MIC2289C
White LED Driver Internal Schottky
Diode and OVP
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
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
0.22µF/50V
95mV
1-Cell
Li Ion 1µF
MIC2289C-34YD6
VIN
EN
SW
FB
OUT
GND
7-Series White LED Driver
70
72
74
76
78
80
82
0 5 10 15 20 25
EFFICIENCY (%)
I
OUT
(mA)
3-Series LED Ef ficien cy
V
IN
=3.6V
Micrel, Inc. MIC2289C
August 2007 2 M9999-081507-B
Ordering Information
Part Number Marking
Code Overoltage
Protection Junction
Temp. Range Package Lead Finish
MIC2289C-34BD6 SM34| 34V –40°C to +125°C 6-Pin Thin SOT-23 Standard
MIC2289C-34YD6 SM34| 34V –40°C to +125°C 6-Pin Thin SOT-23 Pb-Free
Note: Marking bars may not be to scale.
Pin Configur ation
FB GND
EN VOUT
SW
31
6
2
4
SM34
Denotes
Pb-Free
Denotes
MIC2289C
5
VIN
6- Pin Thin SOT-23 (D6)
Pin Description
Pin Number Pin Name Pin Name
1 SW Switch node (Input): Internal power BIPOLAR collector.
2 GND Ground (Return): Ground.
3 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 EN Enable (Input): Logic high enables regulator. Logic low shuts down regulator.
5 VIN Supply (Input): 2.7V to 8V for internal circuitry.
6 OUT
Output Pin and Overvoltage Protection (Output): Connect to the output capacitor
and LEDs.
Micrel, Inc. MIC2289C
August 2007 3 M9999-081507-B
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 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 µA
V
FB
Feedback Voltage (±10%) 85 95 105 mV
I
FB
Feedback Input Current V
FB
= 95mV –450 nA
Line Regulation
(6)
3V ≤ V
IN
≤ 5V 0.5 %
Load Regulation
(6)
5mA ≤ I
OUT
≤ 20mA 0.5 %
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 µA
V
EN
Enable Threshold TURN ON
TURN OFF
1.5
0.4 V
V
I
EN
Enable Pin Current V
EN
= 10V 20 40 µA
f
SW
Oscillator Frequency 1.05 1.2 1.35 MHz
V
D
Schottky Forward Drop I
D
= 150mA 0.8 1 V
I
RD
Schottky Leakage Current V
R
= 30V 4 µA
V
OVP
Overvoltage Protection MIC2289C-34YD6 only 27 32 37 V
T
J
Overtemperature
Threshold Shutdown
Hysteresis
150
10
°C
°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, 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
Micrel, Inc. MIC2289C
August 2007 4 M9999-081507-B
Typical Characteristics
90
91
92
93
94
95
96
97
98
99
100
024681012
FB VOLTAGE (mV)
V
IN
(V)
Feedback Voltage
vs. Input Voltage
0
1
2
3
4
5
024681012
SHUTDOWN CURRENT (µA)
V
IN
(V)
Shutdown Voltage
vs. Input Voltage
0
1
2
3
4
5
024681012
QUIESCENT CURRENT (mA)
V
IN
(V)
Quiescent Current
vs. Input Current
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
-40 -20 0 20 40 60 80 100
SWITCHING FREQUENCY (MHz)
TEMPERATURE (°C)
Switch Frequenc
y
vs. Temperature
0
5
10
15
20
25
30
35
40
45
50
-50 0 50 100
IENABLE (µA)
TEMPERATURE (°C)
EN Pin Bias Current
vs. Temperature
I
EN
=4.2V I
EN
=3.6V
I
EN
=3.0V
I
EN
=10V
0
100
200
300
400
500
600
700
450
550
650
750
850
950
1050
1150
SCHOTTKY FORWARD CURRENT (mA)
SCHOTTKY FORWARD VOLTAGE DROP (mV)
Schottky Forward
Voltage Drop
0
0.5
1
1.5
2
2.5
30 40 50 60 70 80 90 100
SCHOTTKY LEAKAGE CURRENT (µA)
TEMPERATURE (°C)
Schottky Reverse
Leakage Current
V
R
=25V
V
R
= 10V
V
R
= 16V
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 Voltag
e
vs. Current
V
IN
=2.5V
V
IN
=5V
Micrel, Inc. MIC2289C
August 2007 5 M9999-081507-B
Functional Diagram
GND
V
REF
PWM
Generator
Ramp
Generator
1.2MHz
Oscillator
SW
ENFB OUTVIN
95mV
gm
OVP
S
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:
FB
LED
R
95mW
I=
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.
