LM25007 NSC | Alldatasheet
Document overview
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Technical content
Features
n Integrated 0.74 ohm N-Channel MOSFET switch n Guaranteed 0.5Amp output current n Ultra-Fast Transient Response n Up to 800kHz operation n No control loop compensation required n Vin feed forward provides constant operating frequency n 2% accurate 2.5V feedback from -40˚C to 125˚C n Highly efficient operation n Intelligent current limit protection n External shutdown control n Thermal shutdown n MSOP-8 and thermally enhanced LLP packages Typical Applications n 12VDC and 24VDC distributed rail systems n 24VAC systems n Automotive body electronics and telematics n Industrial systems n HB-LED constant current source Package n MSOP - 8 n LLP - 8 (4mm x 4mm) Basic Step-Down Regulator 20165513 February 2006 LM25007 42V, 0.5A Step-Down Switching Regulator © 2006 National Semiconductor Corporation DS201655 www.national.com
8-Lead MSOP, LLP
Ordering Information
1000 Units on Tape and Reel
3500 Units on Tape and Reel
4500 Units on Tape and Reel
Typical Application Circuit and Block Diagram 20165501 LM25007 www.national.com
Description
Application Information
Power switching node. Connect to the inductor, bootstrap capacitor, and free-wheeling diode. BST Boost Boot–strap capacitor input An external capacitor is required between the BST and the SW pins. A 0.01µF ceramic capacitor is recommended. RCL Current Limit OFF time programming pin 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 . RTN Circuit Ground FB Feedback Signal from Regulated Output This pin is connected to the inverting input of the internal regulation comparator. The regulation threshold is 2.5V. RON/SD On-time set pin 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. VCC Output from the internal high voltage bias regulator. 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. VIN Input supply voltage Recommended operating range: 9V to 42V. EP Exposed pad, underside of the LLP package option 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. LM25007 www.national.com
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 45V BST to RTN 59V SW to RTN (Steady State) -1V ESD Rating (Note 5) Human Body Model 2kV BST to VCC 45V BST to SW 14V VCC to RTN 14V All Other Inputs to RTN -0.3 to 7V Storage Temperature Range -65˚C to +150˚C Operating Ratings (Note 1) VIN 9V to 42V Junction Temperature −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 Tempera- ture (TJ) range. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values rep- resent 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 Conditions Min Typ Max Units Startup Regulator VCC Reg VCC Regulator Output 6.6 7.4 V VCC Current Limit (Note 4) mA VCC Supply VCC undervoltage Lockout Voltage (VCC increasing) 6.3 V VCC Undervoltage Hysteresis 206 mV VCC UVLO Delay (filter) µs Operating Current (ICC) Non-Switching, FB = 3V 500 675 µA Shutdown/Standby Current RON/SD = 0V 150 µA Switch Characteristics Buck Switch Rds(on) ITEST = 200mA, VBST −VSW = 6.3V (Note 6) 0.74 1.34 Ω Gate Drive UVLO (VBST – VSW) Rising 3.4 4.5 5.5 V Gate Drive UVLO Hysteresis 400 mV Current Limit Current Limit Threshold 535 725 900 mA Current Limit Response Time Iswitch Overdrive = 0.1A Time to Switch Off 225 ns OFF time generator (test 1) FB=0V, RCL = 100K µs OFF time generator (test 2) FB=2.3V, RCL = 100K 2.65 µs On Time Generator TON -1 Vin = 10V Ron = 200K 2.15 2.77 3.5 µs TON -2 Vin = 40V Ron = 200K 450 615 810 ns Remote Shutdown Threshold Rising 0.45 0.7 1.1 V Remote Shutdown Hysteresis mV LM25007 www.national.com
(Continued) Specifications with standard type are for TJ = 25˚C only; limits in boldface type apply over the full Operating Junction Tempera- ture (TJ) range. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values rep- resent 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 Conditions Min Typ Max Units Minimum Off Time Minimum Off Timer FB = 0V 300 ns Regulation and OV Comparators FB Reference Threshold Internal reference Trip point for switch ON 2.445 2.5 2.550 V FB Over-Voltage Threshold Trip point for switch OFF 2.875 V FB Bias Current 100 nA Thermal Shutdown Tsd Thermal Shutdown Temp. 165 Thermal Shutdown Hysteresis Thermal Resistance θJA Junction to Ambient 200 ˚C/W ˚C/W 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 1.5kΩresistor 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. LM25007 www.national.com
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 20165509 LM25007 Operation: VOUT = 10V, VIN = 42V, IOUT = 250mA CH1: Switch Node, CH2: VOUT (AC), CH4: Inductor Current LM25007 10V Output Efficiency Current Limit Off-Time vs VFB 20165510 20165511 VIN vs TON RON = 100k, 200k, 300k 20165512 LM25007 www.national.com
