Product Folder Sample & Buy Technical Documents Support & Community Tools & Software LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 LM5574-Q1 Simple Switcher® 75 V, 0.5 A Step-Down Switching Regulator 1 Features 3 Description • The LM5574-Q1 is an easy to use SIMPLE SWITCHER® buck regulator which allows design engineers to design and optimize a robust power supply using a minimum set of components. Operating with an input voltage range of 6 - 75 V, the LM5574-Q1 delivers 0.5 A of continuous output current with an integrated 750 mΩ N-Channel MOSFET. The regulator utilizes an Emulated Current Mode architecture which provides inherent line regulation, tight load transient response, and ease of loop compensation without the usual limitation of lowduty cycles associated with current mode regulators. The operating frequency is adjustable from 50 kHz to 500 kHz to allow optimization of size and efficiency. To reduce EMI, a frequency synchronization pin allows multiple ICs from the LM(2)557x family to selfsynchronize or to synchronize to an external clock. The LM5574-Q1 ensures robustness with cycle-bycycle current limit, short-circuit protection, thermal shut-down, and remote shut-down. The device is available in a TSSOP-16 package. The LM5574-Q1 is supported by the full suite of WEBENCH® On-Line design tools. 1 • • • • • • • • • • • • LM5574-Q1 is an Automotive Grade Product That is AEC-Q100 Grade Qualified −40°C to + 150°C Operating Junction Temperature Integrated 75 V, 750 mΩ N-Channel MOSFET Ultra-Wide Input Voltage Range From 6 V to 75 V Adjustable Output Voltage as Low as 1.225 V 1.65% Feedback Reference Accuracy Operating Frequency Adjustable Between 50 kHz and 500 kHz With Single Resistor Master or Slave Frequency Synchronization Adjustable Soft-Start Emulated Current Mode Control Architecture Wide Bandwidth Error Amplifier Built-In Protection Package: – TSSOP-16 2 Applications • • Device Information(1) Automotive Industrial PART NUMBER LM5574-Q1 PACKAGE BODY SIZE (NOM) TSSOP (16) 5.00 mm x 4.40 mm (1) For all available packages, see the orderable addendum at the end of the datasheet. Simplified Application Schematic VIN BST VIN VOUT LM5574 SYNC SW SD IS RT VCC SS RAMP OUT FB COMP GND 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. LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 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 4 4 4 5 5 7 Absolute Maximum Ratings ...................................... Handling Ratings....................................................... Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Typical Characteristics .............................................. 7.3 Feature Description................................................... 9 7.4 Device Functional Modes........................................ 10 8 Application and Implementation ........................ 16 8.1 Application Information............................................ 16 8.2 Typical Application .................................................. 17 9 Power Supply Recommendations...................... 24 10 Layout................................................................... 24 10.1 Layout Guidelines ................................................. 24 10.2 Layout Example .................................................... 25 11 Device and Documentation Support ................. 27 Detailed Description .............................................. 9 11.1 Trademarks ........................................................... 27 11.2 Electrostatic Discharge Caution ............................ 27 11.3 Glossary ................................................................ 27 7.1 Overview ................................................................... 9 7.2 Functional Block Diagram ......................................... 9 12 Mechanical, Packaging, and Orderable Information ........................................................... 27 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision B (April 2013) to Revision C • 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 A (April 2013) to Revision B • 2 Page Page Changed layout of National Data Sheet to TI format ........................................................................................................... 25 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 5 Pin Configuration and Functions 16-Pin TSSOP Package Top View 1 VCC BST SD PRE VIN SW 2 3 4 5 6 7 8 SYNC IS COMP PGND FB OUT RT SS RAMP AGND 16 15 14 13 12 11 10 9 Pin Functions PIN I/O DESCRIPTION APPLICATION INFORMATION NO. NAME 1 VCC O Output of the bias regulator VCC tracks VIN up to 9 V. Beyond 9 V, VCC is regulated to 7 Volts. A 0.1-uF to 1-uF ceramic decoupling capacitor is required. An external voltage (7.5 V – 14 V) can be applied to this pin to reduce internal power dissipation. 2 SD I Shutdown or UVLO input If the SD pin voltage is below 0.7 V, the regulator will be in a low power state. If the SD pin voltage is between 0.7 V and 1.225 V, the regulator will be in standby mode. If the SD pin voltage is above 1.225 V 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 5 µA pull-up current source configures the regulator fully operational. 3 Vin I Input supply voltage Nominal operating range: 6 V to 75 V 4 SYNC I Oscillator synchronization input or output The internal oscillator can be synchronized to an external clock with an external pull-down device. Multiple LM5574-Q1 devices can be synchronized together by connection of their SYNC pins. 5 COMP O Output of the internal error amplifier The loop compensation network should be connected between this pin and the FB pin. 6 FB I Feedback signal from the regulated output This pin is connected to the inverting input of the internal error amplifier. The regulation threshold is 1.225 V. 7 RT I Internal oscillator frequency set input The internal oscillator is set with a single resistor, connected between this pin and the AGND pin. 8 RAMP O 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 50 pF to 2000 pF. 9 AGND Ground Analog ground Internal reference for the regulator control functions 10 SS O Soft-start An external capacitor and an internal 10 µA 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. 