LM22676QMRX-ADJ/NOPB

Product Folder Sample & Buy Technical Documents Support & Community Tools & Software LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 LM22676/-Q1 42 V, 3 A SIMPLE SWITCHER® Step-Down Voltage Regulator with Features 1 Features 3 Description • • • • • • The LM22676 switching regulator provides all of the functions necessary to implement an efficient high voltage step-down (buck) regulator using a minimum of external components. This easy to use regulator incorporates a 42 V N-channel MOSFET switch capable of providing up to 3 A of load current. Excellent line and load regulation along with high efficiency (> 90%) are featured. Voltage mode control offers short minimum on-time, allowing the widest ratio between input and output voltages. Internal loop compensation means that the user is free from the tedious task of calculating the loop compensation components. Fixed 5 V output and adjustable output voltage options are available. A switching frequency of 500 kHz allows for small external components and good transient response. A precision enable input allows simplification of regulator control and system power sequencing. In shutdown mode the regulator draws only 25 µA (typ). Built in soft-start (500 µs, typ) saves external components. The LM22676 also has built in thermal shutdown, and current limiting to protect against accidental overloads. 1 • • • • • • • • • • Wide Input Voltage Range: 4.5 V to 42 V Internally Compensated Voltage Mode Control Stable with Low ESR Ceramic Capacitors 120 mΩ N-Channel MOSFET PFM Package 100 mΩ N-Channel MOSFET PSOP-8 Package Output Voltage Options: -ADJ (Outputs as Low as 1.285 V) -5.0 (Output Fixed to 5 V) ±1.5% Feedback Reference Accuracy Switching Frequency of 500 kHz –40°C to 125°C Operating Junction Temperature Range Precision Enable Pin Integrated Boot-Strap Diode Integrated Soft-Start Fully WEBENCH® Enabled LM22676Q is an Automotive Grade Product that is AEC-Q100 Grade 1 Qualified (–40°C to +125°C Operating Junction Temperature) SO PowerPAD (Exposed Pad PFM (Exposed Pad) The LM22676 is a member of Texas Instruments' SIMPLE SWITCHER® family. The SIMPLE SWITCHER® concept provides for an easy to use complete design using a minimum number of external components and the TI WEBENCH® design tool. TI's WEBENCH® tool includes features such as external component calculation, electrical simulation, thermal simulation, and Build-It boards for easy design-in. 2 Applications • • • • Industrial Control Telecom and Datacom Systems Embedded Systems Conversions from Standard 24 V, 12 V and 5 V Input Rails Device Information(1) PART NUMBER LM22676, LM22676-Q1 PACKAGE BODY SIZE (NOM) HSOP (8) 4.89 mm x 3.90 mm TO-263 (3) 10.16 mm x 9.85 mm (1) For all available packages, see the orderable addendum at the end of the data sheet. Simplified Application Schematic VIN VIN FB LM22676-ADJ BOOT VOUT EN GND SW 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. LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – 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 4 5 6 Absolute Maximum Ratings ...................................... Handling Ratings: LM22676...................................... Handling Ratings: LM22676-Q1................................ Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Typical Characteristics .............................................. Detailed Description .............................................. 8 7.1 Overview ................................................................... 8 7.2 Functional Block Diagram ......................................... 8 7.3 Feature Description................................................... 8 7.4 Device Functional Modes........................................ 10 8 Application and Implementation ........................ 13 8.1 Application Information............................................ 13 8.2 Typical Application .................................................. 14 9 Power Supply Recommendations...................... 17 10 Layout................................................................... 17 10.1 Layout Guidelines ................................................. 17 10.2 Layout Examples................................................... 18 10.3 Thermal Considerations ........................................ 19 11 Device and Documentation Support ................. 20 11.1 11.2 11.3 11.4 11.5 Documentation Support ........................................ Related Links ........................................................ Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 20 20 20 20 20 12 Mechanical, Packaging, and Orderable Information ........................................................... 20 4 Revision History Changes from Revision K (April 2013) to Revision L • Page Added Pin Configuration and Functions section, Handling Rating table, Thermal Information 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 J (April 2013) to Revision K • 2 Page Changed from National format to TI format............................................................................................................................ 