Step-Down Switching Regulator

www.DataSheet4U.com February 2006 LM25007 42V, 0.5A Step-Down Switching Regulator LM25007 42V, 0.5A Step-Down Switching Regulator General Description The LM25007 is a monolithic step-down switching regulator featuring all of the functions needed to implement a low cost, efficient, power supply. Capable of driving a 0.5Amp load over a 9V-42V input voltage range, this device is easy to apply and is provided in the small MSOP-8 and the thermally enhanced LLP-8 packages. Ultra-fast transient response is achieved through the use of a constant on-time architecture with Vin feed forward. This feature provides an almost constant operating frequency over load and input voltage variations. The operating frequency can be adjusted with a single resistor. This architecture is easy to use and tolerant of component selection. An intelligent current limit is implemented in the LM25007 with forced off time that is inversely proportional to Vout thus ensuring recovery from fault conditions. The output voltage may be set from 2.5V to > 30V. To improve efficiency in light load applications, the Vcc pin can be connected to an external voltage source to eliminate the drop through the internal regulator. Additional features include: thermal shutdown, Vcc under-voltage lockout, gate drive under-voltage lockout, and max duty cycle limiter. Features n n n n n n n n n n n n Integrated 0.74 ohm N-Channel MOSFET switch Guaranteed 0.5Amp output current Ultra-Fast Transient Response Up to 800kHz operation No control loop compensation required Vin feed forward provides constant operating frequency 2% accurate 2.5V feedback from -40˚C to 125˚C Highly efficient operation Intelligent current limit protection External shutdown control Thermal shutdown MSOP-8 and thermally enhanced LLP packages Typical Applications n n n n n 12VDC and 24VDC distributed rail systems 24VAC systems Automotive body electronics and telematics Industrial systems HB-LED constant current source Package n MSOP - 8 n LLP - 8 (4mm x 4mm) Basic Step-Down Regulator 20165513 © 2006 National Semiconductor Corporation DS201655 www.national.com LM25007 Connection Diagram 20165502 8-Lead MSOP, LLP Ordering Information Order Number LM25007MM LM25007MMX LM25007SD LM25007SDX Package Type MSOP-8 MSOP-8 LLP-8 LLP-8 NSC Package Drawing MUA08A MUA08A SDC08A SDC08A Supplied As 1000 Units on Tape and Reel 3500 Units on Tape and Reel 1000 Units on Tape and Reel 4500 Units on Tape and Reel Typical Application Circuit and Block Diagram 20165501 www.national.com 2 LM25007 Pin Descriptions Pin 1 2 Name SW BST Switching Node Boost Boot–strap capacitor input Description Application Information Power switching node. Connect to the inductor, bootstrap capacitor, and free-wheeling diode. An external capacitor is required between the BST and the SW pins. A 0.01µF ceramic capacitor is recommended. A resistor between this pin and RTN sets the off-time when current limit is detected. The off-time is preset to 17 µs if FB = 0V . This pin is connected to the inverting input of the internal regulation comparator. The regulation threshold is 2.5V. A resistor between this pin and VIN sets the switch on-time as a function of Vin. The minimum recommended on-time is 300ns at the maximum input voltage. If an auxiliary voltage is available to raise the voltage on this pin above the regulation setpoint (7V), the internal series pass regulator will shutdown, reducing the IC power dissipation. Do not exceed 14V. This output provides gate drive power for the internal Buck switch. An internal diode is provided between this pin and the BST pin. A local 0.1uF decoupling capacitor is recommended. Recommended operating range: 9V to 42V. Exposed metal pad on the LLP package underside. It is recommended to connect this pad to the PC board ground plane to aid in heat dissipation. 3 RCL Current Limit OFF time programming pin 4 5 RTN FB Circuit Ground Feedback Signal from Regulated Output 6 RON/SD On-time set pin 7 VCC Output from the internal high voltage bias regulator. 