MP4420 High Efficiency 2A, 36V, Synchronous Step Down Converter The Future of Analog IC Technology DESCRIPTION FEATURES The MP4420 is a high-frequency, synchronous, rectified, step-down, switch-mode converter with built-in power MOSFETs. It offers a very compact solution to achieve a 2A continuous output current with excellent load and line regulation over a wide input supply range. The MP4420 has synchronous mode operation for higher efficiency over the output current load range. • • • • • • Current-mode operation provides fast transient response and eases loop stabilization. • • • • • • • • Full protection features include over-current protection and thermal shut down. The MP4420 requires a minimal number of readily-available standard external components, and is available in a space-saving 8-pin TSOT23 package. Wide 4V to 30V Continuous Operating Input Range 36V Input Transient Tolerance for Automotive Load Dump 90mΩ/55mΩ Low RDS(ON) Internal Power MOSFETs High-Efficiency Synchronous Mode Operation Default 410kHz Switching Frequency Synchronizes to a 200kHz to 2.2MHz External Clock High Duty Cycle for Automotive Cold-crank Power-Save Mode Internal Soft-Start Power Good OCP Protection and Hiccup Thermal Shutdown Output Adjustable from 0.8V Available in an 8-pin TSOT-23 package APPLICATIONS • • • Automotive Industrial Control System Distributed Power Systems All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, please visit MPS website under Quality Assurance. “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION 2 VIN 1 C3 0.1 F MP4420 Rev.1.0 8/5/2014 R4 20 C4 100nF L1 MP4420 6 EN/SYNC BST 5 IN C1 22 F EN/SYNC SW 3 PG 7 VCC GND 4 FB 8 10 H R3 51k R1 41.2k 3.3V/2A C2 47 F VOUT R2 13k www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 1 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER ORDERING INFORMATION Part Number* MP4420GJ Package TSOT23-8 Top Marking See Below * For Tape & Reel, add suffix –Z (e.g. MP4420GJ–Z); TOP MARKING AFP: product code of MP4420GJ Y: year code; PACKAGE REFERENCE TOP VIEW PG 1 8 FB IN 2 7 VCC SW 3 6 EN/SYNC GND 4 5 BST TSOT23-8 MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 2 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance VIN ................................................ -0.3V to 40V VSW ................................................ -0.3V to 41V VBS ....................................................... VSW+6V All Other Pins ................................ -0.3V to 6V (2) (3) Continuous Power Dissipation (TA = +25°C) TSOT23-8 ................................................ 1.25W Junction Temperature .............................. 150°C Lead Temperature ................................... 260°C Storage Temperature ................. -65°C to 150°C TSOT23-8 ............................. 100 ..... 55 ... °C/W Recommended Operating Conditions Continuous Supply Voltage VIN .......... 4V to 30V Output Voltage VOUT................... 0.8V to 0.9xVIN Operating Junction Temp. (TJ). -40°C to +125°C MP4420 Rev.1.0 8/5/2014 (4) θJA θJC Notes: 1) Absolute maximum ratings are rated under room temperature unless otherwise noted. Exceeding these ratings may damage the device. 2) About the details of EN pin’s ABS MAX rating, please refer to page 14, Enable/SYNC Control section. 3) The maximum allowable power dissipation is a function of the maximum junction temperature TJ (MAX), the junction-toambient thermal resistance θJA, and the ambient temperature TA. The maximum allowable continuous power dissipation at any ambient temperature is calculated by PD (MAX) = (TJ (MAX)-TA)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. 4) Measured on JESD51-7, 4-layer PCB. