Micrel, Inc
MIC3287
MIC3287
1.2MHz PWM White LED Driver with OVP in
Thin SOT-23 and 2mm x 2mm MFL
®
General Description
The MIC3287 is a 1.2MHz pulse width modulated (PWM)
step-up switching regulator that is optimized for constant cur-
rent white LED driving applications. With a switch current of
over 350mA, the MIC3287-24 drives a string of up to 4 white
LEDs in series, ensuring uniform brightness and eliminating
several ballast resistors.
The MIC3287 implements a constant frequency 1.2MHz PWM
current-mode control scheme. The high frequency PWM op-
eration saves board space by reducing external component
sizes. The added benefit of the constant frequency PWM
control scheme as opposed to variable frequency control
schemes is much lower noise and input ripple injected back
to the battery source. To optimize efficiency, the feedback
voltage is set to only 250mV. The MIC3287 is also available
with a maximum 24V over-voltage protection.
The MIC3287 is available in low profile Thin SOT-23 5-pin
and Thin SOT-23 6-pin packages. The MIC3287 has a junc-
tion temperature range of –40°C to +125°C.
All support documentation can be found on Micrel’s web site
at: www.micrel.com.
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
2.8V to 6.5V Input Voltage
350mA Switch Current
1.2 MHz PWM Operation
250mV Feedback Voltage
Optional 24V Output Over-Voltage Protection (OVP)
Up to 36V Output Voltage without OVP
<1% Line and Load Regulation
<1µA Shutdown Current
Over-Temperature Protection
Under-Voltage Lock Out (UVLO)
Low Profile Thin SOT-23-5 Package Option
Low Profile Thin SOT-23-6 Package Option
8-pin 2mm x 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
• LED Flashlights
• Constant Current Power Supplies
Typical Application
10µH
10µH
5
MIC3287YD5
VIN
EN
GND
2
1-Cell
Li Ion
1µF
SW
FB
1
MIC3287-24YD6
6
4
3
0.22µF
250mV
1-Cell
Li Ion
1µF
VIN
EN
SW
OVP
FB
GND
2
1
5
3
4
0.22µF
250mV
3-Series White LED Driver in Thin SOT-23-5
MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.
4-Series White LED Driver
with Output OVP in Thin SOT-23-6
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 2010
1
M9999-042910
Micrel, Inc.
MIC3287
Marking
Code
WGAA
WHAA
WLA
Overvoltage
Protection
N/A
24V
24V
Junction
Temp. Range
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
Ordering Information
Part Number
MIC3287YD5
MIC3287-24YD6
MIC3287-24YML
Package
Thin SOT-23-5
Thin SOT-23-6
8-Pin 2mm x 2mm MLF
Lead Finish
Lead Free
Lead Free
Lead Free
Pin Configuration
FB GND
SW
1
2
3
FB GND
SW
3
2
1
VIN 1
OVP
2
4
EN
5
VIN
4
5
6
EN
OVP
VIN
EN 3
AGND 4
EP
8
7
6
5
PGND
SW
FB
NC
TSOT-23-5
(YD5)
TSOT-23-6
(YD6)
8-Pin 2mm x 2mm MLF™ (YML)
Pin Description
Pin Number Pin Number
TSOT-23-5
TSOT-23-6
1
2
2
3
4
5
—
—
—
1
2
2
3
4
6
5
—
—
Pin Number
8-Pin MLF
7
4
8
6
3
1
2
5
EP
Pin Name
SW
AGND
PGND
FB
EN
VIN
OVP
NC
EP
Pin Function
Switch Node (Input): Internal power bipolar collector.
Analog Ground (Return): Ground.
Power 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 regu-
lator.
Supply (Input): 2.8V to 6.5V for internal circuitry.
Overvoltage Protection (Input): Connect to the output.
Not Connected
Exposed Backside Pad: Connect to ground.
April 2010
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M9999-042910
Micrel, Inc
MIC3287
Absolute Maximum Ratings
(1)
Supply Voltage (V
IN
) ........................................................ 7V
Switch Voltage (V
SW
) ......................................–0.3V to 40V
Enable Pin Voltage (V
EN
) ................................... –0.3 to V
IN
FB Voltage (V
FB
) .............................................................
6V
Switch Current (I
SW
) ..................................................... 1.2A
Ambient Storage Temperature (T
S
) ..........
