MCP1612 Single 1A, 1.4 MHz Synchronous Buck Regulator Features Description • • • • • • • • • The MCP1612 is a 1A, 1.4 MHz, fully-integrated, current mode-controlled, synchronous buck regulator. The MCP1612 is packaged in the 8-pin MSOP and space-saving, 3x3 DFN packages. The DFN package also provides a lower thermal resistance package option for high-power, high ambient temperature applications. With an input operating range from 2.7V to 5.5V, the MCP1612 is ideal for applications that are powered by one single-cell Li-Ion, 2- to 3-cell NiMH, NiCd or alkaline sources. • • • • Fixed Switching Frequency: 1.4 MHz Input Operating Voltage Range: 2.7V to 5.5V Integrated Buck and Synchronous Switches Adjustable-Output Voltage Range: 0.8V to 5.0V 100% Duty Cycle Capable for Low Input Voltage Continuous Output Current Capability: 1A Shutdown Control with IQ < 0.01 µ A (Typ.) Integrated Soft-Start Feature Integrated Undervoltage Lockout (UVLO) Protection Integrated Overtemperature Protection Fast Dynamic Response to Line and Load Steps Small, 8-Pin DFN and MSOP Packages Operating Temperature Range: -40°C to +85°C Applications • • • • • • • • • • Network Interface Cards Portable Computers Set-Top Boxes DSL Modems and Routers USB-Powered Devices GBIC Modules High-Speed Data System Bus Termination Medical Instruments Cellular/GSM/PHS Phones +5V or +3.3V Distributed Voltages The output voltage of the MCP1612 is easily set over the range of 0.8V to 5.0V by using an external resistor divider. The external inductor and output capacitor size are minimized due to an internally-fixed, 1.4 MHz clock being used to set the switching frequency. The fixed clock allows for continuous, fixed-frequency PWM operation over the full load range. The MCP1612 is designed to provide fast dynamic response to sudden changes in input voltage and load current to minimize the necessary amount of external output capacitance. The MCP1612 can be used with ceramic, tantalum or aluminum electrolytic output capacitors. Ceramic capacitors with values as low as 4.7 µF can be used to keep the output ripple voltage low. For applications that require better load step performance, the value of the output capacitor can be increased to 47 µF. Additional features integrated into the MCP1612 include shutdown capability, soft-start, UVLO, overcurrent and overtemperature protection. Package Types 8-Lead DFN VIN 1 VCC 2 © 2005 Microchip Technology Inc. 8 LX 8-Lead MSOP VIN 1 8 LX 7 PGND VCC 2 SHDN 3 6 AGND SHDN 3 6 AGND COMP 4 5 FB COMP 4 5 FB 7 PGND DS21921B-page 1 MCP1612 Functional Block Diagram VCC Undervoltage Lockout (UVLO) UVLO VIN ISENSE P-Channel Slope Comp. + + Peak Current Limit Comp VREF FB – gm + Disable PDRV Disable INSET Circuit LX NDRV IN SoftStart Disable VREF Peak Current Limit 1.4 MHz Clock PGND LeadingEdge Blank PGND VCC VCC UVLO 1.2V A VBG SHDN Disable AGND 0.8V Thermal Shutdown AGND AGND DS21921B-page 2 © 2005 Microchip Technology Inc. MCP1612 Typical Application Circuit MCP1612 3.3V to 1.2V Synchronous Buck Converter 3.3 VIN ±10% CIN 10 µF Ceramic ON 1 VIN Lx 8 L = 3.3 µH MCP1612 10Ω 2 CBYP 0.1 µF Ceramic 3 VCC PGND SHDN AGND 7 1.2V VOUT @ 1A COUT 10 µF Ceramic 100 kΩ 6 200 kΩ OFF 4 Comp FB 5 25 kΩ 1000 pF © 2005 Microchip Technology Inc. DS21921B-page 3 MCP1612 1.0 ELECTRICAL CHARACTERISTICS † Notice: Stresses above those listed under “Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at those or any other conditions above those indicated in the operational listings of this specification is not implied. Exposure to maximum rating conditions for extended periods may affect device reliability. Absolute Maximum Ratings † VIN – AGND .......................................................................6.0V (SHDN, FB, VCC, Comp ........... (AGND – 0.3V) to (VIN + 0.3V) LX to PGND .............................................. -0.3V to (VIN + 0.3V) PGND to AGND................................................... -0.3V to +0.3V Output Short Circuit Current ................................. Continuous Storage temperature .....................................-65°C to +150°C Ambient Temp. with Power Applied.................