Step-Down Switching Regulator

LM25010 42V, 1.0A Step-Down Switching Regulator February 2006 LM25010 42V, 1.0A Step-Down Switching Regulator General Description The LM25010 features all the functions needed to implement a low cost, efficient, buck regulator capable of supplying in excess of 1A load current. This high voltage regulator integrates an N-Channel Buck Switch, and is available in thermally enhanced LLP-10 and TSSOP-14EP packages. The constant on-time regulation scheme requires no loop compensation resulting in fast load transient response and simplified circuit implementation. The operating frequency remains constant with line and load variations due to the inverse relationship between the input voltage and the ontime. The valley current limit detection is set at 1.25A. Additional features include: VCC under-voltage lock-out, thermal shutdown, gate drive under-voltage lock-out, and maximum duty cycle limiter. Features n n n n n n n n n n n n Wide 6V to 42V Input Voltage Range Valley Current Limiting At 1.25A Programmable Switching Frequency Up To 1 MHz Integrated N-Channel Buck Switch Integrated High Voltage Bias Regulator No Loop Compensation Required Ultra-Fast Transient Response Nearly Constant Operating Frequency With Line and Load Variations Adjustable Output Voltage 2.5V, ±2% Feedback Reference Programmable Soft-Start Thermal shutdown Typical Applications n Non-Isolated Telecommunications Regulator n Secondary Side Post Regulator n Power SUpply for Automotive Electronics Package n LLP-10 (4 mm x 4 mm) n TSSOP-14EP n Both Packages Have Exposed Thermal Pad For Improved Heat Dissipation Basic Step-Down Regulator 20172743 © 2006 National Semiconductor Corporation DS201727 www.national.com LM25010 Connection Diagrams 20172702 20172703 Ordering Information Order Number LM25010SD LM25010SDX LM25010MH LM25010MHX Package Type LLP-10 (4x4) LLP-10 (4x4) TSSOP-14EP TSSOP-14EP NSC Package Drawing SDC10A SDC10A MXA14A MXA14A Junction Temperature Range −40˚C to + 125˚C −40˚C to + 125˚C −40˚C to + 125˚C −40˚C to + 125˚C Supplied As 1000 Units on Tape and Reel 4500 Units on Tape and Reel 94 Units in Rail 2500 Units on Tape and Reel www.national.com 2 LM25010 Pin Descriptions Pin Number LLP-10 1 TSSOP-14 2 Name SW Description Switching Node Application Information Internally connected to the buck switch source. Connect to the inductor, free-wheeling diode, and bootstrap capacitor. Connect a capacitor from SW to the BST pin. The capacitor is charged from VCC via an internal diode during the buck switch off-time. During the buck switch off-time, the inductor current flows through the internal sense resistor, and out of the ISEN pin to the free-wheeling diode. The current limit comparator keeps the buck switch off if the ISEN current exceeds 1.25A (typical). Re-circulating current flows into this pin to the current sense resistor. Ground return for all internal circuitry other than the current sense resistor. Input to both the regulation and over-voltage comparators. The FB pin regulation level is 2.5V. An internal 11.5 µA current source charges the SS pin capacitor to 2.5V to soft-start the reference input of the regulation comparator. An external resistor from VIN to the RON/SD pin sets the buck switch on-time. Grounding this pin shuts down the regulator. The voltage at VCC is nominally equal to VIN for VIN < 8.9V, and regulated at 7V for VIN > 8.9V. Connect a 0.47 µF, or larger capacitor from VCC to ground, as close as possible to the pins. An external voltage can be applied to this pin to reduce internal dissipation if VIN is greater than 8.9V. MOSFET body diodes clamp VCC to VIN if VCC > VIN. Nominal input range is 6V to 42V. Input bypass capacitors should be located as close as possible to the VIN pin and RTN pins. No internal connection. Can be connected to ground plane to improve heat dissipation. Exposed metal pad on the underside of the device. It is recommended to connect this pad to the PC board ground plane to aid in heat dissipation. 