MP4459 1.5A, 4MHz, 36V Step-Down Converter The Future of Analog IC Technology FEATURES DESCRIPTION The MP4459 is a high frequency step-down switching regulator with an integrated internal high-side high voltage power MOSFET. It provides 1.5A output with current mode control for fast loop response and easy compensation. The wide 4.5V to 36V input range accommodates a variety of step-down applications, including those in automotive systems. A 100µA operational quiescent current is suitable for use in battery-powered applications. The frequency foldback helps prevent inductor current runaway during startup and thermal shutdown provides reliable, fault tolerant operation. By switching at 4MHz, the MP4459 prevents EMI (Electromagnetic Interference) noise problems, such as those found in AM radio and ADSL applications. The MP4459 is available in thin 10-pin 3mm x 3mm TQFN package. • • • • • • • • • • 100µA Quiescent Current Wide 4.5V to 36V Operating Input Range 150mΩ Internal Power MOSFET Up to 4MHz Programmable Switching Frequency Ceramic Capacitor Stable Internal Soft-Start Precision Current Limit without a Current Sensing Resistor Up to 95% Efficiency Output Adjustable from 0.8V to 36V Available in 10-Pin 3x3 TQFN Package APPLICATIONS • • • • • High Voltage Power Conversion Automotive Systems Industrial Power Systems Distributed Power Systems Battery Powered Systems “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION Efficiency vs Load Current 100 C4 47pF CONTROL EN BST MP4459 FREQ VIN 4.5V to 36V VIN C3 100nF SW 10MQ100N FB GND VOUT 5V @ 1.5A EFFICIENCY (%) COMP VI=5V 90 80 VI=24V VI=12V 70 60 50 40 VO=3.3V 30 20 MP4459 Rev. 0.9 2/20/2007 0 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 500 1000 LOAD CURRENT (mA) 1500 1 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE SW 1 10 BST SW 2 9 VIN EN 3 8 VIN Supply Voltage (VIN) .................... –0.3V to +40V Switch Voltage (VSW) ........... –0.3V to VIN + 0.3V BST to SW..................................... –0.3V to +5V All Other Pins................................. –0.3V to +5V Junction Temperature...............................150°C Lead Temperature ....................................260°C Storage Temperature ..............–65°C to +150°C COMP 4 7 FREQ Recommended Operating Conditions FB 5 6 GND Supply Voltage VIN ........................... 4.5V to 36V Output Voltage VOUT ........................ 0.8V to 36V Operating Temperature .............–40°C to +85°C TOP VIEW EXPOSED PAD ON BACKSIDE Thermal Resistance * Part Number* Package Temperature MP4459DQT 3x3 TQFN10 –40°C to +85°C For Tape & Reel, add suffix –Z (eg. MP4459DQT–Z) For RoHS compliant packaging, add suffix –LF (eg. MP4459DQT–LF–Z) (3) θJA (2) θJC 3x3 TQFN10 ........................... 50 ...... 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 = 12V, VEN = 2.5V, VCOMP = 1.4V, TA = +25°C, unless otherwise noted. Parameter Symbol Condition Feedback Voltage Upper Switch On Resistance Upper Switch Leakage Current Limit Error Amp Voltage Gain (4) Error Amp Transconductance Error Amp Min Source current Error Amp Min Sink current VIN UVLO Threshold VIN UVLO Hysteresis Soft-Start Time (4) VFB RDS(ON) Typ Max Units 0.776 0.8 150 1 2.5 200 60 5 –5 3.0 0.35 1.5 2 4 12 100 0.824 V mΩ µA A V/V µA/V µA µA V V ms MHz MHz µA µA 2.0 ICOMP = ±3µA VFB = 0.7V VFB = 0.9V Oscillator Frequency fS Shutdown Supply Current Quiescent Supply Current IQ MP4459 Rev. 0.9 2/20/2007 4.5V < VIN < 36V VBST – VSW = 5V VEN = 0V, VSW = 0V, VIN = 36V Duty Cycle = 50% Min 0V < VFB < 0.8V RFREQ = 45kΩ RFREQ = 18kΩ VEN = 0V No load, VFB = 0.9V 1.6 3.2 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 2.4 4.8 20 