1 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 5 Pin Configuration and Functions SO PowerPAD Package 8-Pin Top View PFM Package 8-Pin Top View BOOT 1 8 SW NC 2 7 VIN NC 3 6 GND 7 EN 6 FB 5 NC 4 GND 3 BOOT FB 4 5 2 VIN EN 1 SW Exposed Pad Connect to GND Exposed Pad Connect to GND Pin Functions PIN SO NAME PowerPAD BOOT PFM TYPE DESCRIPTION APPLICATION INFORMATION 1 3 I Bootstrap input Provides the gate voltage for the high side N-FET. NC 2, 3 5 — Not Connected Pins are not electrically connected inside the chip. Pins do function as thermal conductor. FB 4 6 I Feedback pin Feedback input to regulator. EN 5 7 I Enable input Used to control regulator start-up and shutdown. See Precision Enable and UVLO section of data sheet. GND 6 4 — Ground input to regulator; system common System ground pin. VIN 7 2 I Input Voltage Input supply to regulator SW 8 1 O Switch pin Switching output of regulator EP EP EP — Exposed Pad Connect to ground. Provides thermal connection to PCB. See Thermal Considerations. Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 3 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings (1) (2) MIN MAX VIN to GND EN Pin Voltage SW to GND (3) V –0.5 6 V –5 VIN V VSW + 7 V 7 V 150 °C BOOT Pin Voltage FB Pin Voltage –0.5 Power Dissipation UNIT 43 Internally Limited Junction Temperature For soldering specifications, refer to Application Report Absolute Maximum Ratings for Soldering (SNOA549). (1) (2) (3) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditions indicate conditions at which the device is functional and should not be operated beyond such conditions. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications. The absolute maximum specification of the ‘SW to GND’ applies to dc voltage. An extended negative voltage limit of –10 V applies to a pulse of up to 50 ns. 6.2 Handling Ratings: LM22676 Tstg Storage temperature range V(ESD) (1) Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins (1) Electrostatic discharge MIN MAX UNIT –65 150 °C –2 2 kV JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. 6.3 Handling Ratings: LM22676-Q1 Tstg Storage temperature range V(ESD) Electrostatic discharge (1) Human body model (HBM), per AEC Q100-002 (1) MIN MAX –65 150 UNIT °C –2 2 kV AEC Q100-002 indicates HBM stressing is done in accordance with the ANSI/ESDA/JEDEC JS-001 specification. 6.4 Recommended Operating Conditions VIN MIN MAX Supply Voltage 4.5 42 UNIT V Junction Temperature –40 125 °C 6.5 Thermal Information LM22676, LM22676-Q1 THERMAL METRIC (1) RθJA (1) 4 Junction-to-ambient thermal resistance DDA NDR 8 PINS 7 PINS 60 22 UNIT °C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 6.6 Electrical Characteristics Typical values represent the most likely parametric norm at TA = TJ = 25°C, and are provided for reference purposes only. Unless otherwise specified: VIN = 12 V. PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) 4.925 5.0 5.075 UNIT LM22676-5.0 VFB Feedback Voltage VIN = 8 V to 42 V VIN = 8 V to 42 V, –40°C ≤ TJ ≤ 125°C 4.9 5.1 V LM22676-ADJ VFB Feedback Voltage VIN = 4.7 V to 42 V 1.266 VIN = 4.7 V to 42 V, –40°C ≤ TJ ≤ 125°C 1.259 1.285 1.304 1.311 V ALL OUTPUT VOLTAGE VERSIONS IQ Quiescent Current ISTDBY Standby Quiescent Current ICL Current Limit IL Output Leakage Current VFB = 5 V 3.4 VFB = 5 V, –40°C ≤ TJ ≤ 125°C 6 EN Pin = 0 V 3.4 –40°C ≤ TJ ≤ 125°C Switch On-Resistance 40 5.3 3.35 5.5 Oscillator Frequency TOFFMIN Minimum Off-time TONMIN Minimum On-time IBIAS Feedback Bias Current VEN Enable Threshold Voltage VENHYST Enable Voltage Hysteresis IEN Enable Input Current TSD Thermal Shutdown Threshold (1) (2) A 0.2 2 µA VSW = –1 V 0.1 3 µA 0.12 0.16 PFM Package 0.22 SO PowerPAD Package 0.10 SO PowerPAD Package fO µA VIN = 42 V, EN Pin = 0 V, VSW = 0 V PFM Package RDS(ON) 25 4.2 mA 0.16 0.20 500 –40°C ≤ TJ ≤ 125°C 400 600 200 –40°C ≤ TJ ≤ 125°C Ω 100 300 kHz ns 100 ns VFB = 1.3 V (ADJ Version Only) 230 nA Falling 1.6 Falling, –40°C ≤ TJ ≤ 125°C EN Input = 0 V 1.3 1.9 V 0.6 V 6 µA 150 °C Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are ensured through correlation using Statistical Quality Control (SQC) methods. Limits are used to calculate TI's Average Outgoing Quality Level (AOQL). Typical values represent most likely parametric norms at the conditions specified and are not ensured. Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 5 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com 6.7 Typical Characteristics Vin = 12 V, TJ = 25°C (unless otherwise specified) 6 Figure 1. Efficiency vs IOUT and VIN, VOUT = 3.3 V Figure 2. Normalized Switching Frequency vs Temperature Figure 3. Current Limit vs Temperature Figure 4. Normalized RDS(ON) vs Temperature Figure 5. Feedback Bias Current vs Temperature Figure 6. Normalized Enable Threshold Voltage vs Temperature Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 Typical Characteristics (continued) Vin = 12 V, TJ = 25°C (unless otherwise specified) Figure 7. Standby Quiescent Current vs Input Voltage Figure 8. Normalized Feedback Voltage vs Temperature Figure 9. Normalized Feedback Voltage vs Input Voltage Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 7 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com 7 Detailed Description 7.1 Overview The LM22676 device incorporates a voltage mode constant frequency PWM architecture. In addition, input voltage feedforward is used to stabilize the loop gain against variations in input voltage. This allows the loop compensation to be optimized for transient performance. The power MOSFET, in conjunction with the diode, produce a rectangular waveform at the switch pin that swings from about zero volts to VIN. The inductor and output capacitor average this waveform to become the regulator output voltage. By adjusting the duty cycle of this waveform, the output voltage can be controlled. The error amplifier compares the output voltage with the internal reference and adjusts the duty cycle to regulate the output at the desired value. The internal loop compensation of the -ADJ option is optimized for outputs of 5 V and below. If an output voltage of 5 V or greater is required, the -5.0 option can be used with an external voltage divider. The minimum output voltage is equal to the reference voltage, that is, 1.285 V (typ). 7.2 Functional Block Diagram VIN VIN Vcc BOOT INT REG, EN,UVLO EN ILimit PWM Cmp. FB + TYPE III COMP + - LOGIC Error Amp. VOUT SW OSC 1.285V & Soft-start GND 7.3 Feature Description 7.3.1 Precision Enable and UVLO The precision enable input (EN) is used to control the regulator. The precision feature allows simple sequencing of multiple power supplies with a resistor divider from another supply. Connecting this pin to ground or to a voltage less than 1.6 V (typ) will turn off the regulator. The current drain from the input supply, in this state, is 25 µA (typ) at an input voltage of 12 V. The EN input has an internal pullup of about 6 µA. Therefore this pin can be left floating or pulled to a voltage greater than 2.2 V (typ) to turn the regulator on. The hysteresis on this input is about 0.6 V (typ) above the 1.6 V (typ) threshold. When driving the enable input, the voltage must never exceed the 6 V absolute maximum specification for this pin. 8 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 Feature Description (continued) Although an internal pullup is provided on the EN pin, it is good practice to pull the input high, when this feature is not used, especially in noisy environments. This can most easily be done by connecting a resistor between VIN and the EN pin. The resistor is required, because the internal zener diode, at the EN pin, will conduct for voltages above about 6 V. The current in this zener must be limited to less than 100 µA. A resistor of 470 kΩ will limit the current to a safe value for input voltages as high 42 V. Smaller values of resistor can be used at lower input voltages. The LM22676 also incorporates an input undervoltage lock-out (UVLO) feature. This prevents the regulator from turning on when the input voltage is not great enough to properly bias the internal circuitry. The rising threshold is 4.3 V (typ) while the falling threshold is 3.9 V (typ). In some cases these thresholds may be too low to provide good system performance. The solution is to use the EN input as an external UVLO to disable the part when the input voltage falls below a lower boundary. This is often used to prevent excessive battery discharge or early turn on during start up. This method is also recommended to prevent abnormal device operation in applications where the input voltage falls below the minimum of 4.5 V. Figure 10 shows the connections to implement this method of UVLO. Equation 1 and Equation 2 can be used to determine the correct resistor values. (1) (2) Where: Voff is the input voltage where the regulator shuts off. Von is the voltage where the regulator turns on. Due to the 6 µA pullup, the current in the divider should be much larger than this. A value of 20 kΩ, for RENB is a good first choice. Also, a zener diode may be needed between the EN pin and ground in order to comply with the absolute maximum ratings on this pin. Vin RENT EN RENB Figure 10. External UVLO Connections 7.3.2 Soft-Start The soft-start feature allows the regulator to gradually reach steady-state operation, thus reducing start-up stresses. The internal soft-start feature brings the output voltage up in about 500 µs. This time is fixed and can not be changed. Soft-start is reset any time the part is shut down or a thermal overload event occurs. 7.3.3 Boot-Strap Supply The LM22676 incorporates a floating high-side gate driver to control the power MOSFET. The supply for this driver is the external boot-strap capacitor connected between the BOOT pin and SW. A good quality 10 nF ceramic capacitor must be connected to these pins with short, wide PCB traces. One reason the regulator imposes a minimum off-time is to ensure that this capacitor recharges every switching cycle. A minimum load of about 5 mA is required to fully recharge the boot-strap capacitor in the minimum off-time. Some of this load can be provided by the output voltage divider, if used. Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 9 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com Feature Description (continued) 7.3.4 Internal Compensation The LM22676 device has internal loop compensation designed to provide a stable regulator over a wide range of external power stage components. The internal compensation of the -ADJ option is optimized for output voltages below 5 V. If an output voltage of 5 V or greater is needed, the -5.0 option with an external resistor divider can be used. Ensuring stability of a design with a specific power stage (inductor and output capacitor) can be tricky. The LM22676 stability can be verified using the WEBENCH Designer online circuit simulation tool. A quick start spreadsheet can also be downloaded from the online product folder. The complete transfer function for the regulator loop is found by combining the compensation and power stage transfer functions. The LM22676 has internal type III loop compensation, as detailed in Figure 11. This is the approximate "straight line" function from the FB pin to the input of the PWM modulator. The power stage transfer function consists of a dc gain and a second order pole created by the inductor and output capacitor(s). Due to the input voltage feedforward employed in the LM22676, the power stage dc gain is fixed at 20 dB. The second order pole is characterized by its resonant frequency and its quality factor (Q). For a first pass design, the product of inductance and output capacitance should conform to Equation 3. L × COUT » 1.1 ´10-9 (3) Alternatively, this pole should be placed between 1.5 kHz and 15 kHz and is determined by Equation 4. (4) The Q factor depends on the parasitic resistance of the power stage components and is not typically in the control of the designer. Of course, loop compensation is only one consideration when selecting power stage components; see the Application Information section for more details. COMPENSATOR GAIN (dB) 40 35 -ADJ -5.0 30 25 20 15 10 5 0 100 1k 10k 100k 1M FREQUENCY (Hz) 10M Figure 11. Compensator Gain In general, hand calculations or simulations can only aid in selecting good power stage components. Good design practice dictates that load and line transient testing should be done to verify the stability of the application. Also, Bode plot measurements should be made to determine stability margins. AN-1889 How to Measure the Loop Transfer Function of Power Supplies (SNVA364) shows how to perform a loop transfer function measurement with only an oscilloscope and function generator. 7.4 Device Functional Modes 7.4.1 Current Limit The LM22676 has current limiting to prevent the switch current from exceeding safe values during an accidental overload on the output. This peak current limit is found in the Electrical Characteristics under the heading of ICL. The maximum load current that can be provided, before current limit is reached, is determined from Equation 5. 10 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 Device Functional Modes (continued) (5) Where: L is the value of the power inductor. When the LM22676 enters current limit, the output voltage will drop and the peak inductor current will be fixed at ICL at the end of each cycle. The switching frequency will remain constant while the duty cycle drops. The load current will not remain constant, but will depend on the severity of the overload and the output voltage. For very severe overloads ("short-circuit"), the regulator changes to a low frequency current foldback mode of operation. The frequency foldback is about 1/5 of the nominal switching frequency. This will occur when the current limit trips before the minimum on-time has elapsed. This mode of operation is used to prevent inductor current "run-away", and is associated with very low output voltages when in overload. Equation 6 can be used to determine what level of output voltage will cause the part to change to low frequency current foldback. (6) Where: Fsw is the normal switching frequency. Vin is the maximum for the application. If the overload drives the output voltage to less than or equal to Vx, the part will enter current foldback mode. If a given application can drive the output voltage to ≤ Vx, during an overload, then a second criterion must be checked. Equation 7 gives the maximum input voltage, when in this mode, before damage occurs. (7) Where: Vsc is the value of output voltage during the overload. Fsw is the normal switching frequency. NOTE If the input voltage should exceed this value, while in foldback mode, the regulator and/or the diode may be damaged. It is important to note that the voltages in these equations are measured at the inductor. Normal trace and wiring resistance will cause the voltage at the inductor to be higher than that at a remote load. Therefore, even if the load is shorted with zero volts across its terminals, the inductor will still see a finite voltage. It is this value that should be used for Vx and Vsc in the calculations. In order to return from foldback mode, the load must be reduced to a value much lower than that required to initiate foldback. This load "hysteresis" is a normal aspect of any type of current limit foldback associated with voltage regulators. The safe operating area, when in short circuit mode, is shown in Figure 12. Operating points below and to the right of the curve represent safe operation. Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 11 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com Device Functional Modes (continued) 45 INPUT VOLTAGE (v) 40 35 30 25 SAFE OPERATING AREA 20 15 10 5 0.0 0.2 0.4 0.6 0.8 1.0 SHORT CIRCUIT VOLTAGE (v) 1.2 Figure 12. SOA 7.4.2 Thermal Protection Internal thermal shutdown circuitry protects the LM22676 should the maximum junction temperature be exceeded. This protection is activated at about 150°C, with the result that the regulator will shutdown until the temperature drops below about 135°C. 7.4.3 Duty-Cycle Limits Ideally the regulator would control the duty cycle over the full range of zero to one. However due to inherent delays in the circuitry, there are limits on both the maximum and minimum duty cycles that can be reliably controlled. This in turn places limits on the maximum and minimum input and output voltages that can be converted by the LM22676. A minimum on-time is imposed by the regulator in order to correctly measure the switch current during a current limit event. A minimum off-time is imposed in order the re-charge the bootstrap capacitor. Equation 8 can be used to determine the approximate maximum input voltage for a given output voltage. (8) Where: Fsw is the switching frequency. TON is the minimum on-time. Both parameters may be found in the Electrical Characteristics. The worst case occurs at the lowest output voltage. If the input voltage, found in the above equation, is exceeded, the regulator will skip cycles, effectively lowering the switching frequency. The consequences of this are higher output voltage ripple and a degradation of the output voltage accuracy. The second limitation is the maximum duty cycle before the output voltage will "dropout" of regulation. Equation 9 can be used to approximate the minimum input voltage before dropout occurs. (9) Where: The values of TOFF and RDS(ON) are found in the Electrical Characteristics. The worst case here occurs at the highest load. In this equation, RL is the dc inductor resistance. Of course, the lowest input voltage to the regulator must not be less than 4.5 V (typ). 12 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 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 LM22676 is a step down dc-to-dc regulator. It is typically used to convert a higher dc voltage to a lower dc voltage with a maximum output current of 3 A. The following design procedure can be used to select components for the LM22676. Alternately, the WEBENCH® software may be used to generate complete designs. When generating a design, the WEBENCH® software utilizes iterative design procedure and accesses comprehensive databases of components. Go to WEBENCH Designer for more details. 8.1.1 Output Voltage Divider Selection For output voltages between about 1.285 V and 5 V, the -ADJ option should be used, with an appropriate voltage divider as shown in Figure 13. Equation 10 can be used to calculate the resistor values of this divider. (10) A good value for RFBB is 1 kΩ. This will help to provide some of the minimum load current requirement and reduce susceptibility to noise pick-up. The top of RFBT should be connected directly to the output capacitor or to the load for remote sensing. If the divider is connected to the load, a local high-frequency bypass should be provided at that location. For output voltages of 5 V, the -5.0 option should be used. In this case no divider is needed and the FB pin is connected to the output. The approximate values of the internal voltage divider are as follows: 7.38 kΩ from the FB pin to the input of the error amplifier and 2.55 kΩ from there to ground. Both the -ADJ and -5.0 options can be used for output voltages greater than 5 V, by using the correct output divider. As mentioned in the Internal Compensation section, the -5.0 option is optimized for output voltages of 5 V. However, for output voltages greater than 5 V, this option may provide better loop bandwidth than the -ADJ option, in some applications. If the -5.0 option is to be used at output voltages greater than 5 V, Equation 11 should be used to determine the resistor values in the output divider. (11) A value of RFBB of about 1 kΩ is a good first choice. Vout RFBT FB RFBB Figure 13. Resistive Feedback Divider A maximum value of 10 kΩ is recommended for the sum of RFBB and RFBT to maintain good output voltage accuracy for the -ADJ option. A maximum of 2 kΩ is recommended for the -5.0 option. For the -5.0 option, the total internal divider resistance is typically 9.93 kΩ. Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 13 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com Application Information (continued) In all cases the output voltage divider should be placed as close as possible to the FB pin of the LM22676, because this is a high impedance input and is susceptible to noise pick-up. 8.1.2 Power Diode A Schottky-type power diode is required for all LM22676 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 of Schottky diodes are particularly important for high input voltage and low output voltage applications common to the LM22676. The reverse breakdown rating of the diode should be selected for the maximum VIN, plus some safety margin. A good rule of thumb is to select a diode with a reverse voltage rating of 1.3 times the maximum input voltage. Select a diode with an average current rating at least equal to the maximum load current that will be seen in the application. 8.2 Typical Application 8.2.1 Typical Buck Regulator Application Figure 14 shows an example of converting an input voltage range of 5.5 V to 42 V, to an output of 3.3 V at 3 A. RFBB 976: VIN 4.5V to 42V FB VIN EN EN C2 22 PF + C1 6.8 PF C3 10 nF LM22676-ADJ BOOT GND RFBT 1.54 k: L1 8.2 PH SW D1 60V, 5A VOUT 3.3V C4 120 PF + GND GND Figure 14. Typical Buck Regulator Application 8.2.1.1 Design Requirements DESIGN PARAMETERS EXAMPLE VALUE Driver Supply Voltage (VIN) 4.5 to 42 V Output Voltage (VOUT) 3.3 V RFBT Calculated based on RFBB and VREF of 1.285 V. RFBB 1 kΩ to 10 kΩ IOUT 3A 8.2.1.2 Detailed Design Procedure 8.2.1.2.1 External Components The following guidelines should be used when designing a step-down (buck) converter with the LM22676. 14 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 8.2.1.2.2 Inductor The inductor value is determined based on the load current, ripple current, and the minimum and maximum input voltages. To keep the application in continuous conduction mode (CCM), the maximum ripple current, IRIPPLE , should be less than twice the minimum load current. The general rule of keeping the inductor current peak-topeak ripple around 30% of the nominal output current is a good compromise between excessive output voltage ripple and excessive component size and cost. Using this value of ripple current, the value of inductor, L, is calculated using Equation 12. (12) Where: Fsw is the switching frequency. Vin should be taken at its maximum value, for the given application. Equation 12 provides a guide to select the value of the inductor L; the nearest standard value will then be used in the circuit. Once the inductor is selected, the actual ripple current can be found from Equation 13: (13) Increasing the inductance will generally slow down the transient response but reduce the output voltage ripple. Reducing the inductance will generally improve the transient response but increase the output voltage ripple. The inductor must be rated for the peak current, IPK, in a given application, to prevent saturation. During normal loading conditions, the peak current is equal to the load current plus 1/2 of the inductor ripple current. During an overload condition, as well as during certain load transients, the controller may trip current limit. In this case the peak inductor current is given by ICL, found in the Electrical Characteristics table. Good design practice requires that the inductor rating be adequate for this overload condition. NOTE If the inductor is not rated for the maximum expected current, it can saturate resulting in damage to the LM22676 and/or the power diode. 8.2.1.2.3 Input Capacitor The input capacitor selection is based on both input voltage ripple and RMS current. Good quality input capacitors are necessary to limit the ripple voltage at the VIN pin while supplying most of the regulator current during switch on-time. Low ESR ceramic capacitors are preferred. Larger values of input capacitance are desirable to reduce voltage ripple and noise on the input supply. This noise may find its way into other circuitry, sharing the same input supply, unless adequate bypassing is provided. A very approximate formula for determining the input voltage ripple is shown in Equation 14. (14) Where: Vri is the peak-to-peak ripple voltage at the switching frequency. Another concern is the RMS current passing through this capacitor. Equation 15 gives an approximation to this current. (15) The capacitor must be rated for at least this level of RMS current at the switching frequency. Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 15 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com All ceramic capacitors have large voltage coefficients, in addition to normal tolerances and temperature coefficients. To help mitigate these effects, multiple capacitors can be used in parallel to bring the minimum capacitance up to the desired value. This may also help with RMS current constraints by sharing the current among several capacitors. Many times it is desirable to use an electrolytic capacitor on the input, in parallel with the ceramics. The moderate ESR of this capacitor can help to damp any ringing on the input supply caused by long power leads. This method can also help to reduce voltage spikes that may exceed the maximum input voltage rating