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 archi- tecture 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 inte- grated internal regulator. Additional protection features in- clude: thermal shutdown, Vcc under-voltage lockout, gate drive under-voltage lockout, and max duty cycle limiter. Hysteretic Control Circuit Overview The LM25007 is a Buck DC-DC regulator that uses a con- stant on-time control scheme. The on-time is programmed by an external resistor and varies inversely with line input voltage (Vin). The core regulation elements of the LM25007 are the feedback comparator and the on-time one-shot. The regulator output voltage is sensed at the feedback pin (FB) and is compared to an internal reference voltage (2.5V). If the FB signal is below the reference voltage, the buck switch is turned on for a fixed time pulse determined by the line voltage and a programming resistor (RON). Following the on period the switch will remain off for at least the minimum off timer period of 300ns. If the FB pin voltage is still below the reference after the 300ns off-time, the switch will turn on again for another on time period. This switching behavior will continue until the FB pin voltage reaches the reference voltage level. The LM25007 operates in discontinuous conduction mode at light load currents or continuous conduction mode at heavier load currents. In discontinuous conduction mode, current through the output inductor starts at zero and ramps up to a peak value during the buck switch on-time and then back to zero during the off-time. The inductor current remains at zero until the next on-time period starts when FB falls below the internal reference. In discontinuous mode the operating fre- quency is relatively low and will vary with load. Therefore at light loads the conversion efficiency is maintained, since the switching losses decrease with the reduction in load current and switching frequency. The approximate discontinuous mode operating frequency can be calculated as follows: In continuous conduction mode, current flows continuously through the inductor and never ramps down to zero. In this mode the operating frequency is greater than the discontinu- ous mode frequency and remains relatively constant with load and line variations. The approximate continuous mode operating frequency can be calculated as follows: The output voltage (Vout) can be programmed by two exter- nal resistors as shown in Figure 1. The regulated voltage is calculated as follows: VOUT = 2.5 x (R3 + R4) / R4 The feedback comparator in hysteretic regulators depends on the output ripple voltage to switch the output transistor on and off at regular intervals. In order for the internal compara- tor to respond quickly to changes in output voltage, propor- tional to inductor current, a minimum amount of capacitor Equivalent Series Resistance (ESR) is required. A ripple voltage of 25mV is recommended at the feedback pin (FB) for stable operation. In cases where the intrinsic capacitor ESR is too small, additional series resistance may be added. For applications where lower output voltage ripple is re- quired the load can be connected directly to the low ESR output capacitor, as shown in Figure 1. The series resistor (R5) will degrade the load regulation. Another technique for enhancing the ripple voltage at the FB pin is to place a capacitor in parallel with the feedback divider resistor R3. The addition of the capacitor reduces the attenuation of the ripple voltage from the feedback divider. High Voltage Bias Regulator (VCC) The LM25007 contains an internal high voltage bias regula- tor. The input pin (Vin) can be connected directly to line voltages from 9 to 42 Volts. To avoid supply voltage tran- sients due to long lead inductances on the input pin (VIN), it is always recommended to connect a low ESR ceramic chip capacitor () 0.1µF) between VIN and RTN pins located close to the LM25007. The regulator is internally current limited to 11mA. Upon power up, the regulator is enabled and sources current into an external capacitor connected to the VCC pin. When the voltage on the VCC pin reaches its UVLO level (6.3V), the controller output is enabled. An external auxiliary supply voltage can be diode connected to the Vcc pin. If the auxiliary voltage is greater than 7 Volts the internal regulator will shutoff, thus reducing internal power dissipation. Do not exceed 14V at VCC. See Figure 2. LM25007 www.national.com
and limit the short circuit current. BST pin and SW pin is recommended. FIGURE 3. Shutdown Implementation
N - Channel Buck Switch and Driver (Continued) An external re-circulating diode from the SW pin to ground is necessary to carry the inductor current after the internal Buck switch turns off. This external diode must be of the Ultra-fast or Schottky type to reduce turn-on losses and current over-shoot. The reverse voltage rating of the re- circulating diode must be greater than the maximum line input voltage. Thermal Protection Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction tem- perature is exceeded. When thermal protection is activated, typically at 165 degrees Celsius, the controller is forced into a low power reset state, disabling the output driver. This feature is provided to prevent catastrophic failures from ac- cidental device overheating. 10V, 400mA Demo Board Bill of Materials (See Typical Application Circuit) ITEM PART NUMBER CAPACITOR, CER, TDK 1µ, 100V C4532X7R1E156M CAPACITOR, CER, TDK 15µ, 25V C1206C104K5RAC CAPACITOR, CER, KEMET 0.1µ, 50V C1206C103K5RAC CAPACITOR, CER, KEMET 0.01µ, 50V C3216X7R2A104KT CAPACITOR, CER, TDK 0.1µ, 100V MURA110T3 DIODE, 100V, ON SEMI SLF7045T-101MR60-1 BUCK INDUCTOR, TDK 100µH CRCW12062003F RESISTOR 200K CRCW12061003F RESISTOR 100K CRCW12063011F RESISTOR 3.01K CRCW12061001F RESISTOR CRCW12061R00F RESISTOR LM25007 REGULATOR, NATIONAL LM25007 www.national.com
inches (millimeters) unless otherwise noted 8-Lead MSOP Package LM25007 www.national.com
inches (millimeters) unless otherwise noted (Continued) 8-Lead LLP Package National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. Leadfree products are RoHS compliant. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: ap.support@nsc.com National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560 www.national.com LM25007 42V, 0.5A Step-Down Switching Regulator