NCP1550 600 kHz PWM/PFM Step−Down DC−DC Controller The NCP1550 is a monolithic micropower high frequency voltage mode step−down controller IC, specially designed for battery operated hand−held electronic products. With appropriate external P−type MOSFET, the device can provide up to 2.0 A loading current with high conversion efficiency. The device operates in Constant−Frequency PWM mode at normal operation, that ensures low output ripple noise, and which will automatically switch to PFM mode at low output loads for higher efficiency. Additionally, value−added features of Chip Enable to reduce IC Off−State current and integrated feedback resistor network, make it the best choice for portable applications. The device is designed to operate for voltage regulation with minimum external components and board space. This device is available in a TSOP−5 package with six standard output voltage options. http://onsemi.com 1 TSOP−5 SN SUFFIX CASE 483 Features • High Efficiency 92%, Typical • Low Quiescent Bias Current of 50 mA • • • • • • • • • • • • • MARKING DIAGRAM (Typical at PFM Mode with No Load) Output Voltage Options from 1.8 V to 3.3 V with High Accuracy $2.0% Low Output Voltage Ripple, 50 mV, Typical PWM Switching Frequency at 600 kHz Automatic PWM/PFM Switchover at Light Load Condition Very Low Dropout Operation, 100% Max. Duty Cycle Chip Enable Pin with On−Chip 150 nA Pullup Current Source Low Shutdown Current, 0.3 mA, Typical Input Voltage Range from 2.45 V to 5.5 V Built−in Soft−Start Internal Undervoltage Lockout (UVLO) Protection Low Profile and Minimum External Components Micro Miniature TSOP−5 Package Pb−Free Packages are Available Typical Applications • • • • • • Personal Digital Assistant (PDA) Camcorders and Digital Still Camera Hand−Held Instrument Distributed Power System Computer Peripheral Conversion from Four NiMH or NiCd or One Lithium−ion Cells to 3.3 V/1.8 V 5 xxx AYW G G 1 xxx = Specific Device Code A = Assembly Location Y = Year W = Work Week G = Pb−Free Package (Note: Microdot may be in either location) PIN CONNECTIONS CE 1 GND 2 VOUT 3 5 VIN 4 EXT (Top View) ORDERING INFORMATION See detailed ordering and shipping information in the package dimensions section on page 16 of this data sheet. © Semiconductor Components Industries, LLC, 2006 July, 2006 − Rev. 8 1 Publication Order Number: NCP1550/D NCP1550 + CP1 2.2 V PWM Controller VOUT 5 VIN 4 EXT 1 CE + − 600 kHz Oscillator TON t TON(PFM) 3 UVLO − A1 − + Driver Voltage Reference and Soft−Start GND 2 M1 Figure 1. Simplified Block Diagram PIN FUNCTION DESCRIPTIONS Pin Symbol Description 1 CE 2 GND Ground Connection 3 VOUT Output voltage monitoring input. This pin must be connected to the regulated output node as a feedback to on−chip control circuitry. VOUT is internally connected to the on−chip voltage divider that determines the output voltage level. 4 EXT Gate drive for external P−MOSFET 5 VIN Power supply input Chip Enable pin, active high (internal pullup current source). By connecting this pin to GND, the switching operation of the controller will be stopped. MAXIMUM RATINGS (TA = 25°C unless otherwise noted) Rating Symbol Value Unit VIN −0.3 to 6.0 V VCE VOUT VEXT −0.3 to 6.0 −0.3 to 6.0 −0.3 to 6.0 RqJA 250 °C/W Operating Junction Temperature Range TJ −40 to +150 °C Operating Ambient Temperature Range TA −40 to +85 °C Storage Temperature Range Tstg −55 to +150 °C Device Power Supply, VIN (Pin 5) Input/Output Pins CE (Pin 1) VOUT (Pin 3) EXT (Pin 4) V Thermal Characteristics TSOP−5 Plastic Package, Case 483−01 Thermal Resistance, Junction−to−Air Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. NOTE: ESD data available upon request. 