X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r February 2013 Rev. 1.0.0 GENERAL DESCRIPTION APPLICATIONS The XRP7674 is a 2A capable synchronous current - mode PWM step down (buck) voltage regulator with improved light current load efficiency. A wide 4.5V to 18V input voltage range allows for single supply operations from industry standard 5V and 12V power rails. With a 340kHz constant operating frequency and integrated high and low - side 10P 0P 026)(7V , the XRP7674 reduces the overall component count and solution footprint. Current - mode control provides fast transient response and cycle - by cycle OCP. An adjustable soft - start prevents inrush current at turn - on, and in shutdown mode the supply current drops to 0 .1µ A. At light current loads, the XRP7674 operates in Discontinuous Conduction Mode ( DCM) and is complemented by a pulse frequency modulation mode (P FM) to provide excellent conversion efficiency. Built - in output over - voltage (open load) , over temperature , cycle - by - cycle over - current , under - voltage lockout (UVLO) and hiccup mode short - circuit protection insure s safe operation under abnormal operating conditions. The XRP7674 is offered in a RoHS compliant, ³JUHHQ´KDORJHQIUHH - pin SOIC package . TYPICAL APPLICATION x Distributed Power Architecture x Portable Equipment x Point of Load Converter x Audio - Video Equipment FEATURES x 2A Continuous Output Current x 4. 5V to 18V Wide Input Voltage 0.925V to 16V Adjustable Output Voltage ±2% Output Voltage Accuracy x PWM Curren t - Mode Control 340kHz Constant Operations Up to 9 5% Efficiency x Light - Load efficiency Discontinuous Conduction Mode (DCM) Pulse Frequency Modulation x Programmable Soft Function Mode (P FM) - Start and Enable x Built - in Thermal , Over - Current , UVLO, Output Over - Voltage and hiccup mode short - circuit protection x 5R+6&RPSOLDQW³*UHHQ´+DOR Free 8 - Pin SOIC Package DIAGRAM Fig. 1: XRP7674 Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA Tel. +1 510 668 www.exar.com - 70 00 ±Fax. +1 510 668 - 70 01 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS Input Voltage VIN ................................ ......... 4.5V to 18 V Ambient Operating Temperature ................ - 40°C to 85 °C Maximum Output Current ................................ .... 2A min 7KHUPDO5HVLVWDQFHLJ ................................ ..... 105 °C/W JA These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extend ed periods of time may affect reliability. Supply Voltage VIN ................................ ...... - 0.3V to 20 V Switch Node Voltage VSW ................................ ......... 21 V Boost Voltage VBS ................................ ... - 0.3 to VSW +6 V Enable Voltage VEN ................................ ......... - 0.3 to VIN All Other Pins ................................ .............. - 0.3 to +6 V Junction Temperature ................................ .......... 150°C Storage Temperature .............................. - 65°C to 150°C Lead Temperature (Soldering, 10 sec) ................... 26 0°C ESD Rating (HBM - Human Body Model) .................... 2kV ESD Rating (MM - Machine Model) ........................... 200V Moisture Sensitivity Level (MSL) ................................ ... 3 ELECTRICAL SPECIFICA TIONS Specifications are for an Operating Ambient Temperature of T A = 25°C only; limits applying over the full Ambient Operating THPSHUDWXUHUDQJHDUHGHQRWHGE\D³´0LQLPXPDQG0D[LPXPOLPLWVDUH through test, design, or statistical correlation. Typical values represent the most likely parametric norm at T A = 25°C, and are provided for reference purposes only. Unless otherwise indicated, V IN = V EN = 12 V, V OUT=3.3V . Typ. Max. Units Shutdown Supply Current Parameter 0.1 10 µA VEN=0V Quiescent Current 1. 