MP1495 High Efficiency 3A, 16V, 500kHz Synchronous Step Down Converter The Future of Analog IC Technology DESCRIPTION FEATURES The MP1495 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 3A continuous output current with excellent load and line regulation over a wide input supply range. The MP1495 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 MP1495 requires a minimal number of readily-available standard external components, and is available in a space-saving 8-pin TSOT23 package. Wide 4.5V-to-16V Operating Input Range 80mΩ/30mΩ Low RDS(ON) Internal Power MOSFETs High-Efficiency Synchronous Mode Operation Fixed 500kHz Switching Frequency Synchronizes to a 200kHz to 2MHz External Clock AAM Power-Save Mode Internal Soft-Start OCP Protection and Hiccup Thermal Shutdown Output Adjustable from 0.8V Available in an 8-pin TSOT-23 package APPLICATIONS • • • • Notebook Systems and I/O Power Digital Set-Top Boxes Flat-Panel Television and Monitors 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 4.5V-16V VIN 2 C1 22 EN/ SYNC 7 R3 90.9k R5 10k EN/SYNC SW VCC FB 1 AAM GND 4 5 VIN=12V, VOUT=3.3V, AAM=0.5V 100 C4 MP1495 6 C3 0.1 BST IN Efficiency vs. Load Current R4 10 3.3V/2A 3 L1 8 R9 33k 95 90 R1 40.2k R2 13k C2 47 85 VIN=5V 80 75 VIN=16V 70 0.01 MP1495 Rev. 1.04 12/26/2012 VIN=12V 0.1 1 LOAD CURRENT(A) www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 10 1 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER ORDERING INFORMATION Part Number* MP1495DJ Package TSOT-23-8 Top Marking ACS For Tape & Reel, add suffix –Z (e.g. MP1495DJ–Z); For RoHS, compliant packaging, add suffix –LF (e.g. MP1495DJ–LF–Z). PACKAGE REFERENCE ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance VIN ..................................................-0.3V to 17V VSW ...................................................................... -0.3V (-5V for <10ns) to 17V (19V for <10ns) VBS ......................................................... VSW+6V All Other Pins ................................ -0.3V to 6V (2) (3) Continuous Power Dissipation (TA = +25°C) ........................................................... 1.25W Junction Temperature ...............................150°C Lead Temperature ....................................260°C Storage Temperature................. -65°C to 150°C TSOT-23-8............................. 100 ..... 55... °C/W Recommended Operating Conditions (4) Supply Voltage VIN ...........................4.5V to 16V Output Voltage VOUT ..................... 0.8V to VIN-3V Operating Junction Temp. (TJ). -40°C to +125°C MP1495 Rev. 1.04 12/26/2012 (5) θJA θJC Notes: 1) Exceeding these ratings may damage the device. 2) About the details of EN pin’s ABS MAX rating, please refer to Page 9, 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) The device is not guaranteed to function outside of its operating conditions. 5) Measured on JESD51-7, 4-layer PCB. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 2 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (6) VIN = 12V, TA = 25°C, unless otherwise noted. Parameter Symbol Supply Current (Shutdown) Supply Current (Quiescent) HS Switch-ON Resistance LS Switch-ON Resistance Switch Leakage Current Limit (6) Oscillator Frequency Fold-Back Frequency Maximum Duty Cycle Minimum ON Time(6) Sync Frequency Range Feedback Voltage Feedback Current EN Rising Threshold EN Falling Threshold EN Input Current EN Turn-Off Delay VIN Under-Voltage Lockout Threshold-Rising VIN Under-Voltage Lockout Threshold-Hysteresis VCC Regulator VCC Load Regulation Soft-Start Period Thermal Shutdown (6) Thermal Hysteresis (6) IIN Iq HSRDS-ON LSRDS-ON SWLKG ILIMIT fSW fFB DMAX tON_MIN fSYNC VFB IFB VEN_RISING VEN_FALLING IEN Condition VEN = 0V VEN = 2V, VFB = 1V, AAM=0.5V VBST-SW=5V VCC =5V VEN = 0V, VSW =12V Under 40% Duty Cycle VFB=0.75V VFB<400mV VFB=700mV TA =25°C -40°C<TA<85°C (7) VFB=820mV Min Typ 0.5 80 30 Max Units 1 1 μA mA mΩ mΩ μA A kHz fSW % ns MHz 1 4.2 440 90 0.2 791 787 1.2 1.1 5 500 0.25 95 60 807 807 10 1.4 1.25 580 2 823 827 50 1.6 1.4 mV nA V V VEN=2V 2 μA VEN=0 0 μA 8 μs ENtd-off 3.7 INUVVth 3.9 4.1 V INUVHYS 650 mV VCC 5 3 1.5 150 20 V % ms °C °C ICC=5mA tSS Notes: 6) Guaranteed by design. 