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 3 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS VIN = 12V, TJ = +25°C, unless otherwise noted. Parameter Symbol Supply Current (Shutdown) ISHDN Supply Current (Quiescent) IQ HS Switch-ON Resistance Condition Min Typ VEN = 0V Max Units 8 μA VEN = 2V, VFB = 1V 0.5 0.7 mA RON_HS VBST-SW =5V 90 105 mΩ LS Switch-ON Resistance RON_LS VCC =5V 55 75 mΩ Switch Leakage ILKG VEN = 0V, VSW =12V 1 μA Current Limit SW ILIMIT Oscillator Frequency fSW Fold-Back Frequency fFB Maximum Duty Cycle DMAX (5) Minimum ON Time tON Under 40% Duty Cycle 3.2 4.2 5.3 A VFB=750mV 320 410 500 kHz VFB<400mV 70 100 130 kHz VFB=750mV, 410kHz 92 95 % 70 ns MIN Sync Frequency Range fSYNC 0.2 Feedback Voltage VFB 780 792 RISING 1.15 FALLING 1.05 1.25 Feedback Current IFB EN Rising Threshold VEN EN Falling Threshold VEN EN Threshold Hysteresis EN Input Current VFB=820mV VEN_HYS IEN 2.4 MHz 804 mV 10 100 nA 1.4 1.65 V 1.45 V 150 mV VEN=2V 4 6 μA VEN=0 0 0.2 μA VIN Under-Voltage Lockout Threshold-Rising VIN Under-Voltage Lockout Threshold-Falling INUVRISING 3.3 3.5 3.7 V INUVFALLING 3.1 3.3 3.5 V VIN Under-Voltage Lockout Threshold-Hysteresis INUVHYS VCC Regulator VCC Thermal Shutdown Thermal Hysteresis 4.6 5.2 V 1.5 4 % 0.55 1.45 2.45 ms 150 170 RISING as percentage of VFB 86.5 90 93.5 % FALLING as percentage of VFB 80.5 84 87.5 % ICC=5mA tSS VOUT from 10% to 90% (5) (5) °C 30 PG Rising Threshold PGVth PG Falling Threshold PGVth MP4420 Rev.1.0 8/5/2014 ICC=0mA mV 4.9 VCC Load Regulation Soft-Start Period 200 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. °C 4 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, TJ = +25°C, unless otherwise noted. Parameter Symbol Condition PG Threshold Hysteresis PGVth_HYS as percentage of VFB Min Typ Max 6 Units % PG Rising Delay PGTd_RISING 40 90 160 μs PG Falling Delay PGTd_FALLING 30 55 95 μs 0.1 0.3 V 10 100 nA PG Sink Current Capability PG Leakage Current VPG Sink 4mA ILKG_PG Notes: 5) Derived from bench characterization. Not tested in production MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 5 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER PIN FUNCTIONS Package Pin # 1 2 3 4 5 6 7 8 Name Description Power Good. The output of this pin is an open drain and goes high if the output voltage exceeds 90% of the nominal voltage. Supply Voltage. The MP4420 operates from a 4V to 30V input rail. Requires C1 to IN decouple the input rail. Connect using a wide PCB trace. SW Switch Output. Connect using a wide PCB trace. System Ground. This pin is the reference ground of the regulated output voltage, and PCB GND layout requires special care. For best results, connect to GND with copper traces and vias. Bootstrap. Requires a capacitor connected between SW and BST pins to form a floating BST supply across the high-side switch driver. A 20Ω resistor placed between SW and BST cap is strongly recommended to reduce SW spike voltage. Enable/Synchronize. EN high to enable the MP4420. Apply an external clock to the EN pin EN/SYNC to change the switching frequency. Bias Supply. Decouple with 0.1μF-to-0.22μF capacitor. Select a capacitor that does not VCC exceed 0.22μF. Feedback. Connect to the tap of an external resistor divider from the output to GND, to set the output voltage. The frequency fold-back comparator lowers the oscillator frequency FB when the FB voltage is below 660mV to prevent current limit runaway during a short-circuit fault condition. MP4420 Rev.1.0 8/5/2014 PG www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 6 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL CHARACTERISTICS MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 7 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL CHARACTERISTICS (continued) MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 8 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VOUT = 3.3V, L = 10µH, RBST=20Ω, TA = +25°C, unless otherwise noted. MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 9 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 12V, VOUT = 3.3V, L = 10µH, RBST=20Ω, TA = +25°C, unless otherwise noted. MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 10 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 12V, VOUT = 3.3V, L = 10µH, RBST=20Ω, TA = +25°C, unless otherwise noted. MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 11 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 12V, VOUT = 3.3V, L = 10µH, RBST=20Ω, TA = +25°C, unless otherwise noted. MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 12 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER BLOCK DIAGRAM Figure 1: Functional Block Diagram MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 13 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER OPERATION The MP4420 is a high-frequency, synchronous, rectified, step-down, switch-mode converter with built-in power MOSFETs. It offers a