of the LM22676. It is good practice to include a high frequency bypass capacitor as close as possible to the LM22676. This small case size, low ESR, ceramic capacitor should be connected directly to the VIN and GND pins with the shortest possible PCB traces. Values in the range of 0.47 µF to 1 µF are appropriate. This capacitor helps to provide a low impedance supply to sensitive internal circuitry. It also helps to suppress any fast noise spikes on the input supply that may lead to increased EMI. 8.2.1.2.4 Output Capacitor The output capacitor is responsible for filtering the output voltage and supplying load current during transients. Capacitor selection depends on application conditions as well as ripple and transient requirements. Best performance is achieved with a parallel combination of ceramic capacitors and a low ESR SP™ or POSCAP™ type. Very low ESR capacitors such as ceramics reduce the output ripple and noise spikes, while higher value electrolytics or polymer provide large bulk capacitance to supply transients. Assuming very low ESR, Equation 16 gives an approximation to the output voltage ripple. (16) Typically, a total value of 100 µF, or greater is recommended for output capacitance. In applications with Vout less than 3.3 V, it is critical that low ESR output capacitors are selected. This will limit potential output voltage overshoots as the input voltage falls below the device normal operating range. 8.2.1.2.5 Boot-Strap Capacitor The bootstrap capacitor between the BOOT pin and the SW pin supplies the gate current to turn on the Nchannel MOSFET. The recommended value of this capacitor is 10 nF and should be a good quality, low ESR ceramic capacitor. In some cases it may be desirable to slow down the turn on of the internal power MOSFET, in order to reduce EMI. This can be done by placing a small resistor in series with the Cboot capacitor. Resistors in the range of 10 Ω to 50 Ω can be used. This technique should only be used when absolutely necessary, because it will increase switching losses and thereby reduce efficiency. 8.2.1.3 Application Curves Figure 15. Efficiency vs IOUT and VIN, VOUT = 3.3 V 16 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 9 Power Supply Recommendations The LM22676 is designed to operate from an input voltage supply range between 4.5 V and 42 V. This input supply should be able to withstand the maximum input current and maintain a voltage above 4.5 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 LM22676 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 LM22676 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 Board layout is critical for the proper operation of switching power supplies. First, the ground plane area must be sufficient for thermal dissipation purposes. Second, appropriate guidelines must be followed to reduce the effects of switching noise. Switch mode converters are very fast switching devices. In such cases, the rapid increase of input current combined with the parasitic trace inductance generates unwanted L di/dt noise spikes. The magnitude of this noise tends to increase as the output current increases. This noise may turn into electromagnetic interference (EMI) and can also cause problems in device performance. Therefore, care must be taken in layout to minimize the effect of this switching noise. The most important layout rule is to keep the ac current loops as small as possible. Figure 16 shows the current flow in a buck converter. The top schematic shows a dotted line which represents the current flow during the FET switch on-state. The middle schematic shows the current flow during the FET switch off-state. The bottom schematic shows the currents referred to as ac currents. These ac currents are the most critical because they are changing in a very short time period. The dotted lines of the bottom schematic are the traces to keep as short and wide as possible. This will also yield a small loop area reducing the loop inductance. To avoid functional problems due to layout, review the PCB layout example. Best results are achieved if the placement of the LM22676, the bypass capacitor, the Schottky diode, RFBB, RFBT, and the inductor are placed as shown in the example. Note that, in the layout shown, R1 = RFBB and R2 = RFBT. It is also recommended to use 2 oz copper boards or heavier to help thermal dissipation and to reduce the parasitic inductances of board traces. See AN1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) for more information. Figure 16. Current Flow in a Buck Application Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 17 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com 10.2 Layout Examples Figure 17. PCB Layout Example for PFM Package Figure 18. PCB Layout Example for SO PowerPAD Package 18 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 LM22676, LM22676-Q1 www.ti.com SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 10.3 Thermal Considerations The components with the highest power dissipation are the power diode and the power MOSFET internal to the LM22676 regulator. The