MP1542 700KHz/1.3MHz Boost Converter with a 2A Switch The Future of Analog IC Technology DESCRIPTION FEATURES 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. • • • • • • • • • 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 APPLICATIONS • • • • 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. LCD Displays Portable Applications Handheld Computers and PDAs Digital Still and Video Cameras “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. EVALUATION BOARD REFERENCE Board Number Dimensions EV1542DK-00A 2.0”X x 2.0”Y TYPICAL APPLICATION D1 VIN 3.3V Efficiency vs Load Current VOUT 8V 95 5 6 7 OFF ON 3 8 IN FSEL EN SS EFFICIENCY (%) 90 SW FB 2 MP1542 GND 4 COMP 1 85 80 75 70 65 60 C3 2.2nF VIN = 3.3V VOUT = 8V 55 C4 10nF 50 MP1542_TAC01 1 10 100 LOAD CURRENT (mA) 1000 MP1542-EC02 MP1542 Rev. 1.2 12/14/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 1 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE FB 2 7 FSEL 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 EN 3 6 IN Recommended Operating Conditions GND 4 5 SW Supply Voltage VIN ........................... 2.5V to 22V Output Voltage VOUT ........................... 3V to 22V Operating Temperature .............–40°C to +85°C TOP VIEW COMP 1 8 SS Connect Exposed Pad to Pin 4 MP1542_PD01-MSOP8 Thermal Resistance Part Number* Package Temperature MP1542DK MSOP8 –40°C to +85°C MP1542DH MSOP8H –40°C to +85°C * For Tape & Reel, add suffix –Z (eg. MP1542DK–Z) For Lead Free, add suffix –LF (eg. MP1542DK–LF–Z) (3) θJA (2) θJC MSOP8 .................................. 150 ..... 65... °C/W MSOP8H (Exposed Pad)....... 120 ..... 12... °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. 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 Symbol Condition VIN VIN Rising FSEL High Threshold FSEL Low Threshold VEN = 0V VFB = 1.35V VFSEL = VIN VFSEL = GND VFSEL Rising VFB = 0V, VFSEL = VIN VFB = 0V, VFSEL = GND VEN Rising Maximum Duty Cycle MP1542 Rev. 1.2 12/14/2005 Typ Max 22 2.45 100 fSW 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 Min 2.5 2.15 1.1 560 0.1 700 1.3 700 0.5 85 92 90 95 mV 1 900 1.5 840 1.5 µA µA MHz KHz V V % 1.5 V V µA µA V nA V/V 0.5 VEN = 0V, 5V Units V V 1 AVEA 6 1.25 –100 1000 GEA 350 µmho 35 µA 1.225 –200 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 1.275 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 Symbol Condition RON Duty Cycle = 0% Duty Cycle = 50% VSW = 20V Min Typ 0.18 2.6 2 Max 1 (4) Units Ω A A µA °C 160 Note: 4) Guaranteed by design. TYPICAL PERFORMANCE CHARACTERISTICS Circuit on front page, VIN = 3.3V, VOUT = 8V, unless otherwise noted. Efficiency vs Load Current Efficiency vs Load Current 95 95 95 90 90 90 85 85 85 80 75 70 65 60 50 1 10 100 LOAD CURRENT (mA) 80 75 70 65 60 VIN = 5V VOUT = 12V 55 EFFICIENCY (%) 100 EFFICIENCY (%) 55 50 1000 MP1542-EC01 1 10 100 LOAD CURRENT (mA) 80 75 70 65 60 VIN = 3.3V VOUT = 8V 50 1000 Feedback Voltage vs Temperature 680 1.258 680 FEEDBACK VOLTAGE (V) 690 640 630 620 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) MP1542-TPC01 MP1542 Rev. 1.2 12/14/2005 1.257 1.256 1.255 1.254 1.253 1.252 1000 Frequency (700KHz) vs Temperature 1.259 650 10 100 LOAD CURRENT (mA) MP1542-EC03 690 660 1 MP1542-EC02 Quiescent Current vs Temperature 670 VIN = 3.3V VOUT = 12V 55 FREQUENCY (KHz) EFFICIENCY (%) Efficiency vs Load Current 670 660 650 640 630 1.251 1.250 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) 620 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) MP1542-TPC02 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. MP1542-TPC03 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 Current Limit vs Duty Cycle 1.28 2.5 CURRENT LIMIT (A) FREQUENCY (MHz) 1.26 1.24 1.22 1.20 1.18 1.16 1.14 -45 -25 0 25 45 65 85 105125145 TEMPERATURE (°C) 2.0 1.5 1.0 0.5 0 0 10 20 30 40 50 60 70 80 90 DUTY CYCLE (%) MP1542-TPC04 MP1542-TPC05 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. MP1542-WF01 VOUT AC Coupled 0.2V/div. IOUT 0.2A/div. MP1542-WF04 MP1542 Rev. 1.2 12/14/2005 MP1542-WF02 MP1542-WF03 VEN 2V/div. VEN 2V/div. VOUT 5V/div. VOUT 5V/div. IINDUCTOR 0.5A/div. IINDUCTOR 0.5A/div. MP1542-WF05 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. MP1542-WF06 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 EN 3 FSEL 7 INTERNAL REGULATOR AND ENABLE CIRCUITRY OSCILLATOR + -- 5 SW 4 GND 2 FB 1 COMP PWM CONTROL LOGIC CURRENT SENSE AMP + --GM SS 8 + 1.25V MP1542_BD01 Figure 1—Functional Block Diagram MP1542 Rev. 1.2 12/14/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 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 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 = MP1542 Rev. 1.2 12/14/2005 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. R2( VOUT − VFB ) VFB www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 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: VRIPPLE ⎛ V ⎞ ⎜1 - IN ⎟ × ILOAD ⎜ V ⎟ OUT ⎠ ⎝ ≈ C2 × f SW 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 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. MP1542 Rev. 1.2 12/14/2005 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 IIN(MAX ) = VOUT × ILOAD (MAX ) VIN × η ∆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. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 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 G EA 2 × π × C3 × A VEA f Z1 = 1 2 × π × C3 × R3 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: 2 fRHPZ = VIN × R LOAD 2 × π × L × VOUT 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. MP1542 Rev. 1.2 12/14/2005 Table 1—Component Selection VIN (V) VOUT (V) C2 (µF) R3 (kΩ) C3 (nF) 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 8 8 8 12 12 12 18 18 18 8 8 8 12 12 12 18 18 18 15 15 15 18 18 18 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 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 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 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. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 8 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. 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. Layout Consideration High frequency switching regulators require very careful layout for stable operation and low TYPICAL APPLICATION D1 VIN 5V 6 7 3 OFF ON 8 VOUT 12V 5 IN FSEL SW FB 2 MP1542 EN SS GND COMP 1 C3 2.2nF 4 C4 10nF MP1542_F02 Figure 2—Typical Application Circuit VOUT3 26V 5mA D2 D3 D1 VIN 3.0V to 3.6V 6 7 OFF ON D4 3 8 5 IN FSEL EN SS SW VOUT1 9V 150mA 2 MP1542 GND 4 C4 22nF FB VOUT2 -9V 10mA COMP 1 C3 2.2nF MP1542_F03 Figure 3—Multiple-Output, Low-Profile (1.2mm max) TFT LCD Power Supply MP1542 Rev. 1.2 12/14/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 9 MP1542 – 700KHz/1.3MHz BOOST CONVERTER WITH A 2A SWITCH PACKAGE INFORMATION MSOP8 NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. 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. 1.2 12/14/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 10