2 1. 4 mA VEN= 3V, V FB=1V 0.925 0.9 43 V 0.1 µA Feedback Voltage Min. VFB 0.90 7 Feedback Overvoltage Threshold 1.1 Feedback Bias Current - 0.1 Error Amplifier Voltage Gain A EA 1 Conditions V VFB=1V 400 V/V 800 µA/V COMP to Current Sense Transconductance G CS 3.5 A/V High - Side switch On Resistance RDSONH 2 100 P I SW =0.2A&0.7A Low - Side switch On Resistance RDSONL 2 100 P I SW = - 0.2A& -0.7A High - Side switch Leakage Current 0.1 µA VIN =18V, V Error Amplifier Transconductance G EA High - Side Switch Current Limit 2.7 Low - Side Switch Current Limit Oscillator Frequency FOSC1 Short Circuit Oscillator Frequency FOSC2 Maximum Duty Minimum Start 28 0 340 - up Minimum Full Load Start Voltage © 2013 Exar Corporation - up EN=0V, V SW =0V A 0 A 40 0 Drain to Source kHz kHz 90 % VFB=0.85V % VFB=1V 10 mA VIN 9 5 V I OUT=0A 4.75 V I OUT=2A 0 MIN - up Current Minimum No Load Start Voltage 3.5 90 Cycle D MAX Minimum Duty Cycle D 10 2/ 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r Parameter EN Shutdown Threshold EN Shutdown Hysteresis Min. Typ. Max. 1.1 1.5 2 1 0.35 EN Lockout Threshold 2.2 EN Lockout Hysteresis 2.5 2.7 0.21 UVLO Threshold 3.65 UVLO Hysteresis 4.00 4.25 0.20 Units V V V 5 µA Soft - start Time 1 15 ms 160 °C 30 °C 1 Thermal Shutdown Hysteresis 1 VIN Rising V Soft - start Current Thermal Shutdown Conditions CSS=0.1µF, I OUT=500mA Note 1: Guaranteed by design. Note 2: RDSON =(V SW1 - VSW2 )/(I SW1 -I SW2 ) BLOCK DIAGRAM Fig. 2: XRP7674 Block Diagram © 2013 Exar Corporation 3/ 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r PIN ASSIGNMENT Fig. 3: XRP7674 Pin Assignment (SOIC - 8) PIN DESCRIPTION Name Pin Number Description BS 1 Bootstrap pin. Connect a 0.01µF or greater bootstrap capacitor between the BS pin and the SW pin. The voltage across the bootstrap capacitor drives the internal high - side power MOSFET. IN 2 Power input pin. A capacitor should be connected between the IN pin and GND pin to keep the input voltage constant. SW 3 Power switch output pin. This pin is connected to the inductor and the bootstrap capacitor. GND 4 Ground pin. 5 Feedback pin. An external resistor divider connected to FB programs the output voltage. If the feedback pin exceeds 1.1V the over - voltage protection will trigger. If the feedback voltage drops below 0.3V the o scillator frequency is lowered to achieve short - circuit protection. 6 Compensation pin. This is the output of transconductance e rror amplifier and the input to the current comparator. It is used to compensate the control loop. Connect an RC network form this pin to GND. EN 7 Control input pin. Drive EN high/low in order to turn on/off the regulator . When the IC is in shutdown mode all functions are disabled to decrease the supply current below 1µA. This input FDQEHFRQQHFWHGWR9,1SLQWKURXJKDNƻUHVL operations. SS 8 Soft - start control input pin. Connect a capacitor from SS to GND to set th e soft - start period. A 0.1µF capacitor sets the soft start period to 1 5ms. To disable the soft - start feature, leave SS unconnected. FB COMP ORDERING INFORMATION Part Number XRP7674 IDTR -F XRP7674 EVB Temperature Range Marking XRP7674 I YYWWF X XRP7674 Evaluation Board - &7 A& Packing Quantity Package SOIC -8 2.5 K/Tape & Reel Note 1 Note 2 RoHS Compliant Halogen Free ³<<´ <HDU ±³::´ :RUN:HHN ±³;´ /RW1XPEHU ; when applicable. © 2013 Exar Corporation 4/ 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r TYPICAL PERFORMANCE CHARACTERISTICS All data taken at V IN = 12 V, VOUT=3.3V, Information section of this datasheet. TJ = T A = 25°C, unless otherwise specified Fig. 5: Quiescent current Fig. 4: Efficiency versus output current Fig. 6: Feedback voltage Fig. 