XRP7674IDTR-F

XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator 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 100mΩ/100mΩ MOSFETs, the XRP7674 reduces the overall component count and solution footprint. Current-mode control provides fast transient response and cycle-bycycle OCP. An adjustable soft-start prevents inrush current at turn-on, and in shutdown mode the supply current drops to 0.1µA. At light current loads, the XRP7674 operates in Discontinuous Conduction Mode (DCM) and is complemented by a pulse frequency modulation mode (PFM) 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 insures safe operation under abnormal operating conditions. The XRP7674 is offered in a RoHS compliant, “green”/halogen free 8-pin SOIC package.  Distributed Power Architecture  Portable Equipment  Point of Load Converter  Audio-Video Equipment FEATURES  2A Continuous Output Current  4.5V to 18V Wide Input Voltage  0.925V to 16V Adjustable Output Voltage  ±2% Output Voltage Accuracy  PWM Current-Mode Control  340kHz Constant Operations  Up to 95% Efficiency  Light-Load efficiency  Discontinuous Conduction Mode (DCM)  Pulse Frequency Modulation Mode (PFM)  Programmable Soft-Start and Enable Function  Built-in Thermal, Over-Current, UVLO, Output Over-Voltage and hiccup mode short-circuit protection  RoHS Compliant, “Green”/Halogen Free 8-Pin SOIC Package TYPICAL APPLICATION DIAGRAM Fig. 1: XRP7674 Application Diagram Exar Corporation 48720 Kato Road, Fremont CA 94538, USA www.exar.com Tel. +1 510 668-7000 – Fax. +1 510 668-7001 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator ABSOLUTE MAXIMUM RATINGS OPERATING RATINGS 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 extended periods of time may affect reliability. Input Voltage VIN ......................................... 4.5V to 18V Ambient Operating Temperature ................ -40°C to 85°C Maximum Output Current.................................... 2A min Thermal Resistance θJA .....................................105°C/W Supply Voltage VIN ...................................... -0.3V to 20V Switch Node Voltage VSW ......................................... 21V Boost Voltage VBS ................................... -0.3 to VSW+6V Enable Voltage VEN ......................................... -0.3 to VIN All Other Pins .............................................. -0.3 to +6V Junction Temperature .......................................... 150°C Storage Temperature .............................. -65°C to 150°C Lead Temperature (Soldering, 10 sec) ................... 260°C ESD Rating (HBM - Human Body Model) .................... 2kV ESD Rating (MM - Machine Model) ...........................200V Moisture Sensitivity Level (MSL) ................................... 3 ELECTRICAL SPECIFICATIONS Specifications are for an Operating Ambient Temperature of TA = 25°C only; limits applying over the full Ambient Operating Temperature range are denoted by a “•”. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TA = 25°C, and are provided for reference purposes only. Unless otherwise indicated, VIN = VEN = 12V, VOUT=3.3V. Typ. Max. Units Shutdown Supply Current Parameter Min. 0.1 10 µA VEN=0V Quiescent Current 1.2 1.4 mA VEN=3V, VFB=1V 0.925 0.943 V 0.1 µA Feedback Voltage VFB 0.907 Feedback Overvoltage Threshold Feedback Bias Current Error Amplifier Voltage Gain AEA 1.1 -0.1 1 Conditions V VFB=1V 400 V/V Error Amplifier Transconductance GEA 800 µA/V COMP to Current Sense Transconductance GCS 3.5 A/V High-Side switch On Resistance RDSONH2 100 mΩ ISW=0.2A&0.7A Low-Side switch On Resistance RDSONL2 100 mΩ ISW=-0.2A&-0.7A High-Side switch Leakage Current 0.1 µA VIN=18V, VEN=0V, VSW=0V High-Side Switch Current Limit 2.7 Low-Side Switch Current Limit Oscillator Frequency FOSC1 10 3.5 A 0 280 340 Short Circuit Oscillator Frequency FOSC2 90 Maximum Duty Cycle DMAX 90 Minimum Duty Cycle DMIN A 400 Drain to Source kHz kHz 0 % VFB=0.85V % VFB=1V VIN≤4.75V Minimum Start-up Current 10 mA Minimum No Load Start-up Voltage 5 V IOUT=0A Minimum Full Load Start-up Voltage 4.75 V IOUT=2A © 2013 Exar Corporation 2/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator Parameter Min. Typ. Max. 1.1 1.5 2 EN Shutdown Threshold EN Shutdown Hysteresis1 0.35 EN Lockout Threshold 2.2 EN Lockout Hysteresis UVLO Threshold 2.5 2.7 0.21 3.65 UVLO Hysteresis Soft-start Current Soft-start Time1 Thermal Shutdown1 Thermal Shutdown Hysteresis1 4.00 4.25 0.20 Units Conditions V V V VIN Rising V 5 µA 15 ms 160 °C 30 °C CSS=0.1µF, IOUT=500mA Note 1: Guaranteed by design. Note 2: RDSON=(VSW1-VSW2)/(ISW1-ISW2) BLOCK DIAGRAM Fig. 2: XRP7674 Block Diagram © 2013 Exar Corporation 3/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator 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 oscillator frequency is lowered to achieve short-circuit protection. 