Micrel, Inc. MIC2289C
August 2007 6
M9999-081507-B
External Component Selecti on
The MIC2289C can be used across a wide rage of
applications. The table below shows recommended
inductor and output capacitor values for various series-
LED applications.
Series LEDs L Manufacturer Min C
OUT
Manufacturer
LQH32CN220K21 (Murata) 0805ZD225KAT(AVX) 22µH
NLC453232T-220K(TDK)
2.2µF
GRM40X5R225K10(Murata)
LQH32CN150K21 (Murata) 0805ZD105KAT(AVX) 15µH
NLC453232T-150K(TDK)
1µF
GRM40X5R105K10(Murata)
LQH32CN100K21 (Murata) 0805ZD224KAT(AVX) 10µH
NLC453232T-100K(TDK)
0.22µF
GRM40X5R224K10(Murata)
LQH32CN6R8K21 (Murata) 0805ZD225KAT(AVX) 6.8µH
NLC453232T-6R8K(TDK)
0.22µF
GRM40X5R225K10(Murata)
LQH32CN4R7K21 (Murata) 0805ZD224KAT(AVX)
2
4.7µH
NLC453232T-4R7K(TDK)
0.22µF
GRM40X5R224K10(Murata)
LQH43MN220K21 (Murata) 0805YD225MAT(AVX) 22µH
NLC453232T-220K(TDK)
2.2µF
GRM40X5R225K16(Murata)
LQH43MN 150K21 (Murata) 0805YD105MAT(AVX) 15µH
NLC453232T-150K(TDK)
1µF
GRM40X5R105K16(Murata)
LQH43MN 100K21 (Murata) 0805YD224MAT(AVX) 10µH
NLC453232T-100K(TDK)
0.22µF
GRM40X5R224K16(Murata)
LQH43MN 6R8K21 (Murata) 0805YD224MAT(AVX) 6.8µH
NLC453232T-6R8K(TDK)
0.22µF
GRM40X5R224K16(Murata)
LQH43MN 4R7K21 (Murata) 0805YD274MAT(AVX)
3
4.7µH
NLC453232T-4R7K(TDK)
0.27µF
GRM40X5R224K16(Murata)
LQH43MN220K21 (Murata) 0805YD105MAT(AVX) 22µH
NLC453232T-220K(TDK)
1µF
GRM40X5R105K25(Murata)
LQH43MN 150K21 (Murata) 0805YD105MAT(AVX) 15µH
NLC453232T-150K(TDK)
1µF
GRM40X5R105K25(Murata)
LQH43MN 100K21 (Murata) 0805YD274MAT(AVX) 10µH
NLC453232T-100K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN 6R8K21 (Murata) 0805YD274MAT(AVX) 6.8µH
NLC453232T-6R8K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN 4R7K21 (Murata) 0805YD274MAT(AVX)
4
4.7µH
NLC453232T-4R7K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN220K21 (Murata) 08053D224MAT(AVX) 22µH
NLC453232T-220K(TDK)
0.22µF
GRM40X5R224K25(Murata)
LQH43MN 150K21 (Murata) 08053D224MAT(AVX) 15µH
NLC453232T-150K(TDK)
0.22µF
GRM40X5R224K25(Murata)
LQH43MN 100K21 (Murata) 08053D274MAT(AVX) 10µH
NLC453232T-100K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN 6R8K21 (Murata) 08053D274MAT(AVX) 6.8µH
NLC453232T-6R8K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN 4R7K21 (Murata) 08053D274MAT(AVX)
5, 6
4.7µH
NLC453232T-4R7K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN220K21 (Murata) 08053D224MAT(AVX) 22µH
NLC453232T-220K(TDK)
0.22µF
GRM40X5R224K25(Murata)
LQH43MN 150K21 (Murata) 08053D224MAT(AVX) 15µH
NLC453232T-150K(TDK)
0.22µF
GRM40X5R224K25(Murata)
LQH43MN 100K21 (Murata) 08053D274MAT(AVX) 10µH
NLC453232T-100K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN 6R8K21 (Murata) 08053D274MAT(AVX) 6.8µH
NLC453232T-6R8K(TDK)
0.27µF
GRM40X5R274K25(Murata)
LQH43MN 4R7K21 (Murata) 08053D274MAT(AVX)
7, 8
4.7µH
NLC453232T-4R7K(TDK)
0.27µF
GRM40X5R274K25(Murata)
Micrel, Inc. MIC2289C
August 2007 7
M9999-081507-B
Dimming Control
There are two techniques for dimming control. One is
PWM dimming, and the other is continuous dimming.
