NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET DESCRIPTION 2A Synchronous Step-down Regulator Operational Input Supply Voltage Range: 4.5V-18V Integrated Upper NMOS and Lower NMOS 340kHz Switching Frequency Input UVLO Enable Programmable External SoftStart Cycle-By-Cycle Over-Current Protection Over Voltage Protection Frequency Fold Back Under Short Condition The controller is equipped with output over-voltage protection which protects the IC under a open load condition. Additional safety features include under voltage lock-out (UVLO), programmable soft-start and over-temperature protection (OTP) to protect the circuit. This IC is available in SOIC-8 package. W W W. Microsemi .CO M NX7101 is a 340kHz fixed frequency, current mode, PWM synchronous buck (step-down) DCDC converter, capable of driving a 2A load with high efficiency, excellent line and load regulation. The device integrates N-channel power MOSFET switches with low on-resistance. Current mode control provides fast transient response and cycle-by-cycle current limit. KEY FEATURES APPLICATIONS Set-Top Box LCD TV's Notebook/Netbook PoE Powered Devices PRODUCT HIGHLIGHT 12V IN(2) VIN CIN 2*10uF(25V,X5R) C4 0.1u BST(1) L1 10uH 3.3V SW(3) SS(8) R4 100k C5 10nF NX7101 R1 26.1k EN(7) GND(4) FB(5) COMP(6) OUT COUT 2*22uF(6.3V,X5R) R2 10k R3 10k C3 3.9nF NX7101 Figure 1 - NX7101 typical application PACKAGE ORDER INFO TA (C) DM Plastic SOIC 8 Pin RoHS Compliant / Pb-free -40 to 85 NX7101IDM Note: Available in Tape & Reel. Append the letters "TR" to the part number. (i.e. NX7101IDM-TR) Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 1 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET ABSOLUTE MAXIMUM RATINGS PACKAGE PIN OUT 1 VIN 2 SW 3 GND 4 W W W. Microsemi .CO M BST MSC 7101IDM XXXX Supply Input Voltage (VIN) ........................................................................... -0.3V to 20V Switch Voltage (SW) ..................................................................................................... 21V EN .................................................................................................................. -0.3V to VIN BST ................................................................................................... -0.3V to (VSW + 6V) COMP, FB, SS ................................................................................................. -0.3V to 6V Maximum Operating Junction Temperature .............................................................. 150C Storage Temperature Range ......................................................................... -65C to 150C Package Peak Temp. for Solder Reflow (40 seconds maximum exposure) ............... 260C 8 SS 7 EN 6 COMP 5 FB DM PACKAGE Note: Exceeding these ratings could cause damage to the device. All voltages are with respect Ground. Currents are positive into, negative out of specified terminal. (Top View) to DM PART MARKING "xxxx" Denote Date Code and Lot Identification RoHS / Pb-free 100% Matte Tin Pin Finish MSL3 THERMAL DATA DM Plastic SOIC 8-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA 105C/W Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. FUNCTIONAL PIN DESCRIPTION Description Pin Name 1 BST Bootstrap pin. A minimum 10nF bootstrap capacitor is connected between the BS pin and SW pin. The voltage across the bootstrap capacitor drives the internal high side NMOS. 2 VIN Supply input pin. A capacitor should be connected between the IN pin and GND pin to keep the input voltage constant. 3 SW Power switch output pin. This pin is connected to the inductor and bootstrap capacitor. 4 GND Ground. Feedback pin. This pin is connected to an external resistor divider to program the system output voltage. When the FB pin voltage exceeds 20% of the nominal regulation value of 0.925V, the over voltage protection is triggered. When the FB pin voltage is below 0.3V, the oscillator frequency is lowered to realize short circuit protection. FB 6 COMP Compensation pin. This pin is the output of the transconductance error amplifier and the input to the current comparator. It is used to compensate the control loop. Connect a series RC network from this pin to GND. In some cases, an additional capacitor from this pin to GND pin is required. 