MICREL MIC2287

MIC2287
Micrel, Inc.
MIC2287
1.2MHz PWM White LED Driver with OVP in
2mm × 2mm MLF™ and Thin SOT-23
General Description
Features
The MIC2287 is a 1.2MHz pulse width modulated (PWM),
boost-switching regulator that is optimized for constantcurrent, 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 protection, 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 MLF™ 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.
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Typical Application
1-Cell
Li Ion
1µF
4
MIC2287BD5
VIN
SW
FB
EN
GND
2
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
CMDSH-3
10µH
5
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
<1µA shutdown current
Over-temperature protection
UVLO
Low profile Thin SOT-23-5 package option
8-lead 2mm × 2mm MLF™ package option
–40°C to +125°C junction temperature range
CMDSH-3
10µH
MIC2287-34BML
1
1-Cell
Li Ion
0.22µF
3
95mV
1µF
VIN
SW
EN
OVP
FB
GND
6.3Ω
3-Series White LED Driver in Thin SOT-23
0.22µF
95mV
6.3Ω
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
July 2005
1
M9999-070105
MIC2287
Micrel, Inc.
Ordering Information
Part Number
Marking
Code
Overvoltage
Protection
Junction
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
SLA
15V
–40°C to 125°C 2mm x 2mm MLF™
Standard
MIC2287-15YML
SLA
15V
–40°C to 125°C 2mm x 2mm MLF™
Lead Free
MIC2287-24BML
SLB
24V
–40°C to 125°C 2mm x 2mm MLF™
Standard
Lead Free
MIC2287-15BML
MIC2287-24YML
SLB
24V
–40°C to 125°C 2mm x 2mm MLF™
MIC2287-34BML
SLC
34V
–40°C to 125°C 2mm x 2mm MLF™
Standard
MIC2287-34YML
SLC
34V
–40°C to 125°C 2mm x 2mm MLF™
Lead Free
Pin Configuration
FB GND SW
1
2
3
4
EN
5
VIN
TSOT-23-5 (BD5)
OUT
1
8
GND
VIN
2
7
SW
EN
3
6
FB
GND
4
5
NC
EP
8-Pin MLF™ (BML)
(Top View)
Fused Lead Frame
Pin Description
Pin Number
Pin Number
TSOT-23-5 2mm ×2mm MLF™
1
7
2
Pin Name
SW
GND
Pin Function
Switch node (Input): Internal power BIPOLAR collector.
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
—
8
PGND
—
5
NC
No connect (no internal connection to die).
—
EP
GND
Ground (Return): Exposed backside pad.
M9999-070105
Analog ground.
Power ground.
2
July 2005
MIC2287
Micrel, Inc.
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN) ..................................................... 12V
Switch Voltage (VSW) ......................................–0.3V to 34V
Enable Pin Voltage (VEN) ................................... –0.3 to VIN
FB Voltage (VFB) ............................................................. 6V
Switch Current (ISW) ........................................................ 2A
Ambient Storage Temperature (TS) .......... –65°C to +150°C
ESD Rating(3) ............................................................... 2kV
Supply Voltage (VIN) ..........................................2.5V to 10V
Junction Temperature Range (TJ) ............ –40°C to +125°C
Package Thermal Impedance
2mm × 2mmMLF™ (θJA) ..................................... 93°C/W
Thin SOT-23-5 (θJA) ......................................... 256°C/W
Electrical Characteristics(4)
TA = 25°C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 10mA, unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤125°C.
Symbol
Parameter
Condition
Min
Supply Voltage Range
2.5
VUVLO
Under Voltage Lockout
1.8
ISD
Shutdown Current
IFB
Feedback Input Current
VIN
IVIN
VFB
Quiescent Current
Feedback Voltage
Line
Regulation(6)
Load Regulation(6)
DMAX
Maximum Duty Cycle
ISW
Switch Current Limit
ISW
Switch Leakage Current
VSW
VEN
IEN
Switch Saturation Voltage
VFB > 200mV, (not switching)
VEN = 0V(5)
(±5%)
5mA ≤ IOUT ≤ 20mA
VEN = 10V
VOVP
Overvoltage Protection
TJ
Overtemperature
Threshold Shutdown
Units
10
V
2.1
2.4
V
2.5
5
mA
0.1
1
µA
95
100
mV
nA
0.5
1
%
0.5
2
%
90
%
750
mA
450
VEN = 0V, VSW = 10V
Enable Pin Current
Oscillator Frequency
85
ISW = 0.5A
TURN ON
TURN OFF
Max
–450
3V ≤ VIN ≤ 5V
Enable Threshold
fSW
90
VFB = 95mV
Typ
MIC2287BML- 15 only
MIC2287BML- 24 only
MIC2287BML- 34 only
0.01
1.5
µA
0.4
V
V
20
40
µA
1.05
1.2
1.35
MHz
13
21
30
14
22.5
32
16
24
34
V
V
V
150
10
Hysteresis
mV
5
°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, TJ(max),
the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. 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. ISD = IVIN.
