MIC2289C
White LED Driver Internal Schottky
Diode and OVP
General Description
The MIC2289C is a PWM (pulse width modulated), boost-
switching regulator that is optimized for constant-current
white LED driver applications. The MIC2289C 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 MIC2289C 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 MIC2289C clamps the output voltage in case of open
LED conditions, protecting itself and the output capacitor.
The MIC2289C is available with an output OVP option of
34V.
The MIC2289C is available in low profile 6-pin Thin SOT-
23 package. The MIC2289C 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 with OVP
Internal Schottky diode
1.2 MHz PWM operation
Over 500mA switch current
95mV feedback voltage
<1% line and load regulation
<1µA shutdown current
Overtemperature protection
UVLO
Thin SOT-23 6-pin package
–40°C to +125°C junction temperature range
For higher performance specifications see the MIC2289
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
3-Series LED Efficiency
MIC2289C-34YD6
1-Cell
Li Ion
VIN
1µF
EN
GND
SW
OUT
FB
95mV
0.22µF/50V
EFFICIENCY (%)
78
76
74
72
70
0
V
IN
=3.6V
5
10
15
I
OUT
(mA)
20
25
7-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
August 2007
M9999-081507-B
Micrel, Inc.
MIC2289C
Ordering Information
Part Number
MIC2289C-34BD6
MIC2289C-34YD6
Marking
Code
SM34|
SM34|
Overoltage
Protection
34V
34V
Junction
Temp. Range
–40°C to +125°C
–40°C to +125°C
Package
6-Pin Thin SOT-23
6-Pin Thin SOT-23
Lead Finish
Standard
Pb-Free
Note:
Marking bars may not be to scale.
Pin Configuration
FB GND SW
1
2
3
Denotes
Pb-Free
SM34
5
4
6
EN VIN VOUT
Denotes
MIC2289C
6- Pin Thin SOT-23 (D6)
Pin Description
Pin Number
1
2
3
4
5
6
Pin Name
SW
GND
FB
EN
VIN
OUT
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.
August 2007
2
M9999-081507-B
Micrel, Inc.
MIC2289C
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
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
D
MAX
I
SW
V
SW
I
SW
V
EN
I
EN
f
SW
V
D
I
RD
V
OVP
T
J
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,
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
(6)
Condition
Min
2.5
1.8
Typ
2.1
2.5
0.1
Max
10
2.4
5
1
105
Units
V
V
mA
µA
mV
nA
%
%
%
mA
mV
V
FB
> 200mV, (not switching)
V
EN
= 0V
(5)
(±10%)
V
FB
= 95mV
3V
≤
V
IN
≤
5V
5mA
≤
I
OUT
≤
20mA
85
I
SW
= 0.5A
V
EN
= 0V, V
SW
= 10V
TURN ON
TURN OFF
V
EN
= 10V
1.05
I
D
= 150mA
V
R
= 30V
MIC2289C-34YD6 only
Hysteresis
27
1.5
85
95
–450
0.5
0.5
90
750
450
0.01
Load Regulation
(6)
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
Overtemperature
Threshold Shutdown
5
0.4
µA
V
V
µA
MHz
V
µA
V
°C
°C
20
1.2
0.8
32
150
10
40
1.35
1
4
37
August 2007
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M9999-081507-B
Micrel, Inc.
MIC2289C
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
August 2007
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M9999-081507-B
1150
450
550
650
750
850
950
0
Micrel, Inc.
MIC2289C
Functional Diagram
VIN
FB
EN
OUT
OVP
SW
g
m
V
REF
95mV
S
PWM
Generator
1.2MHz
Oscillator
Ramp
Generator
GND
MIC2289C Block Diagram
Functional Description
The MIC2289C is a constant frequency, PWM current
mode boost regulator. The block diagram is shown
above. The MIC2289C is composed of an oscillator,
slope compensation ramp generator, current amplifier,
gm 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 gm 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.
August 2007
5
M9999-081507-B
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