NCP1511 Up to 500 mA, High Efficiency Synchronous Step−Down DC−DC Converter in Chip Scale Package The NCP1511 step−down PWM DC−DC converter is optimized for portable applications powered from 1−cell Li−ion or 3−cell Alkaline/NiCd/NiMH batteries. This DC−DC converter utilizes a current−mode control architecture for easy compensation and better line regulation. It also uses synchronous rectification to increase efficiency and reduce external part count. The NCP1511 optimizes efficiency in light load conditions when switched from a normal PWM mode to a “pulsed switching” mode. The device also has a built−in oscillator for the PWM circuitry, or it can be synchronized to an external 500 kHz to 1000 kHz clock signal. Finally, it includes an integrated soft−start, cycle−by−cycle current limiting, and thermal shutdown protection. The NCP1511 is available in a chip scale package. Features • High Efficiency: • • • • • • • • 93% for 1.89 V Output at 3.6 V Input and 150 mA Load Current 92% for 1.89 V Output at 3.6 V Input and 300 mA Load Current Digital Programmable Output Voltages: 1.0, 1.3, 1.5 or 1.89 V Output Current up to 500 mA at Vin = 3.6 V Low Quiescent Current of 14 A in Pulsed Switching Mode Low 0.1 A Shutdown Current −30°C to 85°C Operation Temperature Ceramic Input/Output Capacitor 9 Pin Chip Scale Package Pb−Free Package is Available http://onsemi.com A1 XX A Y WW Cellular Phones, Smart Phones and PDAs Digital Still Cameras MP3 Players and Portable Audio Systems Wireless and DSL Modems Portable Equipment DAL AYWW = Device Code = Assembly Location = Year = Work Week A1 PIN CONNECTIONS A1 B1 C1 A2 B2 C2 A3 B3 C3 Pin: A1. − GNDP A2. − LX A3. − VCC B1. − SYNC B2. − GNDA B3. − FB C1. − SHD C2. − CB1 C3. − CB0 (Bottom View) ORDERING INFORMATION Package Shipping† NCP1511FCT1 Micro Bump 3000 Tape & Reel NCP1511FCT1G Micro Bump (Pb−Free) 3000 Tape & Reel Device Applications • • • • • MARKING DIAGRAM 9 PIN MICRO BUMP FC SUFFIX CASE 499AC †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. 100 90 Pulsed Mode A3 Vin 2.5 V − 5.2 V Cin 10 F C1 B1 VCC SHD SYNC LX FB A2 EFFICIENCY (%) 80 6.8 H B3 Vout Cout 22 F C2 CB1 CB0 and CB1 C3 Control Input CB0 60 50 40 30 Vin = 3.6 V Vout = 1.5 V TA= 25°C 20 10 GNDA GNDP B2 PWM Mode 70 0 0.1 A1 1 10 100 1000 Iout (mA) Figure 1. Typical Application Circuit Semiconductor Components Industries, LLC, 2005 January, 2005 − Rev. 5 Figure 2. Efficiency vs. Output Current 1 Publication Order Number: NCP1511/D NCP1511 ISENS VCC SENFET COMPENSATION RAMP ISENS − OA + FB − CMP + ILIM DVR + CMP − Q1 LX DAMPING SWITCHING CONTROL PWM − CMP + OVP FB PM − ZCL GNDA CB0 − CMP + SELECT LOGIC CB1 BANDGAP REFERENCE AND SOFT START + Q2 DVR THERMAL SHUTDOWN GNDP ENABLE DETECT SHD CMP CONTROL BLOCK (PWM,PM) MODE SELECTION SYNC DETECT AND TIMING BLOCK SYNC Figure 3. Simplified Block Diagram PIN FUNCTION DESCRIPTION Pin No. Symbol Type Description A1 GNDP Power Ground Ground Connection for the NFET Power Stage. A2 LX Analog Output Connection from Power Pass Elements to the Inductor. A3 VCC Analog Input Power Supply Input for Power and Analog VCC. B1 SYNC Analog Input Synchronization input for the PWM converter. If a clock signal is present, the converter uses the rising edge for the turn on. If this pin is low, the converter is in the Pulsed mode. If this pin is high, the converter uses the internal oscillator for the PWM