7 EN Control input pin. Forcing this pin above 2V enables the IC. Forcing this pin below 0.75V shuts down the IC. When the IC is in shutdown mode, all functions are disabled to decrease the supply current below 1A. 8 SS Soft-start control input pin. SS controls the soft start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1F capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS unconnected. Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 2 NX7101 5 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET RECOMMENDED OPERATING CONDITIONS Symbol Input Operating Voltage Maximum Output Current Operating Ambient Temperature NX7101 Typ Min VIN 4. 5 IOUTMAX 2 TA -40 Max 18 Units V A 85 ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply for VIN = VEN =12V, VOUT = 3.3V, TA = 25C. NX7101 Parameter Symbol Test Conditions Min Typ Max Operating Current Quiescent Current IQ VFB = 1V, VEN = 3V 0.86 1.25 1.4 Shutdown Current ISHDN VEN = 0V 0.1 10 UVLO VIN UVLO Threshold VUVLO VIN Rising 3.65 4.0 4.25 Hysteresis VHYS 0.2 Feedback Feedback Voltage VFB TA = -40C to 85C 0.907 0.925 0.943 Feedback Bias Current IFB VFB = 1V -0.1 0.1 Oscillator Internal Oscillator Frequency FOSC1 280 340 400 Short Circuit Oscillator Frequency FOSC2 100 90 C Units mA A V V V A kHz kHz Maximum Duty Cycle DMAX VFB = 0.85V Minimum Duty Cycle Error Amplifier DMIN VFB = 1V Error Amplifier Transconductance GEA 800 A/V AEA 400 V/V GCS 3.5 A/V 6 15 A ms (1) % 0 % RDSONH ISW = 0.2A/ 0.7A 85 115 145 m Low-side Switch On Resistance RDSONL ISW = -0.2A/ -0.7A 75 105 135 m High-side Switch Leakage Current ILEAKH VIN = 18V, VEN = 0V, VSW = 0V 0.1 10 uA High-side Switch Current Limit ILIMH Low-side Switch Current Limit EN EN Shutdown Threshold Voltage EN Shutdown Threshold Voltage (1) Hysteresis EN Lockout Threshold Voltage EN Lockout Hysteresis ILIML Copyright 2010 Rev. 1.7, 2014-06-24 VSS = 0V CSS = 0.1F 2.7 From Drain to Source VEN 1.1 VENH 3.5 A 1.4 A 1.5 2 350 2.2 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 2.5 210 NX7101 Voltage Gain Current Sensing Gain Current Sensing Gain Soft-Start Soft-start Current (1) Soft-start Time Output Stage High-side Switch On Resistance TSS W W W. Microsemi .CO M Parameter V mV 2.7 V mV Page 3 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET W W W. Microsemi .CO M ELECTRICAL CHARACTERISTICS (CONT) Unless otherwise specified, the following specifications apply for V IN = VEN =12V, VOUT = 5V, TA = 25C. NX7101 Parameter Symbol Test Conditions Min Typ Max Protection Over Voltage Protection Threshold VFBOV 1.1 FB Short Circuit Protection 0.23 0.3 0.41 Thermal Shutdown Threshold TOTSD 160 Thermal Shutdown Hysteresis THYS 30 Units V V C C Notes: 1) Guaranteed by design, not tested. SIMPLIFIED BLOCK DIAGRAM 1.5V SD EN Osc 340k/90k 0.925V Slope Compensation Bias Regulator VIN Current Sensing VCC Thermal SD UVLOshutdown BST UVLO SS Soft Start Driver PWM LOGIC SW FB COMP 2.5V 1.1V EN Low Side Current Limit 0.3V GND FB UVLO NX7101 Figure 2 - Simplified Block Diagram Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 4 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET APPLICATION CIRCUIT IN(2) CIN 10uF/25V C4 0.1u BST(1) NX7101 L1 22uH OUT SW(3) SS(8) R4 100k C5 10nF R1 41.2k EN(7) FB(5) COMP(6) GND(4) W W W. Microsemi .CO M VIN COUT 1000uF,170mohm R2 9.3k C6 330pF Figure 3 - 12V Input, 5V Output with Electrolytic Cap VIN IN(2) CIN 10uF/25V C4 0.1u BST(1) NX7101 L1 15uH OUT SW(3) SS(8) R4 100k C5 10nF R1 41.2k EN(7) FB(5) COMP(6) GND(4) COUT 2*22uF(10V,X5R) R2 9.3k R3 18k NX7101 C3 3.9nF Figure 4 - 12V Input, 5V Output with Ceramic Cap Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 5 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET Figure 5. DC Operation at 2A Figure 6. Transient Response Figure 7. Input power recycling Figure 8. Output short operation W W W. Microsemi .CO M TYPICAL WAVEFORMS @ 25C (REFER TO FIGURE 1) NX7101 Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 