7) Not tested in production and guaranteed by over temperature correlation. MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 3 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS Performance waveforms are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 3.3V, AAM=0.5V, TA = 25°C, unless otherwise noted. Load Regulation VIN=4.5V-16V, IOUT=0-2A 100 100 95 95 VIN=12V 90 85 80 75 75 0.5 1 1.5 2 2.5 LOAD CURRENT(A) Line Regulation 1.0 IOUT=0A -0.15 0.5 1 1.5 2 2.5 LOAD CURRENT(A) 3 IOUT=1.5A 0.2 0.0 -0.2 IOUT=3A -0.4 -0.6 -0.8 4 6 8 10 12 14 16 40 4.7 4.3 3.9 20 10 0 -10 20 30 40 50 60 70 -30 4 6 8 10 12 14 16 INPUT VOLTAGE(V) 18 Case Temperature Rise vs. Output Current 30 535 30 -20 3.5 10 INPUT VOLTAGE(V) VIN=6-16V, IOUT=0A 3 VIN=6-16V, IOUT=0A 50 5.1 Enabled Supply Current vs. Input Voltage 0.5 1 1.5 2 2.5 OUTPUT CURRENT(A) Disabled Supply Current vs. Input Voltage INPUT CURRENT(nA) 0.4 540 -0.20 0 5.5 PEAK CURRENT(A) 0.6 VIN=4.5V -0.10 5.9 0.8 -1.0 -0.05 VIN=16V Peak Current vs. Duty Cycle VIN=5-16V VIN=16V 0.00 VIN=12V 70 0 3 VIN=12V 0.10 0.05 85 VIN=16V 0 0.15 VIN=5V 90 VIN=5V 80 70 0.20 IOUT=0-3A 25 530 20 525 520 15 515 10 510 5 505 500 4 MP1495 Rev. 1.04 12/26/2012 6 8 10 12 14 16 INPUT VOLTAGE(V) 18 0 0 0.5 1 1.5 2 2.5 OUTPUT CURRENT(A) 3 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 4 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance waveforms are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 3.3V, AAM=0.5V, TA = 25°C, unless otherwise noted. VOUT/AC 100mV/div. IOUT 1A/div. Start up through Input Voltage Shutdown through Input Voltage IOUT=0A IOUT=0A VEN 5V/div. VEN 5V/div. VOUT 2V/div. VOUT 2V/div. VSW 5V/div. VSW 5V/div. I-inductor 2A/div. I-inductor 2A/div. Start up through Input Voltage Shutdown through Input Voltage IOUT=3A IOUT=3A Startup through Enable IOUT=0A VEN 5V/div. VEN 5V/div. VEN 5V/div. VOUT 2V/div. VOUT 2V/div. VSW 5V/div. VSW 5V/div. I-inductor 2A/div. I-inductor 2A/div. VOUT 2V/div. VSW 5V/div. I-inductor 2A/div. Shuthdown through Enable Startup through Enable Shutdown through Enable IOUT=0A IOUT=3A IOUT=3A VEN 5V/div. VEN 5V/div. VEN 5V/div. VOUT 2V/div. VOUT 2V/div. VOUT 2V/div. VSW 5V/div. VSW 5V/div. I-inductor 2A/div. I-inductor 2A/div. VSW 5V/div. I-inductor 2A/div. MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 5 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance waveforms are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 3.3V, AAM=0.5V, TA = 25°C, unless otherwise noted. Input / Output Ripple Short Circuit Entry Short Circuit Recovery IOUT=3A IOUT=0A IOUT=0A VIN/AC 200mV/div. VOUT 2V/div. VOUT 2V/div. VSW 5V/div. VSW 5V/div. I-inductor 5A/div. I-inductor 5A/div. VOUT/AC 20mV/div. VSW 10V/div. I-inductor 2A/div. MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 6 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER PIN FUNCTIONS Package Pin # 1 2 3 4 5 6 7 8 Name Description Advanced Asynchronous Modulation. Connect the tap of 2 resistor dividers to force the MP1495 into non-synchronous mode under light loads. Drive AAM pin high (VCC) to force the MP1495 into CCM. Supply Voltage. The MP1495 operates from a 4.5V to 16V 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 GND PCB 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 10Ω resistor placed between SW and BST cap is strongly recommended to reduce SW spike voltage. Enable/Synchronize. EN high to enable the MP1495. Apply an external clock to the EN EN/SYNC pin 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. VCC capacitor should be put closely to VCC pin and GND pin. 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 FB frequency when the FB voltage is below 400mV to prevent current limit runaway during a short-circuit fault condition. AAM MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 7 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER BLOCK DIAGRAM Figure 1: Functional Block Diagram MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 8 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER OPERATION The MP1495 is a high-frequency, synchronous, rectified, step-down, switch-mode converter with built-in power MOSFETs. It offers a very compact solution to achieve 3A continuous output current with excellent load and line regulation over a wide input supply range. The MP1495 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 decreases and requires a 0.1µF decoupling ceramic capacitor. 