MIC2289
White LED Driver Internal Schottky
Diode and OVP
General Description
The MIC2289 is a PWM (pulse width modulated), boost-
switching regulator that is optimized for constant-current
white LED driver applications. The MIC2289 features an
internal Schottky diode and three levels of output
overvoltage protection providing a small size and efficient
DC/DC solution that requires only four external
components.
To optimize efficiency, the feedback voltage is set to only
95mV. This reduces power dissipation in the current set
resistor and allows the lowest total output voltage, hence
minimal current draw from the battery.
The MIC2289 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
in caparison to variable frequency is much lower noise and
input ripple injected to the input power source.
The MIC2289 clamps the output voltage in case of open
LED conditions, protecting itself and the output capacitor.
The MIC2289 is available with three output OVP options of
15V, 24V, and 34V. The different OVP options allows the
use of the smallest possible output capacitor with the
appropriate voltage rating for a given application.
The MIC2289 is available in low profile 6-pin Thin SOT-23
and 8-pin 2mm × 2mm MLF
®
package options. The
MIC2289 has a junction temperature range of –40°C to
+125°C.
Data sheets and 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
Internal Schottky diode
15V, 24V, 34V output OVP options
1.2 MHz PWM operation
Over 500mA switch current
95mV feedback voltage
<1% line and load regulation
<1µA shutdown current
Overtemperature protection
UVLO
2mm × 2mm 8-pin MLF
®
package
–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
82
80
EFFICIENCY (%)
MIC2289-15BML
1-Cell
Li Ion
VIN
1µF
EN
GND
SW
OUT
FB
95mV
0.22µF/16V
3-Series LED Efficiency
78
76
74
72
70
0
V
IN
=3.6V
5
10
15
I
OUT
(mA)
20
25
3-Series White LED Driver
MLF and
MicroLeadFrame
are registered 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
July 2007
M9999-071007
Micrel, Inc.
MIC2289
Ordering Information
Part Number
MIC2289-24YD6
MIC2289-15BML
MIC2289-15YML
MIC2289-24BML
MIC2289-24YML
MIC2289-34BML
MIC2289-34YML
Marking
Code
SM24
SNA
SNA
SNB
SNB
SNC
SNC
Overvoltage
Protection
24V
15V
15V
24V
24V
34V
34V
Junction
Temp. Range
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
Package
6-Pin Thin SOT-23
8-Pin 2mm x 2mm MLF
8-Pin 2mm x 2mm MLF
®
®
Lead Finish
Pb-Free
Standard
Pb-Free
Standard
Pb-Free
Standard
Pb-Free
8-Pin 2mm x 2mm MLF
®
8-Pin 2mm x 2mm MLF
®
8-Pin 2mm x 2mm MLF
®
8-Pin 2mm x 2mm MLF
®
Note:
Marking bars may not be to scale.
Pin Configuration
FB GND SW
3
2
1
VOUT
VIN
EN
1
2
3
4
8
7
6
PGND
SW
FB
NC
4
5
6
EN VIN VOUT
AGND
EP
5
6- Pin Thin SOT-23 (D6)
®
8-Pin MLF (ML)
(Top View)
Fused Lead Frame
Pin Description
Pin Number
TSOT-23-6
1
2
3
Pin Number
MLF
®
-8
7
―
6
Pin Name
SW
GND
FB
Pin Name
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 regulator.
Supply (Input): 2.7V to 8V for internal circuitry.
Output Pin and Overvoltage Protection (Output): Connect to the
output capacitor and LEDs.
Analog ground.
Power ground.
No connect (no internal connection to die).
Ground (Return): Exposed backside pad.
4
5
6
―
―
―
―
3
2
1
4
8
5
EP
EN
VIN
VOUT
AGND
PGND
NC
GND
July 2007
2
M9999-071007
Micrel, Inc.
MIC2289
Absolute Maximum Ratings
(1)
Supply Voltage (V
IN
) .......................................................12V
Switch Voltage (V
SW
)....................................... –0.3V to 34V
Enable Pin Voltage (V
EN
)................................... –0.3V to V
IN
FB Voltage (V
FB
)...............................................................6V
Switch Current (I
SW
) .........................................................2A
Ambient Storage Temperature (T
s
) ...........–65°C to +150°C
Schottky Reverse Voltage (V
DA
).....................................34V
EDS Rating
(3)
.................................................................. 2kV
Operating Ratings
(2)
Supply voltage (V
IN
) ........................................ 2.5V to +10V
Output Voltage (V
IN
) ............................................ V
IN
to V
OVP
Junction Temperature (T
J
) ........................ –40°C to +125°C
Package Thermal Resistance
2mm x 2mm MLF
®
(θ
JA
).....................................93°C/W
Thin SOT-23-6 (θ
JA
) ........................................177°C/W
Electrical Characteristics
(4)
T
A
= 25°C, V
IN
= V
EN
= 3.6V, V
OUT
= 10V, I
OUT
= 20mA, unless otherwise noted.
