LM2833 NSC | Alldatasheet
Document overview
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Technical content
Features
■ Input voltage range of 3.0V to 5.5V ■ Output voltage range of 0.6V to 4.5V ■ Tiny eMSOP-10 or LLP-10 package ■ 3.0A steady-state output current ■ High switching frequencies 1.5MHz (LM2833X) 3.0MHz (LM2833Z) ■ Enable pin ■ 56mΩ PMOS switch ■ 0.6V, 2% internal voltage reference over line and temperature ■ Internal soft-start ■ Internally compensated peak current-mode control ■ Cycle-by-cycle current limit and thermal shutdown ■ Frequency foldback protection ■ Input voltage UVLO (Under-voltage lockout) ■ Output over-voltage protection
Applications
■ Multimedia Set Top Box ■ Broadband Communications ■ Core Power in HDDs ■ Data Acquisition/Telemetry ■ USB Powered Devices ■ DSL Modems Typical Application Circuit 30013201 30013212 © 2009 National Semiconductor Corporation 300132 www.national.com LM2833 1.5MHz/3MHz 3.0A Step-Down DC-DC Switching Regulator
Ordering Information
Option Package Type NSC Package Drawing Top Mark Supplied As LM2833XMY 1.5MHz eMSOP-10 MUC10A SPYB 1000 units Tape and Reel LM2833XMYX 3500 units Tape and Reel LM2833XSD LLP-10 SDA10A 2833X 1000 units Tape and Reel LM2833XSDX 4500 units Tape and Reel LM2833ZMY 3MHz eMSOP-10 MUC10A SPZB 1000 units Tape and Reel LM2833ZMYX 3500 units Tape and Reel LM2833ZSD LLP-10 SDA10A 2833Z 1000 units Tape and Reel LM2833ZSDX 4500 units Tape and Reel Pin Descriptions Pin(s) Name Description 1 VINC Input supply for internal bias and control circuitry. Need to locally bypass this pin to GND. 2 EN Enable control input. Logic high enables operation. Do not allow this pin to float or subject to voltages greater than VIN + 0.3V. 3 SGND Signal (analog) ground. Place the bottom resistor of the feedback network as close as possible to this pin for good load regulation. 4 NC No user function, connect this pin to GND. 5 FB Feedback pin. Connect this pin to the external resistor divider to set output voltage. 6 PGND Power ground pin. Provides ground return path for the internal driver. 7, 8 SW Switch pins. Connect these pins to the inductor and catch diode. 9, 10 VIND Input supply voltage. Connect a bypass capacitor locally from these pins to PGND. DAP Die Attach Pad Connect to system ground for low thermal impedance, but it cannot be used as a primary GND connection. www.national.com 2 LM2833
Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VINC, VIND -0.5V to 7V FB Voltage -0.5V to 3V EN Voltage -0.5V to 7V SW Voltage -0.5V to 7V ESD Susceptibility (Note 4) 2kV Junction Temperature (Note 2) 150°C Storage Temperature −65°C to +150°C Soldering Information Infrared/Convection Reflow (15sec) 220°C Operating Ratings VINC, VIND 3V to 5.5V Junction Temperature −40°C to +125°C Electrical Characteristics Unless otherwise specified under the Conditions column, VIN = 5V. Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the junction temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm, and are provided for reference purposes only. Symbol Parameter Conditions Min Typ Max Units ΔVFB/(ΔVINxVFB) Feedback Voltage Line Regulation VIN = 3V to 5.5V 0.08 %/V IB Feedback Input Bias Current 0.1 100 nA UVLO Undervoltage Lockout VIN Rising 2.70 2.90 VVIN Falling 1.85 2.35 UVLO Hysteresis 0.35 V DMAX Maximum Duty Cycle LM2833X 86 95 %LM2833Z 80 90 DMIN Minimum Duty Cycle LM2833X 5 %LM2833Z 7 RDS(ON) Switch On Resistance LLP-10 Package 58 90 mΩeMSOP-10 Package 56 ICL Switch Current Limit 3.4 4.4 A VEN_TH Enable Threshold Voltage 1.8 VShutdown Threshold Voltage 0.4 ISW Switch Leakage 100 nA IEN Enable Pin Current Sink/Source 100 nA IQ Quiescent Current (switching) LM2833X, VFB = 0.55 3.2 5 mALM2833Z, VFB = 0.55 4.3 6.5 Quiescent Current (shutdown) All Options VEN = 0V 300 nA VFB_F FB Frequency Foldback Threshold All Options 0.32 V fFB Foldback Frequency LM2833X, VFB = 0V 400 kHzLM2833Z, VFB = 0V 800 3 www.national.com LM2833
Symbol Parameter Conditions Min Typ Max Units θJA Junction to Ambient
0 LFPM Air Flow (Note 3)