-40°C to +85°C Operating Junction Temperature...................-40°C to +125°C ESD protection on all pins (HBM) ....................................... 4 kV ESD protection on all pins (MM)......................................... 300V DC CHARACTERISTICS Electrical Specifications: Unless otherwise noted, VIN = VCC = VSHDN = 3.3V, VOUT = 1.8V, CIN = COUT = 10 µF, L = 3.3 µH, ILOAD = 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. Parameters Sym Min Typ Max Units Conditions Input Voltage Input Operating Voltage VIN 2.7 — 5.5 V Input Shutdown Current I(VIN) — 0.01 1 µA Shutdown mode (SHDN = GND) Input Quiescent Current I(VIN) — 5 7 mA ILOAD = 0 mA FOSC 1.2 1.4 1.6 MHz RDSon P-Channel RDSon-P — 300 — mΩ IP = 250 mA RDSon N-Channel RDSon-N — 300 — mΩ IN = 250 mA ILX -1 — 1 µA SHDN = 0V, VIN = 5.5V, LX = 0V, LX = 5.5V Positive Current Limit Threshold +ILX(MAX) — 2.3 — A Negative Current Limit Threshold -ILX(MAX) — -1.4 — A gm 35 62 90 µA/V Oscillator Characteristics Internal Oscillator Frequency Internal Power Swicthes LX Pin Leakage Current Feedback Characteristics Transconductance from FB to COMP Output Voltage Output Voltage Range Reference Feedback Voltage Feedback Input Bias Current VOUT 0.8 — VIN V VFB 0.78 0.8 0.82 V IVFB — 1 — nA Line Regulation VLINE-REG — 0.15 0.5 %/V Load Regulation VLOAD-REG — 0.25 — % Note 1: 2: VIN = 2.7V to 5.5V, ILOAD = 100 mA VIN = 4.2V, ILOAD = 100 mA to 1A The integrated MOSFET switches have an integral diode from the LX pin to VIN and from LX to PGND. In cases where these diodes are forward-biased, the package power dissipation limits must be adhered to. Thermal protection is not able to regulate the junction temperature for these cases. UVLO is specified for a falling VIN. Once the UVLO is activated, the UVLO-HYS must be overcome before the device will return to operation. DS21921B-page 4 © 2005 Microchip Technology Inc. MCP1612 DC CHARACTERISTICS (CONTINUED) Electrical Specifications: Unless otherwise noted, VIN = VCC = VSHDN = 3.3V, VOUT = 1.8V, CIN = COUT = 10 µF, L = 3.3 µH, ILOAD = 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. Parameters Sym Min Typ Max Units UVLO 2.4 2.55 2.7 V UVLO-HYS — 200 — mV TSHD — 160 — °C TSHD-HYS — 9 — °C Logic-High Input VIN-HIGH 45 — — % of VIN Logic-Low Input VIN-LOW — — 15 % of VIN Conditions Protection Features Undervoltage Lockout Undervoltage Lockout Hysteresis Thermal Shutdown Thermal Shutdown Hysteresis Note 2 Note 1 Interface Signal (SHDN) Note 1: 2: The integrated MOSFET switches have an integral diode from the LX pin to VIN and from LX to PGND. In cases where these diodes are forward-biased, the package power dissipation limits must be adhered to. Thermal protection is not able to regulate the junction temperature for these cases. UVLO is specified for a falling VIN. Once the UVLO is activated, the UVLO-HYS must be overcome before the device will return to operation. TEMPERATURE SPECIFICATIONS Electrical Specifications: VIN = 3.0V to 5.5V, FOSC = 1 MHz with 10% Duty Cycle, CIN = 0.1 µF. TA = -40°C to +125°C. Parameters Sym Min Typ Max Units Conditions TA -65 — +150 °C Continuous Temperature Ranges Storage Temperature Range Maximum Junction Temperature TJ — — +150 °C Transient Only Operating Junction Temperature Range TA - 40 — + 125 °C Continuous Operation Thermal Resistance, 8L-MSOP θJA — 208 — °C/W Typical 4-layer board interconnecting vias Thermal Resistance, 8L-DFN θJA — 41 — °C/W Typical 4-layer board interconnecting vias Thermal Package Resistances © 2005 Microchip Technology Inc. DS21921B-page 5 MCP1612 2.0 TYPICAL PERFORMANCE CURVES Note: The graphs and tables provided following this note are a statistical summary based on a limited number of samples and are provided for informational purposes only. The performance characteristics listed herein are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified operating range (e.g., outside specified power supply range) and therefore outside the warranted range. 