2 3 BST Boost pin for bootstrap capacitor 3 4 ISEN Current sense 4 5 6 7 5 6 9 10 SGND RTN FB SS Current Sense Ground Circuit Ground Voltage feedback input from the regulated output Softstart 8 11 RON/SD On-time control and shutdown 9 12 VCC Output of the bias regulator 10 13 VIN Input supply voltage 1,7,8,14 NC EP No connection. Exposed Pad 3 www.national.com LM25010 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) BST to VCC BST to SW VCC to RTN SGND to RTN SS to RTN -0.3V to 45V -0.3V to 59V -1.5V 45V 14V -0.3V to 14V -0.3V to +0.3V -0.3V to 4V VIN to SW All Other Inputs to RTN ESD Rating (Note 2) Human Body Model Storage Temperature Range Lead Temperature (Soldering 4 sec) (Note 4) 45V -0.3V to 7V 2kV -65˚C to +150˚C 260˚C Operating Ratings (Note 1) VIN Voltage Junction Temperature LM25010 −40˚C to + 125˚C 6.0V to 42V Electrical Charateristics 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. See (Note 5). Symbol VCC Regulator VCCReg VCC regulated output VIN - VCC VCC Bypass Threshold VCC Bypass Hysteresis VCC output impedance (0 mA ≤ ICC ≤ 5 mA) VCC current limit (Note 3) UVLOVcc VCC under-voltage lock-out threshold UVLOVCC hysteresis UVLOVCC filter delay IIN operating current IIN shutdown current Switch Characteristics RDS(on) UVLOGD Buck Switch RDS(on) Gate Drive UVLO UVLOGD hysteresis SOFT-START Pin ISS Current Limit ILIM Threshold Resistance from ISEN to SGND Response time On Timer, RON/SD Pin tON - 1 tON - 2 On-time On-time Shutdown threshold Threshold hysteresis VIN = 10V, RON = 200 kΩ VIN = 42V, RON = 200 kΩ Voltage at RON/SD rising 2.1 500 0.30 2.75 695 0.7 40 3.4 890 1.05 µs ns V mV Current out of ISEN 1 1.25 130 150 1.5 A mΩ ns Internal current source 8.0 11.5 15 µA ISW = 200mA VBST - VSW Increasing 1.7 0.35 3.0 400 0.80 4.0 Ω V mV ICC = 0 mA, FS ≤ 200 kHz, 6.0V ≤ VIN ≤ 8.5V VIN Increasing VIN Decreasing VIN = 6.0V VIN = 8.0V VIN = 24V VIN = 24V, VCC = 0V VCC Increasing VCC Decreasing 100 mV overdrive Non-switching, FB = 3V RON/SD = 0V 6.6 7 100 8.9 260 55 50 0.21 15 5.25 180 3 645 90 920 170 mA V mV µs µA µA 7.4 Volts mV V mV Ω Parameter Conditions Min Typ Max Units www.national.com 4 LM25010 Electrical Charateristics 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. See (Note 5). (Continued) Symbol Off Timer tOFF VREF Minimum Off-time FB regulation threshold FB over-voltage threshold FB bias current Thermal Shutdown TSD Thermal shutdown temperature Thermal shutdown hysteresis Thermal Resistance θJA θJC Junction to Ambient, 0 LFPM Air Flow Junction to Case SDC Package MXA Package SDC Package MXA Package 40 40 5.2 5.2 ˚C/W ˚C/W 175 20 ˚C ˚C 2.445 260 2.50 2.9 1 2.550 ns V V nA Regulation and Over-Voltage Comparators (FB Pin) Parameter Conditions Min Typ Max Units 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: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. Note 3: VCC provides bias for the internal gate drive and control circuits. Device thermal limitations limit external loading. Note 4: For detailed information on soldering plastic TSSOP and LLP packages refer to the Packaging Data Book available from National Semiconductor Corporation. Note 5: Typical specifications represent the most likely parametric norm at 25˚C operation. 5 www.national.com LM25010 Typical Performance Characteristics VCC vs VIN VCC vs ICC 20172705 20172704 ICC vs Externally Applied VCC On-Time vs VIN and RON 20172706 20172707 Voltage at RON/SD Pin IIN vs VIN 20172710 20172708 www.national.com 6 LM25010 Block Diagram 20172744 7 www.national.com LM25010 20172711 FIGURE 1. Startup Sequence Functional Description The LM25010 Step-Down Switching Regulator features all the functions needed to implement a low cost, efficient buck DC-DC converter capable of supplying in excess of 1A to the load. This high voltage regulator integrates an N-Channel buck switch, with an easy to implement constant on-time controller. It is available in the thermally enhanced LLP-10 and TSSOP-14EP packages. The regulator compares the feedback voltage to a 2.5V reference to control the buck switch, and provides a switch on-time which varies inversely with VIN. This feature results in the operating frequency remaining relatively constant with load and input voltage variations. The switching frequency can range from less than 100 kHz to 1.0 MHz. The regulator requires no loop compensation resulting in very fast load transient response. The valley current limit circuit holds the buck switch off until the free-wheeling inductor current falls below the current limit threshold, nominally set at 1.25A. The LM25010 can be applied in numerous applications to efficiently step-down highe