NX7102

NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET DESCRIPTION KEY FEATURES 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. 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 with exposed pad package. 3A Synchronous Step-down Regulator Operational Input Supply Voltage Range: 4.75V-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 WWW . Microsemi . C OM APPLICATIONS Set-Top Box LCD TV’s Notebook/Netbook PoE Powered Devices PRODUCT HIGHLIGHT 12V VIN CIN 2x10uF(25V,X5R) C4 0.1u IN(2) BST(1) NX7102 SS(8) SW(3) EN(7) FB(5) GND(4) PAD COMP(6) R3 10k C3 5.6nF C5 10nF L1 10uH R1 26.1k R2 10k 3.3V OUT R4 100k COUT 2*22uF(10V,X5R) R5 20k Figure 1 – 12V Input, 3.3V Output with Ceramic Cap PACKAGE ORDER INFO NX7102 TA (°C) -40 to 85 DE Plastic SOIC 8 Pin With Exposed Pad RoHS Compliant / Pb-free NX7102IDE Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. NX7102IDE-TR) Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET ABSOLUTE MAXIMUM RATINGS 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............................................................... 150°C Storage Temperature Range ........................................................................ -65°C to 150°C Package Peak Temp. for Solder Reflow (40 seconds maximum exposure)................ 260°C 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. PACKAGE PIN OUT WWW . Microsemi . C OM BST VIN 1 2 8 SS 7 EN 6 COMP 5 FB MSC 7102IDE XXXX SW 3 GND 4 DE PACKAGE (Top View) DE PART MARKING “xxxx” Denote Date Code and Lot Identification THERMAL DATA RoHS / Pb-free 100% Matte Tin Pin Finish DE Plastic SOIC 8-Pin With Exposed Pad 75°C/W THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA 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 1 2 3 4 5 Name BST VIN SW GND FB Description 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. Supply input pin. A capacitor should be connected between the IN pin and GND pin to keep the input voltage constant. Power switch output pin. This pin is connected to the inductor and bootstrap capacitor. 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. 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. Control input pin. Forcing this pin above 1.5V enables the IC. Forcing this pin below 0.4V shuts down the IC. When the IC is in shutdown mode, all functions are disabled to decrease the supply current below 1μA. 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 0.1μF capacitor sets the soft-start period to 9ms. To disable the softstart feature, leave SS unconnected. 6 COMP 7 EN NX7102 8 SS Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET RECOMMENDED OPERATING CONDITIONS WWW . Microsemi . C OM Parameter Input Operating Voltage Maximum Output Current Operating Ambient Temperature Symbol VIN IOUTMAX TA Min 4.75 3 -40 NX7102 Typ Max 18 85 Units V A °C ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply for VIN = VEN =12V, VOUT = 5V, TA = 25°C. NX7102 Parameter Symbol Test Conditions Min Typ Max Operating Current Quiescent Current IQ VFB =1V 0.8 1.0 1.2 Shutdown Current ISHDN VEN =0V 1 10 UVLO VIN UVLO Threshold VUVLO VIN Rising 3.65 4.05 4.45 Hysteresis VHYS 0.2 Feedback Feedback Voltage VFB 0.900 0.925 0.950 TA = -40°C to 85°C Feedback Bias Current IFB VFB =1V -0.1 0.1 Oscillator Internal Oscillator Frequency FOSC1 300 340 380 Short Circuit Oscillator 65 90 115 FOSC2 Frequency Maximum Duty Cycle DMAX VFB =0.8V 83 90 97 Minimum Duty Cycle Minimum On Time(1) Error Amplifier Error Amplifier Transconductance Voltage Gain(1) Current Sensing Gain Current Sensing Gain Soft-Start Soft-start Current Soft-start Time Output Stage High-side Switch On Resistance Low-side Switch On Resistance High-side Switch Leakage Current High-side Switch Current Limit Low-side Switch Current Limit EN High Threshold Low Threshold VENH VENL 1.5 0.4 DMIN TON GEA AEA GCS 4 560 VFB =1V 180 800 560 5.2 6 9 70 60 VIN=18V, VEN=0V, VSW=0V 4.3 0.85 100 90 0.1 5.5 1.45 130 120 10 6.7 2.05 6.4 970 0 Units mA µA V V V µA kHz kHz % % ns µA/V V/V A/V µA ms mohm mohm µA A A V V TSS RDSONH RDSONL ILEAKH ILIMH ILIML CSS=0.1uF NX7102 Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET ELECTRICAL CHARACTERISTICS (CONT) Unless otherwise specified, the following specifications apply for VIN = VEN =12V, VOUT = 5V, TA = 25°C. NX7102 Parameter Symbol Test Conditions Min Typ Max Protection Over Voltage Protection VFBOV 1 1.1 1.2 Threshold FB Short Circuit Protection 0.23 0.3 0.41 Thermal Shutdown Threshold TOTSD 160 Thermal Shutdown Hysteresis THYS 30 Notes: 1) Guaranteed by design, not tested. WWW . Microsemi . C OM Units V V °C °C SIMPLIFIED BLOCK DIAGRAM 1.1V EN Osc 340k/90k SD 0.925V slope compensation Bias Regualtor VIN VCC Therrnal SD UVLOshutdown UVLO Current Sensing BST PWM LOGIC SS FB COMP Soft Start Driver SW 1.3V Low Side Current Limit 0.3V FB UVLO GND NX7102 Figure 2 – Simplified Block Diagram Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET APPLICATION CIRCUIT WWW . Microsemi . C OM VIN IN(2) CIN 2x(10uF,25V) C4 0.1u BST(1) NX7102 SS(8) SW(3) EN(7) FB(5) GND(4) PAD COMP(6) C6 2200pF C5 10nF L1 22uH R1 42.2k R2 9.53k OUT COUT 1000uF,170mohm R4 100k R5 20k Figure 3 – 12V Input, 5V Output with Electrolytic Cap VIN IN(2) CIN 2*10uF(25V,X5R) C4 0.1u BST(1) NX7102 SS(8) SW(3) EN(7) FB(5) GND(4) PAD COMP(6) R3 