MIC2285 8MHz PWM Synchronous Buck Regulator with LDO Standby Mode General Description Features The Micrel MIC2285 is a high efficiency 8MHz pulse width modulated (PWM) synchronous buck (stepdown) regulator that features a LOWQ™ LDO standby mode that draws only 18µA of quiescent current. The MIC2285 allows an ultra-low noise, small size, and high efficiency solution for portable power applications. • 2.7 to 5.5V supply/input voltage • Light load LOWQ™ LDO mode 20µA quiescent current Low noise, 75µVrms • 8MHz PWM mode Output current to 500mA >90% efficiency 100% maximum duty cycle • Adjustable output voltage option down to 1V Fixed output voltage options available • Ultra-fast transient response • Uses a tiny 0.47µH inductor • Enables sub 1mm profile solution • Fully integrated MOSFET switches • Micropower shutdown • Thermal shutdown and current limit protection • Pb-free 10-pin 3mm x 3mm MLF package • –40°C to +125°C junction temperature range In PWM mode, the MIC2285 operates with a constant frequency 8MHz 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 LOWQ™ mode, the LDO maintains the output voltage and draws only 18µA 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 MIC2285 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 MIC2285 is available in the 10-pin 3mm x 3mm MLF™ package with a junction operating range from –40°C to +125°C. Data sheets and support documentation can be found on Micrel’s web site at: www.micrel.com. Applications • Cellular phones • PDAs • USB peripherals ____________________________________________________________________________________________________ Typical Application 1.8VOUT Efficiency 100 90 VIN =3.2V 80 70 60 50 VIN =3.6V VIN=4.2V 40 30 20 Adjustable Output Buck Regulator with LOWQ™ Mode 10 0 0 100 200 300 400 500 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 January 2006 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Ordering Information Part Number Output Voltage* Junction Temperature Range Package Lead Finish MIC2285YML Adj. –40° to +125°C 10-Pin 3x3 MLF™ Pb-free Note: * Other Voltage options available. Contact Micrel for details. Pin Configuration 10 PGND AGND 1 LDO 2 9 SW BIAS 3 8 VIN AVIN 4 7 LOWQ FB 5 EP 6 EN 10-Pin 3mm x 3mm MLF (ML) Pin Description Pin Number Pin Name 1 AGND Pin Function Analog (signal) Ground. 2 LDO LDO Output (Output): Connect to VOUT for LDO mode operation. 3 BIAS Internal circuit bias supply. Must be filtered from input voltage through an RC lowpass filter with a cutoff frequency ≥ 1 . 2π(20.5Ω )(100nF ) Analog Supply/Input Voltage (Input): Supply voltage for the analog control circuitry and LDO input power. Requires bypass capacitor to GND. 4 AVIN 5 FB 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. 6 EN Enable (Input). Logic low will shut down the device, reducing the quiescent current to less than 5µA. 7 _____ LOWQ 8 VIN Supply/Input Voltage (Input): Supply voltage for the internal switches and drivers. 9 SW Switch (Output): Internal power MOSFET output switches. 10 PGND EP GND January 2006 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. Power Ground. Ground, backside pad. 2 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Absolute Maximum Ratings(1) Operating Ratings(2) 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)................ -60°C to +150°C ESD Rating(3) ....................................................... 3kV Supply Voltage (VIN)............................+2.7V to +5.5V Logic Input Voltage (VEN,VLOWQ) .............. -0.3V to VIN Junction Temperature (TJ) .............. –40°C to +125°C Junction Thermal Resistance 3x3 MLF-10L (θJA)................................... 