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MIC2245
4MHz PWM Synchronous Buck Regulator with LDO Standby Mode
General Description
The Micrel MIC2245 is a high efficiency 4MHz pulse width modulated (PWM) synchronous buck (stepdown) regulator that features a LOWQTM LDO standby mode that draws only 18A of quiescent current. The MIC2245 allows an ultra-low noise, small size, and high efficiency solution for portable power applications. In PWM mode, the MIC2245 operates with a constant frequency 4MHz PWM control. Under light load conditions, such as in system sleep or standby modes, the PWM switching operation can be disabled to reduce switching losses. In this light load LOWQTM mode, the LDO maintains the output voltage and draws only 18A of quiescent current. The LDO mode of operation saves battery life while not introducing spurious noise and high ripple as experienced with pulse skipping or bursting mode regulators. The MIC2245 operates from a 2.7V to 5.5V input voltage and features internal power MOSFETs that can supply up to 500mA output current in PWM mode. It can operate with a maximum duty cycle of 100% for use in low-dropout conditions. The MIC2245 is available in the 10-pin 3mm x 3mm MLFTM package with a junction operating range from -40C to +125C. Data sheet and support documentation can be found on Micrel's web site at: www.micrel.com.
Features
* 2.7 to 5.5V supply/input voltage * Light load LOWQTM LDO mode 20A quiescent current Low noise, 75Vrms * 4MHz PWM mode Output current to 500mA >92% efficiency 100% maximum duty cycle * Adjustable output voltage option down to 1V Fixed output voltage options available * Ultra-fast transient response * Uses a tiny 1H inductor * Fully integrated MOSFET switches * Micropower shutdown operation * Thermal shutdown and current limit protection * Pb-free 10-pin 3mm x 3mm MLFTM package * -40C to +125C junction temperature range
Applications
* Cellular phones * PDAs * USB peripherals
____________________________________________________________________________________________________
Typical Application
1.8VOUT Efficiency
100 90 80 70 60 50 40 30 20 10 0 0
V IN =3.2V VIN=3.6V VIN=4.2V
Adjustable Output Buck Regulator with LOWQTM Mode
100 200 300 400 500 OUTPUT CURRENT (mA)
Patent Pending LOWQ is a trademark of Micrel, Inc 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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MIC2245
Ordering Information
Part Number MIC2245YML
Note: * Other Voltage options available. Contact Micrel for details.
Output Voltage* Adj.
Junction Temperature Range -40 to +125C
Package 10-Pin 3x3 MLFTM
Lead Finish Pb-free
Pin Configuration
AGND 1 LDO 2 BIAS 3 AVIN 4 FB 5 EP 10 PGND 9 SW 8 VIN 7 LOWQ 6 EN
10-Pin 3mm x 3mm MLF (ML)
Pin Description
Pin Number 1 2 3 Pin Name AGND LDO BIAS Pin Function Analog (signal) Ground. LDO Output (Output): Connect to VOUT for LDO mode operation. Internal circuit bias supply. Must be filtered from input voltage through an RC lowpass filter with a cutoff frequency 4 5 AVIN FB
1 . 2(20.5 )(100nF )
Analog Supply/Input Voltage (Input): Supply voltage for the analog control circuitry and LDO input power. Requires bypass capacitor to GND. Feedback. Input to the error amplifier. For the Adjustable option, connect to the external resistor divider network to set the output voltage. For fixed output voltage options, connect to VOUT and an internal resistor network sets the output voltage. Enable (Input). Logic low will shut down the device, reducing the quiescent current to less than 5A. Enable LDO Mode (Input): Logic low enables the internal LDO and disables the PWM operation. Logic high enables the PWM mode and disables the LDO mode. Supply/Input Voltage (Input): Supply voltage for the internal switches and drivers. Switch (Output): Internal power MOSFET output switches. Power Ground. Ground, backside pad.