100 90 80 70 60 50 40 30 20 10 0 0.50 VOUT = 2.5V Dropout Voltage (V) Efficiency (%) Note: Unless otherwise indicated, VIN = VCC = VSHDN = 3.3V, COUT = CIN = 10 µF, L = 3.3 µH, ILOAD = 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. VOUT = 1.2V VOUT = 1.8V VOUT = 2.7V 0.40 0.30 VOUT = 3.3V 0.20 0.10 VIN = 3.3V 0.00 10 100 1000 0 200 Load Current (mA) 100 90 80 70 60 50 40 30 20 10 0 Efficiency vs. Load Current, Efficiency (%) VOUT = 3.3V VOUT = 2.5V VIN = 5.0V 10 100 FIGURE 2-4: Load Current. Input Quiescent Current (mA) FIGURE 2-1: VIN = 3.3V. 6.0 5.5 TA = +85oC 5.0 o 4.5 TA = +25 C 4.0 o TA = -40 C VOUT = 1.8V 3.5 3 VOUT = 1.2V VIN = 3.3V -0.4 VOUT = 1.8V, VIN = 3.3V -0.8 -1 -1.2 VOUT = 3.3V, VIN = 5.0V -1.4 FIGURE 2-5: Input Voltage. Oscillator Frequency (MHz) Change In Output Voltage (mV) 1000 3.5 4 4.5 5 5.5 Input Voltage (V) 0 -0.6 800 6.5 2.5 1000 Efficiency vs. Load Current, -0.2 600 Dropout Voltage vs. Load Current (mA) FIGURE 2-2: VIN = 5.0V. 400 Load Current (mA) Input Quiescent Current vs. 1.42 TA = -40oC 1.41 1.40 TA = +25oC 1.39 1.38 1.37 TA = +85oC 1.36 0 200 400 600 800 1000 2.5 Load Current (mA) FIGURE 2-3: Load Current. DS21921B-page 6 Output Voltage vs. 3 3.5 4 4.5 5 5.5 Input Voltage (V) FIGURE 2-6: Input Voltage. Oscillator Frequency vs. © 2005 Microchip Technology Inc. MCP1612 TYPICAL PERFORMANCE CURVES (Continued) Note: Unless otherwise indicated, VIN = VCC = VSHDN = 3.3V, COUT = CIN = 10 µF, L = 3.3 µH, ILOAD = 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. Start-up from VIN = 0V to 3.3V IOUT = 100 mA to 800 mA VIN = 5.0V VOUT = 3.3V VOUT 100 mV/DIV VIN 2.0V/DIV IOUT 500 mA/DIV VOUT 1.0V/DIV VOUT = 1.8V 1.0 ms/DIV FIGURE 2-7: 500 µs/DIV Power-Up from VIN. FIGURE 2-10: Load Transient Response. Line Step Response, VIN = 3.0V to 4.0V Start-up from SHDN VIN 2.0V/DIV SHDN 2.0V/DIV VOUT 50 mV/DIV VOUT 1.0V/DIV VOUT = 1.8V IOUT = 800 mA VOUT = 1.8V 1.0 ms/DIV FIGURE 2-8: 200 µs/DIV Power-Up from Shutdown. FIGURE 2-11: Line Step Response, VIN = 4.5V to 5.5V IOUT = 100 mA to 800 mA VIN 2.0V/DIV VOUT 200 mV/DIV VOUT 50 mV/DIV IOUT 500 mA/DIV VOUT = 3.3V IOUT = 800 mA VOUT = 1.8V 50 µs/DIV FIGURE 2-9: Line Transient Response. Load Transient Response. © 2005 Microchip Technology Inc. 200 µs/DIV FIGURE 2-12: Line Transient Response. DS21921B-page 7 MCP1612 TYPICAL PERFORMANCE CURVES (Continued) Note: Unless otherwise indicated, VIN = VCC = VSHDN = 3.3V, COUT = CIN = 10 µF, L = 3.3 µH, ILOAD = 100 mA, TA = +25°C. Boldface specifications apply over the TA range of -40°C to +85°C. IOUT = 10 mA, VOUT = 1.8V IOUT = 1A, VOUT = 1.8V LX 5.0V/DIV LX 2.0V/DIV VOUT 10 mV/DIV VOUT 10 mV/DIV IIND 500 mA/DIV IIND 100 mA/DIV VIN = 3.3V VIN = 3.3V 500 ns/DIV FIGURE 2-13: Waveform. DS21921B-page 8 Low Load Current Switching 500 ns/DIV FIGURE 2-14: Waveform. High Load Current Switching © 2005 Microchip Technology Inc. MCP1612 3.0 MCP1612 PIN DESCRIPTIONS The descriptions of the pins are listed in Table 3-1. TABLE 3-1: Pin No. 3.1 PIN FUNCTION TABLE Name Function 1 VIN Input Voltage Pin 2 VCC Analog Input Voltage Pin 3 SHDN Shutdown Control Input Pin 4 COMP Transconductance Amplifier Output Pin 5 FB Feedback Input Pin 6 AGND Analog Ground Pin 7 PGND Power Ground Pin 8 LX Buck Inductor Output Pin Input Voltage Pin (VIN) 3.5 Feedback Pin (FB) Connect the input voltage source to VIN. For normal operation, the voltage on VIN should be between +2.7V and +5.5V. A 10 µF bypass capacitor should be connected between VIN and PGND. Connect the output voltage of the buck converter through an external resistor divider to FB to regulate the output voltage. The nominal voltage compared to this input for pulse termination is 0.8V. 3.2 3.6 Analog Input Voltage Pin (VCC) VCC provides bias for internal analog functions. This voltage is derived by filtering the VIN supply. 3.3 Tie all small-signal ground returns to AGND. Noise on AGND can effect the sensitive internal analog measurements. Shutdown Input Pin (SHDN) Connect SHDN to a logic-level input in order to turn the regulator on or off. A logic-high (>45% of VIN) will enable the regulator. A logic-low (<15% of VIN) will force the regulator into Shutdown mode. When in shutdown, both the P-channel and N-channel switches are turned off. 3.7 Compensation Pin (COMP) COMP is the internal transconductance amplifier output pin. External compensation is connected to COMP for control-loop stabilization. © 2005 Microchip Technology Inc. Power Ground Pin (PGND) Connect all large-signal ground returns to PGND. These large-signal traces should have a small loop area and length to prevent coupling of switching noise to sensitive traces. 