very compact solution to achieve 2A continuous output current with excellent load and line regulation over a wide input supply range. The MP4420 operates in a fixed-frequency, peak-current–control mode to regulate the output voltage. An internal clock initiates a PWM cycle. The integrated high-side power MOSFET turns on and remains on until its current reaches the value set by the COMP voltage. When the power switch is off, it remains off until the next clock cycle starts. If the current in the power MOSFET does not reach the current value set by COMP within 95% of one PWM period, the power MOSFET will be forced to turn off. Internal Regulator The 5V internal regulator power most of the internal circuitries. This regulator takes the VIN input and operates in the full VIN range: When VIN exceeds 5.0V, the output of the regulator is in full regulation; when VIN falls below 5.0V, the output of the regulator decreases following the VIN. A 0.1uF decoupling ceramic capacitor is needed at the pin. Error Amplifier The error amplifier compares the FB pin voltage against the internal 0.8V reference (REF) and outputs a COMP voltage—this COMP voltage controls the power MOSFET current. The optimized internal compensation network minimizes the external component count and simplifies the control loop design. Enable/SYNC Control EN/SYNC is a digital control pin that turns the regulator on and off: Drive EN high to turn on the regulator, drive it low to turn it off. An internal 500kΩ resistor from EN/SYNC to GND allows EN/SYNC to be floated to shut down the chip. The EN pin is clamped internally using a 6.5V series Zener diode, as shown in Figure 2. Connect the EN input pin through a pullup resistor to any voltage connected to the VIN pin— the pullup resistor limits the EN input current to less than 150µA. MP4420 Rev.1.0 8/5/2014 For example, with 12V connected to VIN, RPULLUP ≥ (12V – 6.5V) ÷ 150µA = 36.7kΩ. Connecting the EN pin directly to a voltage source without any pullup resistor requires limiting voltage amplitude to ≤6V to prevent damage to the Zener diode. Figure 2: 6.5V-type Zener Diode Connect an external clock with a range of 200kHz to 2.2MHz 2ms after output voltage is set to synchronize the internal clock rising edge to the external clock rising edge. The pulse width of external clock signal should be less than 1.7μs. Under-Voltage Lockout Under-voltage lockout (UVLO) protects the chip from operating at an insufficient supply voltage. The MP4420 UVLO comparator monitors the output voltage of the internal regulator, VCC. The UVLO rising threshold is about 3.5V while its falling threshold is 3.3V. Internal Soft-Start The soft-start prevents the converter output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start voltage (SS) that ramps up from 0V to 1.2V. When SS is lower than REF, SS overrides REF so the error amplifier uses SS as the reference. When SS exceeds REF, the error amplifier uses REF as the reference. The SS time is internally set to 1.5ms. Over-Current Protection and Hiccup The MP4420 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current limit threshold. If the output voltage starts to drop until FB is below the UnderVoltage (UV) threshold—typically 84% below the reference—the MP4420 enters hiccup mode to periodically restart the part. This protection www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 14 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER mode is especially useful when the output is dead-shorted to ground. The average shortcircuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. The MP4420 exits the hiccup mode once the overcurrent condition is removed. Thermal Shutdown Thermal shutdown prevents the chip from operating at exceedingly high temperatures. When the silicon die temperature exceeds 170°C, it shuts down the whole chip. When the temperature drops below its lower threshold (typically 140°C) the chip is enabled again. Floating Driver and Bootstrap Charging An external bootstrap capacitor power the floating-power-MOSFET driver. A dedicated internal regulator (see figure 3) charges and regulates the bootstrap capacitor voltage to ~5V. When the voltage between the BST and SW nodes drops below regulation, a PMOS pass transistor connected from VIN to BST turns on. The charging