MP1542_06

MP1542 700KHz/1.3MHz Boost Converter with a 2A Switch The Future of Analog IC Technology DESCRIPTION The MP1542 is a current mode step up converter with a 2A, 0.18Ω internal switch to provide a highly efficient regulator with fast response. The MP1542 can be operated at 700KHz or 1.3MHz allowing for easy filtering and low noise. An external compensation pin gives the user flexibility in setting loop dynamics, which allows the use of small, lowESR ceramic output capacitors. Soft-start results in small inrush current and can be programmed with an external capacitor. The MP1542 operates from an input voltage as low as 2.5V and can generate 12V at up to 500mA from a 5V supply. The MP1542 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. The MP1542 is available in low profile 8-pin MSOP packages. FEATURES • • • • • • • • • • • • • 2A, 0.18Ω, 25V Power MOSFET Uses Tiny Capacitors and Inductors Pin Selectable 700KHz or 1.3MHz Fixed Switching Frequency Programmable Soft-Start Operates with Input Voltage as Low as 2.5V and Output Voltage as High as 22V 12V at 500mA from 5V Input UVLO, Thermal Shutdown Internal Current Limit Available in 8-Pin MSOP Packages LCD Displays Portable Applications Handheld Computers and PDAs Digital Still and Video Cameras APPLICATIONS “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. EVALUATION BOARD REFERENCE Board Number EV1542DK-00A Dimensions 2.0”X x 2.0”Y TYPICAL APPLICATION VIN 3.3V D1 VOUT 8V Efficiency vs Load Current 95 90 85 80 75 70 65 60 55 50 1 VIN = 3.3V VOUT = 8V 10 100 LOAD CURRENT (mA) 1000 6 7 OFF ON 3 8 IN FSEL EN SS 5 SW FB 2 MP1542 GND 4 COMP 1 C3 2.2nF C4 10nF EFFICIENCY (%) MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 1 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH PACKAGE REFERENCE ABSOLUTE MAXIMUM RATINGS (1) SW ............................................... –0.5V to +25V IN ............................................... –0.5V to +25V All Other Pins.............................. –0.3V to +6.5V Junction Temperature...............................150°C Lead Temperature ....................................260°C Storage Temperature ..............–65°C to +150°C TOP VIEW COMP FB EN GND 1 2 3 4 8 7 6 5 SS FSEL IN SW Recommended Operating Conditions (2) Supply Voltage VIN ........................... 2.5V to 22V Output Voltage VOUT ........................... 3V to 22V Operating Temperature .............–40°C to +85°C Thermal Resistance Part Number* MP1542DK * Package MSOP8 Temperature –40°C to +85°C (3) MSOP8 .................................. 150 ..... 65... °C/W Notes: 1) Exceeding these ratings may damage the device. 2) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately 1” square of 1 oz copper. θJA θJC For Tape & Reel, add suffix –Z (eg. MP1542DK–Z) For Lead Free, add suffix –LF (eg. MP1542DK–LF–Z) ELECTRICAL CHARACTERISTICS VIN = VEN = 5V, TA = +25°C, unless otherwise noted. Parameter Operating Input Voltage Undervoltage Lockout Undervoltage Lockout Hysteresis Supply Current (Shutdown) Supply Current (Quiescent) Switching Frequency FSEL High Threshold FSEL Low Threshold Maximum Duty Cycle EN High Threshold EN Low Threshold EN Input Bias Current Soft-Start Current FB Voltage FB Input Bias Current Error Amp Voltage Gain Error Amp Transconductance Error Amp Output Current Symbol Condition VIN VIN Rising Min 2.5 2.15 Typ Max 22 2.45 Units V V mV 1 900 1.5 840 1.5 µA µA MHz KHz V V % V V µA µA V nA V/V µmho µA 100 VEN = 0V VFB = 1.35V VFSEL = VIN VFSEL = GND VFSEL Rising VFB = 0V, VFSEL = VIN VFB = 0V, VFSEL = GND VEN Rising VEN = 0V, 5V 1.225 –200 AVEA GEA 6 1.25 –100 1000 350 35 0.1 700 1.3 700 fSW 1.1 560 0.5 85 92 0.5 90 95 1.5 1 1.275 MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 2 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH ELECTRICAL CHARACTERISTICS (continued) VIN = VEN = 5V, TA = +25°C, unless otherwise noted. Parameter SW On-Resistance (4) SW Current Limit (4) SW Current Limit (4) SW Leakage Thermal Shutdown (4) Symbol Condition RON Duty Cycle = 0% Duty Cycle = 50% VSW = 20V Min Typ 0.18 2.6 2 160 Max 1 Units Ω A A µA °C Note: 4) Guaranteed by design. TYPICAL PERFORMANCE CHARACTERISTICS Circuit on front page, VIN = 3.3V, VOUT = 8V, unless otherwise noted. Efficiency vs Load Current 100 95 90 EFFICIENCY (%) EFFICIENCY (%) 85 80 75 70 65 60 55 50 1 VIN = 5V VOUT = 12V 10 100 LOAD CURRENT (mA) 1000 95 90 80 75 70 65 60 55 50 1 VIN = 3.3V VOUT = 8V 10 100 LOAD CURRENT (mA) 1000 EFFICIENCY (%) 85 Efficiency vs Load Current 95 90 85 80 75 70 65 60 55 50 Efficiency vs Load Current VIN = 3.3V VOUT = 12V 1 10 100 LOAD CURRENT (mA) 1000 Quiescent Current vs Temperature 690 FEEDBACK VOLTAGE (V) 680 670 660 650 640 630 