LM3691TLX-1.8

LM3691 High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications June 11, 2008 LM3691 High Accuracy, Miniature 1A, Step-Down DC-DC Converter for Portable Applications General Description The LM3691 step-down DC-DC converter is optimized for powering ultra-low voltage circuits from a single Li-Ion cell or 3 cell NiMH/NiCd batteries. It provides up to 1A load current, over an input voltage range from 2.3V to 5.5V. There are several different fixed voltage output options available. LM3691 has a mode-control pin that allows the user to select Forced PWM mode or ECO mode that changes modes between gated PWM mode and PWM automatically depending on the load. In ECO, LM3691 offers superior efficiency and very low Iq under light load conditions. ECO mode extends the battery life through reduction of the quiescent current during light load conditions and system standby. The LM3691 is available in a 6–bump micro SMD package. Only three external surface-mount components, a 1μH inductor, a 4.7 μF input capacitor and a 4.7μF output capacitor, are required. Features ■ ■ ■ ■ ■ ■ ■ ■ ■ VOUT = 0.75V to 1.8V ±1% DC output voltage precision 2.3 ≤ VIN ≤ 5.5V 4 MHz switching frequency 64 μA (typ.) quiescent current in ECO mode 1A maximum load capability Automatic ECO/PWM mode switching Mode Pin to select ECO/Forced PWM mode 1 μH inductor, 4.7 μF input capacitor (0603(1608) case size) and 4.7 μF output capacitor (0603(1608) case size) ■ Current overload and thermal shutdown protections ■ Only three tiny surface-mount external components required (solution size less than 15 mm2) Applications ■ ■ ■ ■ Mobile Phones Hand-Held Radios MP3 players Portable Hard Disk Drives Efficiency vs. Output Current (VOUT = 1.8V, ECO Mode) Typical Application Circuit 30013430 FIGURE 1. Typical Application Circuit 30013454 © 2008 National Semiconductor Corporation 300134 www.national.com LM3691 Connection Diagram and Package Mark Information 30013406 FIGURE 2. 6-Bump Thin Micro SMD Package, Large Bump NS Package Number TLA06LCA Note: The actual physical placement of the package marking will vary from part to part. The package marking “X” designates the date code; “V” is an NSC internal code for die traceability. Both will vary in production. Pin Descriptions Pin Micro SMD A1 Name EN Description Enable pin. The device is in shutdown mode when voltage to this pin is 1.2V. Do not leave this pin floating. Mode Pin: Mode = 1, Forced PWM Mode = 0, ECO Do not leave this pin floating. Feedback analog input. Connect directly to the output filter capacitor. (Figure 1) Power supply input. Connect to the input filter capacitor. (Figure 1) Switching node connection to the internal PFET switch and NFET synchronous rectifier. Ground pin. B1 Mode C1 A2 B2 C2 FB VIN SW GND www.national.com 2 LM3691 Ordering Information Voltage Option V 0.75 0.85* 0.9* 1.0* 1.1* 1.2 1.3* 1.375* 1.5 1.6* 1.8 Order Number 6–bump Micro SMD LM3691TL-0.75 LM3691TLX–0.75 LM3691TL-0.85 LM3691TLX–0.85 LM3691TL-0.9 LM3691TLX–0.9 LM3691TL-1.0 LM3691TLX–1.0 LM3691TL-1.1 LM3691TLX–1.1 LM3691TL–1.2 LM3691TLX–1.2 LM3691TL–1.3 LM3691TLX–1.3 LM3691TL–1.375 LM3691TLX–1.375 LM3691TL–1.5 LM3691TLX–1.5 LM3691TL–1.6 LM3691TLX–1.6 LM3691TL–1.8 LM3691TLX–1.8 Package Marking V V TBD TBD TBD TBD TBD TBD TBD TBD X X TBD TBD TBD TBD Y Y TBD TBD Z Z Supplied As 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel 250 units, Tape-and-Reel 3000 units, Tape-and-Reel * If any of the voltage options other than the released voltages are required, please contact the National Semiconductor Sales Office/Distributors for availability. 