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MIC2288
Micrel, Inc.
MIC2288
1A 1.2MHz PWM Boost Converter in Thin SOT-23 and 2x2 MLFTM x
General Description
The MIC2288 is a 1.2MHz PWM, DC/DC boost switching regulator available in low-profile Thin SOT-23 and 2mm x 2mm MLFTM package options. High power density is achieved with the MIC2288's internal 34V/1A switch, allowing it to power large loads in a tiny footprint. The MIC2288 implements a constant frequency, 1.2MHz PWM, current mode control scheme with internal compensation that offers excellent transient response and output regulation performance. The high frequency operation saves board space by allowing small, low-profile, external components. The fixed frequency PWM topology also reduces spurious switching noise and ripple to the input power source. The MIC2288 is available in a low-profile Thin SOT-23-5 package and a 2mm x 2mm MLFTM-8 leadless package. The 2mm x 2mm MLFTM-8 package option has an output overvoltage protection feature. The MIC2288 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 range Output voltage adjustable to 34V Over 1A switch current 1.2MHz PWM operation Stable with ceramic capacitors High-efficiency <1% line and load regulation Low input and output ripple <1A shutdown current UVLO Output overvoltage protection (MIC2288BML) Over temperature shutdown Thin SOT-23-5 package option 2mm x 2mm leadless MLFTM-8 package option -40C to +125C junction temperature range
Applications
* * * * * * Organic EL power supply TFT-LCD bias supply 12V supply for DSL applications Multi-output DC/DC converters Positive and negative output regulators SEPIC converters
Typical Application
VIN L1 10H VOUT 15V
90 85
15VOUT Efficiency
VIN = 4.2V
5
VIN EN
SW FB
1
EFFICIENCY (%)
MIC2288BD5 R1
3
80 75 70 65 60 0 0.05 0.1 0.15 LOAD (A) 0.2 VIN = 3.2V
1-Cell Li Ion
4
C1 2.2F
GND
2
R2
C2 10F
VIN = 3.6V
2mm x 2mm MLFTM Boost Regulator
MLF and MicroLeadFrame are 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
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MIC2288
Micrel, Inc.
Ordering Information
Part Number MIC2288BD5 MIC2288YD5 MIC2288BML MIC2288YML Marking Code SHAA SHAA SJA SJA Output Voltage Adjustable Adjustable Adjustable Adjustable Overvoltage Protection - - 34V 34V Junction Temp. Range -40C to 125C -40C to 125C -40C to 125C -40C to 125C Package Thin SOT-23-5 Thin SOT-23-5 2x2 MLFTM-8 2x2 MLFTM-8 Lead Finish Standard Lead Free Standard Lead Free
Pin Configuration
FB GND SW 1 2 3
OVP VIN EN
1 2 3 4 8 7 6
PGND SW FB NC
4 EN
5 VIN
AGND
EP
5
TSOT-23-5 (D5)
8-Pin MLFTM (ML) (Top View) Fused Lead Frame
Pin Description
Pin Number TSOT-23-5 1 2 3 6 Pin Number 2x2 MLFTM-8 x 7 Pin Name SW GND FB Pin Function Switch Node (Input): Internal power Bipolar collector. Ground (Return): Ground. Feedback (Input): 1.24V output voltage sense node. R1 VOUT = 1.24V 1 + R2 Enable (Input): Logic high enables regulator. Logic low shuts down regulator. Supply (Input): 2.5V to 10V input voltage. Output Overvoltage Protection (Input): Tie this pin to VOUT to clamp the output voltage to 34V maximum in fault conditions. Tie this pin to ground if OVP function is not required. No Connect: No internal connection to die. Analog ground. Power ground. Exposed backside pad.