6 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET TYPICAL WAVEFORMS @ 25C (REFER TO FIGURE 3) W W W. Microsemi .CO M 94.00% 92.00% Efficiency(%) 90.00% 88.00% 86.00% 84.00% 82.00% 0 500 1000 1500 2000 2500 IOUT(mA) Figure 9. EN and soft start Figure 10. Efficiency vs. IOUT(VIN=12V,VOUT=5V) NX7101 Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 7 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET THEORY OF OPERATION The NX7101 is a current-mode, PWM synchronous stepdown DC-DC converter with 340kHz fixed working frequency. It can convert input voltages from 4.75V to 18V down to an output voltage as low as 0.925V, and supply up to 2A load current. The NX7101 has two internal N-MOSFETs to step down the voltage. The inductor current is determined by sensing the internal high-side MOSFET current. The output of current sense amplifier is summed with the slope compensation signal to avoid subharmonic oscillation at duty cycles greater than 50%. The combined signal is then compared with the error amplifier output to generate the PWM signal. Current mode control provides not only fast control loop response but also cycle-by-cycle current limit protection. When load current reaches its maximum output level when the inductor peak current triggers the high-side NMOFET current limit. If FB pin voltage drops below 0.3V, the working frequency will be fold back to protect chip from run-away. W W W. Microsemi .CO M DETAIL DESCRIPTION When FB pin voltage exceeds 1.1V, the over voltage protection is triggered. The high side MOSFET is turned off. Once the OVP condition is gone, the chip will resume the operation following soft-start. NX7101 Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 8 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET APPLICATION INFORMATION VIN VOUT IOUT VRIPPLE FS IRIPPLE - Input voltage - Output voltage - Output current - Output voltage ripple - Working frequency - Inductor current ripple DESIGN EXAMPLE The following is typical application for NX7101, the schematic is figure 1. VIN = 12V VOUT =3.3V IOUT =2A OUTPUT INDUCTOR SELECTION The selection of inductor value is based on inductor ripple current, power rating, working frequency and efficiency. A larger inductor value normally means smaller ripple current. However if the inductance is chosen too large, it results in slow response and lower efficiency. Usually the ripple current ranges from 20% to 40% of the output current. This is a design freedom which can be determined by the design engineer according to various application requirements. The inductor value can be calculated by using the following equations: V -V V 1 LOUT IN OUT OUT IRIPPLE VIN FS IRIPPLE k IOUTPUT W W W. Microsemi .CO M SYMBOL USED IN APPLICATION INFORMATION: Where ESR is the output capacitor's equivalent series resistance, COUT is the value of output capacitor. Typically when large value capacitors are selected such as Aluminum Electrolytic, POSCAP and OSCON types are used, the amount of the output voltage ripple is dominated by the first term in equation(2) and the second term can be neglected. If ceramic capacitors are chosen as output capacitors, both terms in equation (2) need to be evaluated to determine the overall ripple. Usually when this type of capacitor is selected, the amount of capacitance per single unit is not sufficient to meet the transient specification, which results in the need for parallel configuration of multiple capacitors. In this design two 22F 6.3V X5R ceramic capacitors are chosen as output capacitors. INPUT CAPACITOR SELECTION Input capacitors are usually a mix of high frequency ceramic capacitors and bulk capacitors. Ceramic capacitors bypass the high frequency noise, and bulk capacitors supply current to the MOSFETs. Usually 1uF ceramic capacitor is chosen to decouple the high frequency noise. The bulk input capacitors are determined by the voltage rating and RMS current rating. The RMS current in the input capacitors can be calculated as: IRMS IOUT D 1- D ... (3) VOUT VIN In this design two 10F 25V X5R ceramic capacitors are chosen. D