620 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) 1.259 1.258 1.257 1.256 1.255 1.254 1.253 1.252 1.251 Feedback Voltage vs Temperature 690 680 FREQUENCY (KHz) 670 660 650 640 630 Frequency (700KHz) vs Temperature 1.250 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) 620 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 3 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH TYPICAL PERFORMANCE CHARACTERISTICS (continued) Circuit on front page, VIN = 3.3V, VOUT = 8V, unless otherwise noted. Frequency (1.3MHz) vs Temperature 1.28 1.26 1.24 1.22 1.20 1.18 1.16 1.14 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) CURRENT LIMIT (A) FREQUENCY (MHz) Current Limit vs Duty Cycle 2.5 2.0 1.5 1.0 0.5 0 0 10 20 30 40 50 60 70 80 90 DUTY CYCLE (%) VSW 5V/div. VSW 5V/div. VOUT AC Coupled 0.2V/div. IINDUCTOR 0.5A/div. IINDUCTOR 0.5A/div. IOUT 0.2A/div. 400ns/div. VOUT AC Coupled 0.2V/div. VEN 2V/div. VEN 2V/div. VOUT 5V/div. IOUT 0.2A/div. IINDUCTOR 0.5A/div. VOUT 5V/div. IINDUCTOR 0.5A/div. MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 4 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH PIN FUNCTIONS Pin # 1 2 3 4 5 6 7 8 Name Description COMP Compensation Pin. Connect a capacitor and resistor in series to ground for loop stability. FB Feedback Input. Reference voltage is 1.25V. Connect a resistor divider to this pin. Regulator On/Off Control Input. A high input at EN turns on the converter, and a low input turns EN it off. When not used, connect EN to the input source (through a 100kΩ pull-up resistor if VIN > 6V) for automatic startup. EN cannot be left floating. GND Ground. Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power SW inductor and output rectifier to SW. SW can swing between GND and 25V. IN Input Supply Pin. IN must be locally bypassed. Frequency Select Pin. Tie to IN (through a 100kΩ resistor if VIN > 6V) for 1.3MHz operation or to FSEL GND for 700KHz operation. Soft-Start Control Pin. Connect a soft-start capacitor to this pin. The soft-start capacitor is SS charged with a constant current of 6µA. OPERATION The MP1542 uses a constant frequency, peak current mode boost regulation architecture to regulate the feedback voltage. The operation of the MP1542 can be understood by referring to the block diagram of Figure 1. IN 6 INTERNAL REGULATOR AND ENABLE CIRCUITRY OSCILLATOR 5 + PWM CONTROL LOGIC CURRENT SENSE AMP EN 3 FSEL 7 SW -- + --GM 4 2 GND FB SS 8 + 1.25V 1 COMP Figure 1—Functional Block Diagram MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 5 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH At the beginning of each cycle, the N-Channel MOSFET switch is turned on, forcing the inductor current to rise. The current at the source of the switch is internally measured and converted to a voltage by the current sense amplifier. That voltage is compared to the error voltage at COMP. The voltage at the output of the error amplifier is an amplified version of the difference between the 1.25V reference voltage and the feedback voltage. When these two voltages are equal, the PWM comparator turns off the switch forcing the inductor current to the output capacitor through the external rectifier. This causes the inductor current to decrease. The peak inductor current is controlled by the voltage at COMP, which in turn is controlled by the output voltage. Thus the output voltage controls the inductor current to satisfy the load. The use of current mode regulation improves transient response and control loop stability. APPLICATION INFORMATION Components referenced below apply to Typical Application Circuit on page 1. Selecting the Soft-Start Capacitor The MP1542 includes a soft-start timer that limits the voltage at COMP during startup to prevent excessive current at the input. This prevents premature termination of the source voltage at startup due to input current overshoot. When power is applied to the MP1542, and enable is asserted, a 6µA internal current source charges the external capacitor at SS. As the SS capacitor is charged, the voltage at SS rises. The MP1542 internally clamps the voltage at COMP to 700mV above the voltage at SS. The soft-start ends when the voltage at SS reaches 0.45V. This limits the inductor current at start-up, forcing the input current to rise slowly to the current required to regulate the output voltage. The soft-start period is determined by the equation: t SS = 75 × C SS where VOUT is the output voltage. For R2 = 10kΩ and VFB = 1.25V, then R1 (kΩ) = 8kΩ (VOUT – 1.25V). Selecting the Input Capacitor An input capacitor is required to supply the AC ripple current to the inductor, while limiting noise at the input source. A low ESR capacitor is