3 www.national.com LM3691 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. VIN Pin to GND EN, MODE pin to GND FB, SW pin Junction Temperature (TJ-MAX) Storage Temperature Range Continuous Power Dissipation (Note 3) Maximum Lead Temperature (Soldering, 10 sec.) ESD Rating (Note 4) Human Body Model Machine Model −0.2V to 6.0V −0.2V to 6.0V (GND−0.2V) to (VIN + 0.2V) w/ 6.0V max +150°C −65°C to +150°C Internally Limited 260°C Operating Ratings (Notes 1, 2) Input Voltage Range 2.3V to 5.5V Recommended Load Current 0 mA to 1000 mA Junction Temperature (TJ) Range −40°C to +125°C Ambient Temperature (TA) Range (Note −40°C to +85°C 5) Thermal Properties Junction-to-Ambient Thermal Resistance (θJA) (Note 6) (micro SMD) 85°C/W 2 kV 200V Electrical Characteristics (Notes 2, 7, 8) Limits in standard typeface are for TA = 25°C. Limits in boldface type apply over the operating ambient temperature range (−30°C ≤ TA= TJ ≤ +85°C). Unless otherwise noted, specifications apply to the LM3691 open loop Typical Application Circuit with VIN = EN = 3.6V. Symbol VFB ISHDN IQ_ECO IQ_PWM RDSON (P) RDSON (N) ILIM VIH VIL IEN,MODE FSW VON Parameter Feedback Voltage Shutdown Supply Current ECO Mode Iq PWM Mode Iq Pin-Pin Resistance for PFET Pin-Pin Resistance for NFET Switch Peak Current Limit Logic High Input Logic Low Input Input Current Switching Frequency UVLO threshold PWM Mode VIN rising VIN falling 3.6 0.01 4 2.2 2.1 Condition PWM Mode. No load VOUT = 1.1V to 1.8V PWM Mode. No load VOUT = 0.75V to 1.0V EN = 0V ECO Mode PWM Mode VIN = VGS = 3.6V, IO = 200 mA VIN = VGS = 3.6V, IO = −200 mA Open loop 1250 1.2 0.4 1 4.4 Min -1 -10 0.03 64 490 160 115 1500 Typ Max +1 +10 1 80 600 250 180 1700 Units % mV µA µA µA mΩ mΩ mA V V µA MHz V V Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and disengages at TJ = 130°C (typ.). Note 4: The Human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin. MIL-STD-883 3015.7 Note 5: In applications where high power dissipation and/or poor package resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX), the maximum power dissipation of the device in the application (PD-MAX) and the junction to ambient thermal resistance of the package (θJA) in the application, as given by the following equation: TA-MAX = TJ-MAX − (θJAx PD-MAX). Due to the pulsed nature of testing the part, the temp in the Electrical Characteristic table is specified as TA = TJ. Note 6: Junction-to-ambient thermal resistance is highly application and board layout dependent. In applications where high power dissipation exists, special care must be given to thermal dissipation issues in board design. Note 7: Min and Max limits are guaranteed by design, test or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. Note 8: The parameters in the electrical characteristic table are tested under open loop conditions at VIN = 3.6V unless otherwise specified. For performance over the input voltage range and closed loop condition, refer to the datasheet curves. www.national.com 4 LM3691 Block Diagram 30013431 FIGURE 3. Simplified Functional Diagram 5 www.national.com LM3691 Typical Performance Characteristics LM3691TL Typical Application Circuit (page 1), VIN = 3.6V, VOUT = 1.8V, TA = 25°, L = 1.0 μH, 2520, (LQM2HP1R0), CIN = COUT = 4.7 μF, 0603(1608), 6.3V, (C1608X5R0J475K) unless otherwise noted. Quiescent Supply current vs. Supply Voltage No Switching (ECO Mode) Quiescent Supply current vs. Supply Voltage No Switching (PWM Mode) 30013455 30013456 Shutdown Current vs. Temp (VOUT = 1.8V) Switching Frequency vs. Temp (VOUT = 1.8V, PWM Mode) 30013457 30013458 www.national.com 6 LM3691 Output Voltage vs. Supply Voltage (VOUT = 0.75V) Output Voltage vs. Supply Voltage (VOUT = 1.8V) 30013459 30013460 Output Voltage vs. Output Current (VOUT = 0.75V) Output Voltage vs. Output Current (VOUT = 1.8V) 30013461 30013462 Input Current vs. Output Current (VOUT = 0.75V) Input Current vs. Output Current (VOUT = 1.8V) 30013463 30013464 7 www.national.com LM3691 Efficiency vs. Output Current (VOUT = 0.75V, ECO Mode) Efficiency vs. Output Current (VOUT = 1.8V, ECO Mode) 30013465 30013466 Efficiency vs. Output Current (VOUT = 0.75V, FPWM Mode) Efficiency vs. Output Current (VOUT = 1.8V, FPWM Mode) 30013467 30013468 Load Current Threshold vs. Supply Voltage (VOUT = 0.75V, ECO Mode to PWM Mode) Load Current Threshold vs. Supply Voltage (VOUT = 