mode. This pin contains an internal pull down resistor. B2 GNDA Analog Ground B3 FB Analog Input Feedback Voltage from the Output of the Power Supply. C1 SHD Analog Input Enable for Switching Regulator. This Pin is Active High to enable the NCP1511. The SHD Pin has an internal pull down resistor to force the converter off if this pin is not connected to the external circuit. C2 CB1 Analog Input Selects Vout. This pin contains an internal pull up resistor. C3 CB0 Analog Input Selects Vout. This pin contains an internal pull down resistor. Ground connection for the Analog Section of the IC. This is the GND for the FB, Ref, Sync, CB, and SHD pins. http://onsemi.com 2 NCP1511 MAXIMUM RATINGS Symbol Value Unit Maximum Voltage All Pins Rating Vmax 5.5 V Maximum Operating Voltage All Pins Vmax 5.2 V Thermal Resistance, Junction−to−Air (Note 1) RJA 159 °C/W TA −30 to 85 °C VESD > 2500 > 150 V Moisture Sensitivity MSL Level 1 Storage Temperature Range Tstg −55 to 150 °C TJ −30 to 125 °C Operating Ambient Temperature Range ESD Withstand Voltage Human Body Model (Note 2) Machine Model (Note 2) Junction Operating Temperature Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage may occur and reliability may be affected. 1. For the 9−Pin Micro Bump package, the RJA is highly dependent of the PCB heatsink area. RJA = 159°C/W with 50 mm2 PCB heatsink area. 2. This device series contains ESD protection and exceeds the following tests: Human Body Model, 100 pF discharge through a 1.5 k following specification JESD22/A114. Machine Model, 200 pF discharged through all pins following specification JESD22/A115. Latchup as per JESD78 Class II: > 100 mA. http://onsemi.com 3 NCP1511 ELECTRICAL CHARACTERISTICS (Vin = 3.6 V, Vo = 1.5 V, TA = 25°C, Fsyn = 600 kHz 50% Duty Cycle square wave for PWM mode; TA = –30 to 85°C for Min/Max values, unless otherwise noted. Characteristic Symbol Min Typ Max Unit Quiescent Current of Sync Mode, Iout = 0 mA Iq PWM − 175 − A Quiescent Current of PWM Mode, Iout = 0 mA Iq PWM − 185 − A Quiescent Current of Pulsed Mode, Iout = 0 mA Iq Pulsed − 14 − A Quiescent Current, SHD Low Iq Off − 0.1 0.5 A Input Voltage Range (Note 3) Vin 2.5 − 5.2 V Input Voltage Vsync −0.3 − Vcc + 0.3 V Frequency Operational Range Fsync 500 600 1000 kHz Minimum Synchronization Pulse Width Dcsync Min − 30 − % Maximum Synchronization Pulse Width VCC Pin Sync Pin Dcsync Max − 70 − % SYNC “H” Voltage Threshold Vsynch − 920 1200 mV SYNC “L” Voltage Threshold Vsyncl 400 830 − mV SYNC “H” Input Current, Vsync = 3.6 V Isynch − 2.2 − A SYNC “L” Input Current, Vsync = 0 V Isyncl −0.5 − − A Vcb −0.3 − Vcc + 0.3 V Output Level Selection Pins Input Voltage CB0, CB1 “H” Voltage Threshold Vcb h − 920 1200 mV CB0, CB1 “L” Voltage Threshold Vcb l 400 830 − mV CB0 “H” Input Current, CB = 3.6 V Icb0 h − 2.2 − A CB0 “L” Input Current, CB = 0 V Icb0 l −0.5 − − A CB1 “H” Input Current, CB = 3.6 V Icb1 h − 0.3 1.0 A CB1 “L” Input Current, CB = 0 V Icb1 l − −2.2 − A Vshd −0.3 − Vcc + 0.3 V Shutdown Pin Input Voltage SHD “H” Voltage Threshold Vshd h − 920 1200 mV SHD “L” Voltage Threshold Vshd l 400 830 − mV SHD “H” Input Current, SHD = 3.6 V Ishd h − 2.2 − A SHD “L” Input Current, SHD = 0 V Ishd l −0.5 − − A Input Voltage Vfb −0.3 − Vcc + 0.3 V Input Current, Vfb = 1.5 V Ifb − 5.0 7.5 A I lim − 800 − mA Minimum On Time Ton min − 75 − nsec Rdson Switching P−FET and