4 5
3 2 1
EN VIN OVP
5 4 8 EP
NC AGND PGND GND
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MIC2288
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 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 2mm MLFTM-8 (JA) ................................. 93C/W Thin SOT-23-5 (JA) .......................................... 256C/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 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. This device is not guaranteed to operate beyond its specified operating rating. 3. IC devices are inherently ESD sensitive. Handling precautions required. Human body model rating: 1.5K in series with 100pF. 4. Specification for packaged product only. 5. ISD = IVIN.
Condition
Min 2.5 1.8
Typ
Max 10
Units V V mA A V V nA
2.1 2.8 0.1
2.4 5 1 1.252 1.265
VFB = 2V, (not switching) VEN = 0V(5) 1.227 1.215 (1%) (2%) (Over Temp) VFB = 1.24V 3V VIN 5V 5mA IOUT 40mA 85
1.24 -450 0.1 0.2 90 1.2
1
% % % A mV
Maximum Duty Cycle Switch Current Limit Switch Saturation Voltage Switch Leakage Current Enable Threshold Enable Pin Current Oscillator Frequency Output Overvoltage Protection Overtemperature Threshold Shutdown MIC2288 MLFTM package option only Hysteresis ISW = 1A VEN = 0V, VSW = 10V Turn on Turn off VEN = 10V
550 0.01 1.5 0.4 20 1.05 30 1.2 32 150 10 40 1.35 34 5
A V V A MHz V C C
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MIC2288
Micrel, Inc.
Typical Characteristics
Feedback Voltage vs. Temperature
91 89 EFFICIENCY (%) 87 85 83 81 79 77 75 0
Efficiency at VOUT = 12V
OUTPUT VOLTAGE (V)
12.2 12.15 12.1 12.05 12 11.95 11.9 11.85 11.8 0
Load Regulation
FEEDBACK VOLTAGE (V)
VIN = 4.2V
1.30 1.28 1.26 1.24 1.22 1.20 1.18 1.16 1.14 1.12
VIN = 3.6V VIN = 3.3V
VIN = 3.6V 25 50 75 100 125 150 LOAD (mA)
25 50 75 100 125 150 OUTPUT CURRENT (mA)
1.10 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
1.8 1.6 CURRENT LIMIT (A) 1.4 1.2 1 0.8 0.6 0.4 0.2 0 2.5
SWITCH SATURATION VOLTAGE (mV)
Current Limit vs. Supply Current
1.4 1.2
CURRENT LIMIT (A)
Current Limit vs. Temperature
300 250 200 150 100 50
Switch Saturation vs. Supply Voltage
1.0 0.8 0.6 0.4 0.2
ISW = 500mA 0 2.5 4 5.5 7 8.5 SUPPLY VOLTAGE (V) 10
4 5.5 7 8.5 SUPPLY VOLTAGE (V)
10
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
SWITCH SATURATION VOLTAGE (mV)
700 600 500 400 300 200 100 0 0
SWITCH SATURATION VOLTAGE (mV)
Switch Saturation vs. Current
700 600 500 400 300 200 100
Switch Saturation vs. Temperature
1.4 FREQUENCY (MHz) 1.3 1.2 1.1 1.0 0.9
Frequency vs. Temperature
VIN = 3.6V 200 400 600 800 1000 SWITCH CURRENT (mA)
VIN = 3.6V I = 500mA
SW
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
0.8 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
MAXIMUM DUTY CYCLE (%)
MAXIMUM DUTY CYCLE (%)
96 94 92 90 88 86 84 82 80 2.5 4 5.5 7 8.5 SUPPLY VOLTAGE (V) 10
97 95 93 91 89 87 VIN = 3.6V
FEEDBACK CURRENT (nA)
100 98
Maximum Duty Cycle vs. Supply Voltage
99
Maximum Duty Cycle vs. Temperature
700 600 500 400 300 200 100
FB Pin Current vs. Temperature
85 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
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MIC2288
Micrel, Inc.
