LM25005_06 NSC | Alldatasheet
Document overview
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Technical content
Features
■ Integrated 42V, 160mΩ N-channel MOSFET ■ Ultra-wide input voltage range from 7V to 42V ■ Internal bias regulator ■ Adjustable output voltage from 1.225V ■ 1.5% feedback reference accuracy ■ Current mode control with emulated inductor current ramp ■ Single resistor oscillator frequency setting ■ Oscillator synchronization input ■ Programmable soft-start ■ Shutdown / Standby input ■ Wide bandwidth error amplifier ■ Thermal Shutdown Package ■ TSSOP-20EP (Exposed Pad) Simplified Application Schematic 20170001 © 2007 National Semiconductor Corporation 201700 www.national.com LM25005 42V, 2.5A Step-Down Switching Regulator
Ordering Information
Order Number Package Type NSC Package Drawing Supplied As LM25005MH Exposed Pad TSSOP-20 MXA20A 73 Units in Rail LM25005MHX Exposed Pad TSSOP-20 MXA20A 2500 Units on Tape and Reel www.national.com 2 LM25005
Pin(S) Name Description Application Information 1 VCC Output of the bias regulator Vcc tracks Vin up to 9V. Beyond 9V, Vcc is regulated to 7 Volts. A 0.1uF to 1uF ceramic decoupling capacitor is required. An external voltage (7.5V – 14V) can be applied to this pin to reduce internal power dissipation. 2 SD Shutdown or UVLO input If the SD pin voltage is below 0.7V the regulator will be in a low power state. If the SD pin voltage is between 0.7V and 1.225V the regulator will be in standby mode. If the SD pin voltage is above 1.225V the regulator will be operational. An external voltage divider can be used to set a line undervoltage shutdown threshold. If the SD pin is left open circuit, a 5µA pull-up current source configures the regulator fully operational. 3, 4 Vin Input supply voltage Nominal operating range: 7V to 42V 5 SYNC Oscillator synchronization input or output The internal oscillator can be synchronized to an external clock with an external pull-down device. Multiple LM25005 devices can be synchronized together by connection of their SYNC pins.
6 COMP Output of the internal error amplifier The loop compensation network should be connected
between this pin and the FB pin.
7 FB Feedback signal from the regulated
This pin is connected to the inverting input of the internal error amplifier. The regulation threshold is 1.225V. 8 RT Internal oscillator frequency set input The internal oscillator is set with a single resistor, connected between this pin and the AGND pin. The recommended frequency range is 50KHz to 500KHz.
9 RAMP Ramp control signal An external capacitor connected between this pin and the
AGND pin sets the ramp slope used for current mode control. Recommended capacitor range 50pF to 2000pF.
10 AGND Analog ground Internal reference for the regulator control functions
11 SS Soft-start An external capacitor and an internal 10µA current source
set the time constant for the rise of the error amp reference. The SS pin is held low during standby, Vcc UVLO and thermal shutdown. 12 OUT Output voltage connection Connect directly to the regulated output voltage. 13, 14 PGND Power ground Low side reference for the PRE switch and the IS sense resistor. 15, 16 IS Current sense Current measurement connection for the re-circulating diode. An internal sense resistor and a sample/hold circuit sense the diode current near the conclusion of the off-time. This current measurement provides the DC level of the emulated current ramp. 17, 18 SW Switching node The source terminal of the internal buck switch. The SW pin should be connected to the external Schottky diode and to the buck inductor.