3.8 3.4 Analog Ground Pin (AGND) Buck Inductor Output Pin (LX) Connect LX directly to the buck inductor. This pin carries large signal-level currents; all connections should be made as short as possible. DS21921B-page 9 MCP1612 4.0 DETAILED DESCRIPTION 4.1 Device Overview The MCP1612 is a 1A synchronous buck converter switching at 1.4 MHz to minimize external component size and cost. While utilizing a fixed-frequency Current mode architecture, the MCP1612 provides fast response to sudden load changes, as well as overcurrent protection in the event of a shorted load. The input voltage range is 2.7V to 5.5V, while the output voltage is adjustable by properly setting an external resistor divider and can range from 0.8V to VIN. Integrated soft-start, UVLO and overtemperature protection minimize external circuitry and component count. 4.2 Current Mode Control Scheme The MCP1612 incorporates a Peak Current mode control scheme. Peak Current mode is used to obtain high gain in the PWM control loop for very fast response to dynamic line and load conditions. With both the P-channel and N-channel MOSFETs turned off, the beginning of a cycle occurs on the negative edge of the internal 1.4 MHz oscillator, the P-channel MOSFET turns on and current ramps up into the buck inductor. The inductor current is sensed and tied to one input of a high-speed comparator. The other input of the high-speed comparator is the error amplifier output. This is the amplified difference between the internal 0.8V reference and the divided-down VOUT signal at the FB pin of the MCP1612. When the sensed inductor current ramps up to the point that is equal to the amplified error signal, the high-speed comparator output switches states and the P-channel MOSFET is turned off until the beginning of the next clock cycle and the N-channel is turned on. The width of the pulse (or duty cycle) is ideally determined by the VOUT/VIN ratio of the DC/DC converter. The actual duty cycle is slightly larger to account for the non-ideal losses of the integrated MOSFET switches and the losses in the external inductor. 4.3 Low-Dropout Operation The MCP1612 is capable of operating over a wide range of input voltages. The PWM architecture allows for the P-channel MOSFET to achieve 100% duty cycle operation for applications that have minimal input voltage headroom. During 100% Duty Cycle mode, the output voltage (VOUT) is equal to the Output Current (IOUT) x Resistance (P-channel RDSON + RINDUCTOR). 4.4 Current Limit Cycle-by-cycle current limit is used to protect the MCP1612 from being damaged when an external short circuit is applied. The typical peak current limit is 2.3A. If the sensed inductor current reaches the 2.3A limit, the P-channel MOSFET is turned off, even if the output voltage is not in regulation. 4.5 Soft-Start During normal power-up, as VIN rises above the UVLO protection setting (or, in the case of a logic-low to logichigh transition on the shutdown pin), the rise time of the MCP1612 output voltage is controlled by the soft-start feature. This is accomplished by allowing the output of the error amplifier to slowly rise. This feature prevents the output voltage from overshooting the desired value and the sudden inrush of current, depleting the input capacitors and causing a large dip in input voltage. This large dip in the input voltage can trip the UVLO threshold, causing the converter to shut down prior to reaching steady-state operation. 