6 Compensation pin. This is the output of transconductance error 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 can be connected to VIN (pin 2) through a 100kΩ resistor for automatic startup operations. SS 8 Soft-start control input pin. Connect a capacitor from SS to GND to set the soft-start period. A 0.1µF capacitor sets the soft start period to 15ms. To disable the soft-start feature, leave SS unconnected. FB COMP ORDERING INFORMATION Part Number XRP7674IDTR-F XRP7674EVB Temperature Range Marking XRP7674I YYWWF X XRP7674 Evaluation Board -40°C≤TA≤+85°C Packing Quantity Package SOIC-8 Note 1 Note 2 2.5K/Tape & Reel RoHS Compliant Halogen Free “YY” = Year – “WW” = Work Week – “X” = Lot Number; when applicable. © 2013 Exar Corporation 4/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator TYPICAL PERFORMANCE CHARACTERISTICS All data taken at VIN = 12V, VOUT=3.3V, TJ = TA = 25°C, unless otherwise specified - Schematic and BOM from Application Information section of this datasheet. Fig. 4: Efficiency versus output current Fig. 5: Quiescent current versus temperature Fig. 6: Feedback voltage versus temperature Fig. 7: Output voltage versus load current Fig. 8: Output voltage versus input voltage Fig. 9: Minimum Start-Up Voltage vs Output Current © 2013 Exar Corporation 5/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator Fig. 10: Output voltage ripple IOUT=2A Fig. 11: Load transient IOUT=1A to 2A Fig. 12: Enable turn on Characteristics VIN=12V, VEN=3.3V, VOUT=3.3V, IOUT=2A Fig. 13: Enable turn off VIN=12V, VEN=3.3V, VOUT=3.3V, IOUT=2A Fig. 14: Short-circuit protection IOUT=2A Fig. 15: Short-circuit recovery IOUT=2A © 2013 Exar Corporation 6/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator THEORY OF OPERATION OVERCURRENT PROTECTION AND HICCUP MODE FUNCTIONAL DESCRIPTION The OCP protects against accidental increase in load current or a short circuit. The current of internal switch M1 is monitored. If this current exceeds 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 softstart is initiated. The regulator 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 achieved by monitoring the current through 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 amplifier to control the output voltage. The regulator utilizes internal N-channel MOSFETs to stepdown the input voltage. A bootstrapping capacitor connected between BS and SW acts as a supply for high-side MOSFET. This capacitor is charged from the internal 5V supply when SW node is low. The XRP7674 has several powerful protection features including OCP, OVP, OTP, UVLO and output short-circuit. OVERVOLTAGE PROTECTION OVP The XRP7674 has internal OVP. When VOUT exceeds the OVP threshold (when VFB exceeds 1.1V) the power switching will be turned off. The XRP7674 will restart when overvoltage condition is removed. OVER-TEMPERATURE PROTECTION OTP If the junction temperature exceeds 160°C the OTP circuit is triggered, turning off the internal control circuit and switched M1 and M2. When junction temperature drops below 130°C the XRP7674 will restart. PROGRAMMABLE SOFT-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: Where: tss is the required soft-start time VFB is the feedback voltage (0.925V nominal) Please note 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 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator APPLICATION INFORMATION VOUT(V) ΔIL(p-p)(A) SETTING THE OUTPUT VOLTAGE 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: 0.70 0.78 0.72 0.66 0.57 L(µH) Inductor Example 4.7 4.7 4.7 4.7 4.7 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 Where: OUTPUT CAPACITOR COUT R1 is the resistor between VOUT and FB Select the output capacitor for voltage rating, capacitance COUT 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 calculate the COUT based on the unloading transient requirement from: R2 is the resistor between FB and