N_FET Rdson − 0.23 − Ileak − 0 1.0 A Vo − 5.0 − % Feedback Pin Sync PWM Mode Characteristics Switching P−FET Current Limit Switching P−FET and N−FET Leakage Current Output Overvoltage Threshold 3. Recommended maximum input voltage is 5 V when the device frequency is synchronized with an external clock signal. http://onsemi.com 4 NCP1511 ELECTRICAL CHARACTERISTICS (continued) (Vin = 3.6 V, Vo = 1.5 V, TA = 25°C, Fsyn = 600 kHz 50% Duty Cycle square wave for PWM mode; TA = –30 to 85°C for Min/Max values, unless otherwise noted. Characteristic Symbol Min Typ Max Unit Feedback Voltage Accuracy, Vout Set = 1.0 V CB0 = L, CB1 = L Vout 0.950 1.000 1.050 V Feedback Voltage Accuracy, Vout Set = 1.3 V CB0 = L, CB1 = H Vout 1.261 1.300 1.339 V Feedback Voltage Accuracy, Vout Set = 1.5 V CB0 = H, CB1 = H Vout 1.450 1.500 1.550 V Feedback Voltage Accuracy, Vout Set = 1.89 V CB0 = H CB1 = L Vout 1.833 1.890 1.947 V Load Transient Response 10 to 100 mA Load Step Vout − 35 − mV Line Transient Response, Iout = 100 mA 3.0 to 3.6 Vin Line Step Vout − 10 − mVpp I lim − 800 − mA Ton min − 75 − nsec Fosc 700 900 1200 kHz Rdson − 0.23 − Ileak − 0 1.0 A Output Overvoltage Threshold Vo − 5.0 − % Feedback Voltage Accuracy, Vout Set = 1.0 V CB0 = L, CB1 = L Vout 0.950 1.000 1.050 V Feedback Voltage Accuracy, Vout Set = 1.3 V CB0 = L, CB1 = H Vout 1.261 1.300 1.339 V Feedback Voltage Accuracy, Vout Set = 1.5 V CB0 = H, CB1 = H Vout 1.450 1.500 1.550 V Feedback Voltage Accuracy, Vout Set = 1.89 V CB0 = H CB1 = L Vout 1.833 1.890 1.947 V Load Transient Response 10 to 100 mA Load Step Vout − 35 − mV Line Transient Response, Iout = 100 mA 3.0 to 3.6 Vin Line Step Vout − 10 − mVpp On Time Ton − 660 − nsec Output Ripple Voltage, Iout = 100 A Vout − 22 − mV Feedback Voltage Accuracy, Vout Set = 1.0 V CB0 = L, CB1 = L Vout 0.930 1.000 1.070 V Feedback Voltage Accuracy, Vout Set = 1.3 V CB0 = L, CB1 = H Vout 1.241 1.300 1.359 V Feedback Voltage Accuracy, Vout Set = 1.5 V CB0 = H, CB1 = H Vout 1.430 1.500 1.570 V Feedback Voltage Accuracy, Vout Set = 1.89 V CB0 = H CB1 = L Vout 1.813 1.890 1.967 V Sync PWM Mode Characteristics (continued) PWM Mode with Internal Oscillator Characteristics Switching P−FET Current Limit Minimum On Time Internal Oscillator Frequency Rdson Switching P−FET and N_FET Switching P−FET and N−FET Leakage Current Pulsed Mode Characteristics http://onsemi.com 5 NCP1511 100 100 90 95 1.89 Vout 70 1.5 Vout 1.3 Vout EFFICIENCY (%) EFFICIENCY (%) 80 1.0 Vout 60 50 40 30 Vin = 3.6 V PWM TA= 25°C 20 10 100 200 300 400 85 1.89 Vout 1.5 Vout 80 1.3 Vout 70 2.5 500 1.0 Vout Iout = 150 mA Freq = 1.0 MHz TA= 25°C 75 0 0 90 3.0 3.5 4.0 4.5 5.0 5.5 Iout (mA) INPUT VOLTAGE (V) Figure 4. Efficiency vs. Output Current in PWM Mode Figure 5. Efficiency vs. Input Voltage in PWM Mode 100 100 90 5.2 Vin 70 EFFICIENCY (%) EFFICIENCY (%) 80 3.6 Vin 60 2.7 Vin 50 40 30 Vout = 1.5 V PWM TA= 25°C 20 10 0 0 100 200 300 400 1.5 Vout 95 1.89 Vout 90 85 Vin = 3.6 V Iout = 150 mA TA = 25°C PWM 80 500 600 700 500 Iout (mA) 800 900 1000 1100 1200 1300 1400 1500 Figure 7. Efficiency vs. Frequency at Iout = 150 mA 100 100 1.89 Vout 90 80 95 1.5 Vout EFFICIENCY (%) EFFICIENCY (%) 1.3 Vout FREQUENCY (kHz) Figure 6. Efficiency vs. Output Current at Different Input Voltage 1.89 Vout 90 85 1.0 Vout Vin = 3.6 V Iout = 300 mA TA = 25°C PWM 80 500 600 700 1.0 Vout 70 1.5 Vout 60 1.3 