4.6 Undervoltage Lockout (UVLO) The UVLO feature uses a comparator to sense the input voltage level (VIN). If the input voltage is lower than the voltage necessary to properly operate the MCP1612, the UVLO feature will hold the converter off. When VIN rises above the necessary input voltage, the UVLO is released and soft-start begins. For the MCP1612, the UVLO protection threshold is at a maximum of 2.7V. Hysteresis is built into the UVLO circuit to compensate for input impedance. For example, if there is any resistance between the input voltage source and the converter (once it starts), there will be a voltage drop at the converter input equal to IIN x RIN. The typical hysteresis for the MCP1612 is 200 mV. 4.7 Overtemperature Protection The MCP1612 has an integrated overtemperature protection circuit that monitors the device junction temperature and shuts the device off if the junction temperature exceeds the typical 160°C threshold. If the overtemperature threshold is reached, the soft-start is reset so that, when the junction temperature cools to approximately 151°C, the device will automatically restart and the output voltage will not overshoot. 4.8 Shutdown Input Operation The SHDN pin is used to turn the MCP1612 on and off. When the SHDN pin is tied low, the MCP1612 is off. When tied high, the MCP1612 will be enabled and begin operation as long as the input voltage is not below the UVLO threshold. DS21921B-page 10 © 2005 Microchip Technology Inc. MCP1612 5.0 APPLICATION CIRCUITS/INFORMATION MCP1612 3.3V to 1.2V Synchronous Buck Converter 3.3VIN ±10% CIN 10 µF Ceramic ON 1 VIN 8 L = 3.3 µH Lx COUT 10 µF Ceramic MCP1612 10Ω 2 CBYP 0.1 µF Ceramic 3 VCC PGND SHDN AGND 1.2V VOUT @ 1A 7 100 kΩ 6 200 kΩ OFF 4 Comp 5 FB 25 kΩ 1000 pF FIGURE 5-1: 5.1 Typical Application Circuit. Typical Applications The MCP1612 buck controller can be used in several different applications where a voltage that is lower than the supply voltage is required. Its small size, low cost and high efficiency make the MCP1612 a good choice for densely-packaged applications. The input voltage range, low-dropout voltage and low shutdown current make this part perfectly suited for battery-powered applications. 5.2 Design Example The step-by-step design of a buck converter with the following parameters is presented to illustrate how easy the MCP1612 is to use. Input voltage = 3.3V Output voltage = 1.2V Output current = 0A to 1A Switching frequency = 1.4 MHz 5.2.1 SETTING OUTPUT VOLTAGE The output voltage of the MCP1612 is set by using an external resistor-divider network. The voltage present at FB is internally compared to a 0.8V reference voltage. A 200 kΩ resistor is recommended for R2, the lower-end of the voltage divider. Using higher-value © 2005 Microchip Technology Inc. resistors will make the circuit more susceptible to noise on the FB pin. Lower-value resistors can be used, if necessary. Equation 5-1, used to calculate the output voltage, is shown below. EQUATION 5-1: V OUT R1 = R 2 × ⎛ ------------- – 1⎞ ⎝ V FB ⎠ Where: VOUT = desired output voltage VFB = MCP1612 internal reference voltage R1 = top resistor value R2 = bottom resistor value For this example: VOUT = 1.2V VFB = 0.8V R2 = 200 kΩ R1 = 100 kΩ The MCP1612 is capable of a 15% duty cycle. Instability may result when the duty cycle is below 15%. If less than 15% duty cycle operation is needed, care must be taken to ensure stable operation. DS21921B-page 11 MCP1612 5.2.2 BUCK INDUCTOR There are many requirements that need to be satisfied when selecting the buck inductor. The application, physical size, current rating, resistance, mounting method, supplier, temperature range, minimum inductance and cost all need to be considered. Many suppliers specify the maximum peak current that an inductor can handle before magnetic saturation occurs. The peak current is equal to the maximum DC output current, plus one-half the peak-to-peak AC ripple current. The value of the buck inductor is chosen to be 3.3 µH. The AC ripple current is controlled by the size of the buck inductor. The value of the inductor will therefore need to be raised so that the converter operates in Continuous Conduction mode. Calculation of the buck inductor current rating follows. VIN = 3.3V VOUT = 1.2V FSW = 1.4 MHz IOUT(MAX) = 1A TON = (1.2V/3.3V) x (1/1.4 MHz) When the P-channel MOSFET is on, the current in the buck