current path is from VIN, BST and then to SW. The external circuit should provide enough voltage headroom to facilitate charging. As long as VIN is significantly higher than SW, the bootstrap capacitor remains charged. When the HS-FET is ON, VIN ≈ VSW so the bootstrap capacitor cannot charge. When the LS-FET is ON, VIN−VSW reaches its maximum for fast charging. When there is no inductor current, VSW=VOUT so the difference between VIN and VOUT can charge the bootstrap capacitor. The floating driver has its own UVLO protection, with a rising threshold of 2.2V and hysteresis of 150mV. A 20Ω resistor placed between SW and BST cap is strongly recommended to reduce SW spike voltage. . Startup and Shutdown If both VIN and EN exceed their appropriate thresholds, the chip starts: The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low, and thermal shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. Power Good The MP4420 has power good (PG) output. The PG pin is the open drain of a MOSFET. It should be connected to VCC or some other voltage source through a resistor (e.g. 100kΩ). In the presence of an input voltage, the MOSFET turns on so that the PG pin is pulled to low before SS is ready. After VFB reaches 90%×REF, the PG pin is pulled high after a delay, typically 90μs. When VFB drops to 84%×REF, the PG pin is pulled low. Also, PG is pulled low if thermal shutdown or EN is pulled low. Figure 3: Internal Bootstrap Charging Circuit MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 15 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER APPLICATION INFORMATION Setting the Output Voltage The external resistor divider sets the output voltage (see Typical Application on page 1). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. Choose R1 around 40kΩ. R2 is then given by: R2 = R1 VOUT −1 0.792V Choose the inductor ripple current to be approximately 30% of the maximum load current. The maximum inductor peak current is: IL(MAX ) = ILOAD + Use a larger inductor for improved efficiency under light-load conditions—below 100mA. VIN UVLO Setting The T-type network—as shown in Figure 4—is highly recommended when VOUT is low. MP4420 has internal fix under voltage lock out (UVLO) threshold: rising threshold is 3.5V while falling threshold is about 3.3V. For the application needs higher UVLO point, external resistor divider between EN and IN as shown in figure 4 can be used to get higher equivalent UVLO threshold. VIN Figure 4: T-Type Network Table 1: Resistor Selection for Common Output Voltages VOUT (V) R1 (kΩ) R2 (kΩ) RT (kΩ) 41.2 (1%) 41.2 (1%) 13 (1%) 7.68 (1%) 51 (1%) 51 (1%) Selecting the Inductor Use a1µH-to-10µH inductor with a DC current rating of at least 25% percent higher than the maximum load current for most applications. For highest efficiency, an inductor with small DC resistance is recommended. For most designs, the inductance value can be derived from the following equation. L1 = IN R5 RT+R1 is used to set the loop bandwidth. Basically, higher RT+R1, lower bandwidth. To ensure the loop stability, it is strongly recommended to limit the bandwidth lower than 40kHz based on the 410kHz default fsw. Table 1 lists the recommended T-type resistors value for common output voltages. 3.3 5 ΔIL 2 EN R6 500k Figure 5: Adjustable UVLO using EN divider The UVLO threshold can be computed from below two equations: INUVRISING = (1 + R5 ) × VEN_RISING 500k//R6 INUVFALLING = (1 + R5 ) × VEN_FALLING 500k//R6 Where VEN_RISING=1.4V, VEN_FALLING=1.25V. When choose R5, make sure it is big enough to limit the current flows into EN pin lower than 150uA. VOUT × (VIN − VOUT ) VIN × ΔIL × fOSC Where ΔIL is the inductor ripple current. MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 16 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER Selecting the Input Capacitor The input current to the step-down converter is discontinuous, therefore requires a capacitor is to supply the AC current to the step-down converter while maintaining the DC input voltage. Use low ESR capacitors for the best performance. Use ceramic capacitors with X5R or X7R dielectrics for best results because of their low ESR and small temperature coefficients. For most application, a 22µF ceramic capacitor is sufficient to maintain the DC input voltage. And it is strongly