11 OUT O Output voltage connection Connect directly to the regulated output voltage. Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 3 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Pin Functions (continued) PIN I/O DESCRIPTION APPLICATION INFORMATION NO. NAME 12 PGND Ground Power ground Low side reference for the PRE switch and the IS sense resistor. 13 IS I Current sense Current measurement connection for the recirculating 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. 14 SW O 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. 15 PRE O Pre-charge assist for the bootstrap capacitor 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 LM5574-Q1 is enabled. An internal pre-charge MOSFET is turned on for 250 ns each cycle just prior to the on-time interval of the buck switch. 16 BST I Boost input for bootstrap capacitor An external capacitor is required between the BST and the SW pins. A 0.022-µF ceramic capacitor is recommended. The capacitor is charged from VCC via an internal diode during the off-time of the buck switch. 6 Specifications 6.1 Absolute Maximum Ratings (1) (2) MAX UNIT VIN to GND MIN 76 V BST to GND 90 V PRE to GND 76 V –1.5 V BST to VCC 76 V SD, VCC to GND 14 V BST to SW 14 V SW to GND (Steady State) OUT to GND Limited to VIN SYNC, SS, FB, RAMP to GND (1) (2) 7 V 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 ensured specifications and test conditions, see the Electrical Characteristics. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. 6.2 Handling Ratings Tstg Storage temperature range V(ESD) Electrostatic discharge (1) MIN MAX UNIT –65 150 °C Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins (1) 2 kV JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. 6.3 Recommended Operating Conditions VIN Operation Junction Temperature 4 Submit Documentation Feedback MIN MAX 6 75 UNIT V –40 150 °C Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 6.4 Thermal Information LM5574-Q1 THERMAL METRIC (1) PW UNIT 16 PINS RθJA Junction-to-ambient thermal resistance 90 RθJC(top) Junction-to-case (top) thermal resistance 30 (1) °C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. 6.5 Electrical Characteristics VIN = 48V, RT = 32.4kΩ, typical values correspond to TJ = 25°C. Minimum and maximum limits apply over -40°C to 125°C junction temperature range unless otherwise stated. PARAMETER TEST CONDITIONS MIN TYP MAX 6.85 7.15 7.5 UNIT STARTUP REGULATOR VCCReg VCC Regulator Output VCC LDO Mode turn-off VCC Current Limit VCC = 0 V VCC UVLO Threshold (VCC increasing) V 9 V 25 mA VCC SUPPLY 5.01 VCC Undervoltage Hysteresis 5.35 5.69 0.35 V V Bias Current (Iin) FB = 1.3 V 3.7 4.5 mA Shutdown Current (Iin) SD = 0 V 57 85 µA 0.7 0.9 V SHUTDOWN THRESHOLDS Shutdown Threshold (SD Increasing) 0.43 Shutdown Hysteresis 0.1 Standby Threshold (Standby Increasing) 1.15 Standby Hysteresis SD Pull-up Current Source 1.225 V 1.3 V 0.1 V 5 µA SWITCH CHARACTERISTICS Buck Switch Rds(on) 750 BOOST UVLO 1650 4 BOOST UVLO Hysteresis mΩ V 0.56 V Pre-charge Switch Rds(on) 70 Ω Pre-charge Switch on-time 250 ns CURRENT LIMIT Cycle by Cycle Current Limit RAMP = 0 V Cycle by Cycle Current Limit Delay RAMP = 2.5 V 0.58 0.7 0.9 75 A ns SOFT-START SS Current Source 7 10 14 µA 180 200 220 kHz 425 485 545 kHz OSCILLATOR Frequency1 Frequency2 RT = 11kΩ SYNC Source Impedance 11 kΩ SYNC Sink Impedance 110 Ω SYNC Threshold (falling) 1.3 SYNC Frequency RT = 11kΩ SYNC Pulse Width Minimum V 550 kHz 15 ns RAMP GENERATOR Ramp Current 1 VIN = 60 V, VOUT=10 V 467 550 633 µA Ramp Current 2 VIN = 10 V, VOUT=10 V 36 50 64 µA Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 5 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Electrical Characteristics (continued) VIN = 48V, RT = 32.4kΩ, typical values correspond to TJ = 25°C. Minimum and maximum limits apply over -40°C to 125°C junction temperature range unless otherwise stated. PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 390 500 590 ns PWM COMPARATOR Forced Off-time Min On-time 80 ns COMP to PWM Comparator Offset 0.7 V ERROR AMPLIFIER Feedback Voltage Vfb = COMP 1.205 1.225 1.245 V FB Bias Current 17 nA DC Gain 70 dB 3 MHz 250 mΩ Thermal Shutdown Threshold 180 °C Thermal Shutdown Hysteresis 25 °C COMP Sink / Source Current 3 Unity Gain Bandwidth mA DIODE SENSE RESISTANCE DSENSE THERMAL SHUTDOWN Tsd 6 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 6.6 Typical Characteristics OSCILLATOR FREQUENCY (kHz) 1000 100 10 1 10 100 1000 RT (k:) Figure 1. Oscillator Frequency vs RT Figure 2. Oscillator Frequency vs Temperature FOSC = 200 kHz 8 VCC (V) 6 4 2 0 0 12 8 4 16 20 24 ICC (mA) 10 6 4 225 40 180 30 135 20 GAIN (dB) VCC (V) 8 50 PHASE 10 45 0 Ramp Down 0 GAIN -10 2 Ramp Up 0 0 2 4 6 -45 -20 -30 10k 8 -90 100k 1M 10M -135 100M 10 FREQUENCY (Hz) VIN (V) Figure 5. VCC vs VIN RL = 7kΩ 90 PHASE (°) Figure 4. VCC vs ICC VIN = 12 V Figure 3. Soft Start Current vs Temperature Figure 6. Error Amplifier Gain And Phase AVCL = 101 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 7 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Typical Characteristics (continued) 100 VIN = 7V 90 EFFICIENCY (%) 80 70 VIN = 75V 60 VIN = 48V 50 40 VIN = 24V 30 20 10 0 0.1 0.2 0.3 0.4 0.5 IOUT (A) Figure 7. Demoboard Efficiency vs IOUT and VIN 8 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 7 Detailed Description 7.1 Overview The LM5574-Q1 switching regulator features all of the functions necessary to implement an efficient high voltage buck regulator using a minimum of external components. This easy to use regulator integrates a 75 V N-Channel buck switch with an output current capability of 0.5 Amps. The regulator control method is based on current mode control utilizing an emulated current ramp. Peak current mode control provides inherent line voltage feedforward, cycle-by-cycle