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 1MΩ 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 6.7V 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 100µA. MP1495 Rev. 1.04 12/26/2012 For example, with 12V connected to VIN, RPULLUP ≥ (12V – 6.5V) ÷ 100µA = 55kΩ. Connecting the EN pin is 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 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 MP1495 UVLO comparator monitors the output voltage of the internal regulator, VCC. The UVLO rising threshold is about 3.9V while its falling threshold is 3.25V. 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 MP1495 has cycle-by-cycle over current limit for when the inductor current peak value exceeds the set current limit threshold. If the output voltage starts to drop until FB is below the Under-Voltage (UV) threshold—typically 50% below the reference—the MP1495 enters hiccup mode to periodically restart the part. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 9 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER This protection mode is especially useful when the output is dead-shorted to ground. The average short-circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. The MP1495 exits the hiccup mode once the over-current condition is removed. Thermal Shutdown Thermal shutdown prevents the chip from operating at exceedingly high temperatures. When the silicon die temperature exceeds 150°C, it shuts down the whole chip. When the temperature drops below its lower threshold (typically 130°C) the chip is enabled again. Floating Driver and Bootstrap Charging An external bootstrap capacitor powers the floating power MOSFET driver. This floating driver has its own UVLO protection, with a rising threshold of 2.2V and hysteresis of 150mV. The bootstrap capacitor voltage is regulated internally by VIN through D1, M1, C4, L1 and C2 (Figure 3). If (VIN-VSW) exceeds 5V, U1 regulates M1 to maintain a 5V BST voltage across C4. A 10Ω resistor placed between SW and BST cap is strongly recommended to reduce SW spike voltage. Figure 3: Internal Bootstrap Charging Circuit, 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. MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 10 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER APPLICATION INFORMATION Setting the Output Voltage The external resistor divider sets the output voltage. The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor (see Typical Application on page 1). Choose R1 around 40kΩ, then R2 is: R1 R2 = VOUT 0.807V −1 R1 RT 8 VOUT R2 Figure 4: T-Type Network Table 1 lists the recommended T-type resistor value for common output voltages. Table 1: Resistor Selection for Common Output Voltages VOUT (V) R1 (kΩ) R2 (kΩ) Rt (kΩ) 1.0 20.5(1%) 82(1%) 82(1%) 1.2 30.1(1%) 60.4(1%) 82(1%) 1.8 40.2(1%) 32.4(1%) 56(1%) 2.5 40.2(1%) 19.1(1%) 33(1%) 3.3 40.2(1%) 13(1%) 33(1%) 5 40.2(1%) 7.68(1%) 33(1%) Selecting the Inductor For most applications, use a 1µH-to-10µH inductor with a DC current rating that is at least 25% percent higher than the maximum load current. Select an inductor with a DC resistance less than 15mΩ for highest efficiency. For most designs, the inductance value can be derived from the following equation. L1 = MP1495 Rev. 1.04 12/26/2012 Choose an inductor ripple current to be approximately 30% of the maximum load current. The maximum inductor peak current is: IL(MAX) = ILOAD + ΔIL 2 Use a larger inductor for light-load conditions (below 100mA) for improved efficiency. Use the T-type network when VOUT is low, as shown in Figure 4. FB Where ΔIL is the inductor ripple current. Setting the AAM Voltage The AAM voltage sets the transition point from AAM to CCM. Select a voltage that balances efficiency, stability, ripple, and