MIC2287C
Micrel
MIC2287C
1.2MHz PWM White LED Driver with OVP in
2mm × 2mm MLF™ and Thin SOT-23
General Description
The MIC2287C is a 1.2MHz pulse width modulated (PWM),
boost-switching regulator that is optimized for constant-cur-
rent, white LED driver applications. With a maximum output
voltage of 37V and a switch current of over 500mA, the
MIC2287C easily drives a string of up to 6 white LEDs in
series, ensuring uniform brightness and eliminating several
ballast resistors.
The MIC2287C 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 MIC2287C 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 MIC2287C is available in low profile Thin SOT-23 5-
lead and an 8-lead 2mm × 2mm MLF™ package options.
The MIC2287C has a junction temperature range of –40°C
to +105°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
Over-temperature protection
UVLO
Low profile Thin SOT-23-5 package option
8-lead 2mm × 2mm MLF™ package option
–40°C to +105°C junction temperature range
For higher performance specifications see the MIC2287
Applications
• White LED driver for backlighting:
- Cell phones
- PDAs
- GPS systems
- Digital cameras
- MP3 players
- IP phones
• LED flashlights
Typical Application
10½H
CMDSH-3
10½H
CMDSH-3
5
MIC2287CBD5
VIN
EN
GND
2
1-Cell
Li Ion
1½F
SW
FB
1
MIC2287C-34BML
0.22½F
95mV
6.3½
1-Cell
Li Ion
1½F
VIN
EN
SW
OVP
FB
GND
95mV
4
3
0.22½F
6.3½
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
February 2006
1
M0510-020906
MIC2287C
Micrel
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 105°C
–40°C to 105°C
Ordering Information
Part Number
MIC2287CBD5
MIC2287CYD5
MIC2287C-15BML
MIC2287C-15YML
MIC2287C-24BML
MIC2287C-24YML
MIC2287C-34BML
MIC2287C-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 105°C 2mm x 2mm MLF™
–40°C to 105°C 2mm x 2mm MLF™
–40°C to 105°C 2mm x 2mm MLF™
–40°C to 105°C 2mm x 2mm MLF™
–40°C to 105°C 2mm x 2mm MLF™
–40°C to 105°C 2mm x 2mm MLF™
Pin Configuration
FB GND SW
1
2
3
Horizontal Mark
Denotes
Pb-Free
SGAA
4
EN
5
VIN
Vertical Mark
Denotes
MIC2287C
Denotes Pb-Free
OVP
VIN
EN
GND
1
2
3
4
8
7
6
GND
SW
FB
NC
Denotes MIC2287C
SLA
TSOT-23-5 (BD5)
EP
5
8-Pin MLF™ (BML)
(Top View)
Pin Description
Pin Number
Pin Number
TSOT-23-5 2mm
×
2mm MLF™ Pin Name
1
2
3
4
5
—
—
—
—
—
6
3
2
1
4
8
5
EP
7
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): 2.7V to 8V 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.
M0510-020906
2
February 2006
MIC2287C
Micrel
Absolute Maximum Ratings
(1)
Supply Voltage (V
IN
) ..................................................... 12V
Switch Voltage (V
SW
) ......................................–0.3V to 37V
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 +105°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
< 105°C.
Symbol
V
IN
V
UVLO
I
VIN
I
SD
V
FB
I
FB
Parameter
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
V
SW
I
SW
V
EN
I
EN
f
SW
V
OVP
Maximum Duty Cycle
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
Enable Threshold
Enable Pin Current
Oscillator Frequency
Overvoltage Protection
MIC2287CBML- 15 only
MIC2287CBML- 24 only
MIC2287CBML- 34 only
Hysteresis
I
SW
= 0.5A
V
EN
= 0V, V
SW
= 10V
TURN ON
TURN OFF
V
EN
= 10V
1.05
11.5
19
27
1.5
20
1.2
14
22.5
32
150
10
V
FB
> 200mV, (not switching)
V
EN
= 0V
(5)
(±10%)
V
FB
= 95mV
3V ≤ V
IN
≤ 5V
5mA ≤ I
OUT
≤ 20mA
85
85
Condition
Min
2.5
1.8
2.1
2.5
0.1
95
–450
0.5
0.5
90
750
450
0.01
5
0.4
40
1.35
16.5
26
37
Typ
Max
10
2.4
5
1
105
Units
V
V
mA
µA
mV
nA
%
%
%
mA
mV
µA
V
V
µA
MHz
V
V
V
°C
°C
T
J
Notes:
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
February 2006
3
M0510-020906
MIC2287C
Micrel
Typical Characteristics
Feedback Voltage
vs. Input Voltage
SHUTDOWN CURRENT (½A)
FB VOLTAGE (mV)
98
97
96
95
94
93
92
91
90
0
2
4
6
V
IN
(V)
8
10
12
4
3
2
1
0
0
2
4
6
V
IN
(V)
8
10
12
QUIESCENT CURRENT (mA)
100
99
5
Shutdown Current
vs. Input Voltage
5
4
3
2
1
0
Quiescent Current
vs. Input Voltage
0
2
4
6
V
IN
(V)
8
10
12
3 Series LED Efficiency
84
82
EFFICIENCY (%)
EFFICIENCY (%)
6 Series LED Efficiency
84
V
IN
= 4.2V
SWITCHING FREQUENCY (MHz)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-40
Switch Frequency
vs. Temperature
V
80
V
IN
= 3.0V
82
80
78
76
V
IN
= 3.6V
78
76
74
IN
IN
= 3.6V
V
IN
= 3.0V
V
= 4.2V
L = 10H
C
= 0.22F
OUT
74
72
72
70
0
5
10
15
I
OUT
(mA)
20
25
70
L = 10H
C
OUT
= 0.22F
0
5
10
15
I
OUT
(mA)
20
25
0
40
80
TEMPERATURE (C)
120
SATURATION VOLTAGE (mV)
CURRENT LIMIT (mA)
IENABLE (A)
50
45
40
35
I = 10V
30
EN
25
20
15
EN Pin Bias Current
vs. Temperature
550
500
450
400
350
Saturation Voltage
vs. Temperature
900
850
800
750
700
650
600
-40
Current Limit
vs. Temperature
I
EN
= 4.2V
10
5
I = 3.0V
0
EN
0
50
-50
TEMPERATURE (C)
I
EN
= 3.6V
100
300
-40
I
SW
= 500mA
0
40
80
TEMPERATURE (C)
120
V
IN
= 2.5V
0
40
80
TEMPERATURE (C)
120
600
Switch Saturation Voltage
vs. Current
SATURATION VOLTAGE (mV)
500
400
300
200
100
0
0
100
200 300
I
SW
(mA)
400
500
V
IN
= 5V
V
IN
= 2.5V
M0510-020906
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February 2006
MIC2287C
Micrel
Functional Diagram
VIN
FB
OVP*
EN
OVP*
SW
g
m
V
REF
PWM
Generator
95mV
1.2MHz
Oscillator
Ramp
Generator
GND
*
OVP available on MLF
TM
package option only
MIC2287C Block Diagram
Functional Description
The MIC2287C is a constant frequency, PWM current mode
boost regulator. The block diagram is shown above. The
MIC2287C 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
February 2006
5
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
R
FB
I
LED
=
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.
M0510-020906
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