inductor is ramped up. The voltage across the inductor, the inductance and the MOSFET on-time are required to determine the peak-to-peak ripple current. When operating in Continuous Current mode, the ontime of the P-channel MOSFET is determined by multiplying the duty cycle by the switching period. The following equation can be used to determine the duty cycle. EQUATION 5-2: V OUT DutyCycle = ------------V IN TON = 260 ns VL = (3.3V – 1.2V) = 2.1V ΔIL = (2.1V/3.3 µH) x 260 ns ΔIL = 165 mA IL(PEAK) = IOUT(MAX) + 1/2 ΔIL IL(PEAK) = 1A + (165 mA)/2 IL(PEAK) = 1.08A The inductor selected must have an inductance of 3.3 µH at a peak current rating of 1.08A. The DC resistance of the inductor should be as low as is feasibly possible. Extremely low DC resistance inductors are available, though a trade-off between size and cost should be considered. The on-time is then defined as follows. 5.2.3 EQUATION 5-3: T ON 1 = DutyCycle × ---------F SW Where: FSW = switching frequency The AC ripple current in the inductor can be calculated by the following relationship. EQUATION 5-4: ΔI L V L = L × -------Δt Solving for ΔIL yields: OUTPUT CAPACITOR The output capacitor is used to filter the inductor AC ripple current and provide storage for load transients. The size and Equivalent Series Resistance (ESR) of the output capacitor determines the amount of ripple voltage present at the output of the converter. When selecting the output capacitor, a design trade-off has to be made between the acceptable ripple voltage and the size/cost of the output capacitor. Ceramic capacitors have very low ESR, but increase in cost with higher values. Tantalum and electrolytic capacitors are relatively inexpensive in higher values, but they also have a much higher ESR. The amount of capacitance needed to obtain the desired ripple voltage is calculated by using the following relationship. EQUATION 5-6: EQUATION 5-5: VL ΔI L = ------ × Δt L ΔV C I C = C × ----------Δt Where: VL = voltage across the inductor (VIN – VOUT) Δt = on-time of the P-channel MOSFET DS21921B-page 12 © 2005 Microchip Technology Inc. MCP1612 5.2.6 Solving for C: Δt C = I C × ----------ΔV C Where: IC = peak-to-peak ripple current Δt = on-time of P-channel MOSFET ΔVC = output ripple voltage There will also be some ripple voltage caused by the ESR of the capacitor. The ripple is defined as follows. EQUATION 5-7: COMPENSATION COMPONENTS An internal transconductance error amplifier is used to compensate the buck converter. An external resistor (RC) and capacitor (CC), connected between COMP and GND, are all that is needed to provide a highbandwidth loop. Table 5-1 identifies values for RC and CC for standard buck inductor (L) and output capacitor (COUT) values. TABLE 5-1: RC and CC VALUES L COUT RC CC 3.3 µH 10.0 µF 25 kΩ 1000 pF 2.2 µH 4.7 µF 10 kΩ 1000 pF V ESRRIPPLE = ESR × IC 5.3 For this example: IC = 165 mA C = 4.7 µF Δt = 260 ns ESR = 8 mΩ ΔVC = (260 ns x 165 mA)/4.7 µF ΔVC = 9.13 mV VESRRIPPLE = 8 mΩ x 165 mA VESRRIPPLE = 1.32 mV ΔVOUT = ΔVC + VESRRIPPLE ΔVOUT = 9.13 mV + 1.32 mV ΔVOUT = 10.45 mV 5.2.4 INPUT CAPACITOR Printed Circuit Board (PCB) Layout The MCP1612 is capable of switching over 1A at 1.4 MHz. As with all high-frequency switching power supplies, good PCB layout techniques are essential to prevent noise generated by the switching power-train from interfering with the sensing circuitry. There are two ground pins (PGND and AGND) on the MCP1612 to separate the large-signal ground current from the small-signal circuit ground. These two grounds should be kept separate, only connecting near the input bulk capacitor. Care must also be taken to minimize the length and loop area of the large signal connections. Components connected to this loop consist of the input bulk capacitor, VIN, PGND and LX pins of the MCP1612, the buck inductor and the output filter capacitor. For the buck topology, the input current is pulled from the source and the input capacitor in pulses. The size of the input capacitor will determine the amount of current pulled from the source. For most applications, a 10 µF ceramic capacitor connected between the MCP1612’s VIN and PGND is recommended to filter the current pulses. Less capacitance can be used for applications that have low source impedance. The ripple current rating for ceramic capacitors are typically very high due to their low loss characteristics. Low-cost electrolytic capacitors can be used, but their ripple current rating should not be exceeded. 