6
EN _____ LOWQ VIN SW PGND GND
7 8 9 10 EP
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MIC2245
Absolute Maximum Ratings(1)
Supply Voltage (VIN) ............................................ +6V Output Switch Voltage (VSW) ............................... +6V Output Switch Current (ISW) ................................... 2A Logic Input Voltage (VEN,VLOWQ) .............. -0.3V to VIN Storage Temperature (Ts)................ -60C to +150C ESD Rating(3) ....................................................... 3kV
Operating Ratings(2)
Supply Voltage (VIN)............................+2.7V to +5.5V Logic Input Voltage (VEN,VLOWQ) .............. -0.3V to VIN Junction Temperature (TJ) .............. -40C to +125C Junction Thermal Resistance 3x3 MLF-10L (JA)................................... 60C/W
Electrical Characteristics(4)
VIN = VEN = VLOWQ =3.6V; L = 1.0H; COUT = 4.7F; TA = 25C, unless noted. Bold values indicate -40C< TJ < +125C Parameter Supply Voltage Range Under-Voltage Lockout Threshold UVLO Hysteresis Quiescent Current, PWM mode Quiescent Current, LDO mode Shutdown Current [Adjustable] Feedback Voltage FB pin input current Current Limit in PWM Mode Output Voltage Line Regulation Output Voltage Load Regulation, PWM Mode Output Voltage Load Regulation, LDO Mode Maximum Duty Cycle PWM Switch ONResistance Oscillator Frequency LOWQ threshold voltage LOWQ Input Current Enable Threshold Enable Input Current LDO Dropout Voltage IOUT = 50mA Note 5 0.5 VFB = 0.9 * VNOM VOUT > 2V; VIN = VOUT+300mV to 5.5V; ILOAD= 100mA VOUT < 2V; VIN = 2.7V to 5.5V; ILOAD= 100mA 20mA < ILOAD < 300mA 100A < ILOAD < 50mA VLOWQ = 0V VFB 0.4V ISW = 50mA VFB = 0.7VFB_NOM (High Side Switch) ISW = -50mA VFB = 1.1VFB_NOM (Low Side Switch) 3.6 0.5 100 0.4 0.4 4 0.85 0.1 0.85 0.1 110 4.4 1.3 2 1.3 2 0.675 VFB = 0.9 * VNOM (not switching) VLOWQ = 0V;IOUT = 0mA VEN = 0V 2% (over temperature) 0.98 (turn-on) Condition Min 2.7 2.45 2.55 100 710 20 0.01 1 1 1 0.13 0.2 0.5 0.8 1 1.85 900 29 5 1.02 Typ Max 5.5 2.65 Units V V mV A A A V nA A % % % % MHz V A V A mV
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MIC2245
Parameter Output Voltage Noise LDO Current Limit Over-Temperature Shutdown Over-Temperature Hysteresis
Notes 1. 2. 3. 4. 5.
Condition LOWQ = 0V; COUT = 4.7F, 10Hz to 100kHz LOWQ = 0V; VOUT = 0V (LDO Mode)
Min
Typ 75
Max
Units Vrms mA C C
60
120 160 20
Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5k in series with 100pF. Specification for packaged product only. Dropout voltage is defined as the input-to-output differential at which the output voltage drops 2% below its nominal value that is initially measured at a 1V differential. For outputs below 2.7V, the dropout voltage is the input-to-output voltage differential with a minimum input voltage of 2.7V.