1. This device series contains ESD protection and exceeds the following tests: Human Body Model (HBM) $2.0 kV per JEDEC standard: JESD22−A114. Machine Model (MM) $200V per JEDEC standard: JESD22−A115. 2. Latchup Current Maximum Rating: 150 mA per JEDEC standard: JESD78. 3. Moisture Sensitivity Level (MSL): 1 per IPC/JEDEC standard: J−STD−020A. http://onsemi.com 2 NCP1550 ELECTRICAL CHARACTERISTICS (VIN = 5.0 V, TA = 25°C for typical value, −40°C v TA v 85°C for min/max values unless otherwise noted.) Characteristic Symbol Min Typ Max Unit VIN 2.45 − 5.50 V 1.764 1.862 2.450 2.646 2.940 3.234 1.8 1.9 2.5 2.7 3.0 3.3 1.836 1.938 2.550 2.754 3.060 3.366 − − − − − − 2.5 2.5 2.5 2.5 2.5 2.5 4.0 4.0 4.0 4.0 4.0 4.0 − 100 − − − − − − − 50 50 50 50 50 50 80 80 80 80 80 80 − − − − − − 0.3 0.3 0.3 0.3 0.3 0.3 0.5 0.5 0.5 0.5 0.5 0.5 TOTAL DEVICE Input Voltage Output Voltage (ILOAD = 0 mA, TA = 25°C) NCP1550SN18T1 NCP1550SN19T1 NCP1550SN25T1 NCP1550SN27T1 NCP1550SN30T1 NCP1550SN33T1 VOUT Input Current into VOUT Pin NCP1550SN18T1 NCP1550SN19T1 NCP1550SN25T1 NCP1550SN27T1 NCP1550SN30T1 NCP1550SN33T1 IVOUT DVOUT/DVT Temperature Coefficient Operating Current (VIN = 5.0 V, VCE = 5.0 V, No External Components) NCP1550SN18T1 NCP1550SN19T1 NCP1550SN25T1 NCP1550SN27T1 NCP1550SN30T1 NCP1550SN33T1 IDD Off−State Current (VIN = 5.0 V, VCE = 0 V, TA = 25°C) NCP1550SN18T1 NCP1550SN19T1 NCP1550SN25T1 NCP1550SN27T1 NCP1550SN30T1 NCP1550SN33T1 IOFF V mA ppm/°C mA mA OSCILLATOR FOSC 510 600 690 kHz DFOSC/DTA − 0.11 − %/°C DMAX 100 − − % TON(PFM) 167 320 500 ns Tss − 8.0 − ms Tprot − 8.0 − ms EXT “H” Output Current (VEXT = VIN – 0.4 V) IEXTH − −60 − mA EXT “L” Output Current (VEXT = 0.4 V) IEXTL − 100 − mA EXT “L−H” Rise Time (CLOAD = 1000 pF) (VIN = 5.0 V) Tr − 65 − ns EXT “H−L” Fall Time (CLOAD = 1000 pF) (VIN = 5.0 V) Tf − 40 − ns EXT “L−H” Rise Time (CLOAD = 5.0 nF) (VIN = 5.0 V) Tr − 140 − ns EXT “H−L” Fall Time (CLOAD = 5.0 nF) (VIN = 5.0 V) Tf − 90 − ns Frequency Frequency Temperature Coefficient (TA = −40°C to 85°C) Maximum Duty Cycle PWM/PFM Switchover ON Time Threshold (Note 4) Soft−Start Delay Time (Note 4) Protection Delay Time (Auto Restart) OUTPUT DRIVE (PIN 4) 4. PWM/PFM Switchover ON Time Threshold min/max guaranteed by design only. http://onsemi.com 3 NCP1550 ELECTRICAL CHARACTERISTICS (continued) (VIN = 5.0 V, TA = 25°C for typical value, −40°C v TA v 85°C for min/max values unless otherwise noted.) Symbol Min Typ Max Unit CE “H” Input Voltage VCEH 1.3 − − V CE “L” Input Voltage VCEL − − 0.3 V CE “H” Input Current (VIN = VCE = 5.0 V) ICEH −0.5 0 0.5 mA CE “L” Input Current (VIN = 5.0, VCE = 0 V) ICEL −0.5 0.15 0.5 mA Undervoltage Lockout Threshold VUVLO 1.60 2.20 2.40 V Undervoltage Lockout Hysteresis VUVLO_HYS − 50 − mV Characteristic CE (PIN 1) Undervoltage Lockout L M VIN VOUT 4 EXT 3 CE 2 VIN 5 CIN 1 SD VOUT COUT CE GND GND GND Figure 2. Typical Application Diagram http://onsemi.com 4 NCP1550 TYPICAL OPERATING CHARACTERISTICS 100 100 VIN = 3.0 V VIN = 4.0 V EFFICIENCY (%) 80 5.0 V 60 NCP1550SN33T1 L = 3.3 mH CIN = 33 mF COUT = 33 mF M = NTGS3441T1 SD = MBRM120LT3 40 20 4.0 V 5.0 V 60 NCP1550SN25T1 L = 5.6 mH CIN = 33 mF COUT = 33 mF M = NTGS3441T1 SD = MBRM120LT3 40 20 0 0 1 10 100 1000 1 10 ILOAD, OUTPUT LOADING CURRENT (mA) Figure 4. Efficiency versus Load