2 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, VEN = 2.5V, VCOMP = 1.4V, TA = +25°C, unless otherwise noted. Parameter VIN UVLO Threshold VIN UVLO Hysteresis Soft-Start Time (4) Symbol Condition Oscillator Frequency Shutdown Supply Current Quiescent Supply Current 0V < VFB < 0.8V RFREQ = 45kΩ RFREQ = 18kΩ VEN = 0V No load, VFB = 0.9V Min 1.6 3.2 Typ 3.0 –0.35 1.5 2 4 12 100 Max 2.4 4.8 18 Units V V ms MHz MHz µA µA Thermal Shutdown 150 °C Thermal Shutdown Hysteresis 15 Minimum Off Time Minimum On Time (4) EN Up Threshold EN Down Threshold 100 100 1.5 1.2 °C ns ns V V 1.15 Thermal Shutdown Thermal Shutdown Hysteresis (4) Minimum Off Time Minimum On Time (4) EN Up Threshold EN Down Threshold 1.15 1.25 150 °C 15 °C ns ns V V 100 100 1.5 1.2 1.25 4) Guaranteed by design. PIN FUNCTIONS Pin # 1, 2 3 4 5 6 7 8, 9 10 Name Description Switch Node. This is the output from the high-side switch. A low Vf Schottky rectifier to ground SW is required. The rectifier must be close to the SW pins to reduce switching spikes. Enable Input. Pulling this pin below the specified threshold shuts the chip down. Pulling it up EN above the specified threshold or leaving it floating enables the chip. Compensation. This node is the output of the GM error amplifier. Control loop frequency COMP compensation is applied to this pin. Feedback. This is the input to the error amplifier. An external resistive divider connected FB between the output and GND is compared to the internal +0.8V reference to set the regulation voltage. Ground. It should be connected as close as possible to the output capacitor avoiding the high GND current switch paths. Switching Frequency Program Input. Connect a resistor from this pin to ground to set the FREQ switching frequency. Input Supply. This supplies power to all the internal control circuitry, both BS regulators and VIN the high-side switch. A decoupling capacitor to ground must e placed close to this pin to minimize switching spikes. Bootstrap. This is the positive power supply for the internal floating high-side MOSFET driver. BST Connect a bypass capacitor between this pin and SW pin. MP4459 Rev. 0.9 2/20/2007 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 3 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER TYPICAL PERFORMANCE CURVES VIN = 12V, VOUT = 5V, fS = 500KHz, TA = +25°C, unless otherwise noted. Efficiency vs Load Current Efficiency vs Load Current 90 80 VI=24V VI=12V 70 60 50 40 VO=3.3V 30 20 0 500 1000 LOAD CURRENT (mA) 100 VI=12V 90 EFFICIENCY (%) EFFICIENCY (%) 100 VI=5V VI=24V 80 70 60 50 40 VO=5V 30 1500 20 0 500 1000 LOAD CURRENT (mA) 80 50 40 VO=2.5V 30 1500 20 0 500 1000 LOAD CURRENT (mA) Steady State Steady State Steady State IOUT = 0.1A IOUT = 1A IOUT = 1.5A VOUT AC Coupled 20mV/div. VSW 10V/div. VSW 10V/div. VSW 10V/div. IL 1A/div. IL 1A/div. IL 1A/div. VI=24V 60 VOUT AC Coupled 20mV/div. OSCILLATIONG EFFICIENCY (KHz) VI=12V 70 VOUT AC Coupled 20mV/div. 4000 VI=5V 90 EFFICIENCY (%) 100 Efficiency vs Load Current 1500 Oscillating Frequency vs Rfreq 3500 3000 2500 2000 1500 1000 500 0 10 MP4459 Rev. 0.9 2/20/2007 100 1000 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 4 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER TYPICAL PERFORMANCE CURVES (continued) VIN = 12V, VOUT = 5V, fS = 500KHz, TA = +25°C, unless otherwise noted. Startup Through EN Shutdown Through EN Startup Through EN IOUT = 0.1A IOUT = 0.1A IOUT = 1A VEN 5V/div. VEN 5V/div. VEN 5V/div. VOUT 2V/div. VOUT 2V/div. VOUT 2V/div. VSW 10V/div. VSW 10V/div. VSW 10V/div. IL 1A/div. IL 1A/div. IL 1A/div. Shutdown Through EN Startup Through EN Shutdown Through EN IOUT = 1A IOUT = 1.5A IOUT = 1.5A VEN 5V/div. VEN 5V/div. VEN 5V/div. VOUT 2V/div. VOUT 2V/div. VOUT 2V/div. VSW 10V/div. IL 1A/div. VSW 10V/div. VSW 10V/div. IL 2A/div. IL 2A/div. Short Circuit Entry Shrot Circuit Recovery Transient Response IOUT = 0.1A IOUT = 0.1A IOUT = 0.5A to 1.5A VOUT 2V/div. VOUT 2V/div. IL 1A/div. IL 1A/div. MP4459 Rev. 0.9 2/20/2007 VOUT AC 100mV/div. IL 1A/div. IOUT 1A/div. