LM25011AMYX

Product Folder Order Now Support & Community Tools & Software Technical Documents LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 42-V 2-A Constant On-Time Switching Regulator With Adjustable Current Limit 1 Features 3 Description • The LM25011 constant on-time step-down switching regulator features all the functions needed to implement a low-cost, efficient, buck bias regulator capable of supplying up to 2 A of load current. This high-voltage regulator contains an N-Channel Buck switch, a startup regulator, current limit detection, and internal ripple control. The constant on-time regulation principle requires no loop compensation, results in fast load transient response, and simplifies circuit implementation. The operating frequency remains constant with line and load. The adjustable valley current limit detection results in a smooth transition from constant voltage to constant current mode when current limit is reached, without the use of current limit foldback. The PGD output indicates the output voltage has increased to within 5% of the expected regulation value. Additional features include: Low output ripple, VIN under-voltage lockout, adjustable soft-start timing, thermal shutdown, gate drive pre-charge, gate drive under-voltage lockout, and maximum duty cycle limit. 1 • • • • • • • • • • • • • • • LM25011-Q1 is an Automotive Grade Product that is AEC-Q100 Grade 1 Qualified (–40°C to +125°C Operating Junction Temperature) LM25011A Allows Low-Dropout Operation at High Switching Frequency Input Operating Voltage Range: 6 V to 42 V Absolute Maximum Input Rating: 45 V Integrated 2-A N-Channel Buck Switch Adjustable Current Limit Allows for Smaller Inductor Adjustable Output Voltage from 2.51 V Minimum Ripple Voltage at VOUT Power Good Output Switching Frequency Adjustable to 2 MHz COT Topology Features: – Switching Frequency Remains Nearly Constant with Load Current and Input Voltage Variations – Ultra-Fast Transient Response – No Loop Compensation Required – Stable Operation with Ceramic Output Capacitors – Allows for Smaller Output Capacitor and Current Sense Resistor Adjustable Soft-Start Timing Thermal Shutdown Precision 2% Feedback Reference Package: 10-Pin, HVSSOP Create a Custom Design Using the LM25011 Family with the WEBENCH Power Designer 2 Applications • • • • Automotive Safety Infotainment Telecommunication Front Camera The LM25011A has a shorter minimum off-time than the LM25011, which allows for higher frequency operation at low input voltages. Device Information(1) PART NUMBER LM25011 / -Q1 LM25011A / -Q1 PACKAGE BODY SIZE (NOM) HVSSOP (10) 3.00 mm × 3.00 mm (1) For all available packages, see the orderable addendum at the end of the data sheet. Typical Application 6V to 42V Input VIN BST CBST LM25011 CIN RT D1 RT VOUT CS RPGD VPGD Power Good L1 SW RS PGD CSG COUT RFB2 SS CSS SGND FB RFB1 1 An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA. LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Pin Configuration and Functions ......................... Specifications......................................................... 1 1 1 2 3 4 6.1 6.2 6.3 6.4 6.5 6.6 6.7 4 4 4 4 5 6 7 Absolute Maximum Ratings ..................................... Handling Ratings: LM25011...................................... Handling Ratings: LM25011-Q1................................ Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Typical Characteristics .............................................. Detailed Description ............................................ 10 7.1 Overview ................................................................. 10 7.2 Functional Block Diagram ....................................... 10 7.3 Feature Description................................................. 10 7.4 Device Functional Modes........................................ 15 8 Application and Implementation ........................ 16 8.1 Application Information............................................ 16 8.2 Typical Application .................................................. 16 9 Power Supply Recommendations...................... 23 10 Layout................................................................... 23 10.1 Layout Guidelines ................................................. 23 10.2 Layout Example .................................................... 23 10.3 Power Dissipation ................................................. 23 11 Device and Documentation Support ................. 24 11.1 11.2 11.3 11.4 11.5 11.6 Custom Design with WEBENCH Tools................. Receiving Notification of Documentation Updates Related Links ........................................................ Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 24 24 24 24 24 24 12 Mechanical, Packaging, and Orderable Information ........................................................... 24 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision G (February 2013) to Revision H • Page Added Pin Configuration and Functions section, Handling Rating table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section ................................................................................................................................................................................... 1 Changes from Revision F (February 2013) to Revision G • 2 Page Changed layout of National Semiconductor Data Sheet to TI format .................................................................................. 23 Submit Documentation Feedback Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 5 Pin Configuration and Functions 10-Pin HVSSOP Package Top View Exposed Pad on Bottom Connect to Ground VIN 1 10 BST RT 2 9 SW PGD 3 8 CS SS 4 7 CSG SGND 5 6 FB Pin Functions PIN I/O DESCRIPTION APPLICATION INFORMATION NUMBER NAME 1 VIN I Input supply voltage Operating input range is 6 V to 42 V. Transient capability is 45 V. A low ESR capacitor must be placed as close as possible to the VIN and SGND pins. 2 RT I On-time Control An external resistor from VIN to this pin sets the buck switch ontime and the switching frequency. 3 PGD – Power Good Logic output indicates when the voltage at the FB pin has increased to above 95% of the internal reference voltage. Hysteresis is provided. An external pull-up resistor to a voltage less than 7 V is required. 4 SS I Soft-Start An internal current source charges an external capacitor to provide the soft-start function. 5 SGND Signal Ground Ground for all internal circuitry other than the current limit sense circuit. 6 FB I Feedback Internally connected to the regulation comparator. The regulation level is 2.51 V. 7 CSG – Current Sense Ground Ground connection for the current limit sensing circuit. Connect to ground and to the current sense resistor. 8 CS I Current sense Connect to the current sense resistor and the anode of the freewheeling diode. 9 SW O Switching Node Internally connected to the buck switch source. Connect to the external inductor, cathode of the free-wheeling diode, and bootstrap capacitor. 10 BST I Bootstrap capacitor connection of Connect a 0.1-µF capacitor from SW to this pin. The capacitor is the buck switch gate driver. charged during the buck switch off-time via an internal diode. - EP – Exposed Pad Copyright © 2009–2014, Texas Instruments Incorporated Exposed pad on the underside of the package. This pad should be soldered to the PC board ground plane to aid in heat dissipation. Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 3 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings (1) MAX UNIT VIN to SGND (TJ = 25°C) MIN 45 V BST to SGND 52 V 45 V SW to SGND (Steady State) –1.5 BST to SW –0.3 7 V CS to CSG –0.3 0.3 V CSG to SGND –0.3 0.3 V PGD to SGND –0.3 7 V SS to SGND –0.3 3 V RT to SGND –0.3 1 V FB to SGND –0.3 7 V 150 °C For soldering specs, see www.ti.com/packaging. Junction Temperature (1) (1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Recommended Operating Conditions are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics . 6.2 Handling Ratings: LM25011 Tstg Storage temperature range V(ESD) (1) (2) Electrostatic discharge MIN MAX UNIT –65 150 °C Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins (1) 2000 Charged device model (CDM), per JEDEC specification JESD22-C101, all pins (2) 750 V JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. 6.3 Handling Ratings: LM25011-Q1 Tstg Storage temperature range MIN MAX UNIT –65 150 °C Human body model (HBM), per AEC Q100-002 (1) V(ESD) (1) Electrostatic discharge Charged device model (CDM), per AEC Q100-011 2000 Corner pins (1, 5, 6, and 10) 750 Other pins 750 V AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification. 