Function Characteristics
Enable Characteristics
OUTPUT VOLTAGE (1mV/div) AC-Coupled
Line Transient Response
OUTPUT VOLTAGE (5V/div)
Output Voltage
ENABLE VOLTAGE (2V/div)
Enable Voltage
INPUT VOLTAGE (2V/div)
4.2V
3.6VIN 12VOUT 150mA Load
3.2V 12VOUT 150mA Load Time (400s/div)
Time (400s/div)
Load Transient Response
LOAD CURRENT OUTPUT VOLTAGE (100mA/div) (100mV/div) AC-Coupled
OUTPUT VOLTAGE (50mV/div)
Switching Waveforms
Output Voltage
INDUCTOR CURRENT (500mA/div)
Inductor Current (10H)
150mA
SWITCH SATURATION (5V/div)
VSW 3.6VIN 12VOUT 150mA
10mA 3.6VIN 12VOUT COUT = 10F Time (400s/div)
Time (400ns/div)
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MIC2288
Micrel, Inc.
Functional Diagram
VIN
FB
OVP*
EN
OVP* SW PWM Generator
gm
VREF
1.24V CA
1.2MHz Oscillator *OVP available on MLFTM package option only.
Ramp Generator
GND
Figure 1. MIC2288 Block Diagram
Functional Description
The MIC2288 is a constant frequency, PWM current mode boost regulator. The block diagram is shown in Figure 1. The MIC2288 is composed of an oscillator, slope compensation ramp generator, current amplifier, gm error amplifier, PWM generator, and a 1A 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 feedback voltage through the external feedback resistors and amplifies the error between the detected signal and the 1.24V 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.
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MIC2288
Micrel, Inc.
Applications Information
DC-to-DC PWM Boost Conversion The MIC2288 is a constant-frequency boost converter. It operates by taking a DC input voltage and regulating a higher DC output voltage. Figure 2 shows a typical circuit. Boost regulation is achieved by turning on an internal switch, which draws current through the inductor (L1). When the switch turns off, the inductor's magnetic field collapses, causing the current to be discharged into the output capacitor through an external Schottky diode (D1). Voltage regulation is achieved by modulating the pulse width or pulse-width modulation (PWM).
VIN L1 10H D1 VOUT
Component Selection
Inductor Inductor selection is a balance between efficiency, stability, cost, size, and rated current. For most applications a 10H is the recommended inductor value. It is usually a good balance between these considerations. Larger inductance values reduce the peak-to-peak ripple current, affecting efficiency. This has the effect of reducing both the DC losses and the transition losses. There is also a secondary effect of an inductor's DC resistance (DCR). The DCR of an inductor will be higher for more inductance in the same package size. This is due to the longer windings required for an increase in inductance. Since the majority of input current (minus the MIC2288 operating current) is passed through the inductor, higher DCR inductors will reduce efficiency. To maintain stability, increasing inductor size will have to be met with an increase in output capacitance. This is due to the unavoidable "right half plane zero" effect for the continuous current boost converter topology. The frequency at which the right half plane zero occurs can be calculated as follows:
Frhpz = VIN
2
MIC2288BML VIN C1 2.2F EN GND GND SW OVP FB R2 GND R1 C2 10F
Figure 2. Typical Application Circuit Duty Cycle Considerations Duty cycle refers to the switch on-to-off time ratio and can be calculated as follows for a boost regulator:
D = 1- VIN VOUT
VOUT x L x IOUT x 2
The duty cycle required for voltage conversion should be less than the maximum duty cycle of 85%. Also, in light load conditions where the input voltage is close to the output voltage, the minimum duty cycle can cause pulse skipping. This is due to the energy stored in the inductor causing the output to overshoot slightly over the regulated output voltage. During the next cycle, the error amplifier detects the output as being high and skips the following pulse. This effect can be reduced by increasing the minimum load or by increasing the inductor value. Increasing the inductor value reduces peak current, which in turn reduces energy transfer in each cycle. Overvoltage Protection For the MLFTM package option, there is an overvoltage protection function. If the feedback resistors are disconnected from the circuit or the feedback pin is shorted to ground, the feedback pin will fall to ground potential. This will cause the MIC2288 to switch at full duty cycle in an attempt to maintain the feedback voltage. As a result, the output voltage will climb out of control. This may cause the switch node voltage to exceed its maximum voltage rating, possibly damaging the IC and the external components. To ensure the highest level of protection, the MIC2288 OVP pin will shut the switch off when an overvoltage condition is detected, saving itself and other sensitive circuitry downstream.
