NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET DESCRIPTION 3A 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 an 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 with exposed pad package. W W W. Microsemi .COM NX7102 is a 340kHz fixed frequency, current mode, PWM synchronous buck (step-down) DCDC converter, capable of driving a 3A 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 2x10uF(25V,X5R) C4 0.1u BST(1) NX7102 L1 10uH 3.3V SW(3) SS(8) R4 100k C5 10nF R1 26.1k EN(7) FB(5) GND(4) PAD COMP(6) OUT COUT 2*22uF(10V,X5R) R2 10k R3 10k C3 5.6nF NX7102 Figure 1 - 12V Input, 3.3V Output with Ceramic Cap PACKAGE ORDER INFO TA (C) DE Plastic SOIC 8 Pin With Exposed Pad RoHS Compliant / Pb-free -40 to 85 NX7102IDE Note: Available in Tape & Reel. Append the letters "TR" to the part number. (i.e. NX7102IDE-TR) Copyright 2010 Rev.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 1 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET ABSOLUTE MAXIMUM RATINGS PACKAGE PIN OUT VIN 2 SW 3 GND 4 8 SS 7 EN 6 COMP 5 FB DE PACKAGE Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal. (Top View) DE PART MARKING "xxxx" Denote Date Code and Lot Identification RoHS / Pb-free 100% Matte Tin Pin Finish THERMAL DATA DE W W W. Microsemi .COM BST 1 MS C 7102I DE XXXX Supply Input Voltage (VIN)............................................................................ -0.3V to 20V Switch Voltage (SW) ............................................................................. -1V to (VIN + 1V) EN ................................................................................................... -0.3V to (VIN + 0.3V) 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 Plastic SOIC 8-Pin With Exposed Pad THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA 60C/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 Pin Name Description 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 VIN 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. 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 2.7V enables the IC. Forcing this pin below 1.1V 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 9ms. To disable the softstart feature, leave SS unconnected. Copyright 2010 Rev.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 2 NX7102 5 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. NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET RECOMMENDED OPERATING CONDITIONS Symbol Input Operating Voltage Maximum Output Current Operating Ambient Temperature VIN IOUTMAX TA Min 4. 5 3 -40 NX7102 Typ Max 18 85 ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply for VIN = VEN =12V, VOUT = 5V, TA = 25C. NX7102 Parameter Symbol Test Conditions Min Typ Max Operating Current Quiescent Current IQ VFB = 1V 1.25 1.4 Shutdown Current ISHDN VEN = 0V .02 1 UVLO VIN UVLO Threshold VUVLO VIN Rising 3.65 4.00 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 FOSC2 100 Frequency Maximum Duty Cycle DMAX VFB = 0.8V 90 Minimum Duty Cycle Error Amplifier Error Amplifier Transconductance (1) Voltage Gain Current Sensing Gain Current Sensing Gain Soft-Start Soft-start Current Soft-start Time Output Stage High-side Switch On Resistance Low-side Switch Current Limit VFB = 1V 0 V A C Units mA A V V V A kHz kHz % % GEA 800 A/V AEA 400 V/V GCS 5.2 A/V 6 15 A ms TSS CSS = 0.1F RDSONH 90 120 150 m RDSONL 70 100 130 m 0.1 10 A ILEAKH VIN = 18V, VEN = 0V, VSW = 0V ILIMH 4.3 5.5 6.7 A ILIML 0.85 1.45 2.05 A VENH 1.1 1.5 2 V NX7102 Low-side Switch On Resistance High-side Switch Leakage Current High-side Switch Current Limit DMIN Units EN EN shutdown Threshold EN shutdown Threshold Hysteresis Copyright 2010 Rev.1.6, 2015-02-20 VENL 350 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 W W W. Microsemi .COM Parameter mV Page 3 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET Units mV V V C C Notes: 1) Guaranteed by design, not tested. W W W. Microsemi .COM ELECTRICAL CHARACTERISTICS (CONT) Unless otherwise specified, the following specifications apply for V IN = VEN =12V, VOUT = 5V, TA = 25C. NX7102 Parameter Symbol Test Conditions Min Typ Max EN Lockout Threshold 2.2 2.5 2.7 EN Lockout Hysteresis 210 Protection Over Voltage Protection VFBOV 1.1 Threshold FB Short Circuit Protection 0.23 0.3 0.41 Thermal Shutdown Threshold TOTSD 160 Thermal Shutdown Hysteresis THYS 30 SIMPLIFIED BLOCK DIAGRAM 1.5V SD EN 0.925V slope Osc 340k/90k compensation Bias Regualtor VIN Current Sensing VCC Thermal SD UVLOshutdown BST UVLO SS Soft Start Driver PWM LOGIC SW FB COMP 2.5V 1.3V EN Low Side Current Limit NX7102 0.3V GND FB UVLO Figure 2 - Simplified Block Diagram Copyright 2010 Rev.