GND (nominally 10kΩ) 0.925V is the nominal feedback voltage. OUTPUT INDUCTOR Select the output inductor for inductance L, DC current rating IDC and saturation current rating ISAT. IDC should be larger than regulator output current. ISAT, as a rule of thumb, should be 50% higher than the regulator output current. Since the regulator is rated at 2A then IDC≥2A and ISAT≥3A. Calculate the inductance from: Where: Where: ΔIL is peak-to-peak inductor current ripple nominally set to 30%-40% of IOUT L is the inductance calculated in the preceding step fS is nominal switching frequency (340kHz) IHigh 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 several common output voltages are shown in tables 1 and 2. VOUT(V) ΔIL(p-p)(A) 5.0 3.3 2.5 1.8 1.5 1.2 L(µH) Inductor Example 10 10 8.2 6.8 6.8 4.7 DR74-100-R DR74-100-R DR74-8R2-R DR74-6R8-R DR74-6R8-R DR74-4R7-R 0.86 0.70 0.70 0.66 0.57 0.68 ILow is the value of load-step after unloading. This is nominally set equal to 50% of regulator current rating (1A). Vtransient is the maximum permissible voltage transient corresponding to the load step mentioned above. Vtransient is typically specified from 3% to 5% of VOUT. ESR of the capacitor has to be selected such that the output voltage ripple requirement ΔVOUT, nominally 1% of VOUT, is met. Voltage ripple ΔVOUT is mainly composed of two 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 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator because of their low ESR which is typically in the range of 5mΩ. Therefore ΔVOUT is mainly capacitive. For ceramic capacitors calculate the ΔVOUT from: EXTERNAL BOOTSTRAP DIODE 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 (VOUT/VIN) is larger than 65%. Where: ΔIL is from table 1 or 2 in previous section 1N4148 COUT is the value calculated above VIN = 5V fs is nominal switching frequency (340kHz) IN If tantalum or electrolytic capacitors are used then ΔVOUT is essentially a function of ESR: BS 10nF XRP7674 SW INPUT CAPACITOR 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 than the regulator’s maximum input voltage. Calculate the capacitor’s current rating from: 1N4148 BS 10nF XRP7674 VOUT = 5V or 3.3V SW Where: COUT IOUT is regulator’s maximum current (2A) D is duty cycle (D=VOUT/VIN) Calculate the CIN capacitance from: Fig. 17: Optional external bootstrap diode where output voltage is 5V or 3.3V 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, the 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: ΔVIN is the permissible input voltage ripple, nominally set at 1% of VIN OPTIONAL SCHOTTKY 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 Voltage/Current Rating B130 SK13 30V/1A 30V/1A MBRS130 30V/1A Vendor Diodes, Inc. Diodes, Inc. International Rectifier Table 3: Optional Schottky diode © 2013 Exar Corporation 9/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator For the typical application circuit, RC=13kΩ and CC=4.7nF 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 compensation of your particular circuit. where Rload is the output load resistance. 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 COUT is used. This simplifies the compensation. The RC and CC, which are placed between the output of XRP7674’s Error Amplifier and ground, constitute a zero. The frequency of this compensating zero is given by: TYPICAL APPLICATIONS Fig. 18: XRP7674 Typical Application Diagram - 12V to 3.3V Conversion © 2013 Exar Corporation 10/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator PACKAGE SPECIFICATION 8-PIN SOIC Unit: mm (inch) © 2013 Exar Corporation 11/12 Rev. 1.0.0 XRP7674 2A 18V Synchronous PFM/PWM Step-Down Regulator REVISION HISTORY Revision Date 1.0.0 02/28/2013 Description Initial release of datasheet FOR FURTHER ASSISTANCE Email: customersupport@exar.com powertechsupport@exar.com Exar Technical Documentation: http://www.exar.com/TechDoc/default.aspx? EXAR CORPORATION HEADQUARTERS AND SALES OFFICES 48720 Kato Road Fremont, CA 94538 – USA Tel.: +1 (510) 668-7000 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 license 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 user’s specific application. While 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 malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. or its in all Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. © 2013 Exar Corporation 12/12 Rev. 1.0.0