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 5 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER BLOCK DIAGRAM VIN VIN EN REFERENCE UVLO/ THERMAL SHUTDOWN 5V + -2.6V INTERNAL REGULATORS + -BST SW VOUT 1.5ms SS -- ISW SS + ISW Level Shift FB SW Gm Error Amp SS 0V8 -- COMP + OSCILLATOR CLK VOUT COMP GND FREQ Figure 1—Functional Block Diagram MP4459 Rev. 0.9 2/20/2007 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 6 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER APPLICATION INFORMATION Setting the Frequency The MP4459 has an externally adjustable frequency. The switching frequency can be set using a resistor: R freq (kΩ) = 180000 f s (KHz)1.1 Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output voltage to FB pin. The voltage divider divides the output voltage down to the feedback voltage by the ratio: VFB = VOUT R2 R1 + R2 Where VFB is the feedback voltage and VOUT is the output voltage. Thus the output voltage is: VOUT = VFB (R1 + R2) R2 A few µA of current from the high-side BS circuitry can be seen at the output when the MP4459 is at no load. In order to absorb this small amount of current, keep R2 under 40kΩ. A typical value for R2 can be 40.2kΩ. With this value, R1 can be determined by: R1 = 50.25 × ( VOUT − 0.8)(kΩ) For example, for a 3.3V output voltage, R2 is 40.2kΩ, and R1 is 127kΩ. MP4459 Rev. 0.9 2/20/2007 Inductor The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A larger value inductor will result in less ripple current that will result in lower output ripple voltage. However, the larger value inductor will have a larger physical size, higher series resistance, and/or lower saturation current. A good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum switch current limit. Also, make sure that the peak inductor current is below the maximum switch current limit. The inductance value can be calculated by: L1 = ⎛ ⎞ VOUT V × ⎜⎜1 − OUT ⎟⎟ fS × ∆IL ⎝ VIN ⎠ Where VIN is the input voltage, fS is the switching frequency, and ∆IL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by: ILP = ILOAD + ⎛ ⎞ VOUT V × ⎜⎜1 − OUT ⎟⎟ 2 × fS × L1 ⎝ VIN ⎠ Where ILOAD is the load current. Table 1 lists a number of suitable inductors from various manufacturers. The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI requirement. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 7 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER Table 1—Selected Inductors Manufacturer Part Number Inductance (µH) Max DCR (Ω) Current Rating (A) Dimensions L x W x H (mm3) Wurth Electronics Wurth Electronics Wurth Electronics Wurth Electronics Wurth Electronics Wurth Electronics 7447789002 7447789003 7447789004 744066100 744771115 744771122 2.2µH 3.3µH 4.7µH 10µH 15µH 22µH 0.019 0.024 0.033 0.035 0.025 0.031 4A 3.42A 2.9A 3.6A 3.75 3.37 7.3x7.3x3.2 7.3x7.3x3.2 7.3x7.3x3.2 10x10x3.8 12x12x6 12x12x6 TDK RLF7030T-2R2 2.2µH 0.012 5.4A 7.3x6.8x3.2 TDK TDK TDK TDK RLF7030T-3R3 RLF7030T-4R7 SLF10145T-100 SLF12565T-150M4R2 3.3µH 4.7µH 10µH 15µH 0.02 0.031 0.0364 0.0237 4.1A 3.4A 3A 4.2 7.3x6.8x3.2 7.3x6.8x3.2 10.1x10.1x4.5 12.5x12.5x6.5 TDK SLF12565T-220M3R5 22µH 0.0316 3.5 12.5x12.5x6.5 TOKO TOKO TOKO TOKO TOKO TOKO FDV0630-2R2M FDV0630-3R3M FDV0630-4R7M #919AS-100M #919AS-160M #919AS-220M 2.2µH 3.3µH 4.7µH 10µH 16µH 22µH 0.021 