6. Guaranteed by design.
July 2005
3
M9999-070105
MIC2287
Micrel, Inc.
Typical Characteristics
5
SHUTDOWN CURRENT (µA)
FB VOLTAGE (mV)
99
98
97
96
95
94
93
92
91
90
0
2
4
6
8
10
4
3
3
2
2
1
0
1
0
2
4
VIN (V)
3 Series LED Efficiency
EFFICIENCY (%)
VIN = 3.6V
74
V
IN
70
= 4.2V
5
0
10
15
IOUT (mA)
20
25
EN Pin Bias Currency
vs. Temperature
50
IENABLE (µA)
40
35
30
I
EN
= 10V
25
20
15
I
EN
= 4.2V
IEN = 3.6V
10
5 I = 3.0V
0 EN
0
50
-50
TEMPERATURE (°C)
L = 10µH
COUT = 0.22µF
100
10
15
IOUT (mA)
5
20
25
Saturation Voltage
vs. Temperature
450
400
350
SATURATION VOL AGE (mV)
ISW = 500mA
0
40
80
TEMPERATURE (°C)
1.4
8
10
120
12
1.2
1
0.8
0.6
0.4
0.2
0
-40
900
500
600
M9999-070105
VIN = 3.0V
76
300
-40
6
Switch Frequency
vs. Temperature
78
550
SATURATION VOL AGE (mV)
45
4
6 Series LED Efficiency
VIN = 3.6V
0
2
VIN (V)
80
70
0
VIN (V)
72
OUT
0
12
74
L = 10µH
C
= 0.22µF
72
10
CURRENT LIMIT (mA)
EFFICIENCY (%)
78
76
8
82
VIN = 3.0V
80
6
VIN = 4.2V
84
84
82
5
4
12
Quiescent Current
vs. Input Voltage
QUIESCENT CURRENT (mA)
100
Shutdown Current
vs. Input Voltage
SWITCHING FREQUENCY (MHz)
Feedback Voltage
vs. Input Voltage
0
40
80
TEMPERATURE (°C)
120
Current Limit
vs. Temperature
850
800
750
700
650
600
-40
VIN = 2.5V
0
40
80
TEMPERATURE (°C)
120
Switch Saturation Voltage
vs. Current
500
400
VIN = 2.5V
300
VIN = 5V
200
100
0
0
100
200 300
ISW (mA)
4
400
500
July 2005
MIC2287
Micrel, Inc.
Functional Diagram
VIN
FB
EN
OVP*
OVP*
SW
VREF
PWM
Generator
gm
95mV
S
Ramp
Generator
1.2MHz
Oscillator
GND
*OVP available on MLFTM package option only
MIC2287 Block Diagram
Functional Description
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:
95mv
ILED =
RFB
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, gm error amplifier, PWM
generator, and a 500mA bipolar output transistor. 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.
July 2005
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.
5
M9999-070105
MIC2287
Micrel, Inc.
External Component Selection
The table below shows recommended inductor and output
capacitor values for various series-LED applications.
The MIC2287 can be used across a wide rage of applications.