8: Output voltage - Schematic and BOM from Application Fig. 7: Output voltage versus versus temperature load current versus input voltage Fig. 9: Minimum Start © 2013 Exar Corporation versus temperature 5/ 12 - Up Voltage vs Output Current Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r Fig. 10 : Output voltage ripple I OUT=2A Fig. 11 : Load transient I OUT= 1A to 2A Fig. 12 : Enable turn on Characteristics VIN =12V, VEN=3.3V, VOUT=3.3V, I OUT=2A Fig. 13 : Enable turn off VIN =12V, V EN=3.3V, V OUT=3.3V, I Fig. 14 : Short - circuit protection I OUT=2A © 2013 Exar Corporation OUT=2A Fig. 15 : Short - circuit recovery I OUT=2A 6/ 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r THEORY OF OPERATION F UNCTIONAL OVERCURRENT PROTECTI MODE D ESCRIPTION The OCP protects against accidental increase in load current or a short circuit. The current of internal switch M1 is monitored. If this current exceed s 3.5A typical then a hiccup mode is triggered . In hiccup mode, internal power FETs are turned off and the SS pin is discharged. When SS reaches 0.2V a softstar t is initiated. The regul ator will stay in hiccup mode until overcurrent is removed. Note that when the soft start pin is below approximately 0.5V the regulator switching frequency is 90kHz. The XRP7674 is a synchronous, current - mode, step - down regulator with light - load efficiency . The light - load efficiency is achiev ed by monitoring the current throu gh M2 and turning it off when current drops below 0A. The XRP7674 regulates input voltages from 4.5V to 18V and supplies up to 2A of load current . It uses current - mode control to regulate the output voltage. The output voltage is measured at FB through a resistive voltage divider and input to a transconductance error amplifier. The high - side switch current is compared to the output of the error amplifi er to control the output voltage. The regulator utilizes internal N - channel MOSFETs to step down the input voltage. A bootstrapping capacitor connected between BS and SW acts as a supply for high - side MOSFET. This capacitor is charge d from the internal 5V supply when SW node is low. The XRP7674 has several powerful protection fe atures including OCP, OVP, OTP, UVLO and output short - circuit . PROGRAMMABLE SOFT ON AND HICCUP OVERVOLTAGE PROTECTI ON OVP The XRP7674 has internal OVP. When V OUT exceeds the OVP thre shold (when V FB exceeds 1.1V) the power switching will be turned off . The XRP7674 will restart when overvoltage condition is removed . OVER - TEMPERATURE PROTECTI ON OTP If the junction temperature exceeds 160 OTP circuit is triggered, turning off the in control circuit and switched M1 and M2. junction temperature drops below 1 XRP7674 will restart. - START The soft - start time is fully programmable via CSS capacitor , placed between the SS and GND pin . The CSS is charged by a 5µA constant - current source, generating a ramp signal fed into non - inverting input of the error amplifier. This ramp regulates the voltage on comp pin during the regulator startup, thus realizing soft - start. Calculate the required CSS from: ° C the ternal When 30° C the ͷɊܣ ܵܵܥ ൎݏݏݐ ൈ ܸ ி Where: tss is the required soft - start time VFB is the feedback voltage (0.925V nominal) Please no te that the above is a simplified equation and will provide an approximate CSS value. For a required soft - start, a more accurate CSS can be determined based on empirical data. © 2013 Exar Corporation 7/ 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r APPLICATION INFORMAT SETTING THE OUTPUT V ION VOUT(V) OLTAGE 3.3 2.5 1.8 1.5 1.2 Use an external resistor divider to set the output voltage. Program the output voltage from: Ʃ, L(p - p) (A) L(µH) 0.70 0.78 0. 72 0.66 0. 