1. PWM dimming control is implemented by
applying a PWM signal on EN pin as shown in
Figure 1. The MIC2289C is turned on and off by
the PWM signal. With this method, the LEDs
operate with either zero or full current. The
average LED current is increased proportionally
to the duty-cycle of the PWM signal. This
technique has high-efficiency because the IC
and the LEDs consume no current during the off
cycle of the PWM signal. Typical frequency
should be between 100Hz and 10kHz.
2. Continuous dimming control is implemented by
applying a DC control voltage to the FB pin of
the MIC2289C through a series resistor as
shown in Figure 2. The LED current is
decreased proportionally with the amplitude of
the control voltage. The LED intensity (current)
can be dynamically varied applying a DC voltage
to the FB pin. The DC voltage can come from a
DAC signal, or a filtered PWM signal. The
advantage of this approach is that a high
frequency PWM signal (>10kHz) can be used to
control LED intensity.
PWM
VIN
EN
SW
FB
OUT
GND
V
IN
Figure 1. PWM Dimming Method
VIN
EN
SW
FB
OUT
5.11k
49.9k
GND
DC
V
IN
Equivalent
Figure 2. Continuous Dimming
Open-Circuit Protection
If the LEDs are disconnected from the circuit, or in case
an LED fails open, the sense resistor will pull the FB pin
to ground. This will cause the MIC2289C to switch with a
high duty-cycle, resulting in output overvoltage. This
would normally cause the SW pin voltage to exceed its
maximum voltage rating, possibly damaging the IC and
the external components. However, the MIC2289C has a
dedicated OVP monitor to limit the output voltage within
safe levels (see Figure 3).
VIN
EN
GND
SW
FB
OUT
V
IN
Figure 3. Thin SOT- 23 Packag e OVP Circuit
Start-Up and Inrush Current
During start-up, inrush current of approximately double
the nominal current flows to set up the inductor current
and the voltage on the output capacitor. If the inrush
current needs to be limited, a soft-start circuit similar to
Figure 4 could be implemented. The soft-start capacitor,
CSS, provides over-drive to the FB pin at start-up,
resulting in gradual increase of switch duty cycle and
limited inrush current.
VIN
EN
10k
2200pF
SW
OUT
FB
C
SS
R
GND
V
IN
Figure 4. One of Soft-Start Circuit
Micrel, Inc. MIC2289C
August 2007 8
M9999-081507-B
6-Series LED Circuit without External Soft-Start
TIME (100µs/div.)
ENABLE
(2V/div)
INPUT CURRENT
(200mA/div)
OUTPUT VOLTAGE
L = 10µH
CIN = 1µF
C
OUT
= 0.22µF
V
IN
= 3.6V
I
OUT
= 20mA
6 LEDs
6-Series LED Circuit with External Soft-Start
TIME (100µs/div.)
ENABLE
(2V/div)
INPUT CURRENT
(200mA/div)
OUTPUT VOLTAGE
L = 10µH
CIN = 1µF
C
OUT
= 0.22µF
V
IN
= 3.6V
I
OUT
= 20mA
6 LEDs
CSS = 2200pF
Figure 5. 6-Series LED Circuit
without External Soft Start
Figure 6. 6-Series LED Circuit
with External Soft Start
Micrel, Inc. MIC2289C
August 2007 9
M9999-081507-B
Package Information
6-Pin Thin SOT-23 (D6)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