transient: A relatively low AAM voltage improves stability and ripple, but degrades transient and efficiency during AAM mode; a relatively high AAM voltage improves the transient and efficiency during AAM, but degrades stability and ripple. AAM voltage is set from the tap of a resistor divider from the VCC (5V) pin, as shown in Figure 5. VCC(5V) R3 AAM R4 Figure 5: AAM Network Generally, choose R4 to be around 10kΩ, then R3 is: ⎛ VCC ⎞ R3 = R4⎜ − 1⎟ ⎝ AAM ⎠ VOUT × (VIN − VOUT ) VIN × ΔIL × fOSC www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 11 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER 0.8 VOUT=2.5V 0.7 VOUT=3.3V VOUT=5V AAM(V) 0.6 0.5 0.4 0.3 VOUT=1.8V 0.2 0.1 ΔVIN = VOUT=1.05V 0 2 4 6 8 10 12 Figure 6: AAM Selection for Common Output Voltages (VIN=4.5V to 16V) Selecting the Input Capacitor The input current to the step-down converter is discontinuous and therefore requires a capacitor to supply the AC current to the step-down converter while maintaining the DC input voltage. Use low-ESR capacitors for the best performance. For best results, use ceramic capacitors with X5R or X7R dielectrics because of their low ESR and small temperature coefficients. Use a 22µF capacitor for most applications. C1 requires an adequate ripple current rating since it absorbs the input switching current. Estimate the RMS current in the input capacitor with: I C1 = ILOAD × VOUT ⎛⎜ VOUT × 1− VIN ⎜⎝ VIN ⎞ ⎟ ⎟ ⎠ The worst case condition occurs at VIN = 2VOUT, where: IC1 = ILOAD 2 For simplification, choose an 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, place a small, high-quality ceramic capacitor (e.g. 0.1μF) as close to the IC as MP1495 Rev. 1.04 12/26/2012 possible. When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at the input. The input voltage ripple caused by capacitance can be estimated by: ⎛ ⎞ 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 thus 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 MP1495 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. © 2012 MPS. All Rights Reserved. 12 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER MP1495 SW R1 C4 SW R6 R5 External BST Diode IN4148 VCC CBST 7 6 5 3 4 R4 8 2 R7 1 R9 C6 VOUT >65% VIN Connect the BST diode from the VCC pin to the BST pin, as shown in Figure 7. BST R3 C5 Duty cycle is high: D= C3 R2 z GND R8 External Bootstrap Diode An external bootstrap diode may enhance the regulator efficiency under the following conditions: z VOUT is 5V or 3.3V; and L1 C1 C1A Vin L C2 COUT C2A GND Figure 7: Optional External Bootstrap Diode for Enhanced Efficiency Vout The recommended external BST diode is IN4148, and the BST capacitor is 0.1 µF to 1μF. PC Board Layout (8) PCB layout is very important to achieve stable operation especially for VCC capacitor and input capacitor placement. For best results, follow these guidelines: 1) Use large ground plane directly connect to GND pin. Add vias near the GND pin if bottom layer is ground plane. 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. 3) Place the ceramic input capacitor close to IN and GND pins. Keep the connection of input capacitor and IN pin as short and wide as possible. 4) Route SW, BST away from sensitive analog areas such as FB. It’s not recommended to route SW, BST trace under chip’s bottom side. 5) Place the T-type feedback resistor R9 close to chip to ensure the trace which connects to FB pin as short as possible GND VCC EN/SYNC BST SW GND Notes: 8) The recommended layout is based on the Figure 8 Typical Application circuit on the next page. MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 13 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL APPLICATION CIRCUITS U1 2 C1A NS 7 VCC R7 90.9k R5 28.7k C5 1nF 6 R6 11k MP1495 SW 1 R8 10k BST IN 5 R4 10 3.3V 3 AAM FB 8 EN/SYNC R9 33k GND 4 C3 15pF R1 40.2k R3 0 R2 13k Figure 8: 12VIN, 3.3V/3A MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 14 MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER PACKAGE INFORMATION TSOT23-8 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. MP1495 Rev. 1.04 12/26/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 15