θJC Junction to Case (Note 3) LLP-10 Package 12 °C/WeMSOP-10 Package 11 TSD Thermal Shutdown Threshold Junction Temperature Rising 165 °C TSD_HYS Thermal Shutdown Hysteresis Junction Temperature Falling 15 °C Note 1: 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 Ratings is not implied. The recommended Operating Ratings indicate conditions at which the device is functional and should not be operated beyond such conditions. Note 2: Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device. Note 3: Applies for packages soldered directly onto a 4” x 3” 4-layer standard JEDEC board in still air. Note 4: Human body model, 1.5kΩ in series with 100pF. www.national.com 4 LM2833
Typical Performance Characteristics Unless otherwise specified, VIN = 5V and TA = 25°C. Efficiency vs Load Current - "LM2833X" and "LM2833Z" 30013213 Efficiency vs Load Current - "LM2833X" 30013214 Efficiency vs Load Current - "LM2833Z" 30013215 Oscillator Frequency vs Temperature - "LM2833X" 30013225 Oscillator Frequency vs Temperature - "LM2833Z" 30013226 Current Limit vs Temperature 30013227 5 www.national.com LM2833
RDS(ON) vs Temperature (LLP-10 Package) 30013229 RDS(ON) vs Temperature (eMSOP-10 Package) 30013230 LM2833X IQ (Quiescent Current) 30013231 LM2833Z IQ (Quiescent Current) 30013232 VFB vs Temperature 30013233 Frequency Foldback 30013228 www.national.com 6 LM2833
Loop Gain and Phase - "LM2833X" 30013235 Loop Gain and Phase - "LM2833Z" 30013236 Load Step Response - "LM2833X" 30013247 Line Transient Response - "LM2833X" 30013248 Startup by EN - "LM2833X" 30013252 Shutdown by EN - "LM2833X" 30013253 7 www.national.com LM2833
Startup with EN tied to VIN - "LM2833X" 30013254 Short-circuit Triggering - "LM2833X" 30013250 Short-circuit Release - "LM2833X" 30013251 Recovery from Thermal Shutdown - "LM2833X" 30013240 www.national.com 8 LM2833
FIGURE 1. Simplified Block Diagram
Application Information
The LM2833 is a constant frequency PWM buck regulator IC that delivers a 3.0A load current. The regulator is available in preset switching frequencies of 1.5MHz or 3.0MHz. This high frequency allows the LM2833 to operate with small surface mount capacitors and inductors, resulting in a DC/DC con- verter that requires a minimum amount of board space. The LM2833 is internally compensated, therefore it is simple to use and requires few external components. The LM2833 uses peak current-mode control to regulate the output voltage. The following description of operation of the LM2833 will refer to the Typical Application Circuit, to the waveforms in Figure 2 and simplified block diagram in Figure 1. The LM2833 sup- plies a regulated output voltage by switching the internal PMOS power switch at a constant frequency and variable du- ty cycle. A switching cycle begins at the falling edge of the reset pulse generated by the internal oscillator. When this pulse goes low, the output control logic turns on the internal PMOS power switch. During this on-time, the SW pin voltage (VSW) swings up to approximately V IN, and the inductor cur- rent (IL) increases with a linear slope. I L is measured by the current sense amplifier, which generates an output propor- tional to the switch current. The sense signal is summed with the regulator’s corrective ramp and compared to the error amplifier’s output, which is proportional to the difference be- tween the feedback voltage and VREF. When the PWM com- parator output goes high, the internal power switch turns off until the next switching cycle begins. During the switch off- time, the inductor current discharges through the catch diode D1, which forces the SW pin to swing below ground by the forward voltage (V D) of the catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output volt- age. 30013266 FIGURE 2. SW Pin Voltage and Inductor Current state after which the internal soft-start process commences. from 0V to its nominal value of 0.6V in approximately 600µs. and minimizes output voltage overshoot. transients that may occur when the input voltage rises slowly. (see Frequency Foldback section for more information). put voltage and high output load current.