Current 100 4.0 V VIN = 3.0 V 80 5.0 V 60 NCP1550SN18T1 L = 6.8 mH CIN = 33 mF COUT = 33 mF M = NTGS3441T1 SD = MBRM120LT3 40 20 0 1 100 ILOAD, OUTPUT LOADING CURRENT (mA) Figure 3. Efficiency versus Load Current EFFICIENCY (%) EFFICIENCY (%) 80 10 100 ILOAD, OUTPUT LOADING CURRENT (mA) Figure 5. Efficiency versus Load Current http://onsemi.com 5 1000 1000 NCP1550 100 VIN = 5.0 V CIN = 33 mF COUT = 33 mF M = NTGS3441T1 SD = MBRM120LT3 0.6 0.3 1.9 V 1.8 V 2.5 V 0 −0.3 2.7 V 3.0 V 3.3 V −0.6 NCP1550 CIN = 33 mF COUT = 33 mF IOUT = 500 mA SD = MBRM120LT3 80 3.3 V 3.0 V 60 2.7 V 40 20 2.5 V 1.8 V 1.9 V 0 −0.9 10 100 1000 2.5 3 3.5 4 4.5 5 ILOAD, OUTPUT LOADING CURRENT (mA) VIN, BATTERY INPUT VOLTAGE (V) Figure 7. Output Ripple Voltage versus Input Voltage 100 80 1.9 V 2.5 V 1.8 V 60 40 3.3 V 3.0 V 2.7 V NCP1550 CIN = 33 mF COUT = 33 mF CE = VIN SD = MBRM120LT3 20 0 2 2 Figure 6. Output Voltage Change versus Load Current 2.5 3 3.5 4 4.5 5 5.5 0.6 1.8 V 0.3 NCP1550 VIN = 5.0 V CIN = 33 mF COUT = 33 mF IOUT = 500 mA SD = MBRM120LT3 −0.3 −0.6 2 3.3 V 2.5 3 3.5 4 4.5 5 VIN, INPUT VOLTAGE (V) Figure 9. Output Voltage Change versus Input Voltage 3.3 V NCP1550 VIN = 5.0 V CIN = 33 mF COUT = 33 mF IOUT = 500 mA SD = MBRM120LT3 3.0 V 2.7 V 45 30 1.9 V 15 1.8 V 2.5 V 0 1 3.0 V 2.7 V −0.9 90 60 1.9 V 2.5 V 0 Figure 8. No Load Operating Current versus Input Voltage 75 10 100 ILOAD, OUTPUT CURRENT (mA) Figure 10. Output Ripple Voltage versus Output Current http://onsemi.com 6 5.5 0.9 VIN, INPUT VOLTAGE (V) VRIPPLE, RIPPLE VOLTAGE (mVp−p) IBATT, NO LOAD OPERATING CURRENT (mA) VRIPPLE, RIPPLE VOLTAGE (mVp−p) 0.9 DVOUT, OUTPUT VOLTAGE CHANGE (mV) DVOUT, OUTPUT VOLTAGE CHANGE (%) TYPICAL OPERATING CHARACTERISTICS 1000 5.5 NCP1550 (VIN = 5.0 V, ILOAD = 500 mA, L = 3.3 mH, COUT = 100 mF) (VIN = 5.0 V, ILOAD = 100 mA, L = 3.3 mH, COUT = 100 mF) Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Figure 11. Continuous Conduction Mode PWM Switching Waveform for VOUT = 3.3 V Figure 12. Discontinuous Conduction Mode PWM Switching Waveform for VOUT = 3.3 V (VIN = 5.0 V, ILOAD = 10 mA, L = 3.3 mH, COUT = 100 mF) (VIN = 5.0 V, ILOAD = 500 mA, L = 5.6 mH, COUT = 33 mF) Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Figure 14. Continuous Conduction Mode PWM Switching Waveform for VOUT = 2.5 V Figure 13. Discontinuous Conduction Mode PFM Switching Waveform for VOUT = 3.3 V http://onsemi.com 7 NCP1550 (VIN = 5.0 V, ILOAD = 100 mA, L = 5.6 mH, COUT = 33 mF) (VIN = 5.0 V, ILOAD = 30 mA, L = 5.6 mH, COUT = 33 mF) Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Figure 15. Discontinuous Conduction Mode PWM Switching Waveform for VOUT = 2.5 V Figure 16. Discontinuous Conduction Mode PFM Switching Waveform for VOUT = 2.5 V (VIN = 5.0 V, ILOAD = 500 mA, L = 6.8 mH, COUT = 33 mF) (VIN = 5.0 V, ILOAD = 60 mA, L = 6.8 mH, COUT = 33 mF) Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Figure 17. Continuous Conduction Mode PWM Switching Waveform for VOUT = 1.8 V Figure 18. Discontinuous Conduction Mode PWM Switching Waveform for VOUT = 1.8 V http://onsemi.com 8 NCP1550 (VIN = 5.0 V, ILOAD = 30 mA, L = 6.8 mH, COUT = 33 mF) Upper Trace: Output Voltage Ripple, 50 mV/Division Middle Trace: Inductor Current, IL, 500 mA/Division Lower Trace: Voltage at Cathode of Schottky Diode, 2.0 V/Division Upper Trace: Input Voltage, 2.0 V/Division Lower Trace: Output Voltage, 2.0 V/Division Figure 19. Discontinuous Conduction Mode PFM Switching Waveform for VOUT = 1.8 V Figure 20. Startup