57 4.7 4.7 4.7 4.7 4.7 Where: OUTPUT CAPACITOR OUT and FB R2 is the resistor between FB and GND QRPLQDOO\N 0.925V is the nominal feedback voltage DR74 -4R7 - R DR74 -4R7 - R DR74 -4R7 - R DR74 -4R7 - R DR74 -4R7 - R Table 2: Suggested inductor values for VIN=5V and IOUT=2A ܸ ை் ܴͳൌܴʹൈ൬ െͳ൰ ͲǤ ͻʹͷ ܸ R1 is the resistor between V Inductor Example . OUTPUT INDUCTOR Select the output inductor for inductance L, DC current rating I DC and saturation current rating I SAT. I DC should be larger than regulator output current. I SAT, as a rule of thumb, should be 50% higher than the regulator output current. Since the regulator is rated at 2A then I DC$ and I SAT$ Calculate the inductance f rom: ܸ ை் ሻ൬ ܮൌሺ ܸ ൰ ூேെܸ ை் ߂ܫ ൈ݂ ௦ൈܸ ூே COUT Select the output capacitor for voltage rating, capacitance C OUT and Equivalent Series Resistance ESR . The voltage rating, as a rule of thumb, should be at least twice the output voltage. When calculating the required capacitance, usually the overriding requirement is current load - step transient. If the unloading transient (i.e., when load transitions from a high to a low current ) is met, then usually the loading transient (when load transitions from a low to a high current ) is met as well. Therefore c alculate the C OUT based on the unload ing transient requirement from: ଶ ଶ ܫ ு െܫ ௪ ܥை்ൌܮൈቆ ቇ ଶെܸ ଶ ሺ ሻ ܸ ை ் ܸ ௧௦௧ ை் Where: Where: Ʃ, L is peak - to - peak inductor current ripple nominally set to 30% - 40% of I OUT L is the inductance calculated in the preceding step f S is nominal switching frequency (340kHz) I High is the value of load - step prior to unloading. This is nominally set equal to regulator current rating (2A). As an example , inductor values for common output voltages are shown in and 2 . VOUT(V) 5.0 3.3 2.5 1.8 1.5 1.2 Ʃ, L( p - p ) (A) L( µ H) 0.86 0.70 0.70 0.66 0.57 0.68 10 10 8.2 6.8 6.8 4.7 several table s 1 I Low is the value of load - step after unloading. This is nominally set equal to 50% of regulator current rating ( 1A). Inductor Example Vtransient is the maximum permissible voltage transient corresponding to the load step mentioned above. V transient is typically specified from 3% to 5% of VOUT. DR74 -100 - R DR74 -100 - R DR74 -8R2 - R DR74 -6R8 - R DR74 -6R8 - R DR74 -4R7 - R ESR of the capacitor ha s to be selected such that the output voltage ripple requirement Ʃ9 OUT, nominally 1% of V OUT, is met. Voltage ripple Ʃ9 is mainly composed of t wo OUT components : the resistive ripple due to ESR and capacitive ripple due to COUT charge transfer. For applications requiring low voltage ripple , ceramic capacitors are recommended Table 1: Suggested inductor values for VIN=12V and IOUT=2A © 2013 Exar Corporation 8/ 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r because of their low ESR which is typically in the range of P . Therefore Ʃ9 is mainly OUT capa citive. For ceramic capacitors c alculate the Ʃ9 OUT from: ߂ܸ ை்ൌ EXTERNAL BOOTSTRAP D A low - cost diode , such as 1N4148 , may provide higher efficiency when the input voltage is 5V or the output is 5V or 3.3V. Circuit configuration is shown in figures 16 and 17. The external bootstrap diode is also recommended where duty cycle (V OUT/V IN ) is larger than 65%. ߂ܫ ͺൈܥை்ൈ݂ ௦ Where: Ʃ, L is from table 1 IODE or 2 in previous section 1N4148 COUT is the value calculated above VI N = 5V f s is nominal switching frequency (340kHz) IN If tantalum or electrolytic capacitors are used WKHQƩ VOUT is essentially a function of ESR: BS SW ߂ܸ ܫ ை்ൌ߂ ൈܴܵܧ INPUT CAPACITOR 10nF XRP7 6 7 4 CIN Fig. 16 : Optional external bootstrap diode where input voltage is fixed 5V Select the input capacitor for voltage rating, RMS current rating and capacitance. The voltage rating should be at