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MIC2245
Typical Characteristics - PWM Mode
2.5VOUT Efficiency
100 90 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 OUTPUT CURRENT (mA) V IN=3.2V VIN=3.6V VIN=4.2V 100 90 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 OUTPUT CURRENT (mA) V IN=3.2V VIN=3.6V VIN=4.2V
1.8VOUT Efficiency
100 90 80 70 60 50 40 30 20 10 0 0
1.5VOUT Efficiency
V IN=3.2V VIN=3.6V VIN=4.2V
100 200 300 400 500 OUTPUT CURRENT (mA)
1.2VOUT Efficiency
100 90 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 OUTPUT CURRENT (mA) V IN=3.2V VIN=3.6V VIN=4.2V 100
1.0VOUT Efficiency
90 V IN=3.2V 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 OUTPUT CURRENT (mA) VIN=3.6V VIN=4.2V 1.004 1.002 1.000 0.998 0.996 0.994 0.992 0.990 0
Load Regulation
VIN=3.6V LowQ=VIN
100 200 300 400 500 OUTPUT CURRENT (mA)
900 850
Quiescent Current vs. Input Voltage
4.5
Frequency vs. Input Voltage
CURRENT LIMIT (mA)
1200 1000 800 600 400 200
Peak Current Limit vs. Supply Voltage
4.3 800 750 700 3.9 650 600 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 INPUT VOLTAGE (V) 3.7 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 INPUT VOLTAGE (V) 4.1
LowQ = VIN 0 2.7 3.4 4.1 4.8 SUPPLY VOLTAGE (V)
5.5
1.5 ENABLE THRESHOLD (V) 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7
Enable Threshold vs. Supply Voltage
0.6 LowQ = V IN 0.5 2.7 3.4 4.1 4.8 SUPPLY VOLTAGE (V)
5.5
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MIC2245
Typical Characteristics - LDO Mode
140 CURRENT LIMIT (mA) 120 100 80 60 40 20 0 2.7 LowQ = 0V 3.4 4.1 4.8 SUPPLY VOLTAGE (V) 5.5
Current Limit vs. Supply Voltage
DROPOUT VOLTAGE (mV)
160 140 120 100 80 60 40 20
Dropout Voltage vs. Temperature
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
VOUT = 3.3V IOUT = 50mA LowQ = 0V
80 DROPOUT VOLTAGE (mV) 70 60 50 40 30 20 10
Dropout Voltage vs. Temperature
DROPOUT VOLTAGE (mV)
40 35 30 25 20 15 10 5
Dropout Voltage vs. Temperature
DROPOUT VOLTAGE (mV)
9 8 7 6 5 4 3 2 1
Dropout Voltage vs. Temperature
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
VOUT = 3.3V IOUT = 25mA LowQ = 0V
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
VOUT = 3.3V IOUT = 10mA LowQ = 0V
0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
VOUT = 3.3V IOUT = 1mA LowQ = 0V
1.5 ENABLE THRESHOLD (V) 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6
Enable Threshold Voltage vs. Supply Voltage
0.5 2.7
LowQ = 0V 3.4 4.1 4.8 SUPPLY VOLTAGE (V) 5.5
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MIC2245
Typical Characteristics - LDO Mode (cont.)
25 QUIESCENT CURRENT (A) 24 23 22 21 20 19 18 17 16 15 0 OUTPUT VOLTAGE (V)
Quiescent Current vs. Output Current
1.836 1.827 1.818 1.809 1.8 1.791 1.782 1.773 1.764 0
Output Voltage vs. Output Current
VIN = 3.6V LowQ = 0V 20 40 60 80 100 OUTPUT CURRENT (mA)
VIN = 3.6V VOUT =1.8V LowQ = 0V 20 40 60 80 100 OUTPUT CURRENT (mA)
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MIC2245
Functional Diagram
MIC2245 Block Diagram
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MIC2245
Functional Characteristics
Load Transient PWM Mode
Output Voltage AC Coupled (50mV/div)
Output Voltage AC Coupled (50mV/div)
Load Transient LDO Mode
Output Current (100mA/div)
Output Current (20mA/div)
10mA COUT = 4.7F Time (20s/div)
10mA COUT = 4.7F Time (20s/div)
Enable Transient PWM Mode
Output Voltage (1V/div)
Output Voltage (1V/div)
Enable Transient LDO Mode
0V
0V
Enable (2V/div)
Enable (2V/div)
0V COUT = 4.7F Time (40s/div)
0V COUT = 4.7F Time (40s/div)
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MIC2245
Functional Description