Vout 50 40 1.0 Vout 30 Vin = 3.6 V PM TA= 25°C 20 1.3 Vout 10 800 900 1000 1100 1200 1300 1400 1500 0 0.01 0.1 1 10 100 Iout (mA) FREQUENCY (kHz) Figure 8. Efficiency vs. Frequency at Iout = 300 mA Figure 9. Efficiency vs. Output Current in Pulsed Mode http://onsemi.com 6 1000 NCP1511 2 20 Vin = 3.6 V Vout = 1.5 V TA = 25°C 15 1.8 1.6 Vout (V) PWM Mode Iin (mA) 1.89 Vout 10 Pulsed Mode 1.4 1.5 Vout 1.2 1.3 Vout 1 5 Vin = 3.6 V TA = 25°C PWM 0.8 1.0 Vout 0.6 0 0 5 10 15 Iout (mA) 20 30 25 0 Figure 10. Input Current Comparison 100 200 300 Iout (mA) 400 500 Figure 11. Output Voltage vs. Output Current 2 15 1.89 Vout 1.8 10 1.0 Vout 1.3 Vout 5 Vout (V) Vout (mV) 1.6 0 1.5 Vout −5 1.5 Vout 1.2 1.3 Vout 1 1.89 Vout 1.0 Vout Vin = 3.6 V TA = 25°C 10 100 0.6 −40 1000 −20 0 20 40 60 80 Iout (mA) TEMPERATURE (°C) Figure 12. Load Regulation in PWM Mode Figure 13. Output Voltage vs. Temperature 950 930 930 FREQUENCY (kHz) 950 910 890 Vin = 3.6 V Vout = 1.5 V Iout = 150 mA 870 850 −40 Vin = 3.6 V Iout = 150 mA PWM 0.8 −10 FREQUENCY (kHz) 1.4 −20 0 20 40 60 80 910 890 Vout = 1.5 V Iout = 150 mA TA = 25°C PWM 870 850 2.5 100 3.0 3.5 4.0 4.5 5.0 Vin (V) TEMPERATURE (°C) Figure 14. Oscillator Frequency vs. Temperature Figure 15. Oscillator Frequency vs. Input Voltage http://onsemi.com 7 100 5.5 NCP1511 2.0 2.0 Vin = 3.6 V Vout = 1.5 V TA= 25°C PWM Mode 1.5 Vout (V) Vout (V) 1.5 Vin = 3.6 V Vout = 1.5 V TA= 25°C PWM Mode 1.0 0.5 1.0 0.5 0 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 0.2 0.4 0.6 0.8 1.0 1.2 VSHD (V) VCB (V) Figure 16. Output Voltage vs. Shutdown Pin Voltage Figure 17. Transition Level of CB Pins VLX 1 V/div VLX 1 V/div Vout AC Coupled 10 mV/div Vout AC Coupled 10 mV/div 1 s/div 1 s/div Figure 18. Light Load PWM Switching Waveform (Vin = 3.6 V, Vout = 1.5 V, Iout = 30 mA) Figure 19. Heavy Load PWM Switching Waveform (Vin = 3.6 V, Vout = 1.5 V, Iout = 300 mA) 2V Vshdn 1 V/div 0 VLX 1 V/div 1.5 V Vout 0.5 V/div Vout AC Coupled 10 mV/div 0 1 s/div 500 ms/div Figure 21. Soft−Start (Vin = 3.6 V, Vout = 1.5 V, Iout = 150 mA) Figure 20. Pulsed Mode Switching Waveform (Vin = 3.6 V, Vout = 1.5 V, Iout = 30 mA) http://onsemi.com 8 1.4 NCP1511 3.6 V 3.6 V 3.0 V 3.0 V Vin 1 V/div Vout = 1.89 V Iout = 300 mA PWM Vout AC Coupled 10 mV/div Vin 1 V/div Vout = 1.89 V Iout = 30 mA PM Vout AC Coupled 10 mV/div 200 s/div 200 s/div Figure 22. Line Transient Response for PWM Figure 23. Line Transient Response for PM 2.0 V 300 mA CB1 2 V/div 0 10 mA Vin 1 V/div 1.89 V Vout 100 mV/div Vout AC Coupled 20 mV/div Vin = 3.6 V Vout = 1.89 V PWM CB0=1 Vin = 3.6 V Iout = 300 mA PWM 1.5 V 50 s/div 200 s/div Figure 24. Load Transient Response Figure 25. Output Voltage Transition from 1.5 V to 1.89 V PWM PM PM SYNC Vout AC Coupled 10 mV/div Vin = 3.6 V Vout = 1.5 V Iout = 30 mA 200 s/div Figure 26. Transition between PWM and PM http://onsemi.com 9 NCP1511 DETAILED OPERATING DESCRIPTION Overview value, the OVP comparator is activated and switch Q1 is turned OFF. Switching will continue when the output voltage falls below the threshold of OVP comparator. The NCP1511 is a monolithic micro−power high frequency PWM step−down DC−DC converter specifically optimized for applications requiring high efficiency and a small PCB footprint such as portable battery powered products. It integrates synchronous rectification to improve efficiency as well as eliminate the