current limiting, and ease of loop compensation. The use of an emulated control ramp reduces noise sensitivity of the pulse-width modulation circuit, allowing reliable processing of very small duty cycles necessary in high input voltage applications. The operating frequency is user programmable from 50 kHz to 500 kHz. An oscillator synchronization pin allows multiple LM5574-Q1 regulators to self synchronize or be synchronized to an external clock. The output voltage can be set as low as 1.225 V. Fault protection features include, current limiting, thermal shutdown and remote shutdown capability. The device is available in the TSSOP-16 package. The functional block diagram and typical application of the LM5574-Q1 are shown in Figure 16. The LM5574-Q1 can be applied in numerous applications to efficiently step-down a high, unregulated input voltage. The device is well suited for telecom, industrial and automotive power bus voltage ranges. 7.2 Functional Block Diagram VIN 7V ± 75V C1 1.0 VIN 3 5 PA R1 OPEN LM5574 7V REGULATOR 1.225V 2 SD STANDBY VCC SHUTDOWN SD 0.7V C2 OPEN R2 OPEN 10 SS BST UVLO C7 0.022 DRIVER S Q 1.225V 16 VIN DIS CLK 10 PA C4 0.01 C8 0.47 THERMAL SHUTDOWN UVLO 1 R Q LEVEL SHIFT SW 14 L1 100 PH 5V PWM 0.7V PRE 15 C_LIMIT 6 FB C6 open C5 0.022 R4 24.9k ERROR AMP 1.4V 2V/A + 5 COMP CLK Ir OSCILLATOR SYNC 4 RAMP 8 RT 7 SYNC R3 21k D1 CMSH2-100M CLK VIN TRACK SAMPLE and HOLD RAMP GENERATOR Ir = (10 PA x (VIN ± VOUT)) + 50 PA IS C9 22 13 PGND 12 AGND 9 CLK OUT 11 R5 5.11k R6 1.65k C3 470p 7.3 Feature Description 7.3.1 Shutdown And Standby The LM5574-Q1 contains a dual level Shutdown (SD) circuit. When the SD pin voltage is below 0.7 V, the regulator is in a low current shutdown mode. When the SD pin voltage is greater than 0.7 V but less than 1.225 V, the regulator is in standby mode. In standby mode the VCC regulator is active but the output switch is disabled. When the SD pin voltage exceeds 1.225 V, the output switch is enabled and normal operation begins. An internal 5 µA pull-up current source configures the regulator to be fully operational if the SD pin is left open. Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 9 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Feature Description (continued) An external set-point voltage divider from VIN to GND can be used to set the operational input range of the regulator. The divider must be designed such that the voltage at the SD pin will be greater than 1.225 V when Vin is in the desired operating range. The internal 5 µA pull-up current source must be included in calculations of the external set-point divider. Hysteresis of 0.1 V is included for both the shutdown and standby thresholds. The SD pin is internally clamped with a 1 kΩ resistor and an 8 V zener clamp. The voltage at the SD pin should never exceed 14 V. If the voltage at the SD pin exceeds 8 V, the bias current will increase at a rate of 1 mA/V. The SD pin can also be used to implement various remote enable / disable functions. Pulling the SD pin below the 0.7 V threshold totally disables the controller. If the SD pin voltage is above 1.225 V the regulator will be operational. 7.3.2 Current Limit The LM5574-Q1 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 2.0 V / A. The emulated ramp signal is applied to the current limit comparator. If the emulated ramp signal exceeds 1.4 V (0.7 A) 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 & hold DC level exceeds the 1.4 V 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 conditions due to propagation delays or inductor saturation since the inductor current is forced to decay following any current overshoot. 7.3.3 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 10 µA, 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. 7.3.4 Thermal Protection Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction temperature is exceeded. When activated, typically at 180°C, 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. 7.4 Device Functional Modes 7.4.1 High Voltage Start-Up Regulator The LM5574-Q1 contains a dual-mode internal high voltage startup regulator that provides the VCC bias supply for the PWM controller and boot-strap MOSFET gate driver. The input pin (VIN) can be connected directly to the input voltage, as high as 75 Volts. For input voltages below 9 V, a low dropout switch connects VCC directly to VIN. In this supply range, VCC is approximately equal to VIN. For VIN voltage greater than 9 V, the low dropout switch is disabled and the VCC regulator is enabled to maintain VCC at approximately 7 V. The wide operating range of 6 V to 75 V is achieved through the use of this dual mode regulator. The output of the VCC regulator is current limited to 25 mA. Upon power up, the regulator sources current into the capacitor connected to the VCC pin. When the voltage at the VCC pin exceeds the VCC UVLO threshold of 5.35 V and the SD pin is greater than 1.225 V, the output switch is enabled and a soft-start sequence begins. The output switch remains enabled until VCC falls below 5.0 V or the SD pin falls below 1.125 V. 10 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Device Functional Modes (continued) An auxiliary supply voltage can be applied to the VCC pin to reduce the IC power dissipation. If the auxiliary voltage is greater than 7.3 V, the internal regulator will essentially shut off, reducing the IC power dissipation. The VCC regulator series pass transistor includes a diode between VCC and VIN that should not be forward biased in normal operation. Therefore the auxiliary VCC voltage should never exceed the VIN voltage. In high voltage applications extra care should be taken to ensure the VIN pin does not exceed the absolute maximum voltage rating of 76 V. During line or load transients, voltage ringing on the VIN line that exceeds the Absolute Maximum Ratings can damage the IC. Both careful PC board layout and the use of quality bypass capacitors located close to the VIN and GND pins are essential. VIN 9V VCC 7V 5.25V Internal Enable Signal Figure 8. VIN and VCCSequencing 7.4.2 Oscillator and Sync Capability The LM5574-Q1 oscillator frequency is set by a single external resistor connected between the RT pin and the AGND pin. The RT resistor should be located very close to the device and connected directly to the pins of the IC (RT and AGND).To set a desired oscillator frequency (F), the necessary value for the RT resistor can be calculated from the following equation: 1 - 580 x 10-9 F RT = 135 x 10-12 (1) The SYNC pin can be used to synchronize the internal oscillator to an external clock. The external clock must be of higher frequency than the free-running frequency set by the RT resistor. A clock circuit with an open drain output is the recommended interface from the external clock to the SYNC pin. The clock pulse duration should be greater than 15 ns. Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 11 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Device Functional Modes (continued) LM5574 LM5574 SYNC SYNC SW SYNC AGND CLK LM5574 SW SYNC 500 ns UP TO 5 TOTAL DEVICES Figure 9. Sync from External Clock Figure 10. Sync from Multiple Devices Multiple LM5574-Q1 devices can be synchronized together simply by connecting the SYNC pins together. In this configuration, all of the devices will be synchronized to the highest frequency device. The diagram in Figure 11 illustrates the SYNC input/output features of the LM5574-Q1. The internal oscillator circuit drives the SYNC pin with a strong pull-down / weak pull-up inverter. When the SYNC pin is pulled low either by the internal oscillator or an external clock, the ramp cycle of the oscillator is terminated and a new oscillator cycle begins. Thus, if the SYNC pins of several LM5574-Q1 IC’s are connected together, the IC with the highest internal clock frequency will pull the connected SYNC pins low first and terminate the oscillator ramp cycles of the other IC’s. The LM5574-Q1 with the highest programmed clock frequency will serve as the master and control the switching frequency of the all the devices with lower oscillator frequency. 5V SYNC 10k I = f(RT) 2.5V Q S Q R DEADTIME ONE-SHOT Figure 11. Simplified Oscillator Block Diagram and SYNC I/O Circuit 7.4.3 Error Amplifier and PWM Comparator The internal high gain error amplifier generates an error signal proportional to the difference between the regulated output voltage and an internal precision reference (1.225 V). The output of the error amplifier is connected to the COMP pin allowing the user to provide loop compensation components, generally a type II network, as illustrated in Figure 16. This network creates a pole at DC, a zero and a noise reducing high frequency pole. The PWM comparator compares the emulated current sense signal from the RAMP generator to the error amplifier output voltage at the COMP pin. 12 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Device Functional Modes (continued) 7.4.4 Ramp Generator The ramp signal used in the pulse width modulator for current mode control is typically derived directly from the buck switch current. This switch current corresponds to the positive slope portion of the output inductor current. Using this signal for the PWM ramp simplifies the control loop transfer function to a single pole response and provides inherent input voltage feed-forward compensation. The disadvantage of using the buck switch current signal for PWM control is the large leading edge spike due to circuit parasitics that must be filtered or blanked. Also, the current measurement may introduce significant propagation delays. The filtering, blanking time and propagation delay limit the minimum achievable pulsewidth. In applications where the input voltage may be relatively large in comparison to the output voltage, controlling small pulsewidths and duty cycles is necessary for regulation. The LM5574-Q1 utilizes a unique ramp generator, which does not actually measure the buck switch current but rather reconstructs the signal. Reconstructing or emulating the inductor current provides a ramp signal to the PWM comparator that is free of leading edge spikes and measurement or filtering delays. The current reconstruction is comprised of two elements; a sample & hold DC level and an emulated current ramp. RAMP (10 P x (VIN ± VOUT) + 50 P) x tON CRAMP Sample and Hold DC Level 2V/A TON Figure 12. Composition of Current Sense Signal The sample & hold DC level illustrated in Figure 12 is derived from a measurement of the re-circulating Schottky diode anode current. The re-circulating diode anode should be connected to the IS pin. The diode current flows through an internal current sense resistor between the IS and PGND pins. The voltage level across the sense resistor is sampled and held just prior to the onset of the next conduction interval of the buck switch. The diode current sensing and sample & hold provide the DC level of the reconstructed current signal. The positive slope inductor current ramp is emulated by an external capacitor connected from the RAMP pin to AGND and an internal voltage controlled current source. The ramp current source that emulates the inductor current is a function of the VIN and VOUT voltages per Equation 2: IRAMP = (10 µ x (VVIN – VOUT)) + 50 µA (2) Proper selection of the RAMP capacitor depends upon the selected value of the output inductor. The value of CRAMP can be selected from: CRAMP = L x 5 x 10-6 where • L is the value of the output inductor in Henrys (3) Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 13 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Device Functional Modes (continued) With this value, the scale factor of the emulated current ramp will be approximately equal to the scale factor of the DC level sample and hold (2.0V / A). The CRAMP capacitor should be located very close to the device and connected directly to the pins of the IC (RAMP and AGND). For duty cycles greater than 50%, peak current mode control circuits are subject to sub-harmonic