6.4 Recommended Operating Conditions over operating free-air temperature range (unless otherwise noted) (1) VIN Voltage Junction Temperature (1) 4 MIN MAX 6.0 42 UNIT V –40 125 °C (1) Absolute Maximum Ratings are limits beyond which damage to the device may occur. Recommended Operating Conditions are conditions under which operation of the device is intended to be functional. For specifications and test conditions, see the Electrical Characteristics . Submit Documentation Feedback Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 6.5 Thermal Information THERMAL METRIC (1) HVSSOP (DGQ) 10 PINS RθJA Junction-to-ambient thermal resistance RθJC(top) Junction-to-case (top) thermal resistance 54.3 RθJB Junction-to-board thermal resistance 34.2 ψJT Junction-to-top characterization parameter 4.0 ψJB Junction-to-board characterization parameter 33.9 RθJC(bot) Junction-to-case (bottom) thermal resistance 10 (1) UNIT 48 °C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 5 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com 6.6 Electrical Characteristics Typical values correspond to TJ = 25°C. Minimum and maximum limits apply over –40°C to 125°C junction temperature range unless otherwise stated. Unless otherwise stated, the following conditions apply: VIN = 12 V, RT = 50 kΩ. (1) (2) (3) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 1200 1600 µA 5.3 5.9 INPUT (VIN PIN) IIN UVLOVIN Input operating current Non-switching, FB = 3 V VIN undervoltage lock-out threshold VIN increasing 4.6 VIN undervoltage lock-out threshold hysteresis 200 V mV SWITCH CHARACTERISTICS RDS(ON) Buck Switch RDS(ON) ITEST = 200 mA UVLOGD Gate Drive UVLO BST-SW 2.4 UVLOGD Hysteresis 0.3 0.6 3.4 4.4 350 Pre-charge switch voltage ITEST = 10 mA into SW pin Pre-charge switch on-time Ω V mV 1.4 V 120 ns SOFT-START PIN VSS Pullup voltage ISS Internal current source VSS-SH Shutdown threshold 2.51 V 10 µA 70 140 mV –146 –130 CURRENT LIMIT VILIM Threshold voltage at CS –115 mV CS bias current FB = 3 V –120 µA CSG bias current FB = 3 V –35 µA ON TIMER, RT PIN tON - 1 On-time VIN = 12 V, RT = 50 kΩ tON - 2 On-time VIN = 32 V, RT = 50 kΩ 150 200 75 250 ns ns tON - 3 On-time (current limit) LM25011 VIN = 12 V, RT = 50 kΩ 100 ns tON - 3 On-time (current limit) LM25011A VIN = 12 V, RT = 50 kΩ 200 ns tON - 4 On-time VIN = 12 V, RT = 301 kΩ 1020 tON - 5 On-time VIN = 9 V, RT = 30.9 kΩ 130 171 215 ns tON - 6 On-time VIN = 12 V, RT = 30.9 kΩ 105 137 170 ns tON - 7 On-time VIN = 16 V, RT = 30.9 kΩ 79 109 142 ns Minimum off-time (LM25011) 90 150 208 ns Minimum off-time (LM25011A) 52 75 93 2.46 2.51 2.56 ns OFF TIMER tOFF REGULATION COMPARATOR (FB PIN) VREF FB regulation threshold SS pin = steady state FB bias current FB = 3 V 100 V nA POWER GOOD (PGD PIN) Threshold at FB, with respect to VREF FB increasing 91% Threshold hysteresis 95% 3.3% PGDVOL Low state voltage IPGD = 1 mA, FB = 0 V 125 PGDLKG Off state leakage VPGD = 7 V, FB = 3 V 0.1 180 mV µA Junction temperature increasing 155 °C 20 °C THERMAL SHUTDOWN TSD Thermal shutdown Thermal shutdown hysteresis (1) (2) (3) 6 Current flow out of a pin is indicated as a negative number. All hot and cold limits are specified by correlating the electrical characteristics to process and temperature variations and applying statistical process control. The junction temperature (TJ in °C) is calculated from the ambient temperature (TA in °C) and power dissipation (PD in watts) as follows: TJ = TA + (PD × RθJA ) where RθJA (in °C/W) is the package thermal impedance provided in the Thermal Information section. Submit Documentation Feedback Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 6.7 Typical Characteristics Figure 1. Efficiency (Circuit of Figure 19) Figure 2. Efficiency at 2 MHz Figure 3. On-Time vs VIN and RT Figure 4. Voltage at the RT Pin Figure 5. Shutdown Current into VIN Figure 6. Operating Current into VIN Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 7 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com Typical Characteristics (continued) 8 Figure 7. PGD Low Voltage vs Sink Current Figure 8. Reference Voltage vs Temperature Figure 9. Current Limit Threshold vs Temperature Figure 10. Operating Current vs Temperature Figure 11. VIN UVLO vs Temperature Figure 12. SS Pin Shutdown Threshold vs Temperature Submit Documentation Feedback Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 Typical Characteristics (continued) 190 MINIMUM OFF-TIME (ns) 170 LM25011 150 130 110 90 LM25011A 70 50 -40 -20 0 20 40 60 80 100 120 JUNCTION TEMPERATURE (°C) Figure 13. On-Time vs Temperature Copyright © 2009–2014, Texas Instruments Incorporated Figure 14. Minimum Off-Time vs Temperature Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 9 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com 7 Detailed Description 7.1 Overview The LM25011 constant on-time step-down switching regulator features all the functions needed to implement a low-cost, efficient buck bias power converter capable of supplying up to 2.0 A to the load. This high-voltage regulator contains an N-Channel buck