Transient Response for VOUT = 3.3 V Upper Trace: Input Voltage, 2.0 V/Division Lower Trace: Output Voltage, 1.0 V/Division Upper Trace: Output Voltage Waveform, 2.0 V/Division Lower Trace: Chip Enable/Disable Pin Waveform, 0.5 V/Division Figure 21. Startup Transient Response for VOUT = 1.8 V Figure 22. Chip Enable/Disable Output Voltage Waveform http://onsemi.com 9 NCP1550 (VIN = 4.0 to 5.0 V, L = 3.3 mH, COUT = 33 mF, ILOAD = 1.0 A) Upper Trace: Output Voltage Ripple, 100 mV/Division Lower Trace: Input Voltage, 2.0 V/Division (VIN = 3.0 to 5.0 V, L = 5.6 mH, COUT = 33 mF, ILOAD = 1.0 A) Upper Trace: Output Voltage Ripple, 100 mV/Division Lower Trace: Input Voltage, 2.0 V/Division Figure 23. Line Transient Response for VOUT = 3.3 V Figure 24. Line Transient Response for VOUT = 2.5 V (VIN = 3.0 to 5.0 V, L = 6.8 mH, COUT = 33 mF, ILOAD = 1.0 A) (VIN = 5.0 V, ILOAD = 100 mA to 1.0 A, L = 3.3 mH, COUT = 33 mF) Upper Trace: Output Voltage Ripple, 200 mV/Division Lower Trace: Load Current, ILOAD, 500 mA/Division Upper Trace: Output Voltage Ripple, 100 mV/Division Lower Trace: Input Voltage, VIN, 2.0 V/Division Figure 25. Line Transient Response for VOUT = 1.8 V Figure 26. Load Transient Response for VOUT = 3.3 V http://onsemi.com 10 NCP1550 (VIN = 5.0 V, ILOAD = 100 mA to 1.0 A, L = 5.6 mH, COUT = 33 mF) (VIN = 5.0 V, ILOAD = 100 mA to 1.0 A, L = 6.8 mH, COUT = 33 mF) Upper Trace: Output Voltage Ripple, 100 mV/Division Lower Trace: Load Current, ILOAD, 500 mA/Division Upper Trace: Output Voltage Ripple, 100 mV/Division Lower Trace: Load Current, ILOAD, 500 mA/Division Figure 27. Load Transient Response for VOUT = 2.5 V Figure 28. Load Transient Response for VOUT = 1.8 V 1.6 3.3 V 1.2 2.5 V 0.8 1.8 V 0.4 0 −50 FOSC, OSCILLATOR FREQUENCY (kHz) IDD, OPERATING CURRENT (mA) 70 −25 0 25 50 75 60 50 2.5 V 3.3 V 1.8 V 40 VIN = 5.0 V VCE = 5.0 V 30 20 −50 100 −25 0 25 50 75 100 TA, AMBIENT TEMPERATURE (°C) TA, AMBIENT TEMPERATURE (°C) Figure 29. Off−Stage Current versus Ambient Temperature Figure 30. Operating Current versus Ambient Temperature 700 450 2.5 V 650 1.8 V 600 3.3 V 550 500 VIN = 5.0 V 450 −50 −25 0 25 50 75 TA, AMBIENT TEMPERATURE (°C) TON(PFM), PWM/PFM SWITCH ON TIME THRESHOLD (ns) IOFF, OFF−STATE CURRENT (mA) 2.0 400 350 2.5 V 300 1.8 V 250 VIN = 5.0 V 200 −50 100 Figure 31. Oscillator Frequency versus Ambient Temperature 3.3 V −25 0 25 50 75 TA, AMBIENT TEMPERATURE (°C) 100 Figure 32. PWM/PFM Switch ON Time Threshold versus Ambient Temperature http://onsemi.com 11 NCP1550 2.55 VOUT, OUTPUT VOLTAGE (V) VOUT, OUTPUT VOLTAGE (V) 3.35 3.33 3.31 3.29 VIN = 5.0 V 3.27 3.25 −50 −25 0 25 50 75 2.53 2.51 2.49 VIN = 5.0 V 2.47 2.45 −50 100 TA, AMBIENT TEMPERATURE (°C) IEXTH, EXT “H” OUTPUT CURRENT (mA) VOUT, OUTPUT VOLTAGE (V) 1.83 1.81 1.79 VIN = 5.0 V 1.77 0 25 50 75 100 3.3 V −60 2.5 V −70 −80 VEXT = VIN − 0.4 V VIN = 5.0 V −90 −100 −50 2.5 V 3.3 V 1.8 V VEXT = 0.4 V VIN = 5.0 V −25 0 25 50 −25 0 25 50 75 100 75 Figure 36. NCP1550 EXT “H” Output Current versus Ambient Temperature IVOUT, INPUT CURRENT INTO VOUT PIN (mA) IEXTH, EXT “L” OUTPUT CURRENT (mA) 170 50 −50 100 TA, AMBIENT TEMPERATURE (°C) 200 80 75 1.8 V −50 TA, AMBIENT TEMPERATURE (°C) 110 50 −40 Figure 35. NCP1550SN18T1 Output Voltage versus Ambient Temperature 140 25 Figure 34. NCP1550SN25T1 Output Voltage versus Ambient Temperature 1.85 −25 0 TA, AMBIENT TEMPERATURE (°C) Figure 33. NCP1550SN33T1 Output Voltage versus Ambient Temperature 1.75 −50 −25 100 3.5 VIN = 5.0 