oscillation. Sub-harmonic oscillation is normally characterized by observing alternating wide and narrow pulses at the switch node. Adding a fixed slope voltage ramp (slope compensation) to the current sense signal prevents this oscillation. The 50 µA of offset current provided from the emulated current source adds some fixed slope to the ramp signal. In some high output voltage, high duty cycle applications, additional slope may be required. In these applications, a pull-up resistor may be added between the VCC and RAMP pins to increase the ramp slope compensation. For VOUT > 7.5 V: Calculate optimal slope current, IOS = VOUT x 10 µA/V. For example, at VOUT = 10 V, IOS = 100 µA. Install a resistor from the RAMP pin to VCC: RRAMP = VCC / (IOS - 50µA) (4) VCC RRAMP RAMP CRAMP Figure 13. RRAMP to VCC for VOUT > 7.5 V 7.4.5 Maximum Duty Cycle and Input Drop-Out Voltage There is a forced off-time of 500 ns implemented each cycle to ensure sufficient time for the diode current to be sampled. This forced off-time limits the maximum duty cycle of the buck switch. The maximum duty cycle will vary with the operating frequency. DMAX = 1 - Fs x 500ns where • Fs is the oscillator frequency. (5) Limiting the maximum duty cycle will raise the input dropout voltage. The input dropout voltage is the lowest input voltage required to maintain regulation of the output voltage. An approximation of the input dropout voltage is: Vout + VD VinMIN = 1 - Fs x 500 ns where • VD is the voltage drop across the re-circulatory diode. (6) Operating at high switching frequency raises the minimum input voltage necessary to maintain regulation. 7.4.6 Boost Pin The LM5574-Q1 integrates an N-Channel buck switch and associated floating high voltage level shift / gate driver. This gate driver circuit works in conjunction with an internal diode and an external bootstrap capacitor. A 0.022-µF 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 -0.5 V and the bootstrap capacitor 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 500 ns to ensure that the bootstrap capacitor is recharged. 14 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Device Functional Modes (continued) 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 250 ns 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. Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 15 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 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 8.1.1 Bias Power Dissipation Reduction Buck regulators operating with high input voltage can dissipate an appreciable amount of power for the bias of the IC. The VCC regulator must step-down the input voltage VIN to a nominal VCC level of 7 V. The large voltage drop across the VCC regulator translates into a large power dissipation within the VCC regulator. There are several techniques that can significantly reduce this bias regulator power dissipation. Figure 14 and Figure 15 depict two methods to bias the IC from the output voltage. In each case the internal VCC regulator is used to initially bias the VCC pin. After the output voltage is established, the VCC pin potential is raised above the nominal 7V regulation level, which effectively disables the internal VCC regulator. The voltage applied to the VCC pin should never exceed 14 V. The VCC voltage should never be larger than the VIN voltage. LM5574 BST VOUT SW L1 COUT D1 IS GND VCC D2 Figure 14. VCC Bias from VOUT for 8 V < VOUT < 14 V 16 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Application Information (continued) LM5574 BST VOUT L1 SW D1 COUT IS GND D2 VCC Figure 15. VCC Bias with Additional Winding on the Output Inductor 8.2 Typical Application VIN 7V ± 75V C1 1.0 VIN 3 5 PA R1 OPEN LM5574 7V REGULATOR 1.225V 2 SD STANDBY VCC SHUTDOWN SD 0.7V C2 OPEN R2 OPEN 10 SS C8 0.47 THERMAL SHUTDOWN UVLO BST UVLO C4 0.01 C7 0.022 DRIVER S Q 1.225V 16 VIN DIS CLK 10 PA 1 R Q LEVEL SHIFT SW 14 L1 100 PH 5V PWM 0.7V PRE 15 C_LIMIT 6 FB C6 open C5 0.022 R4 24.9k ERROR AMP 1.4V 2V/A + 5 COMP CLK Ir OSCILLATOR SYNC 4 RAMP 8 RT 7 SYNC R3 21k D1 CMSH2-100M CLK VIN TRACK SAMPLE and HOLD RAMP GENERATOR Ir = (10 PA x (VIN ± VOUT)) + 50 PA IS C9 22 13 PGND 12 AGND 9 CLK OUT 11 R5 5.11k R6 1.65k C3 470p Figure 16. Typical Application Schematic 8.2.1 Design Requirements The circuit shown in Figure 16 is configured for the following specifications: • VOUT = 5 V • VIN = 7 V to 75 V • Fs = 300 kHz Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 17 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Typical Application (continued) • • Minimum load current (for CCM) = 100 mA Maximum load current = 0.5 A 8.2.2 Detailed Design Procedure 8.2.2.1 External Components The procedure for calculating the external components is illustrated with the following design example. 8.2.2.2 R3 (RT) RT sets the oscillator switching frequency. Generally, higher frequency applications are smaller but have higher losses. Operation at 300 kHz was selected for this example as a reasonable compromise for both small size and high efficiency. The value of RT for 300 kHz switching frequency can be calculated as follows: RT = [(1 / 300 x 103) ± 580 x 10-9] 135 x 10-12 (7) The nearest standard value of 21 kΩ was chosen for RT. 8.2.2.3 L1 The inductor value is determined based on the operating frequency, load current, ripple current, and the minimum and maximum input voltage (VIN(min), VIN(max)). L1 Current IPK+ IRIPPLE IO IPK- 1/Fs 0 mA Figure 17. Inductor Current Waveform To keep the circuit in continuous conduction mode (CCM), the maximum ripple current IRIPPLE should be less than twice the minimum load current, or 0.2 Ap-p. Using this value of ripple current, the value of inductor (L1) is calculated using the following: L1 = VOUT x (VIN(max) ± VOUT) IRIPPLE x FS x VIN(max) (8) 5V x (75V ± 5V) L1 = = 78 PH 0.2A x 300 kHz x 75V (9) This procedure provides a guide to select the value of L1. The nearest standard value (100 µH) will be used. L1 must be rated for the peak current (IPK+) to prevent saturation. During normal loading conditions, the peak current occurs at maximum load current plus maximum ripple. During an overload condition the peak current is limited to 0.7 A nominal (0.85 A maximum). The selected inductor has a conservative 1.0 Amp saturation current rating. For this manufacturer, the saturation rating is defined as the current necessary for the inductance to reduce by 30%, at 20°C. 8.2.2.4 C3 (CRAMP) With the inductor value selected, the value of C3 (CRAMP) necessary for the emulation ramp circuit is: CRAMP = L x 5 x 10-6 where • 18 L is in Henrys. (10) Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Typical Application (continued) With L1 selected for 100µH the recommended value for C3 is 470 pF (nearest standard value). 