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.
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
10µH
CMDSH-3
5
MIC2287BD5
1-Cell
Li Ion
1µF
VIN
EN
SW
FB
GND
2
1
MIC2287-34BML
0.22µF
95mV
6.3Ω
1-Cell
Li Ion
1µF
VIN
EN
SW
OVP
FB
GND
0.22µF
4
3
95mV
6.3Ω
3-Series White LED Driver in Thin SOT-23
MLF and
MicroLeadFrame
are trademarks of Amkor Technology, Inc.
6-Series White LED Driver
with Output OVP in 2mm
×
2mm MLF™-8
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
MIC2287
Micrel, Inc.
Marking
Code
SGAA
SGAA
SLA
SLA
SLB
SLB
SLC
SLC
Overvoltage
Protection
N/A
N/A
15V
15V
24V
24V
34V
34V
Junction
Temp. Range
–40°C to 125°C
–40°C to 125°C
Ordering Information
Part Number
MIC2287BD5
MIC2287YD5
MIC2287-15BML
MIC2287-15YML
MIC2287-24BML
MIC2287-24YML
MIC2287-34BML
MIC2287-34YML
Package
Thin SOT-23-5
Thin SOT-23-5
Lead Finish
Standard
Lead Free
Standard
Lead Free
Standard
Lead Free
Standard
Lead Free
–40°C to 125°C 2mm x 2mm MLF™
–40°C to 125°C 2mm x 2mm MLF™
–40°C to 125°C 2mm x 2mm MLF™
–40°C to 125°C 2mm x 2mm MLF™
–40°C to 125°C 2mm x 2mm MLF™
–40°C to 125°C 2mm x 2mm MLF™
Pin Configuration
FB GND SW
1
2
3
OUT
VIN
4
EN
5
VIN
1
2
3
4
8
7
6
GND
SW
FB
NC
EN
GND
EP
5
TSOT-23-5 (BD5)
8-Pin MLF™ (BML)
(Top View)
Fused Lead Frame
Pin Description
Pin Number
Pin Number
TSOT-23-5 2mm
×2mm
MLF™
1
2
3
4
5
—
—
—
—
—
6
3
2
1
4
8
5
EP
7
Pin Name
SW
GND
FB
EN
VIN
OVP
AGND
PGND
NC
GND
Pin Function
Switch node (Input): Internal power BIPOLAR collector.
Ground (Return): Ground.
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.
Enable (Input): Logic high enables regulator. Logic low shuts down regula-
tor.
Supply (Input): 2.5V to 10V for internal circuitry.
Overvoltage protection (Input): Connect to the output.
Analog ground.
Power ground.
No connect (no internal connection to die).
Ground (Return): Exposed backside pad.
M9999-070105
2
July 2005
MIC2287
Micrel, Inc.
Absolute Maximum Ratings
(1)
Supply Voltage (V
IN
) ..................................................... 12V
Switch Voltage (V
SW
) ......................................–0.3V to 34V
Enable Pin Voltage (V
EN
) ................................... –0.3 to V
IN
FB Voltage (V
FB
) ............................................................. 6V
Switch Current (I
SW
) ........................................................ 2A
Ambient Storage Temperature (T
S
) .......... –65°C to +150°C
ESD Rating
(3)
............................................................... 2kV
Operating Ratings
(2)
Supply Voltage (V
IN
) ..........................................2.5V to 10V
Junction Temperature Range (T
J
) ............ –40°C to +125°C
Package Thermal Impedance
2mm
×
2mmMLF™ (θ
JA
) ..................................... 93°C/W
Thin SOT-23-5 (θ
JA
) ......................................... 256°C/W
Electrical Characteristics
(4)
T
A
= 25°C, V
IN
= V
EN
= 3.6V, V
OUT
= 10V, I
OUT
= 10mA, unless otherwise noted.
Bold
values indicate –40°C ≤ T
J
≤125°C.