V 3.0 2.5 V 2.5 1.8 V 2.0 3.3 V 1.5 −50 −25 0 25 50 75 TA, AMBIENT TEMPERATURE (°C) TA, AMBIENT TEMPERATURE (°C) Figure 37. NCP1550 EXT “L” Output Current versus Ambient Temperature Figure 38. NCP1550 Input Current into VOUT Pin versus Ambient Temperature http://onsemi.com 12 100 NCP1550 DETAILED OPERATING DESCRIPTION Detailed Operating Description voltage at its output. This error voltage is compared with the ramp function to generate the control pulse to drive the external power switch. On a cycle−by−cycle basis, the greater the error voltage, the longer the switch is held on. Hence, corresponding corrective action will be made to keep the output voltage within regulation. Constant−Frequency PWM reduces output voltage ripple and noise, which is one of the important characteristics for noise sensitive communication applications. The high switching frequency allows small size surface mount components to improve layout compactness and reduce PC board area, and eliminate audio and emission interference. The NCP1550 series are step−down (Buck) DC−DC controllers designed primarily for use in portable applications powered by battery cells. With an appropriate external P−channel MOSFET connected, the device can provide up to 2 A loading current with high conversion efficiency. The NCP1550 series using an unique control scheme combines the advantages of Pulse−Frequency− Modulation (PFM) that can provide excellent efficiency even at light loading conditions and Constant−Frequency Pulse−Width−Modulation that can achieve high efficiency and low output voltage ripple at heavy loads. The NCP1550 working at high switching frequency makes it possible to use small size surface mount inductor and capacitors to reduce PCB area and provide better interference handling for noise sensitive applications. The simplified functional blocks of the device are shown in Figure 1 and descriptions for each of the functions are given below. Power−Saving Pulse−Frequency−Modulation (PFM) Control Scheme While the loading is decreasing, the converter enters the Discontinuous Conduction Mode (DCM) operation, which means the inductor current will decrease to zero before the next switching cycle starts. In DCM operation, the ON time for each switching cycle will decrease significantly when the output current decreases. In order to maintain a high conversion efficiency even at light load conditions, the ON time for each switching cycle is closely monitored and for any ON time smaller than the preset value, 320 nsec, the switching pulse will be skipped. As a result, when the loading current is small, the converter will be operating in a “Constant ON time (320 nsec nominal), variable OFF time” Pulse−Frequency Modulation (PFM) mode. This innovative control scheme improves the conversion efficiency for the system at light load and standby operating conditions hence extend the operating life of the battery. The Internal Oscillator An oscillator that governs the switching of a PWM control cycles is required. NCP1550 have an internal Fixed− Frequency oscillator. The oscillator frequency is trimmed to 600 kHz with an accuracy of ±15%. All other timing signals needed for operation are derived from this oscillator signal. Voltage Reference and Soft−Start An internal high accuracy voltage reference is included in NCP1550. This reference voltage is connected to the inverting input terminal of the error amplifier, A1, which compared with portion of the output voltage, VOUT derived