1.8V, ECO Mode to PWM Mode) 30013469 30013470 www.national.com 8 LM3691 Output Voltage Ripple vs. Supply Voltage (VOUT = 0.75V) Output Voltage Ripple vs. Supply Voltage (VOUT = 1.8V) 30013471 30013472 Closed Loop Current Limit vs. Temperature (VOUT = 0.75V) Closed Loop Current Limit vs. Temperature (VOUT = 1.8V) 30013473 30013474 Line Transient Reponse (VOUT = 0.75V, PWM Mode) Line Transient Reponse (VOUT = 1.8V, PWM Mode) 30013475 30013478 9 www.national.com LM3691 Load Transient Reponse (VOUT = 0.75V, ECO Mode 1mA to 25 mA) Load Transient Reponse (VOUT = 0.75V, ECO Mode 25 mA to 1mA) 30013479 30013480 Load Transient Reponse (VOUT = 1.8V, ECO Mode 1mA to 25 mA) Load Transient Reponse (VOUT = 1.8V, ECO Mode 25 mA to 1mA) 30013481 30013482 Load Transient Reponse (VOUT = 0.75V, ECO Mode to PWM Mode) Load Transient Reponse (VOUT = 0.75V, PWM Mode to ECO Mode) 30013483 30013484 www.national.com 10 LM3691 Load Transient Reponse (VOUT = 1.8V, ECO Mode to PWM Mode) Load Transient Reponse (VOUT = 1.8V, PWM Mode to ECO Mode) 30013485 30013486 Load Transient Reponse (VOUT = 0.75V, FPWM Mode) Load Transient Reponse (VOUT = 0.75V, FPWM Mode) 30013487 30013488 Load Transient Reponse (VOUT = 1.8V, FPWM Mode) Load Transient Reponse (VOUT = 1.8V, FPWM Mode) 30013489 30013490 11 www.national.com LM3691 Load Transient Reponse (VOUT = 0.75V, PWM Mode) Load Transient Reponse (VOUT = 1.8V, PWM Mode) 30013491 30013492 Start Up into ECO Mode (VOUT = 1.8V, ROUT = 1.8 kΩ) Start Up into PWM Mode (VOUT = 1.8V, ROUT = 6 Ω) 30013493 30013494 Start Up into ECO Mode (VOUT = 0.75V, ROUT = 750 Ω) Start Up into PWM Mode (VOUT = 0.75V, ROUT = 2.5 Ω) 30013495 30013496 www.national.com 12 LM3691 Operation Description DEVICE INFORMATION The LM3691, a high-efficiency, step-down DC-DC switching buck converter, delivers a constant voltage from either a single Li-Ion or three cell NiMH/NiCd battery to portable devices such as cell phones and PDAs. Using a voltage mode architecture with synchronous rectification, the LM3691 has the ability to deliver up to 1000 mA depending on the input voltage and output voltage, ambient temperature, and the inductor chosen. There are three modes of operation depending on the current required - PWM (Pulse Width Modulation), ECO, and shutdown. The device operates in PWM mode at load currents of approximately 50 mA (typ.) or higher. Lighter output current loads cause the device to automatically switch into ECO mode for reduced current consumption and a longer battery life. Shutdown mode turns off the device, offering the lowest current consumption (ISHUTDOWN = 0.03 µA typ.). Additional features include soft-start, under voltage protection, current overload protection, and thermal shutdown protection. As shown in Figure 1, only three external power components are required for implementation. CIRCUIT OPERATION The LM3691 operates as follows. During the first portion of each switching cycle, the control block in the LM3691 turns on the internal PFET switch. This allows current to flow from the input through the inductor to the output filter capacitor and load. The inductor limits the current to a ramp with a slope of (VIN–VOUT)/L, by storing energy in a magnetic field. During the second portion of each cycle, the controller turns the PFET switch off, blocking current flow from the input, and then turns the NFET synchronous rectifier on. The inductor draws current from ground through the NFET to the output filter capacitor and load, which ramps the inductor current down with a slope of –VOUT/L. The output filter stores charge when the inductor current is high, and releases it when low, smoothing the voltage across the load. The output voltage is regulated by modulating the PFET switch on time to control the average current sent to the load. The effect is identical to sending a duty-cycle modulated rectangular wave formed by the switch and synchronous rectifier at the SW pin to a low-pass filter formed by the inductor and output filter