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MIC2287
Micrel, Inc.
MIC2287
1.2MHz PWM White LED Driver with OVP in 2mm x 2mm MLFTM and Thin SOT-23
General Description
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 x 2mm MLFTM package options. The MIC2287 has a junction temperature range of -40C to +125C. All 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 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 <1A shutdown current Over-temperature protection UVLO Low profile Thin SOT-23-5 package option 8-lead 2mm x 2mm MLFTM package option -40C to +125C 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
10H
CMDSH-3
10H
CMDSH-3
5
MIC2287BD5
1-Cell Li Ion
1F
VIN EN
SW FB GND
2
1
MIC2287-34BML
0.22F 95mV 6.3 1-Cell Li Ion 1F
VIN EN
SW OVP FB GND
0.22F
4
3
95mV
6.3
3-Series White LED Driver in Thin SOT-23
MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc.
6-Series White LED Driver with Output OVP in 2mm x 2mm MLFTM-8
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
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M9999-070105
MIC2287
Micrel, Inc.
Marking Code SGAA SGAA SLA SLA SLB SLB SLC SLC Overvoltage Protection N/A N/A 15V 15V 24V 24V 34V 34V Junction Temp. Range -40C to 125C -40C to 125C
Ordering Information
Part Number MIC2287BD5 MIC2287YD5 MIC2287-15BML MIC2287-15YML MIC2287-24BML MIC2287-24YML MIC2287-34BML MIC2287-34YML
Package Thin SOT-23-5 Thin SOT-23-5
Lead Finish Standard Lead Free Standard Lead Free Standard Lead Free Standard Lead Free
-40C to 125C 2mm x 2mm MLFTM -40C to 125C 2mm x 2mm MLFTM -40C to 125C 2mm x 2mm MLFTM -40C to 125C 2mm x 2mm MLFTM -40C to 125C 2mm x 2mm MLFTM -40C to 125C 2mm x 2mm MLFTM
Pin Configuration
FB GND SW 1 2 3
OUT VIN
4 EN 5 VIN
1 2 3 4
8 7 6
GND SW FB NC
EN GND
EP
5
TSOT-23-5 (BD5)
8-Pin MLFTM (BML) (Top View) Fused Lead Frame
Pin Description
Pin Number Pin Number TSOT-23-5 2mm x2mm MLFTM 1 2 3 4 5 -- -- -- -- -- 6 3 2 1 4 8 5 EP 7 Pin Name SW GND FB EN VIN OVP AGND PGND NC GND Pin Function 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): 2.5V to 10V for internal circuitry. Overvoltage protection (Input): Connect to the output. Analog ground. Power ground. No connect (no internal connection to die). Ground (Return): Exposed backside pad.
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MIC2287
Micrel, Inc.
Absolute Maximum Ratings(1)
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) .......... -65C to +150C ESD Rating(3) ............................................................... 2kV
Operating Ratings(2)
Supply Voltage (VIN) ..........................................2.5V to 10V Junction Temperature Range (TJ) ............ -40C to +125C Package Thermal Impedance 2mm x 2mmMLFTM (JA) ..................................... 93C/W Thin SOT-23-5 (JA) ......................................... 256C/W
Electrical Characteristics(4)
TA = 25C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 10mA, unless otherwise noted. Bold values indicate -40C TJ 125C. Symbol Parameter Condition Min 2.5 1.8 VEN = 0V(5) (5%) VFB > 200mV, (not switching) 90 2.1 2.5 0.1 95 -450 0.5 0.5 85 90 750 ISW = 0.5A 450 0.01 1.5 20 1.05 13 21 30 1.2 14 22.5 32 150 10 5 0.4 40 1.35 16 24 34 VEN = 0V, VSW = 10V 1 2 Typ VIN Supply Voltage Range Under Voltage Lockout Quiescent Current Shutdown Current Feedback Voltage Feedback Input Current Line Regulation(6) Load Regulation(6) DMAX ISW ISW VSW VEN IEN Maximum Duty Cycle Switch Current Limit Switch Saturation Voltage Switch Leakage Current Enable Threshold Enable Pin Current Oscillator Frequency Overvoltage Protection Max 10 2.4 5 1 100 Units V V mA A mV nA % % % mA mV A V V A MHz V V V C C
VUVLO IVIN ISD IFB
VFB
VFB = 95mV
3V VIN 5V
5mA IOUT 20mA
TURN ON TURN OFF VEN = 10V
fSW
VOVP TJ
Notes:
MIC2287BML- 15 only MIC2287BML- 24 only MIC2287BML- 34 only Hysteresis
Overtemperature Threshold Shutdown
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, JA, 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.
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Micrel, Inc.