8.2.2.5 C9 The output capacitor, C9 smoothes the inductor ripple current and provides a source of charge for transient loading conditions. For this design a 22-µF ceramic capacitor was selected. The ceramic capacitor provides ultra low ESR to reduce the output ripple voltage and noise spikes. An approximation for the output ripple voltage is: § ¨ © § 1 'VOUT = 'IL x ¨ESR + 8 x F S x COUT © (11) 8.2.2.6 D1 A Schottky type re-circulating diode is required for all LM5574-Q1 applications. Ultra-fast diodes are not recommended and may result in damage to the IC due to reverse recovery current transients. The near ideal reverse recovery characteristics and low forward voltage drop are particularly important diode characteristics for high input voltage and low output voltage applications common to the LM5574-Q1. The reverse recovery characteristic determines how long the current surge lasts each cycle when the buck switch is turned on. The reverse recovery characteristics of Schottky diodes minimize the peak instantaneous power in the buck switch occurring during turn-on each cycle. The resulting switching losses of the buck switch are significantly reduced when using a Schottky diode. The reverse breakdown rating should be selected for the maximum VIN, plus some safety margin. The forward voltage drop has a significant impact on the conversion efficiency, especially for applications with a low output voltage. “Rated” current for diodes vary widely from various manufacturers. The worst case is to assume a short circuit load condition. In this case the diode will carry the output current almost continuously. For the LM5574-Q1 this current can be as high as 0.7 A. Assuming a worst case 1 V drop across the diode, the maximum diode power dissipation can be as high as 0.7 W. For the reference design a 100 V Schottky in a SMA package was selected. 8.2.2.7 C1 The regulator supply voltage has a large source impedance at the switching frequency. Good quality input capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the switch current during the on-time. When the buck switch turns on, the current into the VIN pin steps to the lower peak of the inductor current waveform, ramps up to the peak value, then drops to zero at turn-off. The average current into VIN during the on-time is the load current. The input capacitance should be selected for RMS current rating and minimum ripple voltage. A good approximation for the required ripple current rating necessary is IRMS > IOUT / 2. Quality ceramic capacitors with a low ESR should be selected for the input filter. To allow for capacitor tolerances and voltage effects, one 1.0-µF, 100 V ceramic capacitor will be used. If step input voltage transients are expected near the maximum rating of the LM5574-Q1, a careful evaluation of ringing and possible spikes at the device VIN pin should be completed. An additional damping network or input voltage clamp may be required in these cases. 8.2.2.8 C8 The capacitor at the VCC pin provides noise filtering and stability for the VCC regulator. The recommended value of C8 should be no smaller than 0.1-µF, and should be a good quality, low ESR, ceramic capacitor. A value of 0.47-µF was selected for this design. 8.2.2.9 C7 The bootstrap capacitor between the BST and the SW pins supplies the gate current to charge the buck switch gate at turn-on. The recommended value of C7 is 0.022-µF, and should be a good quality, low ESR, ceramic capacitor. 8.2.2.10 C4 The capacitor at the SS pin determines the soft-start time, that is the time for the reference voltage and the output voltage, to reach the final regulated value. The time is determined from: Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 19 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Typical Application (continued) tss = C4 x 1.225V 10 PA (12) For this application, a C4 value of 0.01µF was chosen which corresponds to a soft-start time of 1ms. 8.2.2.11 R5, R6 R5 and R6 set the output voltage level, the ratio of these resistors is calculated from: R5/R6 = (VOUT / 1.225V) - 1 (13) For a 5V output, the R5/R6 ratio calculates to 3.082. The resistors should be chosen from standard value resistors, a good starting point is selection in the range of 1.0kΩ - 10kΩ. Values of 5.11kΩ for R5, and 1.65kΩ for R6 were selected. 8.2.2.12 R1, R2, C2 A voltage divider can be connected to the SD pin to set a minimum operating voltage VIN(min) for the regulator. If this feature is required, the easiest approach to select the divider resistor values is to select a value for R1 (between 10kΩ and 100kΩ recommended) then calculate R2 from: § ¨ © § R1 R2 = 1.225 x ¨ -6 © VIN(min) + (5 x 10 x R1) ± 1.225 (14) Capacitor C2 provides filtering for the divider. The voltage at the SD pin should never exceed 8V, when using an external set-point divider it may be necessary to clamp the SD pin at high input voltage conditions. The reference design utilizes the full range of the LM5574-Q1 (6V to 75V); therefore these components can be omitted. With the SD pin open circuit the LM5574-Q1 responds once the VCC UVLO threshold is satisfied. 