external Schottky diode. High switching frequency allows for a low profile inductor and capacitors to be used. Four digital selectable output voltages (1.0, 1.3, 1.5 and 1.89 V) can be generated from the input supply that can range from 2.7−5.2 V. All loop compensation is integrated as well further reducing the external component count as well. The DC−DC converter has two operating modes (normal PWM, pulsed switching), which are intended to allow for optimum efficiency under either light (up to 30 mA) or heavy loads. The user determines the operating mode by controlling the SYNC input. In addition the SYNC input can be used to synchronize the PWM to an external system clock signal in the range of 500−1000 kHz. Pulsed Mode (PM) Under light load conditions (< 30 mA), the NCP1511 can be configured to enter a low current pulsed mode operation to reduce power consumption. This is accomplished by applying a logic LOW to the SYNC pin. The output regulation is implemented by pulse frequency modulation. If the output voltage drops below the threshold of PM comparator (typically Vnom−2%), a new cycle will be initiated by the PM comparator to turn on the switch Q1. Q1 remains ON until the peak inductor current reaches 200 mA (nom). Then ILIM comparator goes high to switch off Q1. After a short dead time delay, switch rectifier Q2 is turn ON. The zero crossing comparator will detect when the inductor current drops to zero and send the signal to turn off Q2. The output voltage continues to decrease through discharging the output capacitor. When the output voltage falls below the threshold of the PM comparator again, a new cycle starts immediately. PWM Operating Mode The NCP1511 can be set to current mode PWM operation by connecting SYNC pin to VCC. In this mode, the output voltage is regulated by modulating the on−time pulse width of the main switch Q1 at a fixed frequency of 1.0 MHz. The switching of the PMOS Q1 is controlled by a flip−flop driven by the internal oscillator and a comparator that compares the error signal from an error amplifier with the sum of the sensed current signal and compensation ramp. At the beginning of each cycle, the main switch Q1 is turned ON by the rising edge of the internal oscillator clock. The inductor current ramps up until the sum of the current sense signal and compensation ramp becomes higher than the error voltage amplifier. Once this has occurred, the PWM comparator resets the flip−flop, Q1 is turned OFF and the synchronous switch Q2 is turned ON. Q2 replaces the external Schottky diode to reduce the conduction loss and improve the efficiency. To avoid overall power loss, a certain amount of dead time is introduced to ensure Q1 is completely turned OFF before Q2 is being turned ON. In continuous conduction mode (CCM), Q1 is turned ON after Q2 is completely turned OFF to start a new clock cycle. In discontinuous conduction mode (DCM), the zero crossing comparator (ZLC) will turn off Q2 when the inductor current drops to zero. Cycle−by−Cycle Current Limit From the block diagram, an ILIM comparator is used to realize cycle−by−cycle current limit protection. The comparator compares the LX pin voltage with the reference voltage from the SENFET, which is biased by a constant current. If the inductor current reaches the limit, the ILIM comparator detects the LX voltage falling below the reference voltage