capacitor. The output voltage is equal to the average voltage at the SW pin. PWM OPERATION During PWM operation, the converter operates as a voltagemode controller with input voltage feed forward. This allows the converter to achieve excellent load and line regulation. The DC gain of the power stage is proportional to the input voltage. To eliminate this dependence, feed forward inversely proportional to the input voltage is introduced. While in PWM mode, the output voltage is regulated by switching at a constant frequency and then modulating the energy per cycle to control power to the load. At the beginning of each clock cycle the PFET switch is turned on and the inductor current ramps up until the comparator trips and the control logic turns off the switch. The current limit comparator can also turn off the switch in case the current limit of the PFET is exceeded. Then the NFET switch is turned on and the inductor current ramps down. The next cycle is initiated by the clock turning off the NFET and turning on the PFET. 30013497 FIGURE 4. Typical PWM Operation Internal Synchronous Rectification While in PWM mode, the LM3691 uses an internal NFET as a synchronous rectifier to reduce rectifier forward voltage drop and associated power loss. Synchronous rectification provides a significant improvement in efficiency whenever the output voltage is relatively low compared to the voltage drop across an ordinary rectifier diode. Current Limiting A current limit feature allows the LM3691 to protect itself and external components during overload conditions. PWM mode implements current limit using an internal comparator that trips at 1500 mA (typ). If the output is shorted to ground and output voltage becomes lower than 0.3V (typ.), the device enters a timed current limit mode where the switching frequency will be one fourth, and NFET synchronous rectifier is disabled, thereby preventing excess current and thermal runaway. ECO OPERATION Setting mode pin low places the LM3691 in Auto mode. By doing so the part switches from ECO (ECOnomy) state to FPWM (Forced Pulse Width Modulation) state based on output load current. At light loads (less than 50 mA), the converter enters ECO mode. In this mode the part operates with low Iq. During ECO operation, the converter positions the output voltage slightly higher (+30 mV typ.) than the nominal output voltage in FPWM operation. Because the reference is set higher, the output voltage increases to reach the target voltage when the part goes from sleep state to switching state. Once this voltage is reached the converter enters sleep mode, thereby reducing switching losses and improving light load efficiency. The output voltage ripple is slightly higher in ECO mode (30 mV peak–peak ripple typ.). 13 www.national.com LM3691 switch, reference, control and bias circuitry of the LM3691 are turned off. Setting EN high (>1.2V) enables normal operation. When turning on the device with EN soft-start is activated. EN pin should be set low to turn off the LM3691 during system power up and under-voltage conditions when the supply is less than 2.3V. Do not leave the EN pin floating. SOFT-START The LM3691 has a soft-start circuit that limits in-rush current during start-up. Output voltage increase rate is 30 mV/µsec (at VOUT = 1.8V typ.) during soft-start. THERMAL SHUTDOWN PROTECTION The LM3691 has a thermal overload protection function that operates to protect itself from short-term misuse and overload conditions. When the junction temperature exceeds around 150°C, the device inhibits operation. Both the PFET and the NFET are turned off. When the temperature drops below 130° C, normal operation resumes. Prolonged operation in thermal overload conditions may damage the device and is considered bad practice. 30013498 FIGURE 5. Typical ECO Operation FORCED PWM MODE Setting Mode pin high (>1.2V) places the LM3691 in Forced PWM. The part is in forced PWM regardless of the load. SHUTDOWN MODE Setting the EN input pin low (