8.2.2.13 R4, C5, C6 These components configure the error amplifier gain characteristics to accomplish a stable overall loop gain. One advantage of current mode control is the ability to close the loop with only two feedback components, R4 and C5. The overall loop gain is the product of the modulator gain and the error amplifier gain. The DC modulator gain of the LM5574-Q1 is as follows: DC Gain(MOD) = Gm(MOD) x RLOAD = 0.5 x RLOAD (15) The dominant low frequency pole of the modulator is determined by the load resistance (RLOAD,) and output capacitance (COUT). The corner frequency of this pole is: fp(MOD) = 1 / (2π RLOAD COUT) (16) For RLOAD = 20Ω and COUT = 22µF then fp(MOD) = 362Hz DC Gain(MOD) = 0.5 x 20 = 20dB For the design example of Figure 16 the following modulator gain vs. frequency characteristic was measured as shown in Figure 18. 20 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Typical Application (continued) REF LEVEL 0.000 dB 0.0 deg /DIV 10.000 dB 45.000 deg GAIN 0 PHASE 100 1k START 100.000 Hz 10k 100k STOP 100 000.000 Hz RLOAD = 20 Ohms COUT = 22µF Figure 18. Gain and Phase of Modulator Components R4 and C5 configure the error amplifier as a type II configuration which has a pole at DC and a zero at fZ = 1 / (2πR4C5). The error amplifier zero cancels the modulator pole leaving a single pole response at the crossover frequency of the loop gain. A single pole response at the crossover frequency yields a very stable loop with 90 degrees of phase margin. For the design example, a target loop bandwidth (crossover frequency) of 25kHz was selected. The compensation network zero (fZ) should be selected at least an order of magnitude less than the target crossover frequency. This constrains the product of R4 and C5 for a desired compensation network zero 1 / (2π R4 C5) to be less than 2kHz. Increasing R4, while proportionally decreasing C5, increases the error amp gain. Conversely, decreasing R4 while proportionally increasing C5, decreases the error amp gain. For the design example C5 was selected for 0.022µF and R4 was selected for 24.9kΩ. These values configure the compensation network zero at 290Hz. The error amp gain at frequencies greater than fZ is: R4 / R5, which is approximately 5 (14dB). REF LEVEL 0.000 dB 0.0 deg /DIV 10.000 dB 45.000 deg PHASE GAIN 0 100 1k START 100.000 Hz 10k 100k STOP 100 000.000 Hz Figure 19. Error Amplifier Gain and Phase The overall loop can be predicted as the sum (in dB) of the modulator gain and the error amp gain. Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 21 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Typical Application (continued) REF LEVEL 0.000 dB 0.0 deg /DIV 10.000 dB 45.000 deg GAIN PHASE 0 100 1k START 100.000 Hz 10k 100k STOP 100 000.000 Hz Figure 20. Overall Loop Gain and Phase If a network analyzer is available, the modulator gain can be measured and the error amplifier gain can be configured for the desired loop transfer function. If a network analyzer is not available, the error amplifier compensation components can be designed with the guidelines given. Step load transient tests can be performed to verify acceptable performance. The step load goal is minimum overshoot with a damped response. C6 can be added to the compensation network to decrease noise susceptibility of the error amplifier. The value of C6 must be sufficiently small since the addition of this capacitor adds a pole in the error amplifier transfer function. This pole must be well beyond the loop crossover frequency. A good approximation of the location of the pole added by C6 is: fp2 = fz x C5 / C6 (17) GAIN (dB) OSCILLATOR FREQUENCY (kHz) 1000 100 50 225 40 180 30 135 20 0 0 GAIN -45 -20 -30 10k 1 10 100 90 45 -10 10 -90 100k 1M 10M -135 100M 1000 FREQUENCY (Hz) RT (k:) Figure 21. Oscillator Frequency vs RT 22 PHASE 10 PHASE (°) 8.2.3 Application Curves Figure 22. Error Amplifier Gain And Phase AVCL = 101 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Typical Application (continued) 100 REF LEVEL 0.000 dB 0.0 deg VIN = 7V 90 /DIV 10.000 dB 45.000 deg EFFICIENCY (%) 80 70 VIN = 75V 60 GAIN VIN = 48V 50 40 VIN = 24V 0 30 PHASE 20 10 0 0.1 0.2 0.3 0.4 0.5 100 1k START 100.000 Hz IOUT (A) Figure 23. Demoboard Efficiency vs IOUT and VIN 10k 100k STOP 100 000.000 Hz Figure 24. Gain and Phase of Modulator Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 23 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com 9 Power Supply Recommendations The LM5574 is designed to operate from an input voltage supply range between 6 V and 75 V. This input supply should be able to withstand the maximum input current and maintain a voltage above 6 V. The resistance of the input supply rail should be low enough that an input current transient does not cause a high enough drop at the LM5574 supply voltage that can cause a false UVLO fault triggering and system reset. If the input supply is located more than a few inches from the LM5574 additional bulk capacitance may be required in addition to the ceramic bypass capacitors. The amount of bulk capacitance is not critical, but a 47-μF or 100-μF electrolytic capacitor is a typical choice. 10 Layout 10.1 Layout Guidelines The circuit in Figure 16 serves as both a block diagram of the LM5575 and a typical application board schematic for the LM5574. In a buck regulator there are two loops where currents are switched very fast. The first loop starts from the input capacitors, to the regulator VIN pin, to the regulator SW pin, to the inductor then out to the load. The second loop starts from the output capacitor ground, to the regulator PGND pins, to the regulator IS pins, to the diode anode, to the inductor and then out to the load. Minimizing the loop area of these two loops reduces the stray inductance and minimizes noise and possible erratic operation. A ground plane in the PC board is recommended as a means to connect the input filter capacitors to the output filter capacitors and the PGND pins of the regulator. Connect all of the low power ground connections (CSS, RT, CRAMP) directly to the regulator AGND pin. Connect the AGND and PGND pins together through the topside copper area covering the entire underside