switch, is easy to implement, and is available in a 10-pin VSSOP, PowerPAD power enhanced package. The operation of the regulator is based on a constant on-time control principle with the on-time inversely proportional to the input voltage. This feature results in the operating frequency remaining relatively constant with load and input voltage variations. The constant on-time feedback control principle requires no loop compensation resulting in very fast load transient response. The adjustable valley current limit detection results in a smooth transition from constant voltage to constant current when current limit is reached. To aid in controlling excessive switch current due to a possible saturating inductor, the on-time is reduced by approximately 40% when the current limit is detected. The Power Good output (PGD pin) indicates when the output voltage is within 5% of the expected regulation voltage. The LM25011 can be implemented to efficiently step-down higher voltages in non-isolated applications. Additional features include: low output ripple, VIN under-voltage lock-out, adjustable soft-start timing, thermal shutdown, gate drive pre-charge, gate drive under-voltage lock-out, and maximum duty-cycle limit. 7.2 Functional Block Diagram 6V to 42V LM25011(A) VIN 5V REGULATOR Input CIN CBYP UVLO CL RT THERMAL SHUTDOWN OFF TIMER ON TIMER RT FINISH START START FINISH BST 2.5V Gate Drive 10 PA SD UVLO VIN CBST SS LOGIC CSS LEVEL SHIFT L1 + FB CL REGULATION COMPARATOR VOUT SW FCIC CONTROL CURRENT LIMIT COMPARATOR D1 + COUT Pre - Chg - RFB2 CS RPGD Power Good 0.8V PGD + SGND CURRENT LIMIT THRESHOLD + 125 mV RS CSG 2.375V RFB2 7.3 Feature Description 7.3.1 Control Circuit Overview The LM25011 buck regulator employs a control principle based on a comparator and a one-shot on-timer, with the output voltage feedback (FB) compared to an internal reference (2.51 V). If the FB voltage is below the reference, the internal buck switch is switched on for the one-shot timer period which is a function of the input voltage and the programming resistor (RT). Following the on-time, the switch remains off until the FB voltage falls below the reference, but never less than the minimum off-time forced by the off-time one-shot timer. When the FB pin voltage falls below the reference and the off-time one-shot period expires, the buck switch is then turned on for another on-time one-shot period. 10 Submit Documentation Feedback Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 Feature Description (continued) When in regulation, the LM25011 operates in continuous conduction mode at heavy load currents and discontinuous conduction mode at light load currents. In continuous conduction mode, the inductor current is always greater than zero and the operating frequency remains relatively constant with load and line variations. The minimum load current for continuous conduction mode is one-half of the ripple current amplitude of the inductor. The approximate operating frequency is calculated as follows: VOUT FS = -11 (4.1 x 10 x (RT + 0.5k)) + (VIN x 15 ns) (1) The buck switch duty cycle is approximately equal to: DC = tON VOUT = tON x FS = tON + tOFF VIN (2) When the load current is less than one-half of the ripple current amplitude of the inductor, the circuit operates in discontinuous conduction mode. The off-time is longer than in continuous conduction mode while the inductor current is zero, causing the switching frequency to reduce as the load current is reduced. Conversion efficiency is maintained at light loads because the switching losses are reduced with the reduction in load and frequency. The approximate discontinuous operating frequency can be calculated as follows: FS = VOUT2 x L1 x 1.19 x 1021 2 RL x R T (3) where RL = the load resistance, and L1 is the inductor in the circuit. The output voltage is set by the two feedback resistors (RFB1, RFB2 in the Functional Block Diagram ). The regulated output voltage is calculated as follows: VOUT = 2.51 V × (RFB1 + RFB2) / RFB1 (4) Ripple voltage, which is required at the input of the regulation comparator for proper output regulation, is generated internally in the LM25011, and externally when the LM25011A is used. In the LM25011 the ERM (emulated ripple mode) control circuit generates the required internal ripple voltage from the ripple waveform at the CS pin. The LM25011A, which is designed for higher frequency operation, requires additional ripple voltage which must be generated externally and provided to the FB pin. This is described in the Application and Implementation section. 