60°C/W Electrical Characteristics(4) VIN = VEN = VLOWQ =3.6V; L = 0.47µH; COUT = 10µF; TA = 25°C, unless noted. Bold values indicate –40°C< TJ < +125°C Parameter Condition Min (turn-on) 2.45 Supply Voltage Range Under-Voltage Lockout Threshold Typ Max 5.5 V 2.55 2.65 V 2.7 UVLO Hysteresis 100 Units mV Quiescent Current, PWM mode VFB = 0.9 * VNOM (not switching) 790 900 µA Quiescent Current, LDO mode VLOWQ = 0V;IOUT = 0mA 20 29 µA Shutdown Current VEN = 0V 0.01 5 µA [Adjustable] Feedback Voltage ± 2% (over temperature) 1 1.02 V 0.98 FB pin input current 1 Current Limit in PWM Mode VFB = 0.9 * VNOM Output Voltage Line Regulation VOUT > 2V; VIN = VOUT+300mV to 5.5V; ILOAD= 100mA VOUT < 2V; VIN = 2.7V to 5.5V; ILOAD= 100mA 0.13 Output Voltage Load Regulation, PWM Mode 20mA < ILOAD < 300mA 0.2 0.8 % Output Voltage Load Regulation, LDO Mode 100µA < ILOAD < 50mA VLOWQ = 0V 0.5 1 % Maximum Duty Cycle VFB ≤ 0.4V PWM Switch ONResistance ISW = 50mA VFB = 0.7VFB_NOM (High Side Switch) ISW = -50mA VFB = 1.1VFB_NOM (Low Side Switch) 0.675 1 nA 1.85 A % % 100 0.4 Ω 0.4 Oscillator Frequency 7.2 8 8.8 MHz LOWQ threshold voltage 0.5 0.85 1.3 V 0.1 2 µA 0.85 1.3 V 0.1 2 µA LOWQ Input Current Enable Threshold 0.5 Enable Input Current LDO Dropout Voltage January 2006 IOUT = 50mA Note 5 110 3 mV M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Parameter Condition Min Output Voltage Noise LOWQ = 0V; COUT = 10µF, 10Hz to 100kHz LDO Current Limit LOWQ = 0V; VOUT = 0V (LDO Mode) Typ Max Units 75 µVrms 120 mA Over-Temperature Shutdown 160 °C Over-Temperature Hysteresis 20 °C 60 Notes 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5kΩ in series with 100pF. 4. Specification for packaged product only. 5. 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. January 2006 4 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Typical Characteristics – PWM Mode 2.5VOUT Efficiency 1.8VOUT Efficiency 100 100 60 100 90 V IN=3.2V 90 80 70 V IN=3.2V VIN=3.6V VIN=4.2V 80 70 60 90 V IN=3.2V 80 VIN=3.6V 70 VIN=3.6V VIN=4.2V 60 50 50 50 40 40 40 30 20 30 20 30 20 10 0 0 10 100 200 300 400 500 OUTPUT CURRENT (mA) 0 0 1.2VOUT Efficiency 0 0 90 50 50 80 70 60 VIN=4.2V 1.018 VIN=3.2V 1.014 VIN=3.6V 1.010 VIN=4.2V 1.006 40 1.002 30 20 30 20 0.998 10 10 0 0 1100 100 200 300 400 500 OUTPUT CURRENT (mA) Quiescent Current vs. Input Voltage 0 0 9.0 1000 Frequency vs. Input Voltage 900 8.0 800 7.5 600 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 INPUT VOLTAGE (V) 1.5 0.990 0 100 200 300 400 500 OUTPUT CURRENT (mA) 8.5 700 VIN=3.6V LowQ=VIN 0.994 1200 CURRENT LIMIT (mA) 40 100 200 300 400 500 OUTPUT CURRENT (mA) Load Regulation 100 90 V IN=3.2V 80 70 VIN=3.6V 60 VIN=4.2V 10 100 200 300 400 500 OUTPUT CURRENT (mA) 1.0VOUT Efficiency 100 ENABLE THRESHOLD (V) 1.5VOUT Efficiency 7.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 INPUT VOLTAGE (V) 100 200 300 400 500 OUTPUT CURRENT (mA) Peak Current Limit vs. Supply Voltage 1000 800 600 400 200 LowQ = VIN 0 2.7 3.4 4.1 4.8 SUPPLY VOLTAGE (V) 5.5 Enable Threshold vs. Supply Voltage 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 LowQ = V IN 0.5 2.7 3.4 4.1 4.8 SUPPLY VOLTAGE (V) January 2006 5.5 5 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Typical Characteristics - LDO Mode 80 60 40 20 60 50 40 30 20 10 VOUT = 3.3V IOUT = 25mA LowQ = 0V 40 DROPOUT VOLTAGE (mV) DROPOUT VOLTAGE (mV) Dropout Voltage vs. Temperature 70 0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) DROPOUT VOLTAGE (mV) 100 0 2.7 80 160 120 LowQ = 0V 3.4 4.1 4.8 SUPPLY VOLTAGE (V) 120 100 80 60 40 20 Dropout Voltage vs. Temperature 9 30 25 20 15 10 VOUT = 3.3V IOUT = 10mA LowQ = 0V 5 0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) VOUT = 3.3V IOUT = 50mA LowQ = 0V 0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) 5.5 35 Dropout Voltage vs. Temperature 140 DROPOUT VOLTAGE (mV) CURRENT LIMIT (mA) 140 Current Limit vs. Supply Voltage Dropout Voltage vs. Temperature 8 7 6 5 4 3 2 1 VOUT = 3.3V IOUT = 1mA LowQ = 0V 0 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) Enable Threshold Voltage vs. Supply Voltage ENABLE THRESHOLD (V) 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 2.7 January 2006 LowQ = 0V 3.4 4.1 4.8 SUPPLY VOLTAGE (V) 6 5.5 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Typical Characteristics – LDO Mode (cont.) Quiescent Current vs. Output Current 1.836 24 23 22 21 20 19 18 17 16 15 0 VIN = 3.6V LowQ = 0V 20 40 60 80 100 OUTPUT CURRENT (mA) January 2006 OUTPUT VOLTAGE (V) QUIESCENT CURRENT (µA) 25 Output Voltage vs. Output Current 1.827 1.818 1.809 1.8 1.791 1.782 1.773 1.764 0 VIN = 3.6V VOUT =1.8V LowQ = 0V 20 40 60 80 100 OUTPUT CURRENT (mA) 7 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Functional Diagram MIC2285 Block Diagram January 2006 8 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Functional Characteristics Load Transient LDO