5.2.5 VCC INPUT The VCC input is used to bias the internal MCP1612 circuitry. A 10Ω resistor is recommended between the unregulated inputs VIN and VCC, along with a 0.1 µF capacitor to ground to help isolate the VCC pin from the switching noise. © 2005 Microchip Technology Inc. DS21921B-page 13 MCP1612 6.0 PACKAGING INFORMATION 6.1 Package Marking Information 8-Lead DFN (3mm x 3mm) XXXX YYWW NNN 8-Lead MSOP XXXXX YWWNNN Legend: XX...X Y YY WW NNN e3 * Note: DS21921B-page 14 Example: 1612 I0532 256 Example: 1612I 532256 Customer-specific information Year code (last digit of calendar year) Year code (last 2 digits of calendar year) Week code (week of January 1 is week ‘01’) Alphanumeric traceability code Pb-free JEDEC designator for Matte Tin (Sn) This package is Pb-free. The Pb-free JEDEC designator ( e3 ) can be found on the outer packaging for this package. In the event the full Microchip part number cannot be marked on one line, it will be carried over to the next line, thus limiting the number of available characters for customer-specific information. © 2005 Microchip Technology Inc. MCP1612 8-Lead Plastic Dual-Flat, No-Lead Package (MF) 3x3x0.9 mm Body (DFN) – Saw Singulated D p b n L EXPOSED METAL PAD (NOTE 2) E PIN 1 ID INDEX AREA (NOTE 1) E2 2 1 D2 TOP VIEW BOTTOM VIEW ALTERNATE EXPOSED PAD CONFIGURATIONS A1 A EXPOSED TIE BAR (NOTE 3) A3 INCHES Units Dimension Limits MIN MILLIMETERS* NOM MAX MIN NOM MAX Pitch n p Overall Height A .031 .035 .039 0.80 0.90 1.00 Standoff A1 .000 .001 .002 0.00 0.02 0.05 Contact Thickness A3 Number of Pins Overall Length Exposed Pad Width Overall Width 8 .026 BSC 0.65 BSC .008 REF. E E2 8 0.20 REF. .118 BSC .043 D .061 3.00 BSC .063 1.09 .118 BSC 1.55 1.60 3.00 BSC D2 .059 .092 .096 1.50 2.37 2.45 Contact Width b .009 .012 .015 0.23 0.30 0.37 Contact Length L .008 .016 .020 0.20 0.40 0.50 Exposed Pad Length * Controlling Parameter Notes: 1. Pin 1 visual index feature may vary, but must be located within the hatched area. 2. Exposed pad varies according to die attach paddle size. 3. Package may have one or more exposed tie bars at ends. BSC: Basic Dimension. Theoretically exact value shown without tolerances. See ASME Y14.5M REF: Reference Dimension, usually without tolerance, for information purposes only. See ASME Y14.5M JEDEC equivalent: M0-229 Drawing No. C04-062 © 2005 Microchip Technology Inc. Revised 07-20-05 DS21921B-page 15 MCP1612 8-Lead Plastic Micro Small Outline Package (MS) (MSOP) E E1 p D 2 B n 1 α c φ L F A2 A A1 β Units MILLIMETERS* INCHES NOM MIN Dimension Limits MIN MAX NOM MAX Number of Pins n Pitch p Overall Height A - - .043 - - 1.10 Molded Package Thickness A2 .030 .033 .037 0.75 0.85 0.95 Standoff A1 .000 - .006 0.00 - 0.15 Overall Width E .193 BSC 4.90 BSC Molded Package Width E1 .118 BSC 3.00 BSC Overall Length D .118 BSC Foot Length L 0.60 0.80 Footprint (Reference) Foot Angle F φ Lead Thickness c .003 .006 .009 0.08 - 0.23 Lead Width B α .009 .012 .016 0.22 - 0.40 Mold Draft Angle Top Mold Draft Angle Bottom β 8 8 .026 BSC .016 0.65 BSC 3.00 BSC .024 .031 0.40 .037 REF 0° 0.95 REF - 8° 0° 8° - 5° - 15° 5° - 15° 5° - 15° 5° - 15° * Controlling Parameter Notes: Dimensions D and E1 do not include mold flash or protrusions. Mold flash or protrusions shall not exceed .010" (0.254mm) per side. BSC: Basic Dimension. Theoretically exact value shown without tolerances. See ASME Y14.5M REF: Reference Dimension, usually without tolerance, for information purposes only. See ASME Y14.5M JEDEC Equivalent: MO-187 Drawing No. C04-111 DS21921B-page 16 Revised 07-21-05 © 2005 Microchip Technology Inc. MCP1612 APPENDIX A: REVISION HISTORY Revision B (September 2005) The following is the list of modifications: 1. 2. 3. 4. 