7.3.2 On-Time Timer The on-time for the LM25011/LM25011A is determined by the RT resistor and the input voltage (VIN), calculated from: tON = 4.1 x 10 -11 x (RT + 500:) (VIN) + 15 ns (5) The inverse relationship with VIN results in a nearly constant frequency as VIN is varied. To set a specific continuous conduction mode switching frequency (FS), the RT resistor is determined from the following: VOUT - (VIN x FS x 15 ns) - 500: RT = -11 FS x 4.1 x 10 (6) The on-time must be chosen greater than 90 ns for proper operation. Equation 1, Equation 5, and Equation 6 are valid only during normal operation; that is, the circuit is not in current limit. When the LM25011 operates in current limit, the on-time is reduced by approximately 40% (this feature is not present in LM25011A). This feature reduces the peak inductor current which may be excessively high if the load current and the input voltage are simultaneously high. This feature operates on a cycle-by-cycle basis until the load current is reduced and the Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 11 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com Feature Description (continued) output voltage resumes its normal regulated value. The maximum continuous current into the RT pin must be less than 2 mA. For high-frequency applications, the maximum switching frequency is limited at the maximum input voltage by the minimum on-time one-shot period (90 ns). At minimum input voltage the maximum switching frequency is limited by the minimum off-time one-shot period which, if reached, prevents achievement of the proper duty cycle. 7.3.3 Current Limit Current limit detection occurs during the off-time by monitoring the voltage across the external current sense resistor RS. Referring to the Functional Block Diagram , during the off-time the recirculating current flows through the inductor, through the load, through the sense resistor, and through D1 to the inductor. If the voltage across the sense resistor exceeds the threshold (VILIM), the current limit comparator output switches to delay the start of the next on-time period. The next on-time starts when the recirculating current decreases such that the voltage across RS reduces to the threshold and the voltage at FB is below 2.51 V. The operating frequency is typically lower due to longer-than-normal off-times. When current limit is detected, the on-time is reduced by approximately 40% (only in LM25011) if the voltage at the FB pin is below its threshold when the voltage across RS reduces to its threshold (VOUT is low due to current limiting). Figure 15 illustrates the inductor current waveform during normal operation and in current limit. During the first normal operation, the load current is I01, the average of the inductor current waveform. As the load resistance is reduced, the inductor current increases until the lower peak of the inductor ripple current exceeds the threshold. During the current limited portion of Figure 15, each on-time is reduced by approximately 40%, resulting in lower ripple amplitude for the inductor current. During this time the LM25011 is in a constant-current mode with an average load current equal to the current limit threshold plus half the ripple amplitude (IOCL), and the output voltage is below the normal regulated value. Normal operation resumes when the load current is reduced (to IO2), allowing VOUT and the on-time to return to their normal values. Note that in the second period of normal operation, even though the peak current of the inductor exceeds the current limit threshold during part of each cycle, the circuit is not in current limit because the inductor current falls below the current limit threshold during each off-time. The peak current allowed through the buck switch is 3.5 A and the maximum allowed average current is 2.0 A. IPK IOCL Current Limit Threshold IO2 'I Inductor Current IO1 0V Voltage at the CS Pin Voltage at the FB Pin 2.51V Load Current Increases Normal Operation Current Limited Load Current Decreases Normal Operation Figure 15. Normal and Current Limit Operation 12 Submit Documentation Feedback Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 Feature Description (continued) 7.3.4 Ripple Requirements The LM25011 requires about 25 mVP-P of ripple voltage at the CS pin. Higher switching frequencies may require more ripple. That ripple voltage is generated by the decreasing recirculating current (the inductor ripple current) through RS during the off-time. See Figure 16. Inductor Current 'I 0V Voltage at CS VRIPPLE tOFF tON Figure 16. CS Pin Waveform The ripple voltage is equal to: VRIPPLE = ΔI × RS (7) where ΔI is the inductor current ripple amplitude, and RS is the current-sense resistor at the CS pin. More ripple can be achieved by decreasing the inductor value. The LM25011A, with its shorter minimum off-time, typically will require more ripple than the LM25011. An external circuit to increase the effective ripple voltage may be needed. Different methods of generating this ripple are explained in the External Components section. 