from the SENFET and releases the signal to turn off the switch Q1. The cycle−by−cycle current limit is set at 800 mA (nom) in PWM and 200 mA in PM. Frequency Synchronization and Operating Mode Selection The SYNC pin can also be used for frequency synchronization by connecting it with an external clock signal. It operates in PWM mode when synchronized to an external clock. The switching cycle initiates by the rising edge of the clock. The 500 kHz to 1000 kHz synchronization clock signal should be between 0.4 V and 1.2 V. Gating on and off the clock, the SYNC pin can also be used to select between PM and PWM modes. It allows efficient dynamical power management by adjusting the converter operation to the specific system requirement. Set SYNC pin low to select PM mode at light load conditions (up to 30 mA) and set SYNC pin high or connect with external clock to select PWM mode at heavy load condition to achieve optimum efficiency. Table 1 shows the mode selection with three different SYNC pin states. Overvoltage Protection The overvoltage protection circuit is present in PWM mode to prevent the output voltage from going too high under light load or fast load transient conditions. The output overvoltage threshold is 5% above nominal set value. If the output voltage rises above 5% of the nominal http://onsemi.com 10 NCP1511 Soft−Start Table 1. Operating Mode Selection SYNC Pin State The NCP1511 uses soft−start to limit the inrush current when the device is initially powered up or enabled. Soft−start is implemented by gradually increasing the reference voltage until it reaches the full reference voltage. During startup, a pulsed current source charges the internal soft−start capacitor to provide gradually increasing reference voltage for the PWM loop. When the voltage across the capacitor ramps up to the nominal reference voltage, the pulsed current source will be switched off and the reference voltage will switch to the regular reference voltage. Operating Mode LOW Pulsed Mode (PM) HIGH PWM, 1 MHz Switch Frequency CLOCK PWM, Frequency Synchronization Output Voltage Selection The output voltage is digitally programmed to one of four voltage levels depending on the logic state of CB0 and CB1. Therefore if the NCP1511’s load, such as a digital cellular phone’s baseband processor, supports dynamic power management, the device can lower or raise its core voltage under software control. When combined with the pulsed current mode function in low load situations, this active voltage management further stretches the useful operating life of the handset battery between charges. The output voltage levels are listed in Table 2. The CB0 has a pull down resistor and the CB1 has a pullup resistor. The default output voltage is 1.3 V when CB0 and CB1 are floating. Shutdown Mode When the SHD pin has a voltage applied of less than 0.4 V, the NCP1511 will be disabled. In shutdown mode, the internal reference, oscillator and most of the control circuitries are turned off. Therefore, the typical current consumption will be 0.1 A (typical value). Applying a voltage above 1.2 V to SHD pin will enable the device for normal operation. The device will go through soft−start to normal operation. Table 2. Truth Table for CB0 and CB1 with the Corresponding Output Voltage Thermal Shutdown CB0 CB1 Vout(V) 0 0 1.0 0 1 1.3 1 1 1.5 1 0 1.89 Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event that the maximum junction temperature is exceeded. If the junction temperature exceeds 160°C, the device shuts down. In this mode switch Q1 and Q2 and the control circuits are all turned off. The device restarts in soft−start after the temperature drops below 135C. This feature is provided to prevent catastrophic failures from accidental device overheating and it is not intended as a substitute for proper heatsinking. http://onsemi.com 11 NCP1511 APPLICATIONS INFORMATION Component Selection Where fs is the switching frequency and ESR is the effective series resistance of the output capacitor. A low ESR, 22 F ceramic capacitor is recommended for NCP1511 in most of applications. For example, with TDK C2012X5R0J226 output capacitor, the output ripple is less than 10 mV at 300 mA. Input Capacitor Selection In PWM operating mode, the input current is pulsating with large switching noise. Using an input bypass capacitor reduces the peak current transients drawn from the input supply source, thereby reducing switching noise significantly. The capacitance needed for the input bypass capacitor depends on the source impedance of the input supply. The RMS capacitor current is calculated as: IRMS IO D D Design Example As a design example, assume that the NCP1511 is used in a single lithium−ion battery application. The input voltage, Vin, is 3.0 V to 4.2 V. Output condition is Vout at 1.5 V with a typical load current of 120 mA and a maximum of 300 mA. For NCP1511, the inductor has a predetermined value, 6.8 H. The inductor ESR will factor into the overall efficiency of the converter. The inductor needs to be selected by the required peak current. Equation 5 is the basic equation for an inductor and describes the voltage across the inductor. The inductance value determines the slope of the current of the inductor. (eq. 1) where: D = duty cycle, which equals Vout/Vin, and D’ = 1 − D. The maximum RMS current occurs at 50% duty cycle with maximum output current, which is IO,max/2. A low profile ceramic capacitor of 10 F should be used for most of the cases. For effective bypass results, the input capacitor should be placed as close as possible to the VCC pin. di VL L L dt Inductor Value Selection Selecting the proper inductor value is based on the desired ripple current. The relationship between the inductance and the inductor ripple current is given by the equation below. Equation 5 is rearranged to solve for the change in current for the on−time of the converter in Continuous Conduction Mode. iL, pk−pk V V iL out 1 out Lfs Vin (eq. 5) (Vin Vout) DTs L (eq. 2) The DC current of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. For NCP1511, the compensation is internally fixed and a fixed 6.8 H inductor is needed for most of the applications. For better efficiency, choose a low DC resistance inductor. (Vin Vout) Vin 1 Vout fs L iL, max IO, max (eq. 6) iL, pk−pk 2 Utilizing Equations 6, the peak−to−peak inductor current is calculated using the following worst−case conditions. Output Capacitor Selection Vin, max 4.2 V, Vout 1.5 V, fs 1 MHz−20%, Selecting the proper output capacitor is based on the desired output ripple voltage. Ceramic capacitors with low ESR values will have the lowest output ripple voltage and are strongly recommended. The output ripple voltage is given by: L 6.8 H−10%, iL, pk−pk 197 