Thermal shutdown limits total power dissipation by turning off the internal power switch when the IC junction temperature typically exceeds 165°C. After thermal shutdown occurs, the power switch does not turn on again until the junction tem- perature drops below approximately 150°C. Design Guide INDUCTOR SELECTION The Duty Cycle (D) can be approximated quickly using the ratio of output voltage (VOUT) to input voltage (VIN): The catch diode (D1) forward voltage drop and the voltage drop across the internal PMOS must be included to calculate a more accurate duty cycle. Calculate D by using the following formula: VSW can be approximated by: VSW = IOUT x RDS(ON) Where IOUT is output load current. The diode forward drop (VD) can range from 0.3V to 0.7V depending on the quality of the diode. The lower the VD, the higher the operating efficien- cy of the converter. The inductor value determines the output ripple current ( ΔiL, as defined in Figure 2). Lower inductor values decrease the size of the inductor, but increase the output ripple current. An increase in the inductor value will decrease the output ripple current. In general, the ratio of ripple current to the output current is optimized when it is set between 0.2 and 0.4 for output currents above 2A. This ratio r is defined as: One must ensure that the minimum current limit (3.4A) is not exceeded, so the peak current in the inductor must be calcu- lated. The peak current (ILPK) in the inductor is calculated by: ILPK = IOUT + ΔiL/2 When the designed maximum output current is reduced, the ratio r can be increased. At a current of 0.1A, r can be made as high as 0.9. The ripple ratio can be increased at lighter loads because the net ripple is actually quite low, and if r re- mains constant the inductor value can be made quite large. An equation empirically developed for the maximum ripple ratio at any current below 2A is: r = 0.387 x IOUT-0.3667 Note that this is just a guideline, and it needs to be combined with two important factors for proper selection of inductance values at any operating condition. The first consideration is at output voltage above 2.5V, one needs to ensure that the in- ductance given by the above guideline should not be less than 1µH for the LM2833X or 0.5µH for the LM2833Z. Since the LM2833 has a fixed internal corrective ramp signal, a very low inductance value at high output voltage will generate a very steep down slope of inductor current, which will result in an insufficient slope compensation, and cause instability known as sub-harmonic oscillation. Another consideration is at low load current, one needs to ensure that the inductance value given by the guideline should not exceed 10µH for the LM2833X and 4.7µH for the LM2833Z, since too much induc- tance effectively flattens the down slope of the inductor cur- rent, and may significantly limit the system bandwidth and phase margin resulting in instability. The LM2833 operates at frequencies allowing the use of ce- ramic output capacitors without compromising transient re- sponse. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple. See the output capacitor section for more details on calculating output volt- age ripple. Now that the ripple current is determined, the inductance is calculated by: where fSW is the switching frequency. When selecting an in- ductor, make sure that it is capable of supporting the peak output current without saturating. Inductor saturation will re- sult in a sudden reduction in inductance and prevent the regulator from operating properly. Because of the operating frequency of the LM2833, ferrite based inductors are pre- ferred to minimize core losses. This presents little restriction since the variety and availability of ferrite-based inductors is large. Lastly, inductors with lower series resistance (DCR) will provide better operating efficiency. For recommended induc- tor selection, refer to Design Examples. INPUT CAPACITOR An input capacitor is necessary to ensure that V IN does not drop excessively during switching transients. The primary specifications of the input capacitor