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 4 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET IN(2) VIN CIN 2x(10uF,25V) C4 0.1u NX7102 SS(8) R4 100k BST(1) C5 10nF L1 22uH OUT SW(3) R1 42.2k EN(7) FB(5) GND(4) PAD COMP(6) W W W. Microsemi .COM APPLICATION CIRCUIT COUT 1000uF,170mohm R2 9.53k C6 2200pF Figure 3 - 12V Input, 5V Output with Electrolytic Cap NX7102 Copyright 2010 Rev.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 5 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET CIN 2*10uF(25V,X5R) C4 0.1u BST(1) NX7102 L1 10uH OUT SW(3) SS(8) R4 100k C5 10nF R1 42.2k EN(7) GND(4) PAD FB(5) COMP(6) W W W. Microsemi .COM IN(2) VIN COUT 2*22uF(10V,X5R) R2 9.53k R3 10k C3 5.6nF Figure 4 - 12V Input, 5V Output with Ceramic Cap TYPICAL WAVEFORMS @ 25C (REFER TO FIGURE 3) Copyright 2010 Rev.1.6, 2015-02-20 NX7102 Figure 5. DC Operation at 3A Figure 6. Transient Response Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 6 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET W W W. Microsemi .COM Figure 7. Start up with no load Figure 8. Input power recycling TYPICAL WAVEFORMS @ 25C (REFER TO FIGURE 3) Copyright 2010 Rev.1.6, 2015-02-20 NX7102 Figure 9. Start into 2A resistive load Figure 10. Output short operation Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 7 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET 90% 80% 80% 70% 70% 60% 60% Efficiency 90% Efficiency 100% W W W. Microsemi .COM 100% 50% 50% 40% 40% 30% 30% 20% 20% 10% VOUT=1V VOUT=2.5V 10% VOUT=1.8V VOUT=3.3V 500 1000 1500 2000 2500 3000 0 Load Current (mA) Figure 11. NX7102 Efficiency VS Load ( VIN=5V) VOUT = 1.8V VOUT = 3.3V 0% 0% 0 VOUT = 1V VOUT = 2.5V 500 1000 1500 2000 2500 3000 Load Current (mA) Figure 12. NX7102 Efficiency VS Load ( VIN=12V) NX7102 Copyright 2010 Rev.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 8 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET THEORY OF OPERATION The NX7102 is a current-mode, PWM synchronous stepdown DC-DC converter with 340kHz fixed working frequency. It can convert input voltages from 4. 5V to 18V down to an output voltage as low as 0.925V, and supply up to 3A load current. The NX7102 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 sub-harmonic 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 no 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 high-side NMOFET current limit. If FB pin voltage drops below 0.3V, the working frequency will be fold back to typically 100kHz to protect chip from run-away. 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. The soft-start time is programmable through the SS pin in order to have desired soft-start time When the input voltage falls below the UVLO threshold, the Lower Side MOSFET turns to discharge the output capacitance. W W W. Microsemi .COM DETAIL DESCRIPTION NX7102 Copyright 2010 Rev.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 9 NX7102 3A High Voltage Synchronous Buck Converter 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 W W W. Microsemi .COM 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 parallel configuration of multiple capacitors. In this design two 22F 6.3V X5R ceramic capacitors are chosen as output capacitors. SYMBOL USED IN APPLICATION INFORMATION: The following is typical application for NX7102, the schematic is figure 1. VIN = 12V VOUT = 3.3V INPUT CAPACITOR SELECTION IOUT = 3A Input capacitors are usually a mix of high frequency ceramic OUTPUT INDUCTOR SELECTION capacitors and bulk capacitors. Ceramic capacitors bypass the The selection of inductor