mA, iL, max 399 mA 1 Vc iL ESR 4fsCout Therefore, the inductor must have a maximum current exceeding 405 mA. Since the compensation is fixed internally in the IC, the input and output capacitors as well as the inductor have a predetermined value too: Cin = 10 F and Cout = 22 F. Low ESR capacitors are needed for best performance. Therefore, ceramic capacitors are recommended. (eq. 3) The RMS output capacitor current is given by: IRMS(Cout) VO (1 D) 2 3 L fs (eq. 4) http://onsemi.com 12 NCP1511 PCB Layout Recommendations for best performance. All connecting traces must be short, direct, and wide to reduce voltage errors caused by resistive losses through the traces. 3. Separate the feedback path of the output voltage from the power path. Keep this path close to the NCP1511 circuit. And also route it away from noisy components. This will prevent noise from coupling into the voltage feedback trace. 4. Place the DC−DC converter away from noise sensitive circuitry, such as RF circuits. The following shows the NCP1511 demo board layout and bill of materials: Good PCB layout plays an important role in switching mode power conversion. Careful PCB layout can help to minimize ground bounce, EMI noise and unwanted feedback that can affect the performance of the converter. Hints suggested below can be used as a guideline in most situations. 1. Use star−ground connection to connect the IC ground nodes and capacitor GND nodes together at one point. Keep them as close as possible. And then connect this to the ground plane through several vias. This will reduce noise in the ground plane by preventing the switching currents from flowing through the ground plane. 2. Place the power components (i.e., input capacitor, inductor and output capacitor) as close together as possible Figure 27. Top and Silkscreen Layer Figure 28. Soldermask Top and Silkscreen Layer http://onsemi.com 13 NCP1511 Figure 29. Bottom Layer Table 3. Bill of Materials Component Value Manufacturer Part Number Size (mm) Iout (mA) ESR (m) Cin 10 F, X5R, 6.3 V TDK Murata C2012X5R0J106 GRM21BR60J106 2.0 x 1.25 x 1.25 − − Cout 22 F, X5R, 6.3 V TDK Murata C2012X5R0J226 GRM21BR60J226 2.0 x 1.25 x 1.25 − − L 6.8 H TDK Coilcraft Coilcraft Sumida VLCF4020−6R8 0805PS−682 LPO4812 CLS4D11 4.0 x 4.0 x 2.0 3.4 x 3.0 x 1.8 4.8 x 4.8 x 1.2 4.9 x 4.9 x 1.2 500** 210* 340* 500** 146 1260 225 220 *Output current calculated from VCC = 4.2 Vmax, 1.5 Vout and Freq = 700 kHz (1.0 MHz − 20 %). **Calculated output current from VCC = 4.2 Vmax and Freq = 700 kHz exceeds 640 mA (Ilim − 20%). Therefore maximum output for these conditions shown as 500 mA. http://onsemi.com 14 NCP1511 PACKAGE DIMENSIONS 9 PIN MICRO BUMP FC SUFFIX CASE 499AC−01 ISSUE B −A− 4X 0.10 C NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETERS. 3. COPLANARITY APPLIES TO SPHERICAL CROWNS OF SOLDER BALLS. D −B− E D1 e TOP VIEW C A 0.10 C B e 0.05 C 9X −C− SEATING PLANE E1 A b 1 2 DIM A A1 A2 D E b e D1 E1 3 0.05 C A B A2 A1 SIDE VIEW 0.03 C BOTTOM VIEW SOLDERING FOOTPRINT* 0.50 0.0197 0.50 0.0197 0.265 0.01 SCALE 20:1 mm inches *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. http://onsemi.com 15 MILLIMETERS MIN MAX 0.540 0.660 0.210 0.270 0.330 0.390 1.550 BSC 1.550 BSC 0.290 0.340 0.500 BSC 1.000 BSC 1.000 BSC NCP1511 ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. 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