0.031 0.049 0.0265 0.0492 0.0776 5.3 4.3 3.3 4.3 3.3 3.0 7.7x7x3 7.7x7x3 7.7x7x3 10.3x10.3x4.5 10.3x10.3x4.5 10.3x10.3x4.5 MP4459 Rev. 0.9 2/20/2007 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 8 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER Output Rectifier Diode The output rectifier diode supplies the current to the inductor when the high-side switch is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky diode. Choose a diode who’s maximum reverse voltage rating is greater than the maximum input voltage, and who’s current rating is greater than the maximum load current. Table 2 lists example Schottky diodes and manufacturers. Table 2—Output Diodes Manufacturer Part Number For simplification, choose the input capacitor whose RMS current rating greater than half of the maximum load current. The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1µF, should be placed as close to the IC as possible. When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input. The input voltage ripple caused by capacitance can be estimated by: Voltage Current Rating Rating Package (V) (A) ∆VIN = ⎛ ILOAD V V × OUT × ⎜⎜1 − OUT fS × C1 VIN ⎝ VIN ⎞ ⎟⎟ ⎠ Diodes Inc. B240A-13-F 40V 2A SMA Where CIN is the input capacitance value. Diodes Inc. B340A-13-F 40V 3A SMA Central semi CMSH2-40M 40V 2A SMA Output Capacitor Central semi CMSH3-40MA 40V 3A SMA Input Capacitor The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. Use low ESR capacitors for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. Since the input capacitor absorbs the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: I C1 = ILOAD × VOUT ⎛⎜ VOUT × 1− VIN ⎜⎝ VIN ⎞ ⎟ ⎟ ⎠ The worse case condition occurs at VIN = 2VOUT, where: IC1 MP4459 Rev. 0.9 2/20/2007 I = LOAD 2 The output capacitor is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: ∆VOUT = VOUT ⎛ V × ⎜1 − OUT f S × L ⎜⎝ VIN ⎞ ⎞ ⎛ 1 ⎟ ⎟⎟ × ⎜ R ESR + ⎜ 8 × f S × C2 ⎟⎠ ⎠ ⎝ Where L is the inductor value, CO is the output capacitance value, and RESR is the equivalent series resistance (ESR) value of the output capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output voltage ripple can be estimated by: ∆VOUT = ⎞ ⎛ V × ⎜⎜1 − OUT ⎟⎟ VIN ⎠ × L × C2 ⎝ VOUT 8 × fS 2 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 9 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: ∆VOUT = VOUT ⎛ V × ⎜1 − OUT f S × L ⎜⎝ VIN ⎞ ⎟⎟ × R ESR ⎠ The characteristics of the output capacitor also affect the stability of the regulation system. The MP1593 can be optimized for a wide range of capacitance and ESR values. Compensation Components MP4459 employs current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP pin is the output of the internal error amplifier. A series capacitor-resistor combination sets a pole-zero combination to control the characteristics of the control system. The DC gain of the voltage feedback loop is given by: A VDC = R LOAD × G CS × A VEA × VFB VOUT Where AVEA is the error amplifier voltage gain, GCS is the current sense transconductance, and RLOAD is the load resistor value. The system has two poles of importance. One is due to the compensation capacitor (C3), the output resistor of error amplifier. The other is due to the output capacitor and the load resistor. These poles are located at: fP1 = GEA 2π × C3 × A VEA fP2 = 1 2π × C2 × R LOAD and MP4459 Rev. 0.9 2/20/2007 The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at: f Z1 = 1 2π × C3 × R3 The system may have another zero of importance, if the output capacitor has a large capacitance and/or a high ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at: fESR = 1 2π × C2 × R ESR In this case (as shown in Figure 