Micrel MIC2287-34YML 1.2mhz pwm white led driver with ovp in 2mm ã 2mm mlfâ ¢ and thin sot-23 Datasheet

MIC2287
Micrel
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.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
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
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
Typical Application
CMDSH-3
10µH
MIC2287BD5
5
1-Cell
Li Ion
VIN
SW
MIC2287-34BML
1
1µF
4
FB
EN
CMDSH-3
10µH
1-Cell
Li Ion
0.22µF
3
1µF
VIN
SW
EN
OVP
95mV
FB
GND
2
GND
6.3Ω
0.22µF
95mV
6.3Ω
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. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
August 2004
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M0510-081104
MIC2287
Micrel
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
Thin SOT-23-5
Lead Free
SGAA
N/A
–40°C to 125°C
MIC2287-15BML
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
MIC2287-24YML
SLB
24V
–40°C to 125°C 2mm x 2mm MLF™
Lead Free
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)
OVP
1
8
PGND
VIN
2
7
SW
EN
3
6
FB
AGND
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
Analog ground.
—
8
PGND
Power ground.
—
5
NC
No connect (no internal connection to die).
—
EP
GND
Ground (Return): Exposed backside pad.
M0510-081104
2
August 2004
MIC2287
Micrel
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
VIN
Supply Voltage Range
2.5
VUVLO
Under Voltage Lockout
1.8
IVIN
Quiescent Current
VFB > 200mV, (not switching)
0V(5)
Typ
Max
Units
10
V
2.1
2.4
V
2.5
5
mA
0.1
1
µA
95
100
mV
ISD
Shutdown Current
VEN =
VFB
Feedback Voltage
(±5%)
IFB
Feedback Input Current
VFB = 95mV
Line Regulation
3V ≤ VIN ≤ 5V
0.5
1
%
Load Regulation
5mA ≤ IOUT ≤ 20mA
0.5
2
%
DMAX
Maximum Duty Cycle
ISW
Switch Current Limit
VSW
Switch Saturation Voltage
ISW
VEN
90
–450
90
%
750
mA
ISW = 0.5A
450
mV
Switch Leakage Current
VEN = 0V, VSW = 10V
0.01
Enable Threshold
TURN ON
TURN OFF
IEN
Enable Pin Current
fSW
Oscillator Frequency
VOVP
Overvoltage Protection
TJ
Overtemperature
Threshold Shutdown
85
nA
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
1.5
VEN = 10V
MIC2287BML- 15 only
MIC2287BML- 24 only
MIC2287BML- 34 only
150
10
Hysteresis
°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.
August 2004
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M0510-081104
MIC2287
Micrel
Typical Characteristics
Feedback Voltage
vs. Input Voltage
Shutdown Current
vs. Input Voltage
SHUTDOWN CURRENT (µA)
97
96
95
94
93
92
0
2
4
6
8
10
5
4
3
2
1
0
12
0
2
4
VIN (V)
EFFICIENCY (%)
EFFICIENCY (%)
80
78
74
VIN = 4.2V
L = 10µH
COUT = 0.22µF
70
0
5
10
15
IOUT (mA)
20
80
78
VIN = 3.0V
76
74
L = 10µH
C
= 0.22µF
72
70
25
OUT
0
5
15
I
EN
= 3.6V
10
5 I = 3.0V
0 EN
0
50
-50
TEMPERATURE (°C)
10
15
IOUT (mA)
20
25
100
6
8
10
12
1
0.8
0.6
0.4
0.2
0
-40
500
850
450
400
350
ISW = 500mA
0
40
80
TEMPERATURE (°C)
0
40
80
TEMPERATURE (°C)
120
Current Limit
vs. Temperature
900
300
-40
4
1.2
550
CURRENT LIMIT (mA)
SATURATION VOLTAGE (mV)
IENABLE (µA)
35
I = 10V
30 EN
25
2
1.4
Saturation Voltage
vs. Temperature
50
45
40
IEN = 4.2V
0
Switch Frequency
vs. Temperature
VIN = 3.6V
EN Pin Bias Current
vs. Temperature
20
1
VIN (V)
82
VIN = 3.0V
72
2
0
12
VIN = 4.2V
84
76
10
3
6 Series LED Efficiency
84
VIN = 3.6V
8
4
VIN (V)
3 Series LED Efficiency
82
6
SWITCHING FREQUENCY (MHz)
FB VOLTAGE (mV)
99
98
QUIESCENT CURRENT (mA)
5
100
91
90
Quiescent Current
vs. Input Voltage
120
800
750
700
650
V = 2.5V
600 IN
-40
0
40
80
TEMPERATURE (°C)
120
Switch Saturation Voltage
vs. Current
SATURATION VOLTAGE (mV)
600
M0510-081104
500
400
VIN = 2.5V
300
VIN = 5V
200
100
0
0
100
200 300
ISW (mA)
4
400
500
August 2004
MIC2287
Micrel
Functional Diagram
VIN
FB
OVP*
EN
OVP*
SW
PWM
Generator
gm
VREF
95mV
Σ
1.2MHz
Oscillator
GND
Ramp
Generator
*OVP available on MLFTM package option only
MIC2287 Block Diagram
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:
Functional Description
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.
