Micrel MIC3287-24YML 1.2mhz pwm white led driver with ovp in thin sot-23 and 2mm x 2mm mfl Datasheet

Micrel, Inc
MIC3287
MIC3287
1.2MHz PWM White LED Driver with OVP in
Thin SOT-23 and 2mm x 2mm MFL®
General Description
Features
The MIC3287 is a 1.2MHz pulse width modulated (PWM)
step-up switching regulator that is optimized for constant current white LED driving applications. With a switch current of
over 350mA, the MIC3287-24 drives a string of up to 4 white
LEDs in series, ensuring uniform brightness and eliminating
several ballast resistors.
The MIC3287 implements a constant frequency 1.2MHz PWM
current-mode control scheme. The high frequency PWM operation saves board space by reducing external component
sizes. The added benefit of the constant frequency PWM
control scheme as opposed to variable frequency control
schemes is much lower noise and input ripple injected back
to the battery source. To optimize efficiency, the feedback
voltage is set to only 250mV. The MIC3287 is also available
with a maximum 24V over-voltage protection.
The MIC3287 is available in low profile Thin SOT-23 5-pin
and Thin SOT-23 6-pin packages. The MIC3287 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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2.8V to 6.5V Input Voltage
350mA Switch Current
1.2 MHz PWM Operation
250mV Feedback Voltage
Optional 24V Output Over-Voltage Protection (OVP)
Up to 36V Output Voltage without OVP
<1% Line and Load Regulation
<1µA Shutdown Current
Over-Temperature Protection
Under-Voltage Lock Out (UVLO)
Low Profile Thin SOT-23-5 Package Option
Low Profile Thin SOT-23-6 Package Option
8-pin 2mm x 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
• LED Flashlights
• Constant Current Power Supplies
Typical Application
10µH
10µH
5
1-Cell
Li Ion
1µF
4
MIC3287YD5
VIN
SW
FB
EN
MIC3287-24YD6
1
6
1-Cell
Li Ion
0.22µF
3
250mV
1µF
4
SW
1
OVP
5
FB
3
VIN
EN
GND
GND
0.22µF
250mV
2
2
4-Series White LED Driver
with Output OVP in Thin SOT-23-6
3-Series White LED Driver in Thin SOT-23-5
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
April 2010
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Micrel, Inc.
MIC3287
Ordering Information
Marking
Code
Part Number
Overvoltage
Protection
Junction
Temp. Range
Package
Lead Finish
MIC3287YD5
WGAA
N/A
-40°C to +125°C
Thin SOT-23-5
Lead Free
MIC3287-24YD6
WHAA
24V
-40°C to +125°C
Thin SOT-23-6
Lead Free
MIC3287-24YML
WLA
24V
-40°C to +125°C
8-Pin 2mm x 2mm MLF
Lead Free
Pin Configuration
FB GND SW
3
2
1
FB GND SW
1
2
3
4
EN
4
5
6
EN OVP VIN
5
VIN
TSOT-23-5 (YD5)
VIN 1
8
PGND
OVP 2
7
SW
EN 3
6
FB
5
NC
AGND 4
TSOT-23-6 (YD6)
EP
8-Pin 2mm x 2mm MLF™ (YML)
Pin Description
Pin Number Pin Number
TSOT-23-5
TSOT-23-6
Pin Number
8-Pin MLF
Pin Name
1
1
7
SW
2
2
4
AGND
Pin Function
Switch Node (Input): Internal power bipolar collector.
Analog Ground (Return): Ground.
2
2
8
PGND
3
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
4
3
EN
Enable (Input): Logic high enables regulator. Logic low shuts down regulator.
5
6
1
VIN
Supply (Input): 2.8V to 6.5V for internal circuitry.
—
5
2
OVP
Overvoltage Protection (Input): Connect to the output.
—
—
5
NC
Not Connected
—
—
EP
EP
Exposed Backside Pad: Connect to ground.
April 2010
Power Ground (Return): Ground.