value is based on inductor ripple high frequency noise, and bulk capacitors supply current to the current, power rating, working frequency and efficiency. A MOSFETs. Usually 1uF ceramic capacitor is chosen to larger inductor value normally means smaller ripple current. decouple the high frequency noise. The bulk input capacitors However if the inductance is chosen too large, it results in are determined by voltage rating and RMS current rating. The slow response and lower efficiency. Usually the ripple RMS current in the input capacitors can be calculated as: current ranges from 20% to 40% of the output current. This IRMS IOUT D 1- D is a design freedom which can be determined by the design ... (3) V engineer according to various application requirements. The D OUT inductor value can be calculated by using the following VIN equations: In this design two 10uF 25V X5R ceramic capacitors are VIN - VOUT VOUT chosen. 1 LOUT IRIPPLE VIN FS OUTPUT VOLTAGE CALCULATION IRIPPLE k IOUTPUT ... (1) where k is between 0.2 to 0.4. In this design, k is set at 0.23 and 10H inductor value is chosen. In order to avoid output oscillation at light load, a minimum 8.2H inductor is required for all NX7102 application. Output voltage is set by reference voltage and external voltage divider. The reference voltage is fixed at 0.925V. The divider consists of the ratio of two resistors so that the output voltage applied at the FB pin is 0.925V when the output voltage is at the desired value. The following equation and picture show the relationship between and voltage divider. OUTPUT CAPACITOR SELECTION Vout Copyright 2010 Rev.1.6, 2015-02-20 NX7102 NX7102 Output capacitor is basically decided by the amount of the output voltage ripple allowed during steady state(DC) load 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). IRIPPLE VRIPPLE ESR IRIPPLE ... (2) 8 FS COUT R1 FB COMP R2 Vref Figure 13 Voltage Divider The pole P3 set by R3 and C6 is given by the equation (10). Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 10 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET APPLICATION INFORMATION R1 ) R2 ... (4) FP3 = In this design choose R1 26.1k, choose R2 10k. The NX7102 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 Gain=AEA GCS RLOAD FB ... (5) VOUT Where AEA is error amplifier voltage gain 560V/V, GCS is current sensing gain 5.2A/V, RLOAD is the load resistor. The system itself has one pole P1, one zero Z1 and double pole PDOUBLE at half of switching frequency FS. The system pole P1 is set by output capacitor and output load resistor. The calculation of this pole is given by the equation (6). 1 2 RL COUT ... (10) The compensation values for typical output voltage application are given in the table below. COMPENSATOR DESIGN FP1 1 2 R3 C6 VOUT 1.8V 2.5V 3.3V 5V L 8.2H 10H 10H 10H 2.5V 10H 5V 10-15H COUT 22Fx2 22Fx2 22Fx2 22Fx2 470F AL. 30m ESR 470F AL. 30m ESR R3 4.02k 5.11k 6.49k 10k C3 5.6nF 5.6nF 5.6nF 5.6nF C6 None None None None 40.2k 390pF 220pF 150k 220pF 120pF W W W. Microsemi .COM VOUT =VREF (1+ ... (6) The system zero Z1 is set by output capacitor and ESR of output capacitor. The calculation of this zero is given by the equation (7). FZ1 = 1 2 RESR COUT ... (7) The crossover frequency is recommended to be set at 1/10th of 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 FP2 = ... (8) 2 AEA C3 Where GEA is error amplifier transconductance 800A/V. The zero Z2 set by R3 and C3 is given by the equation (9). 1 2 R3 C3 NX7102 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.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 11 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET PACKAGE DIMENSIONS W W W. Microsemi .COM DE Plastic SOIC 8 Pin With Exposed Pad NX7102 Copyright 2010 Rev.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 12 NX7102 3A High Voltage Synchronous Buck Converter P RODUCTION D ATA S HEET NOTES W W W. Microsemi .COM NX7102 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.1.6, 2015-02-20 Microsemi Analog Mixed Signal Group One Enterprise, Aliso Viejo, CA, 949-380-6100, Fax: 949-215-4996 Page 13