from an integrated voltage divider with precise trimming to give the required output voltage at ±2% accuracy. NCP1550 also comes with a built−in soft−start circuit that controls the ramping up of the internal reference voltage during the power−up of the converter. This function effectively enables the output voltage to rise gradually over the specified soft−start time, 8 msec typical. This prevents the output voltage from overshooting during startup of the converter. Low Power Shutdown Mode NCP1550 can be disabled whenever the CE pin (Pin 1) is tied to GND. In shutdown, the internal reference, oscillator, control circuitry, driver and internal feedback voltage divider are turned off and the output voltage falls to 0 V. During the shutdown mode, as most of the internal functions are stopped and current paths are cut−off, the device consume extremely small current in this condition. Voltage Mode Pulse−Width−Modulation (PWM) Control Scheme Under−Voltage Lockout (UVLO) For normal operation, NCP1550 is working in Constant−Frequency Pulse−Width−Modulation (PWM) Voltage Mode Control. The controller operates with the internal oscillator, which generates the required ramp function to compare with the output of the error amplifier, A1. The error amplifier compares the internally divided−down output voltage with the voltage reference to produce an error To prevent operation of the P−Channel MOSFET below safe input voltage levels, an Undervoltage Lockout is incorporated into the NCP1550. When the input supply voltage drops below approximately 2.2 V, the comparator, CP1 will turn−off the control circuitry and shut the converter down. http://onsemi.com 13 NCP1550 APPLICATIONS INFORMATION Inductor Value Calculation P−Channel switch duty cycle. At high input voltages, the diode conducts most of the time. In case of VIN approaches VOUT, the diode conducts only a small fraction of the cycle. While the output terminals are shorted, the diode will subject to its highest stress. Under this condition, the diode must be able to safely handle the peak current circulating in the loop. So, it is important to select a flywheel diode that can meet the diode peak current and average power dissipation requirements. Under normal conditions, the average current conducted by the flywheel diode is given by: Selecting the proper inductance is a trade−off between inductor’s physical size, transient respond and power conversion requirements. Lower value inductor saves cost, PC board space and providing faster transient response, but result in higher ripple current and core losses. Considering an application with loading current, IOUT = 0.5 A and the inductor ripple current, IL−RIPPLE(P−P) is designed to be less than 40% of the load current, i.e. 0.5 A x 40% = 0.2 A. The relationship between the inductor value and inductor ripple current is given by, T * (VIN * RDS(ON) IOUT * VOUT) L + ON IL*RIPPLE(P*P) ID + VIN * VOUT VIN ) VF (eq. 1) Input and Output Capacitor Selection (CIN and COUT) 12 In continuous mode operation, the source current of the P−Channel MOSFET is a square wave of duty cycle (VOUT + VF)/VIN. To prevent large input voltage transients, a low ESR input capacitor that can support the maximum RMS input current must be selected. The maximum RMS input current, IRMS(MAX) can be estimated by the equation in below: RDS(ON) = 0.1 W 10 L, INDUCTANCE (mH) (eq. 2) Where ID is the average diode current and VF is the forward diode voltage drop. A fast switching diode must also be used to optimize efficiency. Schottky diodes are a good choice for low forward drop and fast switching times. Where RDS(ON) is the ON resistance of the external P−channel MOSFET. Figure 39 is a plot for recommended inductance against nominal input voltage for different output options. 