19 PRE Pre-charge assist for the bootstrap
This open drain output can be connected to SW pin to aid charging the bootstrap capacitor during very light load conditions or in applications where the output may be pre- charged before the LM25005 is enabled. An internal pre- charge MOSFET is turned on for 250ns each cycle just prior to the on-time interval of the buck switch. 3 www.national.com LM25005
Pin(S) Name Description Application Information
20 BST Boost input for bootstrap capacitor An external capacitor is required between the BST and the
SW pins. A 0.022µF ceramic capacitor is recommended. The capacitor is charged from Vcc via an internal diode during the off-time of the buck switch. NA EP Exposed Pad Exposed metal pad on the underside of the device. It is recommended to connect this pad to the PWB ground plane, in order to aid in heat dissipation. www.national.com 4 LM25005
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 GND 45V BST to GND 60V PRE to GND 45V SW to GND (Steady State) -1.5V BST to VCC 45V VCC to GND 14V BST to SW 14V OUT to GND Limited to Vin SD, SYNC, SS, FB to GND 7V ESD Rating (Note 2) Human Body Model 2kV Storage Temperature Range -65°C to +150°C Operating Ratings (Note 1) VIN 7V to 42V Operation Junction Temperature −40°C to + 125°C Electrical Characteristics Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Junction Temperature range. VIN = 24V, RT = 32.4kΩ unless otherwise stated. (Note 3) Symbol Parameter Conditions Min Typ Max Units STARTUP REGULATOR VccReg Vcc Regulator Output 6.85 7.15 7.45 V Vcc LDO Mode turn-off 9 V Vcc Current Limit Vcc = 0V 20 mA VCC SUPPLY Vcc UVLO Threshold (Vcc increasing) 5.95 6.35 6.75 V Vcc Undervoltage Hysteresis 1 V Bias Current (Iin) FB = 1.3V 3 4.5 mA Shutdown Current (Iin) SD = 0V 50 85 µA SHUTDOWN THRESHOLDS Shutdown Threshold (SD Increasing) 0.5 0.7 0.9 V Shutdown Hysteresis 0.1 V Standby Threshold (Standby Increasing) 1.18 1.225 1.27 V Standby Hysteresis 0.1 V SD Pull-up Current Source 5 µA SWITCH CHARACTERSICS Buck Switch Rds(on) 160 320 mΩ BOOST UVLO 3.8 V BOOST UVLO Hysteresis 0.56 V Pre-charge Switch Rds(on) 75 Ω Pre-charge Switch on-time 275 ns CURRENT LIMIT Cycle by Cycle Current Limit RAMP = 0V 3 3.5 4.25 A Cycle by Cycle Current Limit Delay RAMP = 2.5V 100 ns SOFT-START SS Current Source 7 10 14 µA OSCILLATOR Frequency1 180 200 220 KHz Frequency2 RT = 11kΩ 425 485 525 KHz SYNC Source Impedance 10 kΩ SYNC Sink Impedance 160 Ω SYNC Threshold (falling) 1.4 V Upper SYNC Frequency 550 KHz SYNC Pulse Width Minimum 15 ns 5 www.national.com LM25005
Symbol Parameter Conditions Min Typ Max Units RAMP GENERATOR Ramp Current 1 Vin = 36V, Vout=10V 136 160 184 µA Ramp Current 2 Vin = 10V, Vout=10V 18 25 32 µA PWM COMPARATOR Forced Off-time 500 ns Min On-time 80 ns COMP to PWM Comparator Offset 0.7 V ERROR AMPLIFIER Feedback Voltage Vfb = COMP 1.207 1.225 1.243 V FB Bias Current 10 nA DC Gain 70 dB COMP Sink / Source Current 3 mA Unity Gain Bandwidth 3 MHz THERMAL SHUTDOWN Tsd Thermal Shutdown Threshold 165 °C Thermal Shutdown Hysteresis 25 °C THERMAL RESISTANCE θJC Junction to Case 4 °C/W θJA Junction to Ambient 40 °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: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. Note 3: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL). Typical Performance Characteristics Oscillator Frequency vs RT 20170020 Oscillator Frequency vs Temperature FOSC = 200kHz 20170021 www.national.com 6 LM25005
Soft Start Current vs Temperature 20170022 VCC vs ICC VIN = 12V 20170023 VCC vs VIN RL = 7kΩ 20170024 Error Amplifier Gain/Phase AVCL = 101 20170025 Demoboard Efficiency vs IOUT and VIN 20170026 7 www.national.com LM25005
Typical Application Circuit and Block Diagram 20170003 FIGURE 1. www.national.com 8 LM25005
industrial and automotive power bus voltage ranges. Vcc regulator is enabled to maintain Vcc at approximately 7V. the use of this dual mode regulator. The output of the Vcc regulator is current limited to 20mA. until Vcc falls below 5.3V or the SD pin falls below 1.125V. FIGURE 2. Vin and Vcc Sequencing
FIGURE 5. Simplified Oscillator Block Diagram and SYNC I/O Circuit the error amplifier output voltage at the COMP pin. propagation delay limit the minimum achievable pulsewidth.
