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MIC2289
Micrel
MIC2289
2mm x 2mm White LED Driver with Internal Schottky Diode and OVP
General Description
The MIC2289 is a PWM (pulse width modulated), boostswitching regulator that is optimized for constant-current white LED driver applications. The MIC2289 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 MIC2289 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 varible frequency is much lower noise and input ripple injected to the input power source. The MIC2289 clamps the output voltage in case of open LED conditions, protecting itself and the output capacitor. The MIC2289 is available with three output OVP options of 15V, 24V, and 34V. The different OVP options allows the use of the smallest possible output capacitor with the appropriate voltage rating for a given application. The MIC2289 is available in a 2mm x 2mm 8-pin MLFTM package and 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 Internal Schottky diode 15V, 24V, 34V output OVP options 1.2 MHz PWM operation Over 500mA switch current 95mV feedback voltage <1% line and load regulation <1mA shutdown current Overtemperature protection UVLO 2mm x 2mm 8-pin MLFTM package -40C to +125C 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
3-Series LED Efficiency
10H
82 80
EFFICIENCY (%)
MIC2289-15BML 1-Cell Li Ion VIN 1F OUT EN GND 6.3 FB 95mV SW 0.22F/16V
78 76 74 72 70 0 VIN =3.6V 5 10 15 IOUT (mA) 20 25
3-Series White LED Driver
MicroLeadFrame and MLF 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
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Ordering Information
Part Number MIC2289-15BML MIC2289-15YML MIC2289-24BML MIC2289-24YML MIC2289-34BML MIC2289-34YML Marking Code SNA SNA SNB SNB SNC SNC Overvoltage Protection 15V 15V 24V 24V 34V 34V Junction Temp. Range -40C to 125C -40C to 125C -40C to 125C -40C to 125C -40C to 125C -40C to 125C Package 2mm x 2mm MLFTM-8 2mm x 2mm MLFTM-8 2mm x 2mm MLFTM-8 2mm x 2mm MLFTM-8 2mm x 2mm MLFTM-8 2mm x 2mm MLFTM-8 Lead Finish Standard Lead Free Standard Lead Free Standard Lead Free
Pin Configuration
OUT VIN EN AGND
1 2 3 4 8 7 6
PGND SW FB NC
EP
5
MLFTM-8 (BML) (Top View) Fused Lead Frame
Pin Description
Pin Number 1 2 3 5 6 7 4,8 EP Pin Name OUT VIN EN NC FB SW GND GND Pin Function Output Pin and Overvoltage Protection (Output): Connect to the output capacitor and LEDs Supply (Input): Input voltage. Enable (Input): Logic high enables regulator, logic low shuts down regulator. No connect (no internal connection to die). 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. Switch Node (Input): Internal power transistor collector. Ground (Return): Ground. Ground (Return): Backside pad.
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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 Schottky Reverse Voltage (VDA) ................................... 34V ESD Rating(3) ................................................................ 2kV
Operating Ratings(2)
Supply Voltage (VIN) ........................................ 2.5V to 10V Output Voltage (VOUT) ..................................... VIN to VOVP Junction Temperature Range (TJ) ........... -40C to +125C Package Thermal Impedance 2mm x 2mmMLFTM-8 (JA) .................................. 93C/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 Load Regulation DMAX ISW VSW ISW VEN IEN fSW VD IRD VOVP 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 ID = 150mA VR = 30V MIC2289-15 MIC2289-24 MIC2289-34 Hysteresis 13 21 30 14 22.5 32 150 10 ISW = 0.5A VEN = 0V, VSW = 10V TURN ON TURN OFF VEN = 10V 1.05 1.5 0.4 20 1.2 0.8 40 1.35 1 4 16 24 34 VFB > 200mV, (not switching) VEN = (5%) VFB = 95mV 3V VIN 5V 5mA IOUT 20mA 85 0V(5) 90 Condition Min 2.5 1.8 2.1 2.5 0.1 95 -450 0.5 0.5 90 750 450 0.01 5 1 2 Typ Max 10 2.4 5 1 100 Units V V mA A mV nA % % % mA mV A V V A MHz V A V V V C C
TJ
Notes:
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 rating. 3. Devices are inherently ESD sensitive. Handling precautions required. Human body model. 4. Specification for packaged product only. 5. ISD = IVIN.