of the device. Place several vias in this underside copper area to the ground plane. The two highest power dissipating components are the re-circulating diode and the LM5574 regulator IC. The easiest method to determine the power dissipated within the LM5574 is to measure the total conversion losses (PIN – POUT) then subtract the power losses in the Schottky diode, output inductor and snubber resistor. An approximation for the Schottky diode loss is P = (1-D) x Iout x Vfwd. An approximation for the output inductor power is P = IOUT2 x R x 1.1, where R is the DC resistance of the inductor and the 1.1 factor is an approximation for the AC losses. If a snubber is used, an approximation for the damping resistor power dissipation is P = VIN2 x Fsw x Csnub, where Fsw is the switching frequency and Csnub is the snubber capacitor. The regulator has an exposed thermal pad to aid power dissipation. Adding several vias under the device to the ground plane will greatly reduce the regulator junction temperature. Selecting a diode with an exposed pad will aid the power dissipation of the diode. The most significant variables that affect the power dissipated by the LM5576 are the output current, input voltage and operating frequency. The power dissipated while operating near the maximum output current and maximum input voltage can be appreciable. The operating frequency of the LM5574 evaluation board has been designed for 300 kHz. When operating at 3 A output current with a 70 V input the power dissipation of the LM5574 regulator is approximately 2.5 W. The junction-to-ambient thermal resistance of the LM5574 will vary with the application. The most significant variables are the area of copper in the PC board, the number of vias under the IC exposed pad and the amount of forced air cooling provided. Referring to the evaluation board artwork, the area under the LM5576 (component side) is covered with copper and there are 5 connection vias to the solder side ground plane. Additional vias under the IC will have diminishing value as more vias are added. The integrity of the solder connection from the IC exposed pad to the PC board is critical. Excessive voids will greatly diminish the thermal dissipation capacity. The junction-to-ambient thermal resistance of the LM5576 mounted in the evaluation board varies from 45°C/W with no airflow to 25°C/W with 900 LFM (Linear Feet per Minute). With a 25°C ambient temperature and no airflow, the predicted junction temperature for the LM5576 will be 25 + (45 x 2.5) = 137.5°C. If the evaluation board is operated at 3 A output current and 70 V input voltage for a prolonged period of time the thermal shutdown protection within the IC will activate. The IC will turn off allowing the junction to cool, followed by restart with the soft-start capacitor reset to zero. 24 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 Layout Guidelines (continued) One or more of the following modifications will prevent the thermal shutdown from being activated: apply forced air cooling, reduce the maximum input voltage, lower the maximum output current, reduce the operating frequency, add more heat sinking to the PC board. For example, applying forced air cooling of 225 LFM will reduce the LM5576 thermal resistance to approximately 30°C/W. The junction temperature will be reduced to 25 + (2.5 x 30) = 100°C. If the maximum input voltage for the application is 48 V, then the IC power dissipation reduces to 2 W (at 3 A output current). With the same forced air cooling the junction temperature reduces to 25 + (2 x 30) = 85°C. 10.2 Layout Example Figure 25. Component Side Figure 26. Solder Side Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 25 LM5574-Q1 SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 www.ti.com Layout Example (continued) Figure 27. Silkscreen 26 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 LM5574-Q1 www.ti.com SNOSB22C – OCTOBER 2008 – REVISED OCTOBER 2014 11 Device and Documentation Support 11.1 Trademarks SIMPLE SWITCHER, WEBENCH are registered trademarks of Texas Instruments. All other trademarks are the property of their respective owners. 11.2 Electrostatic Discharge Caution These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. 11.3 Glossary SLYZ022 — TI Glossary. This glossary lists and explains terms, acronyms, and definitions. 12 Mechanical, Packaging, and Orderable Information The following pages include mechanical, packaging, and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation. Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM5574-Q1 27 PACKAGE OPTION ADDENDUM www.ti.com 16-Oct-2015 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (°C) Device Marking (4/5) LM5574Q0MT/NOPB LIFEBUY TSSOP PW 16 92 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM LM5574 Q0MT LM5574Q0MTX/NOPB LIFEBUY TSSOP PW 16 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM LM5574 Q0MT LM5574QMT/NOPB ACTIVE TSSOP PW 16 92 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM5574 QMT LM5574QMTX/NOPB ACTIVE TSSOP PW 16 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM5574 QMT (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 16-Oct-2015 Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. 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OTHER QUALIFIED VERSIONS OF LM5574-Q1 : • Catalog: LM5574 NOTE: Qualified Version Definitions: • Catalog - TI's standard catalog product Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 6-Nov-2015 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) W Pin1 (mm) Quadrant LM5574Q0MTX/NOPB TSSOP PW 16 2500 330.0 12.4 6.95 5.6 1.6 8.0 12.0 Q1 LM5574QMTX/NOPB TSSOP PW 16 2500 330.0 12.4 6.95 5.6 1.6 8.0 12.0 Q1 Pack Materials-Page 1 PACKAGE MATERIALS INFORMATION www.ti.com 6-Nov-2015 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM5574Q0MTX/NOPB TSSOP PW 16 2500 367.0 367.0 35.0 LM5574QMTX/NOPB TSSOP PW 16 2500 367.0 367.0 35.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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