2.5 V 8 6 IOUT 1.9 V 1.8 V 1 4 IRMS(MAX) [ IOUT 3.3 V 2.7 V 0 2.2 2.7 3.2 3.7 4.2 4.7 (eq. 3) VIN Above estimation has a maximum value at VIN = 2VOUT, where IRMS(MAX) = IOUT/2. As a general practice, this simple worst−case condition is used for design. Selection of the output capacitor, COUT is primarily governed by the required effective series resistance (ESR) of the capacitor. Typically, once the ESR requirement is met, the capacitance will be adequate for filtering. The output voltage ripple, VRIPPLE is approximated by: 3.0 V 2 VOUT(VIN * VOUT) 2 5.2 VIN, INPUT VOLTAGE OF NCP1550 (V) Figure 39. Inductor Selection Chart P−Channel Power MOSFET Selection VRIPPLE [ IL * RIPPLE(P*P) An external P−Channel power MOSFET must be used with the NCP1550. The key selection criteria for the power MOSFET are the gate threshold, VGS, the “ON” resistance, RDS(ON) and its total gate charge, QT. For low input voltage operation, we need to select a low gate threshold device that can work down to the minimum input voltage level. RDS(ON) determines the conduction losses for each switching cycle, the lower the ON resistance, the higher the efficiency can be achieved. A power MOSFET with lower gate charge can give lower switching losses but the fast transient can cause unwanted EMI to the system. Compromise in between is required during the design stage. For 1.0 A and 2.0 A load current, NTGS3441T1 and NTGS3443T1 are tested to be appropriate for most applications. (ESR ) (eq. 4) 1 ) 4 FOSCCOUT Where FOSC is the switching frequency and ESR is the effective series resistance of the output capacitor. From equation (4), it can be noted that the output voltage ripple contributed by two parts. For most of the case, the major contributor is the capacitor ESR. Ordinary aluminum−electrolytic capacitors have high ESR and should be avoided. Higher quality Low ESR aluminum−electrolytic capacitors are acceptable and relatively inexpensive. For even better performance, Low ESR tantalum capacitors should be used. Surface−mount tantalum capacitors are better and provide neat and compact solution for space sensitive applications. Flywheel Diode Selection The flywheel diode is turned on and carries load current during the off time. The average diode current depends on the http://onsemi.com 14 NCP1550 PCB Layout Recommendations 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 feedbacks that can affect the performance of the converter. Suggested hints below can be used as a guideline in most situations. Components Placement Grounding Feedback Path Star−ground connection should be used to connect the output power return ground, the input power return ground and the device power ground together at one point. All high current running paths must be thick enough for current flowing through and producing insignificant voltage drop along the path. Feedback signal path must be separated from the main current path and sensing directly at the anode of the output capacitor. Feedback of the output voltage must be a separate trace separated from the power path. The output voltage sensing trace to the feedback (VOUT, pin 3) pin should be connected to the output voltage directly at the