Typical Characteristics
Feedback Voltage vs. Input Voltage
SHUTDOWN CURRENT (A)
100 99 98 97 96 95 94 93 92 91 90 0
5 4 3 2 1 0
Shutdown Current vs. Input Voltage
5
QUIESCENT CURRENT (mA)
Quiescent Current vs. Input Voltage
FB VOLTAGE (mV)
4 3 2 1 0
2
4
6 VIN (V)
8
10
12
0
2
4
6 VIN (V)
8
10
12
0
2
4
6 VIN (V)
8
10
12
3 Series LED Efficiency
84 82
EFFICIENCY (%)
EFFICIENCY (%) 84
6 Series LED Efficiency
SWITCHING FREQUENCY (MHz)
VIN = 4.2V
1.4 1.2 1 0.8 0.6 0.4 0.2 0 -40
Switch Frequency vs. Temperature
80
VIN = 3.0V
82 80 78 76
VIN = 3.6V
78 76 74
VIN = 3.6V
VIN = 3.0V
V
IN
= 4.2V
74 72
72 70
0 5
L = 10H C = 0.22F
OUT
10 15 IOUT (mA)
20
25
70
L = 10H COUT = 0.22F
0
5
10 15 IOUT (mA)
20
25
0 40 80 TEMPERATURE (C)
120
50 45 40
IENABLE (A)
EN Pin Bias Currency vs. Temperature
SATURATION VOL AGE (mV)
550 500 450 400 350
Saturation Voltage vs. Temperature
900
Current Limit vs. Temperature
35 30 25 20 15
I
EN
= 10V
CURRENT LIMIT (mA)
ISW = 500mA
0 40 80 TEMPERATURE (C) 120
850 800 750 700 650 600 -40
I
EN
= 4.2V
10 5 I = 3.0V 0 EN 0 50 -50 TEMPERATURE (C)
IEN = 3.6V
100
300 -40
VIN = 2.5V
0 40 80 TEMPERATURE (C) 120
600
Switch Saturation Voltage vs. Current
SATURATION VOL AGE (mV)
500 400 300 200 100 0 0 100 200 300 ISW (mA) 400 500
VIN = 2.5V
VIN = 5V
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MIC2287
Micrel, Inc.
Functional Diagram
VIN
FB
OVP*
EN
OVP*
SW
gm 95mV
S
VREF
PWM Generator
1.2MHz Oscillator
*OVP available on MLFTM package option only
Ramp Generator
GND
MIC2287 Block Diagram
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.
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 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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MIC2287
Micrel, Inc. 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 2 L 22H 15H 10H 6.8H 4.7H 3 22H 15H 10H 6.8H 4.7H 4 22H 15H 10H 6.8H 4.7H 5, 6 22H 15H 10H 6.8H 4.7H 7, 8 22H 15H 10H 6.8H 4.7H
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)
Min COUT 2.2F 1F 0.22F 0.22F 0.22F 2.2F 1F 0.22F 0.22F 0.27F 1F 1F 0.27F 0.27F 0.27F 0.22F 0.22F 0.27F 0.27F 0.27F 0.22F 0.22F 0.27F 0.27F 0.27F
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)
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MIC2287 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.
VIN
Micrel, Inc. 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 EN GND
SW FB OVP
Figure 3. MLFTM Package OVP Circuit
VIN
VIN
PWM
SW FB GND
VIN EN
SW FB GND
5.11k
EN
Figure 1. PWM Dimming Method
VIN
Figure 4. Thin SOT-23 Package 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 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 EN
SW FB GND 5.11k 49.9k
DC 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 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 x 2mm MLFTM with overvoltage protection (OVP). The extra pins of the 8-lead 2mm x 2mm MLFTM package allow a dedicated OVP monitor with
VIN EN GND SW FB
CSS 2200pF
R 10k
Figure 5. Soft-Start Circuit
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M9999-070105
MIC2287
Micrel, Inc.
6-Series LED Circuit without External Soft-Start
6-Series LED Circuit with External Soft-Start
OUTPUT VOL AGE INPUT CURREN T ENABLE (200mA/div) (2V/div)
OUTPU VOL AGE T INPUT CURREN T ENABLE (200mA/div) (2V/div)
L = 10H CIN = 1F COUT = 0.22F VIN = 3.6V IOUT = 20mA 6 LEDs
L = 10H CIN = 1F COUT = 0.22F VIN = 3.6V IOUT = 20mA 6 LEDs CSS = 2200pF R = 10kW
TIME (100s/div.)
TIME (100s/div.)
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MIC2287
Micrel, Inc.
Package Information
5-Pin TSOT (BD5)
8-Pin MLFTM (BML)
July 2005
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M9999-070105
MIC2287 Recommended Land Pattern for MLFTM 2x2 8 Lead
Micrel, Inc.
MICREL INC.
TEL
+ 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
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. (c) 2004 Micrel, Inc. M9999-070105
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July 2005

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