Bold
values indicate –40°C< T
J
< +125°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)
(6)
Condition
Min
2.5
1.8
Typ
2.1
2.5
0.1
Max
10
2.4
5
Units
V
V
mA
µA
mV
nA
%
%
%
mA
mV
V
FB
> 200mV, (not switching)
V
EN
= 0V
(±5%)
V
FB
= 95mV
3V
≤
V
IN
≤
5V
5mA
≤
I
OUT
≤
20mA
(5)
1
100
1
90
95
–450
0.5
0.5
Load Regulation
D
MAX
I
SW
V
SW
I
SW
V
EN
I
EN
f
SW
V
D
I
RD
V
OVP
Maximum Duty Cycle
Switch Current Limit
Switch Saturation Voltage
Switch Leakage Current
Enable Threshold
Enable Pin Current
Oscillator Frequency
Schottky Forward Drop
Schottky Leakage Current
Overvoltage Protection
I
D
= 150mA
V
R
= 30V
MIC2289-15
MIC2289-24
MIC2289-34
Hysteresis
I
SW
= 0.5A
V
EN
= 0V, V
SW
= 10V
TURN ON
TURN OFF
V
EN
= 10V
85
90
750
450
0.01
5
0.4
µA
V
V
µA
MHz
V
µA
V
V
V
°C
°C
1.5
20
1.05
1.2
0.8
13
21
30
14
22.5
32
150
10
40
1.35
1
4
16
24
34
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. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model.
4. Specification for packaged product only.
5. I
SD
= I
VIN
.
6. Guaranteed by design
July 2007
3
M9999-071007
Micrel, Inc.
MIC2289
Typical Characteristics
100
99
FB VOLTAGE (mV)
98
97
96
95
94
93
92
91
90
0
2
4
6
V
IN
(V)
8
10
12
Feedback Voltage
vs. Input Voltage
SHUTDOWN CURRENT (µA)
5
4
3
2
1
0
Shutdown Voltage
vs. Input Voltage
QUIESCENT CURRENT (mA)
5
4
3
2
1
0
Quiescent Current
vs. Input Current
0
2
4
6
V
IN
(V)
8
10
12
0
2
4
6
V
IN
(V)
8
10
12
SCHOTTKY FORWARD CURRENT (mA)
SWITCHING FREQUENCY (MHz)
1.4
1.2
Switch Frequency
vs. Temperature
50
45
40
IENABLE (µA)
EN Pin Bias Current
vs. Temperature
700
600
500
400
300
200
100
Schottky Forward
Voltage Drop
1.0
0.8
0.6
0.4
0.2
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
35
I = 10V
30
E N
25
20
I = 4.2V
15
E N
I
10
5 I = 3.0V
EN
0
-50
0
50
TEMPERATURE (°C)
EN
= 3.6V
1050
100
SCHOTTKY FORWARD VOLTAGE DROP (mV)
SCHOTTKY LEAKAGE CURRENT (µA)
2.5
2
1.5
1
0.5
Schottky Reverse
Leakage Current
SATURATION VOLTAGE (mV)
550
500
450
400
350
300
-40
Saturation Voltage
vs. Temperature
900
CURRENT LIMIT (mA)
850
800
750
700
650
600
-40
Current Limit
vs. Temperature
V
R
= 25V
V
R
= 16V
V
R
= 10V
0
30
40
50 60 70 80 90 100
TEMPERATURE (°C)
I
S W
= 500mA
0
40
80
TEMPERATURE (°C)
120
V
IN
= 2.5V
0
40
80
TEMPERATURE (°C)
120
600
SATURATION VOLTAGE (mV)
500
400
300
200
100
Switch Saturation Voltage
vs. Current
V
IN
= 2.5V
V
IN
= 5V
0
0
100
200 300
I
SW
(mA)
400
500
July 2007
4
M9999-071007
1150
450
550
650
750
850
950
0
Micrel, Inc.
MIC2289
Functional Diagram
VIN
FB
EN
OUT
OVP
SW
g
m
V
REF
95mV
S
PWM
Generator
1.2MHz
Oscillator
Ramp
Generator
GND
MIC2289 Block Diagram
Functional Description
The MIC2289 is a constant frequency, PWM current
mode boost regulator. The block diagram is shown
above. The MIC2289 is composed of an oscillator, slope
compensation ramp generator, current amplifier, g
m
error
amplifier, PWM generator, 500mA bipolar output
transistor, and Schottky rectifier diode. 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 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.
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 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, maintaining the constant
frequency current-mode PWM control. The LED is set by
the feedback resistor:
I
LED
=
95mW
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 2007
5
M9999-071007
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