VIN VIN provides power to the MOSFETs for the switch mode regulator section, along with the current limiting sensing. Due to the high switching speeds, a 1F capacitor is recommended close to VIN and the power ground (PGND) pin for bypassing. Please refer to layout recommendations. AVIN Analog VIN (AVIN) provides power to the LDO section. AVIN and VIN must be tied together. Careful layout should be considered to ensure high frequency switching noise caused by VIN is reduced before reaching AVIN. LDO The LDO pin is the output of the linear regulator and should be connected to the output. In LOWQ mode (LOWQ<1.5V), the LDO provides the output voltage. In PWM mode (LOWQ>1.5V), the LDO pin is high impedance. EN The enable pin provides a logic level control of the output. In the off state, supply current of the device is greatly reduced (typically <1A). Also, in the off state, the output drive is placed in a "tri-stated" condition, where both the high side P-channel Mosfet and the low-side N-channel are in an "off" or non-conducting state. Do not drive the enable pin above the supply voltage. LOWQ The LOWQ pin provides a logic level control between the internal PWM mode and the low noise linear regulator mode. With LOWQ pulled low (<0.5V), quiescent current of the device is greatly reduced by switching to a low noise linear regulator mode that has a typical IQ of 20A. In linear (LDO) mode, the output can deliver 60mA of current to the output. By placing LOWQ high (>1.5V), this transitions the device into a constant frequency PWM buck regulator mode. This allows the device the ability to efficiently deliver up to 500mA of output current at the same output voltage. BIAS The BIAS pin supplies the power to the internal power to the control and reference circuitry. The bias is powered from the input voltage through an RC lowpass filter. The RC lowpass filter frequency 1 must be . 2 (20.5 )(100nF )
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FB The feedback pin (FB) provides the control path to control the output. For adjustable versions, a resistor divider connecting the feedback to the output is used to adjust the desired output voltage. The output voltage is calculated as follows:
R1 VOUT = VREF x + 1 R2
where VREF is equal to 1.0V. A feedforward capacitor is recommended for most designs using the adjustable output voltage option. To reduce battery current draw, a 100K feedback resistor is recommended from the output to the FB pin (R1). Also, a feedforward capacitor should be connected between the output and feedback (across R1). The large resistor value and the parasitic capacitance of the FB pin can cause a high frequency pole that can reduce the overall system phase margin. By placing a feedforward capacitor, these effects can be significantly reduced. Typically an 82pF small ceramic capacitor is recommended.
SW The switch (SW) pin connects directly to the inductor and provides the switching current necessary to operate in PWM mode. Due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. PGND Power ground (PGND) is the ground path for the high current PWM mode. The current loop for the power ground should be as small as possible and separate from the Analog ground (AGND) loop. Refer to the layout considerations for more details. AGND Signal ground (AGND) is the ground path for the biasing and control circuitry. The current loop for the signal ground should be separate from the Power ground (PGND) loop. Refer to the layout considerations for more details.
Micrel, Inc.
MIC2245
Applications Information
The MIC2245 is a 500mA PWM power supply that utilizes a LOWQTM light load mode to maximize battery efficiency in light load conditions. This is achieved with a LOWQ control pin that when pulled low, shuts down all the biasing and drive current for the PWM regulator, drawing only 20A of operating current. This allows the output to be regulated through the LDO output, capable of providing 60mA of output current. This method has the advantage of producing a clean, low current, ultra-low noise output in LOWQTM mode. During LOWQTM mode, the SW node becomes high impedance, blocking current flow. Other methods of reducing quiescent current, such as pulse frequency modulation (PFM), or bursting techniques, create large amplitude, low frequency ripple voltages that can be detrimental to system operation. When more than 60mA is required, the LOWQ pin can be forced high, causing the MIC2245 to enter PWM mode. In this case, the LDO output makes a "hand-off" to the PWM regulator with virtually no variation in output voltage. The LDO output then turns off allowing up to 500mA of current to be efficiently supplied through the PWM output to the load.