The right half plane zero has the undesirable effect of increasing gain, while decreasing phase. This requires that the loop gain is rolled off before this has significant effect on the total loop response. This can be accomplished by either reducing inductance (increasing RHPZ frequency) or increasing the output capacitor value (decreasing loop gain). Output Capacitor Output capacitor selection is also a trade-off between performance, size, and cost. Increasing output capacitance will lead to an improved transient response, but also an increase in size and cost. X5R or X7R dielectric ceramic capacitors are recommended for designs with the MIC2288. Y5V values may be used but to offset their tolerance over temperature, more capacitance is required. The following table shows the recommended ceramic (X5R) output capacitor value vs. output voltage. Output Voltage Recomended Output Capacitance <6V 22F <16V 10F <34V 4.7F Table 1. Output Capacitor Selection Diode Selection The MIC2288 requires an external diode for operation. A Schottky diode is recommended for most applications due to their lower forward voltage drop and reverse recovery time. Ensure the diode selected can deliver the peak inductor current and the maximum reverse voltage is rated greater than the output voltage.
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MIC2288 Input capacitor A minimum 1F ceramic capacitor is recommended for designing with the MIC2288. Increasing input capacitance will improve performance and greater noise immunity on the source. The input capacitor should be as close as possible to the inductor and the MIC2288, with short traces for good noise performance.
Micrel, Inc. Feedback Resistors The MIC2288 utilizes a feedback pin to compare the output to an internal reference. The output voltage is adjusted by selecting the appropriate feedback resistor network values. The R2 resistor value must be less than or equal to 5k (R2 5k).The desired output voltage can be calculated as follows:
R1 VOUT = VREF x + 1 R2
where VREF is equal to 1.24V.
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MIC2288
Micrel, Inc.
Application Circuits
VIN 3V to 4.2V L1 4.7H D1 VOUT 5V @ 400mA
VIN 3V to 4.2V
L1 10H
D1
VOUT 15V @ 100mA
MIC2288BML C1 4.7F 6.3V VIN SW OVP EN GND GND FB R2 1.87k R1 5.62k C2 22F 6.3V
MIC2288BML C1 2.2F 10V VIN SW OVP EN GND
GND
R1 54.9k
FB R2 5k
C2 10F 16V
GND
GND
C1 C2 D1 L1
4.7F, 6.3V, 0805 X5R Ceramic Capacitor 22F, 6.3V, 0805 X5R Ceramic Capacitor 1A, 40V Schotty Diode 4.7H, 650mA Inductor
08056D475MAT 12066D226MAT MBRM140T3
AVX AVX ON Semi.
