN
SW
FB
GND
VIN
5.11k
Figure 4. Thin SOT-23 Package OVP Circuit
Start-Up and Inrush Current
During start-up, inrush current of approximately double the
nominal current flows to set up the inductor current and the
voltage on the output capacitor. If the inrush current needs
to be limited, a soft-start circuit similar to Figure 5 could be
implemented. The soft-start capacitor, CSS, provides over-
drive to the FB pin at start-up, resulting in gradual increase
of switch duty cycle and limited inrush current.
VIN
EN
SW
FB
CSS
2200pF
R
10k
GND
VIN
Figure 5. Soft-Start Circuit
MIC2287 Micrel, Inc.
M9999-070105 8 July 2005
6-Series LED Circuit without External Soft-Start
TIME (100µs/div.)
ENABLE
(2V/div)
INPUT CURRENT
(200mA/div)
OUTPUT VOL
T
AGE
L = 10µH
CIN = 1µF
COUT = 0.22µF
VIN = 3.6V
IOUT = 20mA
6 LEDs
6-Series LED Circuit with External Soft-Start
TIME (100µs/div.)
ENABLE
(2V/div)
INPUT CURRENT
(200mA/div)
OUTPUT VOL
T
AGE
L = 10µH
C
IN
= 1µF
COUT = 0.22µF
VIN = 3.6V
IOUT = 20mA
6 LEDs
C
SS
= 2200pF
R = 10kW
July 2005 9 M9999-070105
MIC2287 Micrel, Inc.
Package Information
5-Pin TSOT (BD5)
8-Pin MLF™ (BML)
MIC2287 Micrel, Inc.
M9999-070105 10 July 2005
Recommended Land Pattern for MLF™ 2×2 8 Lead
MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's
use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2004 Micrel, Inc.