required to keep the noise at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. Use an input capacitor value greater than 4.7µF. The capacitor can be electrolytic, tantalum or ceramic. However since it absorbs the input switching current it requires an adequate ripple current rating. Use a capacitor with RMS current rating greater than the inductor ripple current (see Selecting The Inductor to determine the inductor ripple current). To insure stable operation place the input capacitor as close to the IC as possible. Alternately a smaller high quality ceramic 0.1µF capacitor may be placed closer to the IC with the larger capacitor placed further away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type. All ceramic capacitors should be placed close to the MP1542. Where CSS (in nF) is the soft-start capacitor from SS to GND, and tSS (in µs) is the soft-start period. Determine the capacitor required for a given soft-start period by the equation: C SS = 0.0133 × t SS Setting the Output Voltage Set the output voltage by selecting the resistive voltage divider ratio. Use 10kΩ for the low-side resistor R2 of the voltage divider. Determine the high-side resistor R1 by the equation: R1 = R2( VOUT − VFB ) VFB MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 6 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH Selecting the Output Capacitor The output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the output voltage ripple to a minimum. The characteristic of the output capacitor also affects the stability of the regulation control system. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. In the case of ceramic capacitors, the impedance of the capacitor at the switching frequency is dominated by the capacitance, and so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be: ⎛ V⎞ ⎜1 - IN ⎟ × ILOAD ⎜V ⎟ OUT ⎠ ⎝ ≈ C2 × f SW Selecting the Inductor The inductor is required to force the higher output voltage while being driven by the input voltage. A larger value inductor results in less ripple current that results in lower peak inductor current, reducing stress on the internal N-Channel.switch. However, the larger value inductor has a larger physical size, higher series resistance, and/or lower saturation current. A 4.7µH inductor is recommended for most 1.3MHz applications and a 10µH inductor is recommended for most 700KHz applications. However, a more exact inductance value can be calculated. A good rule of thumb is to allow the peak-to-peak ripple current to be approximately 30-50% of the maximum input current. Make sure that the peak inductor current is below 75% of the current limit at the operating duty cycle to prevent loss of regulation due to the current limit. Also make sure that the inductor does not saturate under the worst-case load transient and startup conditions. Calculate the required inductance value by the equation: L= VIN × (VOUT - VIN ) VOUT × f SW × ∆I VOUT × ILOAD (MAX ) VIN × η VRIPPLE Where VRIPPLE is the output ripple voltage, VIN and VOUT are the DC input and output voltages respectively, ILOAD is the load current, fSW is the switching frequency, and C2 is the capacitance of the output capacitor. In the case of tantalum or low-ESR electrolytic capacitors, the ESR dominates the impedance at the switching frequency, and so the output ripple is calculated as: (1 − VRIPPLE ≈ VIN ) × ILOAD VOUT I × R ESR × VOUT + LOAD C2 × f SW VIN IIN(MAX ) = Where RESR is the equivalent series resistance of the output capacitors. Choose an output capacitor to satisfy the output ripple and load transient requirements of the design. A 4.7µF-22µF ceramic capacitor is suitable for most applications. ∆I = (30% − 50%)IIN(MAX ) Where ILOAD(MAX) is the maximum load current, ∆I is the peak-to-peak inductor ripple current, and η is efficiency. Selecting the Diode The output rectifier diode supplies current to the inductor when the internal MOSFET is off. To reduce losses due to diode forward voltage and recovery time, use a Schottky diode with the MP1542. The diode should be rated for a reverse voltage equal to or greater than the output voltage used. The average current rating must be greater than the maximum load current expected, and the peak current rating must be greater than the peak inductor current. MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 7 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH Compensation The output of the transconductance error amplifier (COMP) is used to compensate the regulation control system. The system uses two poles and one zero to stabilize the control loop. The poles are fP1 set by the output capacitor C2 and load resistance and fP2 set by the compensation capacitor