C1 C2 D1 L1
2.2F, 10V, 0805 X5R Ceramic Capacitor 10F, 16V, 1206 X5R Ceramic Capacitor 1A, 40V Schotty Diode 10H, 650mA Inductor
08052D225KAT 1206YD106MAT MBRM140T3 LQH43CN100K03
AVX AVX ON Semi. Murata
LQH32CN4R7M11 Murata
Figure 3. 3.3VIN to 5VOUT @ 400mA
Figure 6. 3.3VIN - 4.2VIN to 15VOUT @ 100mA
VIN 3V to 4.2V
L1 10H
D1
VOUT 9V @ 180mA
VIN 3V to 4.2V
L1 10H
D1
VOUT 24V @ 50mA
MIC2288BML C1 2.2F 10V VIN SW OVP EN GND GND FB R2 5k R1 31.6k C2 10F 16V
C1 2.2F 10V
MIC2288BML VIN SW OVP EN GND FB R2 1k R1 18.2k C2 4.7F 25V
GND
GND
GND
C1 C2 D1 L1
2.2F, 10V, 0805 X5R Ceramic Capacitor 10F, 16V, 1206 X5R Ceramic Capacitor 1A, 40V Schotty Diode 10H, 650mA Inductor
08052D225KAT 1206YD106MAT MBRM140T3 LQH43CN100K03
AVX AVX ON Semi. Murata
C1 C2 D1 L1
2.2F, 10V, 0805 X5R Ceramic Capacitor 4.7F, 25V, 1206 X5R Ceramic Capacitor 1A, 40V Schotty Diode 10H, 650mA Inductor
08052D225KAT 12063D475MAT MBRM140T3 LQH43CN100K03
AVX AVX ON Semi. Murata
Figure 4. 3.3VIN - 4.2VIN to 9VOUT @ 180mA
Figure 7. 3.3VIN - 4.2VIN to 24VOUT @ 50mA
VIN 3V to 4.2V
L1 10H
D1
VOUT 12V @ 100mA
VIN 5V
L1 10H
D1
VOUT 9V @ 330mA
MIC2288BML MIC2288BML C1 2.2F 10V VIN SW OVP EN GND GND FB R2 5k R1 42.3k C2 10F 16V C1 2.2F 10V VIN SW OVP EN GND GND GND
C1 C1 C2 D1 L1 2.2F, 10V, 0805 X5R Ceramic Capacitor 10F, 16V, 1206 X5R Ceramic Capacitor 1A, 40V Schotty Diode 10H, 650mA Inductor 08052D225KAT 1206YD106MAT MBRM140T3 LQH43CN100K03 AVX AVX ON Semi. Murata C2 D1 L1 2.2F, 10V, 0805 X5R Ceramic Capacitor 10F, 16V, 1206 X5R Ceramic Capacitor 1A, 40V Schotty Diode 10H, 650mA Inductor 08052D225KAT 1206YD106MAT MBRM140T3 LQH43CN100K03 AVX AVX ON Semi. Murata
R1 31.6k
FB R2 5k
C2 10F 16V
GND
Figure 5. 3.3VIN - 4.2VIN to 12VOUT @ 100mA
Figure 8. 5VIN to 9VOUT @ 330mA
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MIC2288
VIN 5V L1 10H D1 VOUT 12V @ 250mA VIN 5V L1 10H D1
Micrel, Inc.
VOUT 24V @ 80mA
MIC2288BML C1 2.2F 10V VIN SW OVP EN GND GND FB R2 5k R1 43.2k C2 10F 16V C1 2.2F 10V
MIC2288BML VIN SW OVP EN GND GND GND FB R2 1k R1 18.2k C2 4.7F 25V
GND
C1 C2 D1 L1
2.2F, 10V, 0805 X5R Ceramic Capacitor 10F, 16V, 1206 X5R Ceramic Capacitor 1A, 40V Schotty Diode 10H, 650mA Inductor
08052D225KAT 1206YD106MAT MBRM140T3 LQH43CN100K03
AVX AVX ON Semi. Murata
C1 C2 D1 L1
2.2F, 10V, 0805 X5R Ceramic Capacitor 4.7F, 25V, 1206 X5R Ceramic Capacitor 1A, 40V Schotty Diode 10H, 650mA Inductor
08052D225KAT 12066D475MAT MBRM140T3
AVX AVX ON Semi.
LQH32CN4R7M11 Murata
Figure 9. 5VIN to 12VOUT @ 250mA
Figure 10. 5VIN to 24VOUT @ 80mA
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MIC2288
Micrel, Inc.
Package Information
All Dimensions are in millimeters
5-Pin TSOT (D5)
8-Pin MLFTM (ML)
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
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, Incorporated.
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