anode of the output capacitor. Power components, i.e. input capacitor, inductor and output capacitor, must be placed as close together as possible. All connecting traces must be short, direct and thick. High current flowing and switching paths must be kept away from the feedback (VOUT, pin 3) terminal to avoid unwanted injection of noise into the feedback path. External Component Reference Data Inductor (L) External MOSFET (M) Diode (SD) Output and Input Capacitor COUT/CIN Device VOUT Inductor Model NCP1550SN18T1 1.8 V CDD5D23 6R8 (1A) CDRH6D38 6R8 (2A) Sumida 6.8 mH NTGS3441T1 (1A) NTGS3443T1 (2A) ON Semiconductor MBRM120LT3 ON Semiconductor 33 mF/33 mF (1A) 68 mF/33 mF (2A) KEMET (T494 series) NCP1550SN19T1 1.9 V CDC5D23 6R8 (1A) CDRH6D38 6R8 (2A) Sumida 6.8 mH NTGS3441T1 (1A) NTGS3443T1 (2A) ON Semiconductor MBRM120LT3 ON Semiconductor 33 mF/33 mF (1A) 68 mF/33 mF (2A) KEMET (T494 series) NCP1550SN25T1 2.5 V CDC5D23 5R6 (1A) CDRH6D38 5R0 (2A) Sumida 5.6 mH 5.0 mH NTGS3441T1 (1A) NTGS3443T1 (2A) ON Semiconductor MBRM120LT3 ON Semiconductor 33 mF/33 mF (1A) 68 mF/33 mF (2A) KEMET (T494 series) NCP1550SN27T1 2.7 V CDC5D23 5R6 (1A) CDRH6D38 5R0 (2A) Sumida 5.6 mH 5.0 mH NTGS3441T1 (1A) NTGS3443T1 (2A) ON Semiconductor MBRM120LT3 Semiconductor 33 mF/33 mF (1A) 68 mF/33 mF (2A) KEMET (T494 series) NCP1550SN30T1 3.0 V CDC5D23 4R7 (1A) CDRH6D28 5R0 (2A) Sumida 5.6 mH 5.0 mH NTGS3441T1 (1A) NTGS3443T1 (2A) ON Semiconductor MBRM120LT3 ON Semiconductor 33 mF/33 mF (1A) 68 mF/33 mF (2A) KEMET (T494 series) NCP1550SN33T1 3.3 V CD43 3R3 (1A) CDRH6D38 3R3 (2A) Sumida 3.3 mH NTGS3441T1 (1A) NTGS3443T1 (2A) ON Semiconductor MBRM120LT3 ON Semiconductor 68 mF/33 mF (1A) 100 mF/68 mF (2A) KEMET (T494 series) http://onsemi.com 15 NCP1550 ORDERING INFORMATION Part Number Output Voltage (VOUT) Switching Frequency Device Marking Package NCP1550SN33T1 3.3 V DCD TSOP−5 NCP1550SN33T1G 3.3 V DCD TSOP−5 (Pb−Free) NCP1550SN30T1 3.0 V DBF TSOP−5 NCP1550SN30T1G 3.0 V DBF TSOP−5 (Pb−Free) NCP1550SN27T1 2.7 V DCB TSOP−5 NCP1550SN27T1G 2.7 V DCB TSOP−5 (Pb−Free) NCP1550SN25T1 2.5 V DCA TSOP−5 NCP1550SN25T1G 2.5 V DCA TSOP−5 (Pb−Free) NCP1550SN19T1 1.9 V DBE TSOP−5 NCP1550SN19T1G 1.9 V DBE TSOP−5 (Pb−Free) NCP1550SN18T1 1.8 V DBZ TSOP−5 NCP1550SN18T1G 1.8 V DBZ TSOP−5 (Pb−Free) 600 kHz Shipping† 3000 Tape & Reel †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. http://onsemi.com 16 NCP1550 PACKAGE DIMENSIONS THIN SOT23−5/TSOP−5/SC59−5 SN SUFFIX CASE 483−02 ISSUE F NOTE 5 2X 0.10 T 2X 0.20 T NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M, 1994. 2. CONTROLLING DIMENSION: MILLIMETERS. 3. MAXIMUM LEAD THICKNESS INCLUDES LEAD FINISH THICKNESS. MINIMUM LEAD THICKNESS IS THE MINIMUM THICKNESS OF BASE MATERIAL. 4. DIMENSIONS A AND B DO NOT INCLUDE MOLD FLASH, PROTRUSIONS, OR GATE BURRS. 5. OPTIONAL CONSTRUCTION: AN ADDITIONAL TRIMMED LEAD IS ALLOWED IN THIS LOCATION. TRIMMED LEAD NOT TO EXTEND MORE THAN 0.2 FROM BODY. D 5X 0.20 C A B 5 1 4 2 3 M B S K L DETAIL Z G A DIM A B C D G H J K L M S DETAIL Z J C 0.05 SEATING PLANE H T MILLIMETERS MIN MAX 3.00 BSC 1.50 BSC 0.90 1.10 0.25 0.50 0.95 BSC 0.01 0.10 0.10 0.26 0.20 0.60 1.25 1.55 0_ 10 _ 2.50 3.00 SOLDERING FOOTPRINT* 0.95 0.037 1.9 0.074 2.4 0.094 1.0 0.039 0.7 0.028 SCALE 10:1 mm Ǔ ǒinches *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. 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. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. 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