8 - VIN EP Input supply voltage Exposed pad, underside of the LLP package option 3 www.national.com LM25007 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN to RTN BST to RTN SW to RTN (Steady State) ESD Rating (Note 5) Human Body Model BST to VCC 2kV 45V 45V 59V -1V BST to SW VCC to RTN All Other Inputs to RTN Storage Temperature Range 14V 14V -0.3 to 7V -65˚C to +150˚C Operating Ratings (Note 1) VIN Junction Temperature 9V to 42V −40˚C to + 125˚C Electrical Characteristics Specifications with standard type are for TJ = 25˚C only; limits in boldface type apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25˚C, and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VIN = 24V, RON = 200kΩ. (Note 3). Symbol Startup Regulator VCC Reg VCC Supply VCC undervoltage Lockout Voltage (VCC increasing) VCC Undervoltage Hysteresis VCC UVLO Delay (filter) Operating Current (ICC) Shutdown/Standby Current Switch Characteristics Buck Switch Rds(on) ITEST = 200mA, VBST −VSW = 6.3V (Note 6) Rising 3.4 0.74 1.34 Ω Non-Switching, FB = 3V RON/SD = 0V 6.3 206 3 500 70 675 150 V mV µs µA µA VCC Regulator Output VCC Current Limit (Note 4) 6.6 7 11 7.4 V mA Parameter Conditions Min Typ Max Units Gate Drive UVLO (VBST – VSW) Gate Drive UVLO Hysteresis Current Limit Current Limit Threshold Current Limit Response Time OFF time generator (test 1) OFF time generator (test 2) On Time Generator TON -1 TON -2 Remote Shutdown Threshold Remote Shutdown Hysteresis 4.5 400 5.5 V mV 535 Iswitch Overdrive = 0.1A Time to Switch Off FB=0V, RCL = 100K FB=2.3V, RCL = 100K Vin = 10V Ron = 200K Vin = 40V Ron = 200K Rising 2.15 450 0.45 725 225 17 2.65 2.77 615 0.7 40 900 mA ns µs µs 3.5 810 1.1 µs ns V mV www.national.com 4 LM25007 Electrical Characteristics (Continued) Specifications with standard type are for TJ = 25˚C only; limits in boldface type apply over the full Operating Junction Temperature (TJ) range. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25˚C, and are provided for reference purposes only. Unless otherwise stated the following conditions apply: VIN = 24V, RON = 200kΩ. (Note 3). Symbol Parameter Minimum Off Timer Conditions FB = 0V Internal reference Trip point for switch ON Trip point for switch OFF 2.445 Min Typ 300 2.5 2.875 100 165 25 MUA Package SDC Package 200 40 2.550 Max Units ns V V nA ˚C ˚C ˚C/W ˚C/W Minimum Off Time Regulation and OV Comparators FB Reference Threshold FB Over-Voltage Threshold FB Bias Current Thermal Shutdown Tsd Thermal Shutdown Temp. Thermal Shutdown Hysteresis Thermal Resistance θJA Junction to Ambient Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: For detailed information on soldering plastic MSOP and LLP packages, refer to the Packaging Data Book available from National Semiconductor Corporation. Note 3: All limits are guaranteed. All electrical characteristics having room temperature limits are tested during production with TA = TJ = 25˚C. All hot and cold limits are guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control. Note 4: The VCC output is intended as a self bias for the internal gate drive power and control circuits. Device thermal limitations limit external loading. Note 5: The human body model is a 100pF capacitor discharge through a 1.5kΩ resistor into each pin. The human body ESD compliance level for Pin 7 and 8 is 1000V. Note 6: For devices procurred in the LLP-8 package the Rds(on) limits are guaranteed by design characterization data only. 5 www.national.com LM25007 Typical Performance Characteristics Operational Waveforms Operational Waveforms 20165508 LM25007 Operation: VOUT = 10V, VIN = 20V, IOUT = 250mA CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current LM25007 Operation: VOUT = 10V, VIN = 42V, IOUT = 250mA CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current 20165509 LM25007 10V Output Efficiency Current Limit Off-Time vs VFB 20165510 20165511 VIN vs TON RON = 100k, 200k, 300k 20165512 www.national.com 6 LM25007 Detailed Operating Description The LM25007 is a monolithic step-down switching regulator featuring all of the functions needed to implement low cost, efficient, power supply. Capable of driving a 0.5Amp load over a 9-42V input voltage range, this device is easy to apply and is provided in the small MSOP-8 and the thermally enhanced LLP-8 packages. Ultra-fast transient response is achieved through the use of a constant on-time architecture with Vin feed forward. This feature provides and almost constant operating frequency over load and input voltage variations. The operating frequency may be adjusted up to 800kHz depending on input and output voltages. This architecture is easy to use and tolerant of component selection. An intelligent current limit is implemented in the LM25007 with forced off time that is inversely proportional to Vout to ensure recovery from fault conditions. The output voltage may be set from 2.5V to > 30V. To improve efficiency in light load applications, the Vcc pin can be tied to an external voltage source thus eliminating the drop through the integrated internal regulator. Additional protection fea