Series LEDs
2
L
22µH
15µH
10µH
6.8µH
4.7µH
3
22µH
15µH
10µH
6.8µH
4.7µH
4
22µH
15µH
10µH
6.8µH
4.7µH
5, 6
22µH
15µH
10µH
6.8µH
4.7µH
7, 8
22µH
15µH
10µH
6.8µH
4.7µH
M9999-070105
Manufacturer
LQH32CN220K21 (Murata)
NLC453232T-220K(TDK)
LQH32CN150K21 (Murata)
NLC453232T-150K(TDK)
LQH32CN100K21 (Murata)
NLC453232T-100K(TDK)
LQH32CN6R8K21 (Murata)
NLC453232T-6R8K(TDK)
LQH32CN4R7K21 (Murata)
NLC453232T-4R7K(TDK)
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
6
Min COUT
2.2µF
1µF
0.22µF
0.22µF
0.22µF
2.2µF
1µF
0.22µF
0.22µF
0.27µF
1µF
1µF
0.27µF
0.27µF
0.27µF
0.22µF
0.22µF
0.27µF
0.27µF
0.27µF
0.22µF
0.22µF
0.27µF
0.27µF
0.27µF
Manufacturer
0805ZD225KAT(AVX)
GRM40X5R225K10(Murata)
0805ZD105KAT(AVX)
GRM40X5R105K10(Murata)
0805ZD224KAT(AVX)
GRM40X5R224K10(Murata)
0805ZD225KAT(AVX)
GRM40X5R225K10(Murata)
0805ZD224KAT(AVX)
GRM40X5R224K10(Murata)
0805YD225MAT(AVX)
GRM40X5R225K16(Murata)
0805YD105MAT(AVX)
GRM40X5R105K16(Murata)
0805YD224MAT(AVX)
GRM40X5R224K16(Murata)
0805YD224MAT(AVX)
GRM40X5R224K16(Murata)
0805YD274MAT(AVX)
GRM40X5R224K16(Murata)
0805YD105MAT(AVX)
GRM40X5R105K25(Murata)
0805YD105MAT(AVX)
GRM40X5R105K25(Murata)
0805YD274MAT(AVX)
GRM40X5R274K25(Murata)
0805YD274MAT(AVX)
GRM40X5R274K25(Murata)
0805YD274MAT(AVX)
GRM40X5R274K25(Murata)
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
July 2005
MIC2287
Micrel, Inc.
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
MIC2287 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 PWM 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
MIC2287 through a series resistor as shown in
Figure 2. 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 a high frequency PWM signal (>10kHz)
that can be used to control LED intensity.
options for 15V, 24V, or 34V (see Figure 3). The reason for
the three OVP levels is to let users choose the suitable level
of OVP for their application. For example, a 3-LED application
would typically see an output voltage of no more than 12V, so
a 15V OVP option would offer a suitable level of protection.
This allows the user to select the output diode and capacitor
with the lowest voltage ratings, as well as smallest size and
lowest cost. The OVP will clamp the output voltage to within
the specified limits. For the Thin SOT-23-5 package, an OVP
pin is not available. An external zener diode can be connected
from the output of the converter to FB pin as shown in Figure
4. to implement similar protection.
VIN
VIN
SW
EN
FB
GND
OVP
Figure 3. MLF™ Package OVP Circuit
VIN
VIN
PWM
VIN
SW
EN
FB
VIN
SW
EN
FB
GND
GND
Figure 1. PWM Dimming Method
Figure 4. Thin SOT-23 Package OVP Circuit
VIN
VIN
SW
EN
FB
GND
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 5 could be
implemented. The soft-start capacitor, CSS, provides overdrive to the FB pin at start-up, resulting in gradual increase
of switch duty cycle and limited inrush current.
5.11k
49.9k
DC
Equivalent
VIN
CSS
2200pF
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 MIC2287 to switch with a high
duty-cycle, resulting in output overvoltage. This may cause
the SW pin voltage to exceed its maximum voltage rating,
possibly damaging the IC and the external components. To
ensure the highest level of protection, the MIC2287 has 3
product options in the 8-lead 2mm × 2mm MLF™ with overvoltage protection (OVP). The extra pins of the 8-lead 2mm
× 2mm MLF™ package allow a dedicated OVP monitor with
July 2005
5.11k
VIN
SW
EN
FB
GND
R
10k
Figure 5. Soft-Start Circuit
7
M9999-070105
MIC2287
Micrel, Inc.
6-Series LED Circuit with External Soft-Start
OUTPUT VOL AGE
INPUT CURRENT
ENABLE
(200mA/div)
(2V/div)
OUTPUT VOL AGE
INPUT CURRENT
ENABLE
(200mA/div)
(2V/div)
6-Series LED Circuit without External Soft-Start
L = 10µH
CIN = 1µF
COUT = 0.22µF
VIN = 3.6V
IOUT = 20mA
6 LEDs
TIME (100µs/div.)
M9999-070105
L = 10µH
CIN = 1µF
COUT = 0.22µF
VIN = 3.6V
IOUT = 20mA
6 LEDs
CSS = 2200pF
R = 10kW
TIME (100µs/div.)
8
July 2005
MIC2287
Micrel, Inc.
Package Information
5-Pin TSOT (BD5)
8-Pin MLF™ (BML)
July 2005
9
M9999-070105
MIC2287
Micrel, Inc.
Recommended Land Pattern for MLF™ 2×2 8 Lead
MICREL INC.
TEL
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
+ 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
This 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.
© 2004 Micrel, Inc.
M9999-070105
10
July 2005