5. Changed pin 6 in Package Types diagram on front page. Removed device qualification note in Package Marking section. Removed device qualification note in Package Outline drawing. Removed device qualification note in Package Identification System section Replaced MSOP and QFN package diagrams. Revision A (December 2004) • Original Release of this Document. © 2005 Microchip Technology Inc. DS21921B-page 17 MCP1612 NOTES: DS21921B-page 18 © 2005 Microchip Technology Inc. MCP1612 PRODUCT IDENTIFICATION SYSTEM To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office. PART NO. X /XX Device Temperature Range Package Device: MCP1612: Synchronous Buck Regulator MCP1612T: Synchronous Buck Regulator (Tape and Reel) Temperature Range: I Package: MF = Dual Flat, No Lead (3x3mm Body), 8-lead MS = Plastic MSOP, 8-lead Examples: a) b) c) d) MCP1612-ADJI/MS: Industrial Temperature, 8LD MSOP package. MCP1612T-ADJI/MS: Tape and Reel Industrial Temperature, 8LD MSOP package. MCP1612-ADJI/MF: Industrial Temperature, 8LD DFN package. MCP1612T-ADJI/MF: Tape and Reel Industrial Temperature, 8LD DFN package. = -40°C to +85°C © 2005 Microchip Technology Inc. DS21921B-page 19 MCP1612 NOTES: DS21921B-page 20 © 2005 Microchip Technology Inc. MCP1612 Note the following details of the code protection feature on Microchip devices: • Microchip products meet the specification contained in their particular Microchip Data Sheet. • Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the intended manner and under normal conditions. • There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data Sheets. Most likely, the person doing so is engaged in theft of intellectual property. • Microchip is willing to work with the customer who is concerned about the integrity of their code. • Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable.” Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act. Information contained in this publication regarding device applications and the like is provided only for your convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. MICROCHIP MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION, INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR FITNESS FOR PURPOSE. Microchip disclaims all liability arising from this information and its use. Use of Microchip’s products as critical components in life support systems is not authorized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any Microchip intellectual property rights. Trademarks The Microchip name and logo, the Microchip logo, Accuron, dsPIC, KEELOQ, microID, MPLAB, PIC, PICmicro, PICSTART, PRO MATE, PowerSmart, rfPIC, and SmartShunt are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. AmpLab, FilterLab, Migratable Memory, MXDEV, MXLAB, PICMASTER, SEEVAL, SmartSensor and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. Analog-for-the-Digital Age, Application Maestro, dsPICDEM, dsPICDEM.net, dsPICworks, ECAN, ECONOMONITOR, FanSense, FlexROM, fuzzyLAB, In-Circuit Serial Programming, ICSP, ICEPIC, Linear Active Thermistor, MPASM, MPLIB, MPLINK, MPSIM, PICkit, PICDEM, PICDEM.net, PICLAB, PICtail, PowerCal, PowerInfo, PowerMate, PowerTool, rfLAB, rfPICDEM, Select Mode, Smart Serial, SmartTel, Total Endurance and WiperLock are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. SQTP is a service mark of Microchip Technology Incorporated in the U.S.A. All other trademarks mentioned herein are property of their respective companies. © 2005, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. Microchip received ISO/TS-16949:2002 quality system certification for its worldwide headquarters, design and wafer fabrication facilities in Chandler and Tempe, Arizona and Mountain View, California in October 2003. The Company’s quality system processes and procedures are for its PICmicro® 8-bit MCUs, KEELOQ® code hopping devices, Serial EEPROMs, microperipherals, nonvolatile memory and analog products. In addition, Microchip’s quality system for the design and manufacture of development systems is ISO 9001:2000 certified. © 2005 Microchip Technology Inc. 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