August 2004
95mv
ILED =
RFB
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.
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M0510-081104
MIC2287
Micrel
The table below shows recommended inductor and output
capacitor values for various series-LED applications.
External Component Selection
The MIC2287 can be used across a wide rage of applications.
Series LEDs
L
Manufacturer
Min COUT
Manufacturer
2
22µH
LQH32CN220K21 (Murata)
NLC453232T-220K(TDK)
2.2µF
0805ZD225KAT(AVX)
GRM40X5R225K10(Murata)
15µH
LQH32CN150K21 (Murata)
NLC453232T-150K(TDK)
1µF
0805ZD105KAT(AVX)
GRM40X5R105K10(Murata)
10µH
LQH32CN100K21 (Murata)
NLC453232T-100K(TDK)
0.22µF
0805ZD224KAT(AVX)
GRM40X5R224K10(Murata)
6.8µH
LQH32CN6R8K21 (Murata)
NLC453232T-6R8K(TDK)
0.22µF
0805ZD225KAT(AVX)
GRM40X5R225K10(Murata)
4.7µH
LQH32CN4R7K21 (Murata)
NLC453232T-4R7K(TDK)
0.22µF
0805ZD224KAT(AVX)
GRM40X5R224K10(Murata)
22µH
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
2.2µF
0805YD225MAT(AVX)
GRM40X5R225K16(Murata)
15µH
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
1µF
0805YD105MAT(AVX)
GRM40X5R105K16(Murata)
10µH
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
0.22µF
0805YD224MAT(AVX)
GRM40X5R224K16(Murata)
6.8µH
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
0.22µF
0805YD224MAT(AVX)
GRM40X5R224K16(Murata)
4.7µH
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
0.27µF
0805YD274MAT(AVX)
GRM40X5R224K16(Murata)
22µH
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
1µF
0805YD105MAT(AVX)
GRM40X5R105K25(Murata)
15µH
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
1µF
0805YD105MAT(AVX)
GRM40X5R105K25(Murata)
10µH
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
0.27µF
0805YD274MAT(AVX)
GRM40X5R274K25(Murata)
6.8µH
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
0.27µF
0805YD274MAT(AVX)
GRM40X5R274K25(Murata)
4.7µH
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
0.27µF
0805YD274MAT(AVX)
GRM40X5R274K25(Murata)
22µH
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
0.22µF
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
15µH
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
0.22µF
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
10µH
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
0.27µF
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
6.8µH
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
0.27µF
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
4.7µH
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
0.27µF
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
22µH
LQH43MN220K21 (Murata)
NLC453232T-220K(TDK)
0.22µF
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
15µH
LQH43MN 150K21 (Murata)
NLC453232T-150K(TDK)
0.22µF
08053D224MAT(AVX)
GRM40X5R224K25(Murata)
10µH
LQH43MN 100K21 (Murata)
NLC453232T-100K(TDK)
0.27µF
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
6.8µH
LQH43MN 6R8K21 (Murata)
NLC453232T-6R8K(TDK)
0.27µF
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
4.7µH
LQH43MN 4R7K21 (Murata)
NLC453232T-4R7K(TDK)
0.27µF
08053D274MAT(AVX)
GRM40X5R274K25(Murata)
3
4
5, 6
7, 8
M0510-081104
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August 2004
MIC2287
Micrel
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.
with 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 4. Thin SOT-23 Package OVP Circuit
Figure 1. PWM Dimming Method
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.
VIN
VIN
SW
EN
FB
5.11k
49.9k
GND
VIN
DC
Equivalent
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
August 2004
5.11k
VIN
SW
EN
FB
GND
R
10k
Figure 5. Soft-Start Circuit
7
M0510-081104
MIC2287
Micrel
6-Series LED Circuit with External Soft-Start
OUTPUT VOLTAGE
INPUT CURRENT
ENABLE
(200mA/div)
(2V/div)
OUTPUT VOLTAGE
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.)
M0510-081104
L = 10µH
CIN = 1µF
COUT = 0.22µF
VIN = 3.6V
IOUT = 20mA
6 LEDs
CSS = 2200pF
R = 10kΩ
TIME (100µs/div.)
8
August 2004
MIC2287
Micrel
Package Information
All Dimensions are in millimeters
5-Pin TSOT (BD5)
8-Pin MLF™ (BML)
August 2004
9
M0510-081104
MIC2287
Micrel
×2 8 Lead
Recommended Land Pattern for MLF™ 2×
MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 474-1000
WEB
USA
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 at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2004 Micrel, Incorporated.
M0510-081104
10
August 2004
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