2), a third pole set by the compensation capacitor (C6) and the compensation resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. This pole is located at: f P3 = 1 2π × C6 × R3 The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover frequency where the feedback loop has the unity gain is important. Lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause system unstable. A good rule of thumb is to set the crossover frequency to approximately onetenth of the switching frequency. The Table 3 lists the typical values of compensation components for some standard output voltages with various output capacitors and inductors. The values of the compensation components have been optimized for fast transient responses and good stability at given conditions. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 10 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER Table 3—Compensation Values for Typical Output Voltage/Capacitor Combinations VOUT L CO R3 C3 C6 1.8V 4.7µH 47µF ceramic 105k 100pF None 2.5V 4.7µH6.8µH 22µF ceramic 54.9k 220pF None 6.8µH10µH 15µH22µH 22µH33µH 22µF ceramic 22µF ceramic 22µF ceramic 68.1k 220pF None 100k 150pF None 147k 150pF None 3.3V 5V 12V To optimize the compensation components for conditions not listed in Table 3, the following procedure can be used. If this is the case, then add the second compensation capacitor (C6) to set the pole fP3 at the location of the ESR zero. Determine the C6 value by the equation: C6 = High Frequency Operation The switching frequency of MP4459 can be programmed up to 4MHz by an external resistor. Please pay attention to the following if the switching frequency is above 2MHz. The minimum on time of MP4459 is about 80ns (typ). Pulse skipping operation can be seen more easily at higher switching frequency due to the minimum on time. Recommended operating voltage at 4MHz is 12V or below, and 24V or below at 2MHz. Input Max vs Switching Frequency 1. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine the R3 value by the following equation: 2π × C2 × f C VOUT × G EA × G CS VFB Where fC is the desired crossover frequency (which typically has a value no higher than 1/10th of switching frequency). 2. Choose the compensation capacitor (C3) to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero, fZ1, below one forth of the crossover frequency provides sufficient phase margin. Determine the C3 value by the following equation: C3 > 30 MAX INPUT VOLTAGE (V) R3 = C2 × R ESR R3 25 20 VO=3.3V 15 10 5 1.5 VO=2.5V 2.0 2.5 3.0 fS (MHz) 3.5 4.0 Figure 2—Recommended Input vs. fS 4 2π × R3 × f C Where R3 is the compensation resistor value. 3. Determine if the second compensation capacitor (C6) is required. It is required if the ESR zero of the output capacitor is located at less than half of the switching frequency, or the following relationship is valid: f 1 < S 2π × C2 × R ESR 2 MP4459 Rev. 0.9 2/20/2007 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 11 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER Since the internal bootstrap circuitry has higher impedance, which may not be adequate to charge the bootstrap capacitor during each charging period, an external bootstrap charging diode is strongly recommended if the switching frequency is above 2MHz (see External Bootstrap Diode section for detailed implementation information). With higher switching frequencies, the inductive reactance (XL) of a capacitor dominates, such that the ESL of the input/output capacitor determines the input/output ripple voltage at higher switching frequencies. As a result, high frequency ceramic capacitors are strongly recommended as input decoupling capacitors and