Mode Output Current (20mA/div) Output Current (100mA/div) Output Voltage AC Coupled (50mV/div) Output Voltage AC Coupled (50mV/div) Load Transient PWM Mode 10mA 10mA COUT = 4.7µF COUT = 4.7µF Time (20µs/div) Time (20µs/div) Enable Transient LDO Mode Output Voltage (1V/div) 0V Enable (2V/div) 0V Enable (2V/div) Output Voltage (1V/div) Enable Transient PWM Mode 0V 0V COUT = 4.7µF COUT = 4.7µF Time (40µs/div) Time (40µs/div) January 2006 9 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Functional Description 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: 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 1µF capacitor is recommended close to VIN and the power ground (PGND) pin for bypassing. Please refer to layout recommendations. ⎛ R1 ⎞ VOUT = VREF × ⎜ + 1⎟ ⎝ R2 ⎠ 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. 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. 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 <1µA). 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. 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. 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 20µA. 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. 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. 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 ≥ 2π (20.5Ω )(100nF ) January 2006 10 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Applications Information Output Capacitor The MIC2285 is optimized for a 10µF output capacitor. A larger value can be used to improve transient response. The MIC2285 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. The MIC2285 is a 500mA PWM power supply that utilizes a LOWQ™ 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 20µA 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 LOWQ™ mode. During LOWQ™ 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. In addition to a 10µF, 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. Inductor Selection The MIC2285 is designed for use with a 0.47µH 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 40°C 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: When more than 60mA is required, the LOWQ pin can be forced high, causing the MIC2285 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. Input Capacitor A minimum 1µF 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 1µF 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. January 2006 IPK = IOUT 11 ⎛ V VOUT ⎜⎜1 − OUT VIN ⎝ + 2× f ×L ⎞ ⎟ ⎟ ⎠ M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Layout Recommendation Component Placement C4 L1 C1 C2 R5 U1 R1 R2 C3 Evaluation Board Layout TOP BOTTOM January 2006 12 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Typical Application Circuit with Bill of Materials (BOM) Adjustable Output Item Part Number 0603D105MAT2A C1 GRM185R60J105KE21D C1608X5R1A105K C1608X5R0J106K C4 06036D106MAT2A GRM188R60J106M C1005X5R0J104M C2 04026D104MAT2A GRM155R60J104K C3 L1 R1(7) R2(7) Description Manufacturer 1µF 6.3V X5R 0402 Ceramic Capacitor 1µF 10V X5R 0402 Ceramic Capacitor 10µF 6.3V X5R 0603 Ceramic Capacitor 10µF 6.3V X7R 0603 Ceramic Capacitor 0.1µF 6.3V X5R 0402 Ceramic Capacitor AVX Murata 1 TDK TDK AVX 1 Murata TDK AVX 0.1µF 6.3V X7R 0402 Ceramic Capacitor Murata VJ0402A820KXQCW1BC 82pF X7R 0402 Ceramic Capacitor Vishay C1005COG1H820J 82pF COG 0402 Ceramic Capacitor TDK DO2010-501ML 0.5µH Inductor Colicraft LQM21PNR47M00 0.47µH Inductor Murata CRCW04021003F 100kΩ 1% 0402 Resistor Vishay CRCW04026652F 66.5kΩ 1% 0402 Resistor for 2.5VOUT Vishay CRCW04021243F 124kΩ 1% 0402 Resistor for 1.8VOUT Vishay CRCW04022003F 200kΩ 1% 0402 Resistor for 1.5VOUT Vishay CRCW04024993F 499kΩ 1% 0402 Resistor for 1.2VOUT Vishay Open Qty 1 1 1 1 1 for 1.0VOUT R3 CRCW040220R5F 20.5Ω 1% 0402 Resistor Vishay 1 U1 MIC2285YML 8MHz PWM Step-Down Converter/LDO Micrel 1 Notes: 1. 2. 3. 4. 5. 6. 7. AVX: www.avxcorp.com Murata: www.murata.com TDK: www.tdk.com Vishay: www.vishay.com Coilcraft: www.coilcraft.com Micrel, Inc.: www.micrel.com For Adjustable Version Only January 2006 13 M9999-012406 www.micrel.com Micrel, Inc. MIC2285 Package Information 10-Pin 3mm x 3mm MLF™ (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. © 2006 Micrel, Incorporated. January 2006 14 M9999-012406 www.micrel.com