least 50% higher 1N4148 than the regul ator ¶V maximum input voltage. BS &DOFXODWHWKHFDSDFLWRU¶VFXUUHQWUDWLQJIURP 10nF XRP7 6 7 4 ܫ ൈඥܦൈሺ ͳെܦሻ ூே ǡ ோெௌൌܫ ை் VOUT = 5V or 3.3V SW Where: I OUT LVUHJXODWRU¶VPD[LPXPFXUUHQW$ D is duty cycle (D=V Calculate the C ܥூேൌ IN OUT /V IN ) capacitance from: Fig. 17 : Optional external bootstrap diode where output voltage is 5V or 3.3V ሻ ܫ ൈܸ ൈሺ ܸ ை் ை் ூேെܸ ை் ଶ ݂ ܸ ௦ൈܸ ூே ൈ߂ ூே LOOP COMPENSATION Where: XRP7674 utilizes current - mode control . This allows using a minimum of external components to compensate the regulator. In general only two components are needed: RC and CC. Proper compensation of the regulator (determining RC and CC) results in optimum transient response. In terms of power supply control theory, t he goals of compensation are to choose RC and CC such that the regulator loop gain has a crossover frequency fc between 15kHz and 34kHz. The corresponding phase - margin should be between 45 degrees and 65 degrees. An important characteristic of current - mode buck regulator is its dominant pole. The frequency of the dominant pole is given by: Ʃ9 IN is the permissible input voltage ripple, nominally set at 1% of V IN O PTIONAL S CHOTTKY DIODE An optional Schottky diode may be paralleled between the GND pin and SW pin to improve the regulator efficiency. See Table 3. Part Number COUT Voltage/Current Rating B130 SK13 30V/1A 30V/1A MBRS130 30V/1A Vend or Diodes, Inc. Diodes, Inc. International Rectifier Table 3: Optional Schottky diode © 2013 Exar Corporation 9/ 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r ݂ ൌ where R load ͳ ʹߨൈܥை்ൈܴௗ is the output load resistance ݂ ௭ൌ . The uncompensated regulator has a constant gain up to its pole frequency, beyond which the gain decreases at - 20dB/decade. The zero arising from the output capacitor ¶ s ESR is inconsequential if ceramic C is used. This OUT simplifies the compensation. The RC and CC, which are placed between the output of XRP7674 ¶V (UURU $PSOLILHU constitute a zero. The frequency of this compensating zero is given by: ͳ ʹߨൈܴܥൈܥܥ For the typical application circuit, RC= 13 N and CC= 4.7 nF provide a satisfactory compensation . The XRP7674 can also be used as a pin to pin upgrade replacement for XRP7664 based designs; in this instance, the recommended RC network for XRP7664, RC=5.6k and CC=3.3nF , can be used with satisfactory results with the XRP7674 . Please contact EXAR if you need assistance with the DQG JURXQG compensation of your particular circuit. TYPICAL APPLICATIONS Fig. 18 : XRP7674 Typical Application Diagram © 2013 Exar Corporation 10 / 12 - 12V to 3.3V Conversion Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r PACKAGE SPECIFICATIO N 8 - P IN SOIC Unit: mm (inch) © 2013 Exar Corporation 11 / 12 Rev. 1.0.0 X RP7 6 7 4 2 A 1 8 V Sy n c h r o n o u s P FM / P W M St e p - D o w n R e g u l a t o r REVISION HISTORY Revision Date 1.0.0 02/28 /2013 FOR FURTHER ASSISTAN Description Initial release of datasheet CE Email: [email protected] [email protected] Exar Technical Documentation: http://www.exar.com/TechDoc/default.aspx? EXAR CORPORATION H EADQUARTERS AND S ALES O FFICES 48720 Kato Road Fremont, CA 94538 ±USA Tel.: +1 (510) 668 - 70 00 Fax: +1 (510) 668 - 7030 www.exar.com NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no li cense under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a XVHU¶VVSHFLILFDSSOLFDWLRQ:KLOH the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of th e product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to it s satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Reproduction, in part or whole, without the prior wr © 2013 Exar Corporation itten consent of EXAR Corporation is prohibited. 12 / 12 Rev. 1.0.0