easiest method to determine the power dissipation within the LM22676 is to measure the total conversion losses then subtract the power losses in the diode and inductor. The total conversion loss is the difference between the input power and the output power. An approximation for the power diode loss is shown in Equation 17. (17) Where: VD is the diode voltage drop. An approximation for the inductor power is shown in Equation 18. (18) Where: RL is the dc resistance of the inductor. The 1.1 factor is an approximation for the ac losses. The regulator has an exposed thermal pad to aid power dissipation. Adding multiple vias under the device to the ground plane will greatly reduce the regulator junction temperature. Selecting a diode with an exposed pad will also aid the power dissipation of the diode. The most significant variables that affect the power dissipation of the regulator are 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 junction-to-ambient thermal resistance of the LM22676 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. A large continuous ground plane on the top or bottom PCB layer will provide the most effective heat dissipation. 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 LM22676 SO PowerPAD package is specified in the Electrical Characteristics table. See AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419) for more information. Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 Submit Documentation Feedback 19 LM22676, LM22676-Q1 SNVS587L – SEPTEMBER 2008 – REVISED NOVEMBER 2014 www.ti.com 11 Device and Documentation Support 11.1 Documentation Support 11.1.1 Related Documentation • AN-1889 How to Measure the Loop Transfer Function of Power Supplies (SNVA364) • AN-1885 LM22670 Evaluation Board (SNVA361) • AN-1229 SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) • AN-2020 Thermal Design By Insight, Not Hindsight (SNVA419) 11.2 Related Links The table below lists quick access links. Categories include technical documents, support and community resources, tools and software, and quick access to sample or buy. Table 1. Related Links PARTS PRODUCT FOLDER SAMPLE & BUY TECHNICAL DOCUMENTS TOOLS & SOFTWARE SUPPORT & COMMUNITY LM22676 Click here Click here Click here Click here Click here LM22676-Q1 Click here Click here Click here Click here Click here 11.3 Trademarks WEBENCH, SIMPLE SWITCHER are registered trademarks of Texas Instruments. All other trademarks are the property of their respective owners. 11.4 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. 11.5 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. 20 Submit Documentation Feedback Copyright © 2008–2014, Texas Instruments Incorporated Product Folder Links: LM22676 LM22676-Q1 PACKAGE OPTION ADDENDUM www.ti.com 10-Dec-2020 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) LM22676MR-5.0/NOPB ACTIVE SO PowerPAD DDA 8 95 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 5.0 LM22676MR-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 95 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 ADJ LM22676MRE-5.0/NOPB ACTIVE SO PowerPAD DDA 8 250 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 5.0 LM22676MRE-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 250 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 ADJ LM22676MRX-5.0/NOPB ACTIVE SO PowerPAD DDA 8 2500 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 5.0 LM22676MRX-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 2500 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 ADJ LM22676QMR-5.0/NOPB ACTIVE SO PowerPAD DDA 8 95 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 Q5.0 LM22676QMR-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 95 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 QADJ LM22676QMRE-5.0/NOPB ACTIVE SO PowerPAD DDA 8 250 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 Q5.0 LM22676QMRE-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 250 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 QADJ LM22676QMRX-5.0/NOPB ACTIVE SO PowerPAD DDA 8 2500 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 Q5.0 LM22676QMRX-ADJ/NOPB ACTIVE SO PowerPAD DDA 8 2500 RoHS & Green SN Level-3-260C-168 HR -40 to 125 L22676 QADJ LM22676QTJ-5.0/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 QTJ-5.0 LM22676QTJ-ADJ/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 QTJ-ADJ LM22676QTJE-5.0/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 QTJ-5.0 LM22676QTJE-ADJ/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 QTJ-ADJ LM22676TJ-5.0/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com Orderable Device 10-Dec-2020 Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) TJ-5.0 LM22676TJ-ADJ/NOPB ACTIVE TO-263 NDR 7 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 TJ-ADJ LM22676TJE-5.0/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 TJ-5.0 LM22676TJE-ADJ/NOPB ACTIVE TO-263 NDR 7 250 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 LM22676 TJ-ADJ (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) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of