C3. The zero fZ1 is set by the compensation capacitor C3 and the compensation resistor R3. These are determined by the equations: fP1 = fP2 = 1 π × C2 × RLOAD Table 1—Component Selection VIN (V) 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 3.3 5 5 5 5 5 5 5 5 5 12 12 12 12 12 12 VOUT (V) 8 8 8 12 12 12 18 18 18 8 8 8 12 12 12 18 18 18 15 15 15 18 18 18 C2 (µF) 4.7 10 22 4.7 10 22 4.7 10 22 4.7 10 22 4.7 10 22 4.7 10 22 4.7 10 22 4.7 10 22 R3 (kΩ) 10 10 10 15 15 15 20 20 30 10 10 15 15 15 20 20 20 30 10 10 15 5.1 5.1 15 C3 (nF) 2.2 2.2 2.2 1 1 2.2 1 1 2.2 4.7 4.7 1 2.2 2.2 1 1 1 1 2.2 2.2 1 2.2 2.2 1 G EA 2 × π × C3 × A VEA 1 2 × π × C3 × R3 f Z1 = Where RLOAD is the load resistance, GEA is the error amplifier transconductance, and AVEA is the error amplifier voltage gain. The DC loop gain is: A VDC = 1.5 × A VEA × VIN × R LOAD × VFB VOUT 2 Where VFB is the feedback regulation threshold. There is also a right-half-plane zero (fRHPZ) that exists in continuous conduction mode (inductor current does not drop to zero on each cycle) step-up converters. The frequency of the right half plane zero is: fRHPZ = VIN × R LOAD 2 × π × L × VOUT 2 2 Table 1 lists generally recommended compensation components for different input voltage, output voltage and capacitance of most frequently used output ceramic capacitors. Ceramic capacitors have extremely low ESR, therefore the second compensation capacitor (from COMP to GND) is not required. For faster control loop and better transient response, set the capacitor C3 to the recommended value in Table 1. Then slowly increase the resistor R3 and check the load step response on a bench to make sure the ringing and overshoot on the output voltage at the edge of the load steps is minimal. Finally, the compensation needs to be checked by calculating the DC loop gain and the crossover frequency. The crossover frequency where the loop gain drops to 0dB or a gain of 1 can be obtained visually by placing a –20dB/decade slope at each pole, and a +20dB/decade slope at each zero. The crossover frequency should be at least one decade below the frequency of the right-half-plane zero at maximum output load current to obtain high enough phase margin for stability. 8 MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH AMLCD Application Figure 3 shows a power supply for active matrix (TFT-LCD) flat-panel displays. The positive and negative charge pump outputs are configured with discrete components. Adjust the output capacitance and compensation component values as necessary to meet transient performance. Layout Consideration High frequency switching regulators require very careful layout for stable operation and low noise. All components must be placed as close to the IC as possible. Keep the path between the SW pin, output diode, output capacitor and GND pin extremely short for minimal noise and ringing. The input capacitor must be placed close to the IN pin for best decoupling. All feedback components must be kept close to the FB pin to prevent noise injection on the FB pin trace. The ground return of the input and output capacitors should be tied close to the GND pin. See the MP1542 demo board layout for reference. TYPICAL APPLICATION VIN 5V 6 7 OFF ON 3 8 IN FSEL EN SS 5 SW FB 2 D1 VOUT 12V MP1542 GND 4 COMP 1 C4 10nF C3 2.2nF Figure 2—Typical Application Circuit VOUT3 26V 5mA D2 D3 D4 VOUT2 -9V 10mA VIN 3.0V to 3.6V 7 OFF ON 3 8 D1 6 IN FSEL EN SS 5 SW FB 2 VOUT1 9V 150mA MP1542 GND 4 COMP 1 C4 22nF C3 2.2nF Figure 3—Multiple-Output, Low-Profile (1.2mm max) TFT LCD Power Supply MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 9 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH PACKAGE INFORMATION MSOP8 0.114(2.90) 0.122(3.10) 8 5 PIN 1 ID (NOTE 5) 0.114(2.90) 0.122(3.10) 0.187(4.75) 0.199(5.05) 0.010(0.25) 0.014(0.35) 1 4 0.0256(0.65)BSC BOTTOM VIEW TOP VIEW GAUGE PLANE 0.010(0.25) 0.043(1.10)MAX SEATING PLANE 0.002(0.05) 0.006(0.15) 0o-6o 0.016(0.40) 0.026(0.65) 0.004(0.10) 0.008(0.20) 0.030(0.75) 0.037(0.95) FRONT VIEW SIDE VIEW NOTE: 1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS. 2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSION OR GATE BURR. 3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSION. 4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX. 5) PIN 1 IDENTIFICATION HAS HALF OR FULL CIRCLE OPTION. 6) DRAWING MEETS JEDEC MO-187, VARIATION AA. 7) DRAWING IS NOT TO SCALE. 0.181(4.60) 0.040(1.00) 0.016(0.40) 0.0256(0.65)BSC RECOMMENDED LAND PATTERN NOTICE: The information in this document is subject to change without notice. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP1542 Rev. 1.3 9/7/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 10