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MIC2289C
White LED Driver Internal Schottky Diode and OVP
General Description
The MIC2289C is a PWM (pulse width modulated), boostswitching 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 SOT23 package. The MIC2289C has a junction temperature range of -40C to +125C. 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 <1A shutdown current Overtemperature protection UVLO Thin SOT-23 6-pin package -40C to +125C 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
10H
82 80
3-Series LED Efficiency
MIC2289C-34YD6 1-Cell Li Ion VIN 1F EN GND SW OUT FB 95mV 0.22F/50V
EFFICIENCY (%)
78 76 74 72 70 0 VIN =3.6V 5 10 15 IOUT (mA) 20 25
7-Series White LED Driver
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
Micrel, Inc.
MIC2289C
Ordering Information
Part Number MIC2289C-34BD6 MIC2289C-34YD6 Marking Code SM34| SM34| Overoltage Protection 34V 34V Junction Temp. Range -40C to +125C -40C to +125C Package 6-Pin Thin SOT-23 6-Pin Thin SOT-23 Lead Finish Standard Pb-Free
Note: Marking bars may not be to scale.
Pin Configuration
FB GND SW 1 2 3
Denotes Pb-Free
SM34
5 4 6 EN VIN VOUT
Denotes MIC2289C
6- Pin Thin SOT-23 (D6)
Pin Description
Pin Number 1 2 3 4 5 6 Pin Name SW GND FB EN VIN OUT Pin Name 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): 2.7V to 8V for internal circuitry. Output Pin and Overvoltage Protection (Output): Connect to the output capacitor and LEDs.
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MIC2289C
Absolute Maximum Ratings(1)
Supply Voltage (VIN) .......................................................12V Switch Voltage (VSW)....................................... -0.3V to 34V Enable Pin Voltage (VEN)................................... -0.3V to VIN FB Voltage (VFB)...............................................................6V Switch Current (ISW) .........................................................2A Ambient Storage Temperature (Ts) ...........-65C to +150C Schottky Reverse Voltage (VDA).....................................34V EDS Rating(3) .................................................................. 2kV
Operating Ratings(2)
Supply voltage (VIN) ........................................ 2.5V to +10V Output Voltage (VIN) ............................................ VIN to VOVP Junction Temperature (TJ) ........................ -40C to +125C Package Thermal Resistance Thin SOT-23-6 (JA) ........................................177C/W
Electrical Characteristics(4)
TA = 25C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 20mA, unless otherwise noted. Bold values indicate -40C< TJ < +125C.
Symbol VIN VUVLO IVIN ISD VFB IFB Parameter Supply Voltage Range Under Voltage Lockout Quiescent Current Shutdown Current Feedback Voltage Feedback Input Current Line Regulation(6) Load Regulation DMAX ISW VSW ISW VEN IEN fSW VD IRD VOVP TJ
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, 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. 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. ISD = IVIN. 6. Guaranteed by design
(6)
Condition
Min 2.5 1.8
Typ 2.1 2.5 0.1
Max 10 2.4 5 1 105
Units V V mA A mV nA % % % mA mV
VFB > 200mV, (not switching) VEN = 0V(5) (10%) VFB = 95mV 3V VIN 5V 5mA IOUT 20mA 85 ISW = 0.5A VEN = 0V, VSW = 10V TURN ON TURN OFF VEN = 10V 1.05 ID = 150mA VR = 30V MIC2289C-34YD6 only Hysteresis 27 1.5 85
95 -450 0.5 0.5 90 750 450 0.01
Maximum Duty Cycle Switch Current Limit Switch Saturation Voltage Switch Leakage Current Enable Threshold Enable Pin Current Oscillator Frequency Schottky Forward Drop Schottky Leakage Current Overvoltage Protection Overtemperature Threshold Shutdown