recommended to use another lower value capacitor (e.g. 0.1µF) with small package size (0603) to absorb high frequency switching noise. Make sure place the small size capacitor as close to IN and GND pins as possible (see PCB LAYOUT section). Since C1 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 = ILOAD 2 For simplification, choose an input capacitor with an 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, add a small, high quality ceramic capacitor (e.g. 1μF) 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 MP4420 Rev.1.0 8/5/2014 voltage ripple at input. The input voltage ripple caused by capacitance can be estimated by: ΔVIN = ⎛ ⎞ ILOAD V V × OUT × ⎜ 1 − OUT ⎟ fS × C1 VIN ⎝ VIN ⎠ Selecting the Output Capacitor The output capacitor (C2) maintains the DC output voltage. Use ceramic, tantalum, or lowESR electrolytic capacitors. For best results, use low ESR capacitors to keep the output voltage ripple low. The output voltage ripple can be estimated by: ΔVOUT = VOUT ⎛ VOUT × ⎜1 − fS × L1 ⎝ VIN ⎞ ⎛ ⎞ 1 ⎟ × ⎜ RESR + ⎟ 8 × f × C2 S ⎠ ⎝ ⎠ Where L1 is the inductor value and RESR is the equivalent series resistance (ESR) value of the output capacitor. For ceramic capacitors, the capacitance dominates the impedance at the switching frequency, and the capacitance causes the majority of the output voltage ripple. For simplification, the output voltage ripple can be estimated by: ΔVOUT = ⎛ V ⎞ VOUT × ⎜ 1 − OUT ⎟ VIN ⎠ 8 × fS × L1 × C2 ⎝ 2 For tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: ΔVOUT = VOUT ⎛ V ⎞ × ⎜ 1 − OUT ⎟ × RESR fS × L1 ⎝ VIN ⎠ The characteristics of the output capacitor also affect the stability of the regulation system. The MP4420 can be optimized for a wide range of capacitance and ESR values. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 17 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER BST Resistor and External BST Diode A 20ohm resistor in series with BST capacitor is recommended to reduce the SW spike voltage. Higher resistance is better for SW spike reduction, but will compromise the efficiency on the other hand. An external BST diode can enhance the efficiency of the regulator when the duty cycle is high (>65%). A power supply between 2.5V and 5V can be used to power the external bootstrap diode and VCC or VOUT is the good choice of this power supply in the circuit as shown in Figure 6. 3) Use large ground plane directly connect to GND pin. Add vias near the GND pin if bottom layer is ground plane. 4) Route SW, BST away from sensitive analog areas such as FB. 5) Place the T-type feedback resistor close to chip to ensure the trace which connects to FB pin as the short as possible. VCC 7 External BST diode 1N4148 BST 5 VCC/VOUT RBST SW 3 CBST L VOUT COUT Top Layer Figure 6: Optional External Bootstrap Diode to Enhance Efficiency The recommended external BST diode is IN4148, and the BST capacitor value is 0.1µF to 1μF. PCB Layout PCB layout, especially the input capacitor and VCC capacitor placement, is very important to achieve stable operation. For the best results, follow these guidelines: 1) Place the ceramics input capacitor as close to IN and GND pins as possible, especially the small package size (0603) input bypass capacitor. Keep the connection of input capacitor and IN pin as short and wide as possible. 2) Place the VCC capacitor to VCC pin and GND pin as close as possible. Make the trace length of VCC pin-VCC capacitor anode-VCC capacitor cathode-chip GND pin as short as possible. MP4420 Rev.1.0 8/5/2014 Bottom Layer Figure 7: Recommended PCB Layout www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 18 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL APPLICATION CIRCUITS Figure 8: 3.3V Output Typical Application Circuit MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 19 MP4420 – 36V, 2A SYNCHRONOUS STEP-DOWN CONVERTER PACKAGE INFORMATION TSOT23-8 RECOMMENDED LAND PATTERN TOP VIEW SEATING PLANE SEE DETAIL ’’A’’ FRONT VIEW SIDE VIEW NOTE: DETAIL ’’A’’ 1) ALL DIMENSIONS ARE 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 0.10 MILLIMETERS MAX. 5) JEDEC REFERENCE IS MO-193, VARIATION BA. 6) DRAWING IS NOT TO SCALE. 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. MP4420 Rev.1.0 8/5/2014 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 20