Symbol
Parameter
Condition
Min
2.5
1.8
V
EN
=
V
FB
> 200mV, (not switching)
0V
(5)
(±5%)
90
2.1
2.5
0.1
95
–450
0.5
0.5
85
90
750
I
SW
= 0.5A
450
0.01
1.5
20
1.05
13
21
30
1.2
14
22.5
32
150
10
5
0.4
40
1.35
16
24
34
V
EN
= 0V, V
SW
= 10V
1
2
Typ
V
IN
Supply Voltage Range
Under Voltage Lockout
Quiescent Current
Shutdown Current
Feedback Voltage
Feedback Input Current
Line Regulation
(6)
Load Regulation
(6)
D
MAX
I
SW
I
SW
V
SW
V
EN
I
EN
Maximum Duty Cycle
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
Enable Threshold
Enable Pin Current
Oscillator Frequency
Overvoltage Protection
Max
10
2.4
5
1
100
Units
V
V
mA
µA
mV
nA
%
%
%
mA
mV
µA
V
V
µA
MHz
V
V
V
°C
°C
V
UVLO
I
VIN
I
SD
I
FB
V
FB
V
FB
= 95mV
3V ≤ V
IN
≤ 5V
5mA ≤ I
OUT
≤ 20mA
TURN ON
TURN OFF
V
EN
= 10V
f
SW
V
OVP
T
J
Notes:
MIC2287BML- 15 only
MIC2287BML- 24 only
MIC2287BML- 34 only
Hysteresis
Overtemperature
Threshold Shutdown
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, T
J
(max),
the junction-to-ambient thermal resistance,
θ
JA
, and the ambient temperature, T
A
. 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.
I
SD
= I
VIN
.
6.
Guaranteed by design.
July 2005
3
M9999-070105
MIC2287
Micrel, Inc.
Typical Characteristics
Feedback Voltage
vs. Input Voltage
SHUTDOWN CURRENT (µA)
100
99
98
97
96
95
94
93
92
91
90
0
5
4
3
2
1
0
Shutdown Current
vs. Input Voltage
5
QUIESCENT CURRENT (mA)
Quiescent Current
vs. Input Voltage
FB VOLTAGE (mV)
4
3
2
1
0
2
4
6
V
IN
(V)
8
10
12
0
2
4
6
V
IN
(V)
8
10
12
0
2
4
6
V
IN
(V)
8
10
12
3 Series LED Efficiency
84
82
EFFICIENCY (%)
EFFICIENCY (%)
84
6 Series LED Efficiency
SWITCHING FREQUENCY (MHz)
V
IN
= 4.2V
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-40
Switch Frequency
vs. Temperature
80
V
IN
= 3.0V
82
80
78
76
V
IN
= 3.6V
78
76
74
V
IN
= 3.6V
V
IN
= 3.0V
V
IN
= 4.2V
74
72
72
70
0
5
L = 10µH
C
= 0.22µF
OUT
10
15
I
OUT
(mA)
20
25
70
L = 10µH
C
OUT
= 0.22µF
0
5
10
15
I
OUT
(mA)
20
25
0
40
80
TEMPERATURE (°C)
120
50
45
40
IENABLE (µA)
EN Pin Bias Currency
vs. Temperature
SATURATION VOL AGE (mV)
550
500
450
400
350
Saturation Voltage
vs. Temperature
900
Current Limit
vs. Temperature
35
30
25
20
15
I
EN
= 10V
CURRENT LIMIT (mA)
I
SW
= 500mA
0
40
80
TEMPERATURE (°C)
120
850
800
750
700
650
600
-40
I
EN
= 4.2V
10
5
I = 3.0V
0
EN
0
50
-50
TEMPERATURE (°C)
I
EN
= 3.6V
100
300
-40
V
IN
= 2.5V
0
40
80
TEMPERATURE (°C)
120
600
Switch Saturation Voltage
vs. Current
SATURATION VOL AGE (mV)
500
400
300
200
100
0
0
100
200 300
I
SW
(mA)
400
500
V
IN
= 2.5V
V
IN
= 5V
M9999-070105
4
July 2005
MIC2287
Micrel, Inc.
Functional Diagram
VIN
FB
OVP*
EN
OVP*
SW
g
m
95mV
S
V
REF
PWM
Generator
1.2MHz
Oscillator
*
OVP available on MLF
TM
package option only
Ramp
Generator
GND
MIC2287 Block Diagram
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, g
m
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 g
m
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 g
m
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
I
LED
=
R
FB
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
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