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Typical Characteristics
Feedback Voltage vs. Input Voltage
100 99 98 97 96 95 94 93 92 91 90
SHUTDOWN CURRENT (A)
Shutdown Current vs. Input Voltage
5 4 3 2 1 0
QUIESCENT CURRENT (mA)
Quiescent Current vs. Input Voltage
5 4 3 2 1 0
FB VOLTAGE (mV)
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
SWITCHING FREQUENCY (MHz)
1.4 1.2
IENABLE (A)
50 45 40 35 I = 10V 30 EN 25 20 15 10
SCHOTTKY FORWARD CURRENT (mA)
Switch Frequency vs. Temperature
EN Pin Bias Current vs. Temperature
Schottky Forward Voltage Drop
700 600 500 400 300 200 100
1 0.8 0.6 0.4 0.2 0 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
IEN = 4.2V
IEN = 3.6V
1050
SCHOTTKY FORWARD VOLTAGE DROP (mV)
SCHOTTKY LEAKAGE CURRENT (A)
Schottky Reverse Leakage Current
2.5 SATURATION VOLTAGE (mV) 2 1.5 1 0.5 VR = 10V 0 30 40 50 60 70 80 90 100 TEMPERATURE (C) VR = 25V 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 = 16V
ISW = 500mA 0 40 80 TEMPERATURE (C) 120
VIN = 2.5V 600 -40 0 40 80 TEMPERATURE (C)
120
Switch Saturation Voltage vs. Current
600 SATURATION VOLTAGE (mV) 500 400 300 200 100 0 0 100 200 300 ISW (mA) 400 500 VIN = 5V VIN = 2.5V
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5 I = 3.0V EN 0 -50 0 50 TEMPERATURE (C)
450
550
650
750
850
950
100
0
MIC2289
Micrel
Functional Diagram
VIN
FB
EN
OUT
OVP SW gm VREF 95mV PWM Generator
1.2MHz Oscillator
Ramp Generator
GND
MIC2289 Block Diagram
Functional Description
The MIC2289 is a constant frequency, PWM current mode boost regulator. The block diagram is shown above. The MIC2289 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:
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. 5
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MIC2289
Micrel
The table below shows recommended inductor and output capacitor values for various series-LED applications:
External Component Selection
The MIC2289 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
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)
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)
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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 MIC2289 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 MIC2289 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 EN GND VIN SW OUT PWM EN GND FB
Micrel
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 MIC2289 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 MIC2289 has 3 product options in the 2mm x 2mm MLFTM-8 with overvoltage protection, OVP. The extra pins of the 2mm x 2mm MLFTM-8 package allow a dedicated OVP monitor 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, therefore smallest size and lowest cost. The OVP will clamp the output voltage to within the specified limits.
VIN
VIN
SW OUT FB
Figure 3. MLFTM 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 4 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
5.11k 49.9k
Figure 1. PWM Dimming Method
VIN
VIN
SW OUT
EN GND
FB
CSS
2200pF
VIN
DC Equivalent
SW OUT
Figure 2. Continuous Dimming
EN GND
FB R 10k
Figure 4. One of Soft-Start Circuit
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6-Series LED Circuit without External Soft-Start 6-Series LED Circuit with External Soft-Start
Micrel
OUTPUT VOLTAGE INPUT CURRENT ENABLE (200mA/div) (2V/div)
L = 10H CIN = 1F COUT = 0.22F VIN = 3.6V IOUT = 20mA 6 LEDs
OUTPUT VOLTAGE INPUT CURRENT ENABLE (200mA/div) (2V/div)
L = 10H CIN = 1F COUT = 0.22F VIN = 3.6V IOUT = 20mA 6 LEDs CSS = 2200pF R = 10k TIME (100s/div.)
TIME (100s/div.)
Figure 6. 6-Series LED Circuit without External Soft-Start
Figure 7. 6-Series LED Circuit with External Soft-Start
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Package Information
8-Pin MLFTM (BML)
MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
USA
+ 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 at Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2004 Micrel, Incorporated.
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