7.3.5 N-Channel Buck Switch and Driver The LM25011 integrates an N-Channel buck switch and associated floating high-voltage gate driver. The gate driver circuit works in conjunction with an external bootstrap capacitor (CBST) and an internal high-voltage diode. A 0.1-µF capacitor connected between BST and SW provides the supply voltage for the driver during the ontime. During each off-time, the SW pin is at approximately –1 V, and CBST is recharged from the internal 5-V regulator for the next on-time. The minimum off-time ensures a sufficient time each cycle to recharge the bootstrap capacitor. In applications with relatively high output voltage and low minimum load current, the internal pre-charge device of the LM25011 may not pull the SW pin sufficiently low during the off-time to maintain the voltage on the bootstrap capacitor. If the bootstrap capacitor (CBST) discharges during the long off-times, and the regulator will cycle on and off at a low frequency. Decreasing the values of the feedback resistors RFB1 and RFB2 to provide a minimum load of typically 1mA at nominal VOUT will increase the minimum switching frequency and maintain sufficient bootstrap capacitor voltage. 7.3.6 Soft-Start The soft-start feature allows the converter to gradually reach a steady-state operating point, thereby reducing startup stresses and current surges. Upon turn-on, when VIN reaches its undervoltage lock-out threshold an internal 10-µA current source charges the external capacitor at the SS pin to 2.51 V (t1 in Figure 17). The ramping voltage at SS ramps the non-inverting input of the regulation comparator and the output voltage, in a controlled manner. For proper operation, the soft-start capacitor should be no smaller than 1000 pF. Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 13 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com Feature Description (continued) The LM25011 can be employed as a tracking regulator by applying the controlling voltage to the SS pin. The output voltage of the regulator tracks the applied voltage, gained up by the ratio of the feedback resistors. The applied voltage at the SS pin must be within the range of 0.5 V to 2.6 V. The absolute maximum rating for the SS pin is 3.0 V. If the tracking function causes the voltage at the FB pin to go below the thresholds for the PGD pin, the PGD pin will switch low (see the Power Good Output (PGD) section). An internal switch grounds the SS pin if the input voltage at VIN is below its undervoltage lock-out threshold or if the thermal shutdown activates. If the tracking function (described above) is used, the tracking voltage applied to the SS pin must be current limited to a maximum of 1 mA. UVLO VIN SW Pin Inductor Current SS Pin VOUT PGD t1 Figure 17. Startup Sequence 7.3.7 Power Good Output (PGD) The Power Good output (PGD) indicates when the voltage at the FB pin is close to the internal 2.51-V reference voltage. The rising threshold at the FB pin for the PGD output to switch high is 95% of the internal reference. The falling threshold for the PGD output to switch low is approximately 3.3% below the rising threshold. The PGD pin is internally connected to the drain of an N-channel MOSFET switch. An external pull-up resistor (RPGD), connected to an appropriate voltage not exceeding 7 V, is required at PGD to indicate the LM25011 status to other circuitry. When PGD is low, the pin voltage is determined by the current into the pin. See Figure 7, PGD Low Voltage vs Sink Current. 14 Submit Documentation Feedback Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 Feature Description (continued) Upon powering up the LM25011, the PGD pin is high until the voltage at VIN reaches 2 V, at which time PGD switches low. As VIN is increased, PGD stays low until the output voltage takes the voltage at the FB pin above 95% of the internal reference voltage, at which time PGD switches high. As VIN is decreased (during shutdown), PGD remains high until either the voltage at the FB pin falls below approximately 92% of the internal reference or when VIN falls below its lower UVLO threshold, whichever occurs first. PGD then switches low, and remains low until VIN falls below 2 V, at which time PGD switches high. If the LM25011 is used as a tracking regulator (see the Soft-Start section), the PGD output is high as long as the voltage at the FB pin is above the thresholds mentioned above. 