The LM25005 contains a unique current monitoring scheme for control and over-current protection. When set correctly, the emulated current sense signal provides a signal which is proportional to the buck switch current with a scale factor of 0.5 V / A. The emulated ramp signal is applied to the current limit comparator. If the emulated ramp signal exceeds 1.75V (3.5A) the present current cycle is terminated (cycle-by-cycle current limiting). In applications with small output inductance and high input voltage the switch current may overshoot due to the propagation delay of the current limit comparator. If an overshoot should occur, the diode current sampling circuit will detect the excess inductor current during the off-time of the buck switch. If the Sample and Hold DC Level exceeds the 1.75V current limit threshold, the buck switch will be disabled and skip pulses until the diode current sampling circuit detects the inductor current has decayed below the current limit threshold. This approach prevents current runaway condi- tions due to propagation delays or inductor saturation since the inductor current is forced to decay following any current overshoot. Soft-Start The soft-start feature allows the regulator to gradually reach the initial steady state operating point, thus reducing start-up stresses and surges. The internal soft-start current source, set to 10µA, gradually increases the voltage of an external soft-start capacitor connected to the SS pin. The soft-start capacitor voltage is connected to the reference input of the error amplifier. Various sequencing and tracking schemes can be implemented using external circuits that limit or clamp the voltage level of the SS pin. In the event a fault is detected (over-temperature, Vcc UVLO, SD) the soft-start capacitor will be discharged. When the fault condition is no longer present a new soft-start sequence will commence. Boost Pin The LM25005 integrates an N-Channel buck switch and as- sociated floating high voltage level shift / gate driver. This gate driver circuit works in conjunction with an internal diode and an external bootstrap capacitor. A 0.022µF ceramic capacitor, connected with short traces between the BST pin and SW pin, is recommended. During the off-time of the buck switch, the SW pin voltage is approximately - 0.5V and the bootstrap ca- pacitor is charged from Vcc through the internal bootstrap diode. When operating with a high PWM duty cycle, the buck switch will be forced off each cycle for 500ns to ensure that the bootstrap capacitor is recharged. Under very light load conditions or when the output voltage is pre-charged, the SW voltage will not remain low during the off-time of the buck switch. If the inductor current falls to zero and the SW pin rises, the bootstrap capacitor will not receive sufficient voltage to operate the buck switch gate driver. For these applications, the PRE pin can be connected to the SW pin to pre-charge the bootstrap capacitor. The internal pre- charge MOSFET and diode connected between the PRE pin and PGND turns on each cycle for 250ns just prior to the onset of a new switching cycle. If the SW pin is at a normal negative voltage level (continuous conduction mode), then no current will flow through the pre-charge MOSFET/diode. Thermal Protection Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction temper- ature is exceeded. When activated, typically at 165 degrees Celsius, the controller is forced into a low power reset state, disabling the output driver and the bias regulator. This feature is provided to prevent catastrophic failures from accidental device overheating. 13 www.national.com LM25005
tions (C SS, R T, C RAMP) directly to the regulator AGND pin. side copper area covering the entire underside of the device. power dissipation of the diode. TABLE 1. 5V, 2.5A Demo Board Bill of Materials
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Physical Dimensions inches (millimeters) unless otherwise noted 20-Lead TSSOP Package www.national.com 20 LM25005
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LM25005 42V, 2.5A Step-Down Switching Regulator THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS. EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: Life support devices or systems are devices 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. A critical component is any component in 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. National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. Copyright© 2007 National Semiconductor Corporation For the most current product information visit us at www.national.com National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 National Semiconductor Europe Customer Support Center Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +49 (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