VRIPPLE ESR IRIPPLE Copyright 2010 Rev. 1.7, 2014-06-24 IRIPPLE 8 FS COUT NX7101 ... (1) where k is between 0.2 to 0.4. OUTPUT VOLTAGE CALCULATION In this design, k is set at 0.35 and 10H inductor value is chosen. In order to avoid output oscillation at light load, a Output voltage is set by reference voltage and external minimum 8.2H inductor is required for all NX7101 voltage divider. The reference voltage is fixed at 0.925V. The divider consists of two ratioed resistors so that the application. output voltage applied at the FB pin is 0.925V when the OUTPUT CAPACITOR SELECTION output voltage is at the desired value. The following Output capacitor is basically decided by the amount of the equation and picture show the relationship between and output voltage ripple allowed during steady state (DC) load voltage divider. condition as well as specification for the load transient. The optimum design may require a couple of iterations to satisfy both conditions. The amount of voltage ripple during the DC load condition is determined by equation (2). ... (2) Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 9 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET APPLICATION INFORMATION R1 ) R2 ... (4) Vout In this design R1 is 26.1k, R2 is 10k. W W W. Microsemi .CO M VOUT =VREF (1+ NX7101 R1 FB COMPENSATOR DESIGN The NX7101 uses peak current mode control to provide fast transient and simple compensation. The DC gain of close loop can be estimated by the equation (5). V ... (5) Gain=AEA GCS RLOAD FB VOUT COMP R2 Vref Figure 11 Voltage Divider The pole P3 set by R3 and C6 is given by the equation (10). Where AEA is error amplifier voltage gain 560V/V, GCS is current sensing gain 3.5A/V, RLOAD is the load resistor. 1 ... (10) The system itself has one pole P1, one zero Z1 and double pole FP3 = 2 R C 3 6 PDOUBLE at half of switching frequency FS. The system pole P1 is set by output capacitor and output load The compensation values for typical output voltage resistor. The calculation of this pole is given by the equation application are given in the table below. (6). VOUT L COUT R3 C3 C6 1 ... (6) FP1 1.8V 10H 6k 3.9nF None 22Fx2 2 RL COUT 2.5V 8k 3.9nF None 10H 22Fx2 The system zero Z1 is set by output capacitor and ESR of 3.3V 10k 3.9nF None 10H 22Fx2 output capacitor. The calculation of this zero is given by the 5V 18k 3.9nF None 15 H 22 Fx2 equation (7). 470F AL. 1 2.5V 85k 250pF 150pF 10H ... (7) FZ1= 30m ESR 2 RESR COUT 15470F AL. 5V 150k 220nF 82pF The crossover frequency is recommended to be set at 1/10th of 22H 30m ESR switching frequency. In order to achieve this desired crossover frequency and make system stable, the resistor R3 and the capacitor C3 is needed in typical applications which use ceramic capacitors as output capacitors. The pole P2 set by output resistance of error amplifier and C3 is given by the equation (8). GEA ... (8) FP2 = 2 AEA C3 Where GEA is error amplifier transconductance 800uA/V. The zero Z2 set by R3 and C3 is given by the equation (9). 1 2 R3 C3 NX7101 FZ2 = ... (9) When Aluminum Electrolytic capacitors are chosen as output capacitors, the ESR zero is much lower and extra capacitor C6 from COMP pin to ground is needed to stabilize the system. Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 10 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET PACKAGE DIMENSIONS W W W. Microsemi .CO M DM Plastic SOIC 8 Pin A P B G L M C D K J IM A B G P C D K L J F M MILLIMETERS MIN MAX 4.700 5.100 3.800 4.000 1.270 BSC 5.800 6.200 1.350 1.750 0.330 0.510 0.100 0.300 0.320 BSC 0.190 0.250 0.450 0.800 8 INCHES MIN MAX 0.185 0.201 0.150 0.157 0.050 BSC 0.228 0.244 0.053 0.069 0.013 0.020 0.004 0.012 0.013 BSC 0.007 0.010 0.017 0.031 8 F NX7101 Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 11 NX7101 2A, High Voltage Synchronous Buck Regulator P RODUCTION D ATA S HEET NOTES W W W. Microsemi .CO M NX7101 PRODUCTION DATA - Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time. Copyright 2010 Rev. 1.7, 2014-06-24 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA 92656 949-380-6100, fax 949-215-4996 Page 12