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Micrel, Inc
MIC3287
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN)......................................................... 7V
Switch Voltage (VSW).......................................–0.3V to 40V
Enable Pin Voltage (VEN).................................... –0.3 to VIN
FB Voltage (VFB).............................................................. 6V
Switch Current (ISW)...................................................... 1.2A
Ambient Storage Temperature (TS)........... –65°C to +150°C
ESD Rating(3)................................................................. 2kV
Supply Voltage (VIN)..........................................2.8V to 6.5V
Output Voltage (VOUT)..........................................VIN to 36V
Output Voltage (VOUT)(4)....................................VIN to VOVP
Junction Temperature Range (TJ)............. –40°C to +125°C
Package Thermal Impedance
Thin SOT-23-5 (θJA)(5). ...................................... 207°C/W
Thin SOT-23-6 (θJA)(5). ...................................... 134°C/W
8-Pin MLF (θJA).................................................... 90°C/W
Electrical Characteristics(6)
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
Typ
Max
Units
Supply Voltage Range
2.8
6.5
V
VUVLO
Under Voltage Lockout
1.8
2.1
2.4
V
ISD
Shutdown Current
IFB
Feedback Input Current
VIN
IVIN
VFB
Quiescent Current
Feedback Voltage
Line Regulation
Load Regulation
2.1
5
mA
VEN = 0V(7)
VFB > 500mV, (not switching)
0.04
1
µA
250
269
mV
VFB = 250mV
–450
1
%
5mA ≤ IOUT ≤ 20mA(8)
0.5
%
(±7.5%)
3V ≤ VIN ≤
231
5V(8)
0.4
Maximum Duty Cycle
85
ISW
Switch Current Limit
350
ISW
Switch Leakage Current
DMAX
VSW
Switch Saturation Voltage
Enable Threshold
VEN
IEN
Enable Pin Current
VIN = 3.6V
VIN = 3.6V, ISW = 300mA
VEN = 0V, VSW = 10V
VEN = 10V
Oscillator Frequency
1
TJ
Overtemperature Threshold Shutdown
Hysteresis
%
mA
250
mV
1
µA
0.01
TURN ON
1.5
TURN OFF
0.4
fSW
Overvoltage Protection
VOVP
90
nA
V
V
21
40
µA
1.2
1.4
MHz
MIC3287-24YD6
17
19
24
MIC3287-24YML
150
10
V
°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. For options with OVP.
5. Using 4 layer PCB.
6. Specification for packaged product only.
7. ISD = IVIN.
8. Guaranteed by design.
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MIC3287
Typical Characteristics
60
L = 10µH
COUT = 0.22µF
Frequency
vs. Temperature
FREQUENCY (MHz)
VIN=4.2V
VIN=3.6V
45
2
260
Feedback Voltage
vs. Temperature
VIN=3.2V
VIN=3.6V
248
Quiescent Current
vs. Input Voltage
SHUTDOWN CURRENT (uA)
254
VEN=1.8V
Feedback Voltage
vs. Input Voltage
251
248
2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6
INPUT VOLTAGE (V)
900
CURRENT LIMIT (mA)
800
Curremt Limit
vs. Temperature
VIN=3.6V
750
2.2
700
2.1
840
2
VEN=3.3V
850
2.3
0.001
2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6
INPUT VOLTAGE (V)
4
VEN=2.5V
249
2.4
0.002
6
250
240
-40 -25 -10 5 20 35 50 65 80
TEMPERATURE (°C)
2.5
8
252
QUIESCENT CURRENT (mA)
Shutdown Current
vs. Input Voltage
VEN=5V
253
256
244
1.0
-40 -25 -10 5 20 35 50 65 80
TEMPERATURE (°C)
Enable Pin Current
vs. Temperature
0
-40 -25 -10 5 20 35 50 65 80
TEMPERATURE (°C)
4 6 8 10 12 14 16 18 20
WHITE LED CURRENT (mA)
252
1.1
0.003
L = 10µH
COUT = 0.22µF
50
4 6 8 10 12 14 16 18 20
WHITE LED CURRENT (mA)
1.4
1.2
VIN=4.2V
55
50
1.3
65
60
55
1.5
VIN=3.2V
70
VIN=4.2V
12
10
75
70
45
2
VIN=3.6V
80
EFFICIENCY (%)
EFFICIENCY (%)
75 VIN=3.2V
4 Series
White LED Efficiency
ENABLE PIN CURRENT (µA)
VIN=3.6V
80
65
85
FEEDBACK VOLTAGE (mV)
3 Series
White LED Efficiency
FEEDBACK VOLTAGE (mV)
85
650
2.0
2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6
INPUT VOLTAGE (V)
600
-40 -25 -10 5 20 35 50 65 80
TEMPERATURE (°C)
Current Limit
vs. Input Voltage
CURRENT LIMIT (mA)
820
800
780
760
740
720
2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6
INPUT VOLTAGE (V)
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MIC3287
Functional Diagram
VIN
FB
EN
OVP*
OVP
VREF
SW
Error
Amplifier
VREF
PWM
Generator
gm
250mV
∑
Current
Amplifier
1.2MHz
Oscillator
Ramp
Generator
GND
* OVP available on TSOP-23-6 and MLF™ package options only.