are capacitance, voltage rating, RMS current rating, and ESL (Equivalent Series In- ductance). The input voltage rating is specifically stated by the capacitor manufacturer. Make sure to check any recom- mended deratings and also verify if there is any significant change in capacitance at the operating input voltage and the operating temperature. The input capacitor maximum RMS input current rating (IRMS-IN) must be greater than: Neglecting inductor ripple simplifies the above equation to: It can be shown from the above equation that maximum RMS capacitor current occurs when D = 0.5. Always calculate the RMS at the point where the duty cycle D is closest to 0.5. The ESL of an input capacitor is usually determined by the effec- tive cross sectional area of the current path. As a rule of thumb, a large leaded capacitor will have high ESL and a 1206 ceramic chip capacitor will have very low ESL. At the operat- ing frequencies of the LM2833, leaded capacitors may have an ESL so large that the resulting impedance (2 πfL) will be higher than that required to provide stable operation. It is strongly recommended to use ceramic capacitors due to their low ESR and low ESL. A 22µF multilayer ceramic capacitor 13 www.national.com LM2833
(MLCC) is a good choice for most applications. In cases where large capacitance is required, use surface mount ca- pacitors such as Tantalum capacitors and place at least a 4.7µF ceramic capacitor close to the VIN pin. For MLCCs it is recommended to use X7R or X5R dielectrics. Consult capac- itor manufacturer datasheet to see how rated capacitance varies over operating conditions. OUTPUT CAPACITOR The output capacitor is selected based upon the desired out- put ripple and transient response. The initial current of a load transient is provided mainly by the output capacitor. The out- put ripple of the converter is: When using MLCCs, the ESR is typically so low that the ca- pacitive ripple may dominate. When this occurs, the output ripple will be approximately sinusoidal and 90° phase shifted from the switching action. Given the availability and quality of MLCCs and the expected output voltage of designs using the LM2833, there is really no need to review any other capacitor technologies. Another benefit of ceramic capacitors is their ability to bypass high frequency noise. A certain amount of switching edge noise will couple through parasitic capaci- tances in the inductor to the output. A ceramic capacitor will bypass this noise while a tantalum will not. Since the output capacitor is one of the two external components that control the stability of the regulator control loop, most applications will require a minimum of 22µF output capacitance. In the case of low output voltage, a larger output capacitance is required to ensure sufficient phase margin. Capacitance can often, but not always, be increased significantly with little detriment to the regulator stability. Like the input capacitor, recommended multilayer ceramic capacitors are X7R or X5R types. Again, verify actual capacitance at the desired operating voltage and temperature. Check the RMS current rating of the capacitor. The maximum RMS current rating of the capacitor is: One may select a 1206 size MLCC for output capacitor, since its current rating is typically above 1A, more than enough for the requirement. CATCH DIODE The catch diode conducts during the switch off-time. A Schot- tky diode is recommended for its fast switching time and low forward voltage drop. The catch diode should be chosen such that its current rating is greater than: ID = IOUT x (1-D) The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin. To im- prove efficiency, choose a Schottky diode with a low forward voltage drop. OUTPUT VOLTAGE The output voltage is set using the following equation where R2 is connected between the FB pin and GND, and R1 is connected between VOUT and the FB pin. A good value for R2 is 2kΩ. VREF = 0.60V EFFICIENCY ESTIMATION The complete LM2833 DC/DC converter efficiency can be calculated in the following manner: Or Calculations for determining the