7.3.8 Thermal Shutdown The LM25011 should be operated so the junction temperature does not exceed 125°C. If the junction temperature increases above that, an internal thermal shutdown circuit activates (typically) at 155°C, taking the controller to a low-power reset state by disabling the buck switch and taking the SS pin to ground. This feature helps prevent catastrophic failures from accidental device overheating. When the junction temperature decreases below 135°C (typical hysteresis = 20°C), normal operation resumes. 7.4 Device Functional Modes 7.4.1 Shutdown Function The SS pin can be used to shutdown the LM25011 by grounding the SS pin as shown in Figure 18. Releasing the pin allows normal operation to resume. SS STOP RUN LM25011 CSS Figure 18. Shutdown Implementation Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 15 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com 8 Application and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 8.1 Application Information The LM25011/LM25011-Q1 is a non-synchronous buck regulator designed to operate over a wide input voltage range and output current. Spreadsheet-based quick-start calculation tools and the on-line WEBENCH® software can be used to create a buck design with the bill of materials, estimated efficiency, and the complete solution cost. 8.2 Typical Application 8.2.1 LM25011 Example Circuit The final circuit is shown in Figure 19, and its performance is shown in Figure 20 and Figure 21. The current limit measures approximately 1.62 A at VIN = 8 V, and 1.69 A at VIN = 36 V. 8V to 36V Input RT 118 k: CIN 4.7 PF BST VIN CBYP 0.1 PF CBST 0.1 PF L1 10 PH LM25011 SW RT VOUT D1 5V VPGD CS RPGD 10 k: Power Good COUT 10 PF RS 80 m: PGD RFB2 4.99 k: CSG SS CSS 0.022 PF SGND FB RFB1 4.99 k: Figure 19. Example Circuit 8.2.1.1 Design Requirements Table 1 shows the design parameters. Table 1. Design Parameters DESIGN PARAMETER Input voltage range Output voltage 5V Maximum load current (IOUT(max)) 1.5 A Minimum load current (IOUT(min)) 300 mA Switching frequency (FSW) 1 MHz Soft-start time 16 VALUE 8 V to 36 V Submit Documentation Feedback 5 ms Copyright © 2009–2014, Texas Instruments Incorporated Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 www.ti.com SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 8.2.1.2 Detailed Design Procedure 8.2.1.2.1 Custom Design with WEBENCH Tools Click here to create a custom design using the LM25011 device with the WEBENCH® Power Designer. 1. Start by entering your VIN, VOUT and IOUT requirements. 2. Optimize your design for key parameters like efficiency, footprint and cost using the optimizer dial and compare this design with other possible solutions from Texas Instruments. 3. WEBENCH Power Designer provides you with a customized schematic along with a list of materials with real time pricing and component availability. 4. In most cases, you will also be able to: – Run electrical simulations to see important waveforms and circuit performance, – Run thermal simulations to understand the thermal performance of your board, – Export your customized schematic and layout into popular CAD formats, – Print PDF reports for the design, and share your design with colleagues. 5. Get more information about WEBENCH tools at www.ti.com/webench. 8.2.1.2.2 External Components The procedure for calculating the external components is illustrated with a design example using the LM25011. Referring to the Functional Block Diagram , the circuit is to be configured for the following specifications: • VOUT = 5 V • VIN = 8 V to 36 V • Minimum load current for continuous conduction mode IOUT(min) = 300 mA • Maximum load current IOUT(max) = 1.5 A • Switching frequency (FSW) = 1.0 MHz • Soft-start time = 5 ms RFB2 and RFB1: These resistors set the output voltage, and their ratio is calculated from: RFB2/RFB1 = (VOUT / 2.51 V) – 1 (8) For this example, RFB2/RFB1 = 0.992. RFB1 and RFB2 should be chosen from standard value resistors in the range of 1.0 kΩ to 10 kΩ which satisfy the above ratio. For this example, 4.99 kΩ is chosen for both resistors, providing a 5.02-V output. RT: This resistor sets the on-time and (by default) the switching frequency. First check that the desired frequency does not require an on-time or off-time shorter than