MIC3287 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 internal 250mV 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, thus maintaining the constant frequency current-mode PWM control.
The LED current is set by the feedback resistor:
250mV
ILED =
R FB
The enable pin shuts down the internal power bipolar
transistor and disables the control circuitry to reduce input
current-to-leakage levels. Enable pin input current is zero
at zero volts.
The MIC3287 is a constant frequency pulse width modulated
(PWM) current-mode step-up regulator. The block diagram
is shown above. The MIC3287 is composed of an oscillator,
slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, and a 350mA minimum 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.
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MIC3287
External Component Selection
The table below shows recommended inductor and output
capacitor combinations for optimal performance.
Series LEDs
L
Min COUT
2
22µH
2.2µF
3
4
April 2010
15µH
1µF
10µH
0.22µF
6.8µH
0.22µF
4.7µH
0.22µF
22µH
2.2µF
15µH
1µF
10µH
0.22µF
6.8µH
0.22µF
4.7µH
0.27µF
22µH
1µF
15µH
1µF
10µH
0.22µF
6.8µH
0.27µF
4.7µH
0.27µF
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MIC3287
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 to the EN pin, as shown in Figure
1. The MIC3287 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 time 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 MIC3287 through a series resistor, as shown
in Figure 2. The LED intensity (current) can be
dynamically varied with the applied DC control
voltage. The DC voltage can come from a DAC
signal, or a filtered PWM signal. The advantage
of the filtered PWM signal approach is a high
frequency PWM signal (>10kHz) can be used to
control LED intensity (current).
Open-Circuit Protection
If the LEDs are disconnected from the circuit, or in the case
that an LED fails, the sense resistor will then pull the FB pin to
ground. This will cause the MIC3287 to switch with a high dutycycle, resulting in output over-voltage. This may cause the SW
pin voltage to exceed its maximum voltage rating, damaging
the IC and the external components. To ensure the highest
level of protection, the MIC3287 has buit-in 24V over-voltage
protection functionality in the TSOT-23-6 pin and 8-pin MLF™
package options. The OVP will clamp the output voltage to
within the specified limits.
Start-Up and Inrush Current
If the inrush current needs to be limited, a soft-start circuit, similar to Figure 3, 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 in rush current.
VIN
CSS
2200pF
VIN
SW
EN
FB
GND
VIN
PWM
VIN
SW
EN
FB
R
10k
Figure 3. Soft-Start Circuit
GND
Figure 1. PWM Dimming Method
VIN
VIN
SW
EN
FB
GND
5.11k
49.9k
DC�
Equivalent
Figure 2. Continuous Dimming
April 2010
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MIC3287
Package Information
5-Pin TSOT (YD5)
6-Pin TSOT (YD6)
April 2010
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Micrel, Inc
MIC3287
8-Pin 2mm x 2mm MLF® (ML)
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.
© 2006 Micrel, Inc.
April 2010
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