Output Capacitor The MIC2245 is optimized for a 4.7F output capacitor. The MIC2245 utilizes type III internal compensation and utilizes an internal high frequency zero to compensate for the double pole roll off of the LC filter. For this reason, larger output capacitors can create instabilities. X5R or X7R dielectrics are recommended for the output capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore, not recommended.
In addition to a 4.7F, a small 10nF is recommended close to the load for high frequency filtering. Smaller case size capacitors are recommended due to there lower ESR and ESL.
Input Capacitor A minimum 1F ceramic is recommended on the VIN pin for bypassing. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics lose most of their capacitance over temperature and are therefore, not recommended.
A minimum 1F is recommended close to the VIN and PGND pins for high frequency filtering. Smaller case size capacitors are recommended due to their lower ESR and ESL. Please refer to layout recommendation section of data sheet for proper layout of the input capacitor.
Inductor Selection The MIC2245 is designed for use with a 1.0H inductor. Proper selection should ensure the inductor can handle the maximum average and peak currents required by the load. Maximum current ratings of the inductor are generally given in two methods; permissible DC current and saturation current. Permissible DC current can be rated either for a 40C temperature rise or a 10% to 20% loss in inductance. Ensure that the inductor selected can handle the maximum operating current. When saturation current is specified, make sure that there is enough margin that the peak current will not saturate the inductor. Peak inductor current can be calculated as follows:
V VOUT 1 - OUT VIN + 2x f xL
IPK = IOUT
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MIC2245
Layout Recommendation
Component Placement
C4
L1
C2 R5
C1 U1
R1 C3
R2
Evaluation Board Layout
TOP
BOTTOM
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MIC2245
Typical Application Circuit with Bill of Materials (BOM)
Adjustable Output
Item C1
Part Number 0603D105MAT2A GRM185R60J105KE21D C1608X5R1A105K C1608X5R0J475M GRM188R60J475KE19D VJ0603Y475KXQCW1BC 06036D475MAT2A C1005X5R0J104M
Description 1F 6.3V X5R 0402 Ceramic Capacitor 1F 10V X5R 0402 Ceramic Capacitor
Manufacturer AVX Murata TDK TDK Murata Vishay AVX Murata AVX TDK Vishay TDK Colicraft TDK Vishay Vishay Vishay Vishay Vishay Vishay Micrel
Qty 1
C4
4.7F 6.3V X5R 0603 Ceramic Capacitor
1
C2
04026D104MAT2A GRM155R60J104K VJ0402A820KXQCW1BC C1005COG1H820J DO2010-102ML GLF2518T1R0M CRCW04021003F CRCW04026652F CRCW04021243F
0.1F 6.3V X5R 0402 Ceramic Capacitor 0.1F 6.3V X7R 0402 Ceramic Capacitor 82pF X7R 0402 Ceramic Capacitor 82pF COG 0402 Ceramic Capacitor 1H Inductor 1H Inductor 100k 1% 0402 Resistor 66.5k 1% 0402 Resistor for 2.5VOUT 124k 1% 0402 Resistor for 1.8VOUT 200k 1% 0402 Resistor for 1.5VOUT 499k 1% 0402 Resistor for 1.2VOUT Open for 1.0VOUT 20.5 1% 0402 Resistor 4MHz PWM Step-Down Converter/LDO
1
C3 L1 R1(7)
1 1 1
R2(7)
CRCW04022003F CRCW04024993F
1
R3 U1
CRCW040220R5F MIC2245YML
1 1
Notes: 1. AVX: www.avxcorp.com 2. Murata: www.murata.com 3. TDK: www.tdk.com 4. Vishay: www.vishay.com 5. Coilcraft: www.coilcraft.com 6. Micrel, Inc.: www.micrel.com 7. For Adjustable Version Only
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MIC2245
Package Information
10-Pin 3mm x 3mm 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
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) 2006 Micrel, Incorporated.
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