August 2004
1
M0510-081104
MIC2287
Micrel
MIC2287
1.2MHz PWM White LED Driver with OVP in
2mm
2mm MLFTM 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 MLFTM 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
10
H
0.22
F
6.3
95mV
1-Cell
Li Ion
1
F
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
<1
A shutdown current
Over-temperature protection
UVLO
Low profile Thin SOT-23-5 package option
8-lead 2mm
2mm MLFTM 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. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 http://www.micrel.com
MLF and
Micro
LeadFrame are trademarks of Amkor Technology, Inc.
10
H
0.22
F
1
F
1-Cell
Li Ion
6.3
MIC2287-34BML
VIN
EN
SW
OVP
FB
GND
95mV
CMDSH-3
6-Series White LED Driver
with Output OVP in 2mm
2mm MLFTM-8
MIC2287
Micrel
M0510-081104
2
August 2004
Pin Description
Pin Number
Pin Number
TSOT-23-5 2mm
2mm MLFTM 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 regulator.
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
3
1
5
2
4
TSOT-23-5 (BD5)
OVP
VIN
EN
AGND
PGND
SW
FB
NC
1
2
3
4
8
7
6
5
EP
8-Pin MLFTM (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 MLFTM
Standard
MIC2287-15YML
SLA
15V
40
C to 125
C 2mm x 2mm MLFTM
Lead Free
MIC2287-24BML
SLB
24V
40
C to 125
C 2mm x 2mm MLFTM
Standard
MIC2287-24YML
SLB
24V
40
C to 125
C 2mm x 2mm MLFTM
Lead Free
MIC2287-34BML
SLC
34V
40
C to 125
C 2mm x 2mm MLFTM
Standard
MIC2287-34YML
SLC
34V
40
C to 125
C 2mm x 2mm MLFTM
Lead Free
August 2004
3
M0510-081104
MIC2287
Micrel
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
2mmMLFTM (
JA
) ..................................... 93
C/W
Thin SOT-23-5 (
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
Typ
Max
Units
V
IN
Supply Voltage Range
2.5
10
V
V
UVLO
Under Voltage Lockout
1.8
2.1
2.4
V
I
VIN
Quiescent Current
V
FB
> 200mV, (not switching)
2.5
5
mA
I
SD
Shutdown Current
V
EN
= 0V
(5)
0.1
1
A
V
FB
Feedback Voltage
(
5%)
90
95
100
mV
I
FB
Feedback Input Current
V
FB
= 95mV
450
nA
Line Regulation
3V
V
IN
5V
0.5
1
%
Load Regulation
5mA
I
OUT
20mA
0.5
2
%
D
MAX
Maximum Duty Cycle
85
90
%
I
SW
Switch Current Limit
750
mA
V
SW
Switch Saturation Voltage
I
SW
= 0.5A
450
mV
I
SW
Switch Leakage Current
V
EN
= 0V, V
SW
= 10V
0.01
5
A
V
EN
Enable Threshold
TURN ON
1.5
V
TURN OFF
0.4
V
I
EN
Enable Pin Current
V
EN
= 10V
20
40
A
f
SW
Oscillator Frequency
1.05
1.2
1.35
MHz
V
OVP
Overvoltage Protection
MIC2287BML- 15 only
13
14
16
V
MIC2287BML- 24 only
21
22.5
24
V
MIC2287BML- 34 only
30
32
34
V
T
J
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, T
J
(max),
the junction-to-ambient thermal resistance,
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
.
MIC2287
Micrel
M0510-081104
4
August 2004
Typical Characteristics
90
91
92
93
94
95
96
97
98
99
100
0
2
4
6
8
10
12
FB VOLTAGE (mV)
V
IN
(V)
Feedback Voltage
vs. Input Voltage
0
1
2
3
4
5
0
2
4
6
8
10
12
SHUTDOWN CURRENT (
A)
V
IN
(V)
Shutdown Current
vs. Input Voltage
0
1
2
3
4
5
0
2
4
6
8
10
12
QUIESCENT CURRENT (mA)
V
IN
(V)
Quiescent Current
vs. Input Voltage
70
72
74
76
78
80
82
84
EFFICIENCY (%
)
I
OUT
(mA)
3 Series LED Efficiency
L = 10
H
C
OUT
= 0.22
F
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3.0V
0
5
10
15
20
25
70
72
74
76
78
80
82
84
EFFICIENCY (%
)
I
OUT
(mA)
6 Series LED Efficiency
L = 10
H
C
OUT
= 0.22
F
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3.0V
0
5
10
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 (
A)
TEMPERATURE (
C)
EN Pin Bias Current
vs. Temperature
I
EN
= 4.2V
I
EN
= 3.6V
I
EN
= 3.0V
I
EN
= 10V
300
350
400
450
500
550
-40
0
40
80
120
SATURATION VOLTAGE (mV)
TEMPERATURE (
C)
Saturation Voltage
vs. Temperature
I
SW
= 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 VOLTAGE (mV)
I
SW
(mA)
Switch Saturation Voltage
vs. Current
V
IN
= 2.5V
V
IN
= 5V
August 2004
5
M0510-081104
MIC2287
Micrel
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 transis-
tor and to reset the slope compensation 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 compensation ramp generator. This summed
current-loop signal is fed to one of the inputs of the PWM
generator.
Functional Diagram
GND
V
REF
PWM
Generator
Ramp
Generator
1.2MHz
Oscillator
SW
EN
FB
OVP*
VIN
95mV
*
OVP available on MLF
TM
package option only
g
m
OVP*
MIC2287 Block Diagram
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:
I
LED
=
95mv
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.
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