10k C3 5.6nF C5 10nF L1 10uH R1 42.2k R2 9.53k OUT COUT 2*22uF(10V,X5R) R4 100k R5 20k NX7102 Figure 4 – 12V Input, 5V Output with Ceramic Cap Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET TYPICAL WAVEFORMS @ 25°C (REFER TO FIGURE 3) WWW . Microsemi . C OM Figure 5. DC Operation at 3A Figure 6. Transient Response Figure 7. Start up with no load Figure 8. Input power recycling NX7102 Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET TYPICAL WAVEFORMS @ 25°C (REFER TO FIGURE 3) WWW . Microsemi . C OM Figure 9. Start into 2A resistive load Figure 10. Output short operation NX7102 Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET THEORY OF OPERATION WWW . Microsemi . C OM DETAIL DESCRIPTION The NX7102 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 3A load current. The NX7102 has two internal N-MOSFET 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 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 90kHz 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, however when VIN rises very fast, it is necessary to add a resistor divider connected between the VIN and EN pin, so that system will not start until VIN reaches 4V. The typical resistor value on EN pin is shown in figure 4 for VIN≥8V application. NX7102 Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET APPLICATION INFORMATION WWW . Microsemi . C OM Where ESR is the output capacitor’s equivalent series resistance, COUT is the value of output capacitor. VIN - Input voltage Typically when large value capacitors are selected such as Aluminum Electrolytic, POSCAP and OSCON types are VOUT - Output voltage used, the amount of the output voltage ripple is dominated by IOUT - Output current the first term in equation(2) and the second term can be ΔVRIPPLE - Output voltage ripple neglected. FS - Working frequency If ceramic capacitors are chosen as output capacitors, both - Inductor current ripple ΔIRIPPLE terms in equation (2) need to be evaluated to determine the overall ripple. Usually when this type of capacitor is selected, DESIGN EXAMPLE the amount of capacitance per single unit is not sufficient to The following is typical application for NX7102, the meet the transient specification, which results in parallel schematic is figure 1. configuration of multiple capacitors. VIN = 12V In this design two 22uF 6.3V X5R ceramic capacitors are VOUT =3.3V chosen as output capacitors. IOUT =3A INPUT CAPACITOR SELECTION OUTPUT INDUCTOR SELECTION Input capacitors are usually a mix of high frequency ceramic SYMBOL USED IN APPLICATION INFORMATION: 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 × VIN FS ΔIRIPPLE IRIPPLE = k × IOUTPUT 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 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 10uF 25V X5R ceramic capacitors are chosen. D= ... (1) OUTPUT VOLTAGE CALCULATION Output voltage is set by reference voltage and external voltage divider. The reference voltage is fixed at 0.925V. The divider consists of two ratioed 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. where k is between 0.2 to 0.4. In this design, k is set at 0.23 and 10uH inductor value is chosen. In order to avoid output oscillation at light load, a minimum 8.2uH inductor is required for all NX7102 application. OUTPUT CAPACITOR SELECTION 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 condition. The amount of voltage ripple during the DC load condition is determined by equation (2). ΔIRIPPLE ΔVRIPPLE = ESR × ΔIRIPPLE + ... (2) 8 × FS × COUT Copyright © 2010 Rev.1.3, 2011-04-22 Vout R1 R2 FB NX7102 NX7102 COMP Vref Figure 5 Voltage Divider Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 9 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET APPLICATION INFORMATION WWW . Microsemi . C OM VOUT =VREF × (1+ R1 ) R2 ... (4) In this design choose R1 26.1kΩ, choose R2 10kΩ. COMPENSATOR DESIGN The pole P3 set by R3 and C6 is given by the equation (10). 1 FP3 = ... (10) 2 × π × R 3 × C6 The compensation values for typical output voltage application are given in the table below. VOUT 1.8V 2.5V 3.3V 5V 2.5V 5V L 8.2uH 10uH 10uH 10uH 10uH 1015uH COUT 22uFx2 22uFx2 22uFx2 22uFx2 470uF AL. 30mΩ ESR 470uF AL. 30mΩ ESR R3 4.02k 5.11k 6.49k 10k 40.2k 150k C3 5.6nF 5.6nF 5.6nF 5.6nF 390pF 220pF C6 None None None None 220pF 120pF 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=A EA × 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 FP1 = ... (6) 2 × π × RL × COUT 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). 1 FZ1 = ... (7) 2 × π × RESR × COUT 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 × π × A EA × C3 Where GEA is error amplifier transconductance 800uA/V. The zero Z2 set by R3 and C3 is given by the equation (9). 1 FZ2 = ... (9) 2 × π × R 3 × C3 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. NX7102 Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET PACKAGE DIMENSIONS WWW . Microsemi . C OM DE Plastic SOIC 8 Pin With Exposed Pad NX7102 Copyright © 2010 Rev.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 11 NX7102 TM ® 3A High Voltage Synchroous Buck Converter P RODUCTION D ATA S HEET NOTES WWW . Microsemi . C OM 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.1.3, 2011-04-22 Microsemi Analog Mixed Signal Group 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 12