most significant power loss- es are shown below. Other losses totaling less than 2% are not discussed. The main power loss (P LOSS) in the converter includes two basic types of losses: switching loss and conduction loss. In addition, there is loss associated with the power required for the internal circuitry of IC. Conduction losses usually domi- nate at higher output loads, whereas switching losses domi- nate at lower output loads. The first step in determining the losses is to calculate the duty cycle (D): VSW is the voltage drop across the internal power switch when it is on, and is equal to: VSW = IOUT x RDS(ON) VD is the forward voltage drop across the catch diode. It can be obtained from the diode manufactures Electrical Charac- teristics section. If the DC voltage drop across the inductor (VDCR) is accounted for, the equation becomes: The conduction losses in the catch diode are calculated as follows: PDIODE = VD x IOUT x (1-D) Often this is the single most significant power loss in the cir- cuit. Care should be taken to choose a Schottky diode with a low forward voltage drop. Another significant external power loss is the conduction loss in the output inductor. The equation can be simplified to: PIND = IOUT2 x RDCR The LM2833 conduction loss is mainly associated with the internal power switch: www.national.com 14 LM2833
3.2mA for the LM2833X, and 4.3mA for the LM2833Z. TABLE 1. Power Loss Tabulation C2, which should be near the GND connections of C1 and D1. any other traces that are switching. noise can be decreased by choosing a shielded inductor. example of a four-layer layout.
FIGURE 12. LM2833X (1.5MHz): VIN = 5V, Output = 3.3V/3.0A
FIGURE 13. LM2833Z (3MHz): VIN = 3.3V, Output = 1.2V/3.0A
FIGURE 14. LM2833Z (3MHz): VIN = 5V, Output = 3.3V/3.0A
Physical Dimensions inches (millimeters) unless otherwise noted 10-Lead eMSOP Package 10-Lead LLP Package www.national.com 20 LM2833
21 www.national.com LM2833
LM2833 1.5MHz/3MHz 3.0A Step-Down DC-DC Switching Regulator For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage Reference www.national.com/vref Design Made Easy www.national.com/easy PowerWise® Solutions www.national.com/powerwise Solutions www.national.com/solutions Serial Digital Interface (SDI) www.national.com/sdi Mil/Aero www.national.com/milaero Temperature Sensors www.national.com/tempsensors Solar Magic® www.national.com/solarmagic Wireless (PLL/VCO) www.national.com/wireless Analog University® www.national.com/AU THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. NATIONAL ASSUMES NO LIABILITY FOR APPLICATIONS ASSISTANCE OR BUYER PRODUCT DESIGN. BUYERS ARE RESPONSIBLE FOR THEIR PRODUCTS AND APPLICATIONS USING NATIONAL COMPONENTS. PRIOR TO USING OR DISTRIBUTING ANY PRODUCTS THAT INCLUDE NATIONAL COMPONENTS, BUYERS SHOULD PROVIDE ADEQUATE DESIGN, TESTING AND OPERATING SAFEGUARDS. EXCEPT AS PROVIDED IN NATIONAL’S TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, NATIONAL ASSUMES NO LIABILITY WHATSOEVER, AND NATIONAL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY RELATING TO THE SALE AND/OR USE OF NATIONAL PRODUCTS INCLUDING LIABILITY OR WARRANTIES RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS PRIOR WRITTEN APPROVAL OF THE CHIEF EXECUTIVE OFFICER AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: Life support devices or systems are devices which (a) are intended for surgical implant into the body, or (b) support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness. National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. Copyright© 2009 National Semiconductor Corporation For the most current product information visit us at www.national.com National Semiconductor Americas Technical Support Center Email: support@nsc.com Tel: 1-800-272-9959 National Semiconductor Europe Technical Support Center Email: europe.support@nsc.com German Tel: +49 (0) 180 5010 771 English Tel: +44 (0) 870 850 4288 National Semiconductor Asia Pacific Technical Support Center Email: ap.support@nsc.com National Semiconductor Japan Technical Support Center Email: jpn.feedback@nsc.com www.national.com