the minimum allowed values (90 ns and 150, respectively). The minimum on-time occurs at the maximum input voltage. For this example: VOUT tON(min) = VIN(max) x FS = 5V = 139 ns 36V x 1 MHz (9) The minimum off-time occurs at the minimum input voltage. For this example: tOFF(min) = VIN(min) - VOUT VIN(min) x FS = 8V - 5V = 375 ns 8V x 1 MHz (10) Both the on-time and off-time are acceptable because they are significantly greater than the minimum value for each. The RT resistor is calculated from Equation 6 using the minimum input voltage: 5 - (8V x 1MHz x 15 ns) - 500: = 118.5 k: RT = -11 1MHz x 4.1 x 10 (11) A standard value 118-kΩ resistor is selected. The minimum on-time calculates to 152 ns at VIN = 36 V, and the maximum on-time calculates to 672 ns at VIN = 8 V. Copyright © 2009–2014, Texas Instruments Incorporated Submit Documentation Feedback Product Folder Links: LM25011 LM25011-Q1 LM25011A LM25011A-Q1 17 LM25011, LM25011-Q1, LM25011A, LM25011A-Q1 SNVS617H – APRIL 2009 – REVISED NOVEMBER 2014 www.ti.com L1: The parameters controlled by the inductor are the inductor current ripple amplitude (IOR), and the ripple voltage amplitude across the current sense resistor RS. The minimum load current is used to determine the maximum allowable ripple to maintain continuous conduction mode (the lower peak does not reach 0 mA). This is not a requirement of the LM25011, but serves as a guideline for selecting L1. For this example, the maximum ripple current should be less than: IOR(max) = 2 × IOUT(min) = 600 mAP-P (12) For applications where the minimum load current is zero, a good starting point for allowable ripple is 20% of the maximum load current. In this case substitute 20% of IOUT(max) for IOUT(min) in Equation 12. The ripple amplitude calculated in Equation 12 is then used in Equation 13: L1(min) = tON(min) x (VIN(max) - VOUT) = 7.85 PH IOR(max) (13) A standard value 10-µH inductor is chosen. Using this inductor value, the maximum ripple current amplitude, which occurs at maximum VIN, calculates to 472 mAP-P, and the peak current is 1736 mA at maximum load current. Ensure the selected inductor is rated for this peak current. The minimum ripple current, which occurs at minimum VIN, calculates to 200 mAP-P. RS: The minimum current limit threshold is calculated at maximum load current using the minimum ripple current calculated above. The current limit threshold is the lower peak of the inductor current waveform when in current limit (see Figure 15). ILIM = 1.5 A – (0.2 A / 2) = 1.4 A (14) Current limit detection occurs when the voltage across the sense resistor (RS) reaches the current limit threshold. To allow for tolerances, the sense resistor value is calculated using the minimum threshold specification: RS = 115 mV / 1.4 A = 82 mΩ (15) The next smaller standard value, 80 mΩ, is selected. The next step is to ensure that sufficient ripple voltage occurs across RS with this value sense resistor. As mentioned in the Ripple Requirements section, a minimum of 15-mVP-P voltage ripple is required across the RS sense resistor during the off-time to ensure the regulation circuit operates properly. The ripple voltage is the product of the inductor ripple current amplitude and the sense resistor value. In this case, the minimum ripple voltage calculates to: VRIPPLE = ΔI × RS = 200 mA × 0.080 Ω = 16 mV (16) If the ripple voltage had calculated to less than 15 mVP-P, the inductor value would have to be reduced to increase the ripple current amplitude. This would have required a recalculation of ILIM and RS in the above equations. Because the minimum requirement is satisfied in this case, no change is necessary. The nominal current limit threshold calculates to 1.63 A. The minimum and maximum thresholds calculate to 1.44 A and 1.83 A, respectively, using the minimum and maximum limits for the current limit threshold specification. The load current is equal to the threshold current plus one-half of the ripple current. Under normal load conditions, the maximum power dissipation in RS occurs at maximum load current, and at maximum input voltage where the on-time duty cycle is minimum. In this design example, the minimum on-time duty cycle is: Duty Cycle = D = VOUT 5V = 13.9% = 36V VIN (17) At maximum load current, the power dissipation in RS is equal to: P(RS) = (1.5 A)2 × 0.080 Ω × (1 – 0.139) = 155 mW (18) When in current limit the maximum power dissipation in RS calculates to P(RS) = (1.83 A + 0.472 A / 4)2 × 0.080 Ω = 304 mW (19) Duty cycle is not included in this power calculation because the on-time duty cycle is typically