5 0.4
A V V A MHz V A V C C
20 1.2 0.8 32 150 10
40 1.35 1 4 37
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MIC2289C
Typical Characteristics
100 99 FB VOLTAGE (mV) 98 97 96 95 94 93 92 91 90 0 2 4 6 VIN (V) 8 10 12
Feedback Voltage vs. Input Voltage
SHUTDOWN CURRENT (A)
5 4 3 2 1 0
Shutdown Voltage vs. Input Voltage
QUIESCENT CURRENT (mA)
5 4 3 2 1 0
Quiescent Current vs. Input Current
0
2
4
6 VIN (V)
8
10
12
0
2
4
6 VIN (V)
8
10
12
SCHOTTKY FORWARD CURRENT (mA)
SWITCHING FREQUENCY (MHz)
1.4 1.2
Switch Frequency vs. Temperature
50 45 40 IENABLE (A)
EN Pin Bias Current vs. Temperature
700 600 500 400 300 200 100
Schottky Forward Voltage Drop
1.0 0.8 0.6 0.4 0.2 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
35 I = 10V 30 E N 25 20 I = 4.2V 15 E N
I = 3.6V EN 10 5 I = 3.0V EN 0 -50 0 50 TEMPERATURE (C)
1050
100
SCHOTTKY FORWARD VOLTAGE DROP (mV)
SCHOTTKY LEAKAGE CURRENT (A)
2.5 2 1.5 1 0.5
Schottky Reverse Leakage Current
SATURATION VOLTAGE (mV)
550 500 450 400 350 300 -40
Saturation Voltage vs. Temperature
900 CURRENT LIMIT (mA) 850 800 750 700 650
Current Limit vs. Temperature
VR = 25V VR = 16V
VR = 10V 0 30 40 50 60 70 80 90 100 TEMPERATURE (C)
IS W = 500mA 0 40 80 TEMPERATURE (C) 120
VIN = 2.5V 600 -40 0 40 80 TEMPERATURE (C)
600 SATURATION VOLTAGE (mV) 500 400 300 200 100
Switch Saturation Voltage vs. Current
VIN = 2.5V VIN = 5V
0 0
100
200 300 ISW (mA)
400
500
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1150
450
550
650
750
850
950
0
120
Micrel, Inc.
MIC2289C
Functional Diagram
VIN FB EN OUT
OVP SW gm VREF 95mV S PWM Generator
1.2MHz Oscillator
Ramp Generator
GND
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:
ILED = 95mW R FB
The Enable pin shuts down the output switching and disables control circuitry to reduce input current-toleakage levels. Enable pin input current is zero at zero volts.
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MIC2289C inductor and output capacitor values for various seriesLED applications.
External Component Selection
The MIC2289C can be used across a wide rage of applications. The table below shows recommended
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) M9999-081507-B
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MIC2289C
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.
VIN
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
VIN
SW OUT
EN GND
FB
Figure 3. Thin SOT-23 Package OVP Circuit
VIN
SW OUT
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 CSS 2200pF
PWM
EN
FB GND
Figure 1. PWM Dimming Method
VIN
SW OUT
VIN
EN
GND
FB R 10k
VIN
SW OUT
Figure 4. One of Soft-Start Circuit
EN GND
FB
5.11k 49.9k
DC Equivalent
Figure 2. Continuous Dimming
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MIC2289C
6-Series LED Circuit without External Soft-Start
6-Series LED Circuit with External Soft-Start
OUTPUT VOLTAGE INPUT CURREN T ENABLE (200mA/div) (2V/div)
L = 10H CIN = 1F COUT = 0.22F VIN = 3.6V IOUT = 20mA 6 LEDs
OUTPUT VOLTAGE INPUT CURREN T ENABLE (200mA/div) (2V/div)
L = 10H CIN = 1F COUT = 0.22F VIN = 3.6V IOUT = 20mA 6 LEDs CSS = 2200pF
TIME (100s/di v.)
TIME (100s/di v.)
Figure 5. 6-Series LED Circuit without External Soft Start
Figure 6. 6-Series LED Circuit with External Soft Start
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MIC2289C
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. (c) 2005 Micrel, Incorporated.
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