output filtering capacitors. Layout becomes more important when the device switches at higher frequency. It is essential to place the input decoupling capacitor, catch diode and the MP4459 as close together as possible, with traces that are very short and fairly wide. This can help to greatly reduce the voltage spikes on SW and also lower the EMI noise level. Try to run the feedback trace as far from the inductor and noisy power traces as possible. It is a good idea to run the feedback trace on the side of the PCB opposite of the inductor with a ground plane separating the two. The compensation components should be placed close to the MP4459. Do not place the compensation components close to or under the high dv/dt SW node, or inside the high di/dt power loop. If you have to do so, the proper ground plane must be in place to isolate these nodes. Switching losses are expected to increase at high switching frequencies. To help improve the thermal conduction, a grid of thermal vias can be created right under the exposed pad. It is recommended that they be small (15mil barrel diameter) so that the hole is essentially filled up during the plating process, thus aiding conduction to the other side. Too large a hole can cause solder wicking problems during the reflow soldering process. The pitch (distance between the centers) of several such thermal vias in an area is typically 40mil. MP4459 Rev. 0.9 2/20/2007 PC Board Layout The high current paths (GND, IN and SW) should be placed very close to the device with short, direct and wide traces. The input capacitor needs to be as close as possible to the IN and GND pins. The external feedback resistors should be placed next to the FB pin. Keep the switch node traces short and away from the feedback resistor divider and compensation network. External Bootstrap Diode It is recommended that an external bootstrap diode be added when the input voltage is no greater than 5V or the 5V rail is available in the system. This helps improve the efficiency of the regulator. The bootstrap diode can be a low cost one such as IN4148 or BAT54. 5V BS MP4459 SW Figure 2—External Bootstrap Diode This diode is also recommended for high duty cycle operation (when VOUT/VIN >65%) or low VIN (<5VIN) applications. At no load or light load, the converter may operate in pulse skipping mode in order to maintain the output voltage in regulation. Thus there is less time to refresh the BS voltage. In order to have enough gate voltage under such operating conditions, the difference of VIN-VOUT should be greater than 3V. For example, if the output voltage is set to 3.3V, the input voltage needs to be higher than 3.3V+3V=6.3V to maintain enough BS voltage at no load or light loads. To meet this requirement, the EN pin can be used to program the input UVLO voltage to VOUT+3V. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 12 MP4459 – 1.5A, 4MHz, 36V STEP-DOWN CONVERTER PACKAGE INFORMATION 3mm x 3mm TQFN10 2.90 3.10 0.30 0.50 PIN 1 ID MARKING 0.18 0.30 2.90 3.10 PIN 1 ID INDEX AREA 1.45 1.75 PIN 1 ID SEE DETAIL A 10 1 2.25 2.55 0.50 BSC 5 6 TOP VIEW BOTTOM VIEW PIN 1 ID OPTION A R0.20 TYP. PIN 1 ID OPTION B R0.20 TYP. 0.70 0.80 0.20 REF 0.00 0.05 SIDE VIEW DETAIL A NOTE: 2.90 0.70 1) ALL DIMENSIONS ARE IN MILLIMETERS. 2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH. 3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETER MAX. 4) DRAWING CONFORMS TO JEDEC MO-229, VARIATION VEED-5. 5) DRAWING IS NOT TO SCALE. 1.70 0.25 2.50 0.50 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. MP4459 Rev. 0.9 2/20/2007 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2007 MPS. All Rights Reserved. 13