–65°C to +150°C
ESD Rating
(3)
................................................................ 2kV
Operating Ratings
(2)
Supply Voltage (V
IN
) .........................................2.8V
to 6.5V
Output Voltage (V
OUT
) .........................................V
IN
to 36V
Output Voltage (V
OUT
)
(4)
...................................V
IN
to V
OVP
Junction Temperature Range (T
J
) ............ –40°C to +125°C
Package Thermal Impedance
Thin SOT-23-5 (θ
JA
)
(5)
....................................... 207°C/W
Thin SOT-23-6 (θ
JA
)
(5)
....................................... 134°C/W
8-Pin MLF (θ
JA
) ................................................... 90°C/W
Electrical Characteristics
(6)
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
V
IN
Parameter
Condition
Min
2.8
1.8
V
EN
= 0V
(7)
(±7.5%)
V
FB
> 500mV, (not switching)
231
2.1
2.1
0.04
250
–450
0.4
0.5
85
350
250
0.01
1.5
21
1
17
1.2
19
150
10
1
0.4
40
1.4
24
90
1
Typ
Supply Voltage Range
Under Voltage Lockout
Quiescent Current
Shutdown Current
Feedback Voltage
Feedback Input Current
Line Regulation
Load Regulation
D
MAX
V
SW
V
EN
I
EN
I
SW
I
SW
Maximum Duty Cycle
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
Enable Threshold
Enable Pin Current
Oscillator Frequency
Overvoltage Protection
Overtemperature
Threshold Shutdown
Max
6.5
2.4
5
1
269
Units
V
V
mA
µA
mV
nA
%
%
%
mA
mV
µA
V
V
µA
MHz
V
°C
°C
I
VIN
I
SD
I
FB
V
UVLO
V
FB
V
FB
= 250mV
5mA ≤ I
OUT
≤ 20mA
(8)
V
IN
= 3.6V
3V ≤ V
IN
≤ 5V
(8)
V
EN
= 0V, V
SW
= 10V
TURN ON
TURN OFF
V
IN
= 3.6V, I
SW
= 300mA
V
OVP
T
J
Notes:
f
SW
V
EN
= 10V
MIC3287-24YD6
MIC3287-24YML
Hysteresis
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.
For options with OVP.
5.
Using 4 layer PCB.
6.
Specification for packaged product only.
8.
Guaranteed by design.
7.
I
SD
= I
VIN
.
April 2010
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M9999-042910
Micrel, Inc.
MIC3287
Typical Characteristics
85
80
EFFICIENCY (%)
3 Series
White LED Efficiency
V
IN
=3.6V
85
80
EFFICIENCY (%)
4 Series
White LED Efficiency
V
IN
=3.6V
V
IN
=3.2V
V
IN
=4.2V
12
ENABLE PIN CURRENT (µA)
Enable Pin Current
vs. Temperature
V
EN
=5V
75
V
IN
=3.2V
70
65
60
55
50
45
2
L = 10µH
C
OUT
= 0.22µF
4 6
8 10 12 14 16
18
20
WHITE LED CURRENT (mA)
V
IN
=4.2V
75
70
65
60
55
50
45
2
10
8
6
4
2
V
EN
=2.5V
V
EN
=1.8V
V
EN
=3.3V
L = 10µH
C
OUT
= 0.22µF
4 6
8 10 12 14 16
18
20
WHITE LED CURRENT (mA)
0
-40 -25 -10 5 20 35 50
65
80
TEMPERATURE (°C)
1.5
FREQUENCY (MHz)
Frequency
vs. Temperature
260
FEEDBACK VOLTAGE (mV)
Feedback Voltage
vs. Temperature
254
FEEDBACK VOLTAGE (mV)
Feedback Voltage
vs. Input Voltage
1.4
1.3
1.2
1.1
V
IN
=3.6V
V
IN
=4.2V
256
252
248
244
240
-40 -25 -10 5 20 35 50
65
80
TEMPERATURE (°C)
V
IN
=3.6V
253
252
251
250
249
248
2.8 3.2
3.6
4.0 4.4 4.8 5.2
5.6
INPUT VOLTAGE (V)
V
IN
=3.2V
1.0
-40 -25 -10 5 20 35 50
65
80
TEMPERATURE (°C)
QUIESCENT CURRENT (mA)
0.003
SHUTDOWN CURRENT (uA)
Shutdown Current
vs. Input Voltage
2.5
2.4
2.3
2.2
2.1
Quiescent Current
vs. Input Voltage
900
CURRENT LIMIT (mA)
Curremt Limit
vs. Temperature
850
800
750
700
650
600
-40 -25 -10 5 20 35 50
65
80
TEMPERATURE (°C)
V
IN
=3.6V
0.002
0.001
2.8 3.2
3.6
4.0 4.4 4.8 5.2
5.6
INPUT VOLTAGE (V)
2.0
2.8 3.2
3.6
4.0 4.4 4.8 5.2
5.6
INPUT VOLTAGE (V)
840
CURRENT LIMIT (mA)
Current Limit
vs. Input Voltage
820
800
780
760
740
720
2.8 3.2
3.6
4.0 4.4 4.8 5.2
5.6
INPUT VOLTAGE (V)
April 2010
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M9999-042910
Micrel, Inc
MIC3287
Functional Diagram
VIN
FB
OVP*
EN
OVP
V
REF
Error
Amplifier
V
REF
g
m
250mV
∑
Current
Amplifier
1.2MHz
Oscillator
Ramp
Generator
GND
SW
PWM
Generator
* OVP available on TSOP-23-6 and MLF™ package options only.
MIC3287 Block Diagram
Functional Description
The MIC3287 is a constant frequency pulse width modulated
(PWM) current-mode step-up regulator. The block diagram
is shown above. The MIC3287 is composed of an oscillator,
slope compensation ramp generator, current amplifier, g
m
er-
ror amplifier, PWM generator, and a 350mA minimum bipolar
output transistor. The oscillator 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 com-
pensation ramp generator. 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 compensa-
tion 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 internal 250mV 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, thus main-
taining the constant frequency current-mode PWM control.
The LED current is set by the feedback resistor:
250mV
I
LED
=
R
FB
The enable pin shuts down the internal power bipolar
transistor and disables the control circuitry to reduce input
current-to-leakage levels. Enable pin input current is zero
at zero volts.
April 2010
5
M9999-042910
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