LM2832 High Frequency 2.0A Load - Step-Down DC-DC Regulator General Description Features The LM2832 regulator is a monolithic, high frequency, PWM step-down DC/DC converter in a 6 Pin LLP and a 8 Pin eMSOP package. It provides all the active functions to provide local DC/DC conversion with fast transient response and accurate regulation in the smallest possible PCB area. With a minimum of external components, the LM2832 is easy to use. The ability to drive 2.0A loads with an internal 150 mΩ PMOS switch using state-of-the-art 0.5 µm BiCMOS technology results in the best power density available. The world-class control circuitry allows on-times as low as 30ns, thus supporting exceptionally high frequency conversion over the entire 3V to 5.5V input operating range down to the minimum output voltage of 0.6V. Switching frequency is internally set to 550 kHz, 1.6 MHz, or 3.0 MHz, allowing the use of extremely small surface mount inductors and chip capacitors. Even though the operating frequency is high, efficiencies up to 93% are easy to achieve. External shutdown is included, featuring an ultra-low stand-by current of 30 nA. The LM2832 utilizes current-mode control and internal compensation to provide high-performance regulation over a wide range of operating conditions. Additional features include internal soft-start circuitry to reduce inrush current, pulse-by-pulse current limit, thermal shutdown, and output over-voltage protection. n n n n n n n n n n Input voltage range of 3.0V to 5.5V Output voltage range of 0.6V to 4.5V 2.0A output current High Switching Frequencies 1.6MHz (LM2832X) 0.55MHz (LM2832Y) 3.0MHz (LM2832Z) 150mΩ PMOS switch 0.6V, 2% Internal Voltage Reference Internal soft-start Current mode, PWM operation Thermal Shutdown Over voltage protection Applications n n n n n Local 5V to Vcore Step-Down Converters Core Power in HDDs Set-Top Boxes USB Powered Devices DSL Modems Typical Application Circuit 20197564 20197581 © 2006 National Semiconductor Corporation DS201975 www.national.com LM2832 High Frequency 2.0A Load - Step-Down DC-DC Regulator August 2006 LM2832 Connection Diagrams 20197501 20197502 6-Pin LLP 8-Pin eMSOP Ordering Information Order Number Frequency Option LM2832XMY LM2832XMYX LM2832XSD LM2832YMY LM2832YSD LM2832ZMY LM2832ZSD Top Mark eMSOP-8 MUY08A SLBB LLP-6 SDE06A L196B eMSOP-8 MUY08A SLCB LLP-6 SDE06A L197B eMSOP-8 MUY08A SLDB LLP-6 SDE06A L198B 0.55MHz LM2832YSDX LM2832ZMYX NSC Package Drawing 1.6MHz LM2832XSDX LM2832YMYX Package Type 3MHz LM2832ZSDX NOPB versions available as well www.national.com 2 Supplied As 1000 units Tape and Reel 3500 units Tape and Reel 1000 units Tape and Reel 4500 units Tape and Reel 1000 units Tape and Reel 3500 units Tape and Reel 1000 units Tape and Reel 4500 units Tape and Reel 1000 units Tape and Reel 3500 units Tape and Reel 1000 units Tape and Reel 4500 units Tape and Reel LM2832 Pin Descriptions 8-Pin eMSOP Pin Name Function 1 VIND Power Input supply. 2 VINA Control circuitry supply voltage. Connect VINA to VIND on PC board. 3, 5, 7 GND Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin. 4 EN 6 FB Feedback pin. Connect to external resistor divider to set output voltage. 8 SW Output switch. Connect to the inductor and catch diode. DAP Die Attach Pad Enable control input. Logic high enables operation. Do not allow this pin to float or be greater than VIN + 0.3V. Connect to system ground for low thermal impedance, but it cannot be used as a primary GND connection. Pin Descriptions 6-Pin LLP Pin Name Function 1 FB 2 GND Feedback pin. Connect to external resistor divider to set output voltage. 3 SW 4 VIND Power Input supply. 5 VINA Control circuitry supply voltage. Connect VINA to VIND on PC board. 6 EN DAP Die Attach Pad Signal and power ground pin. Place the bottom resistor of the feedback network as close as possible to this pin. Output switch. Connect to the inductor and catch diode. Enable control input. Logic high enables operation. Do not allow this pin to float or be greater than VINA + 0.3V. Connect to system ground for low thermal impedance, but it cannot be used as a primary GND connection. 3 www.national.com LM2832 Absolute Maximum Ratings (Note 1) Storage Temperature If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Soldering Information VIN -0.5V to 7V FB Voltage -0.5V to 3V EN Voltage -0.5V to 7V SW Voltage -0.5V to 7V ESD Susceptibility Infrared or Convection Reflow (15 sec) 220˚C Operating Ratings VIN 3V to 5.5V Junction Temperature 2kV Junction Temperature (Note 2) −65˚C to +150˚C −40˚C to +125˚C 150˚C Electrical Characteristics VIN = 5V unless otherwise indicated under the Conditions column. 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 at TJ = 25˚C, and are provided for reference purposes only. Symbol VFB ∆VFB/VIN IB UVLO Parameter Feedback Voltage Feedback Voltage Line Regulation Min Typ Max LLP-6 Package Conditions 0.588 0.600 0.612 eMSOP-8 Package 0.584 0.600 0.616 VIN = 3V to 5V 0.02 Feedback Input Bias Current Undervoltage Lockout VIN Rising VIN Falling 1.85 UVLO Hysteresis FSW DMAX DMIN RDS(ON) ICL VEN_TH Switching Frequency Maximum Duty Cycle Minimum Duty Cycle Switch On Resistance Switch Current Limit IEN Enable Pin Current Quiescent Current (switching) Quiescent Current (shutdown) www.national.com 2.90 V 2.3 V 1.2 1.6 1.95 LM2832-Y 0.4 0.55 0.7 LM2832-Z 2.25 3.0 3.75 LM2832-X 86 94 LM2832-Y 90 96 LM2832-Z 82 90 LM2832-X 5 LM2832-Y 2 LM2832-Z 7 LLP-6 Package 150 eMSOP-8 Package 155 % 240 3.25 100 100 LM2832X VFB = 0.55 3.3 V nA nA 5 LM2831Y VFB = 0.55 2.8 4.5 LM2832Z VFB = 0.55 4.3 6.5 All Options VEN = 0V 30 4 mΩ A 1.8 Sink/Source MHz % 0.4 Enable Threshold Voltage Switch Leakage IQ nA 2.73 Shutdown Threshold Voltage ISW %/V 100 LM2832-X 2.4 V 0.1 0.43 VIN = 3.3V Units mA nA Symbol Parameter Conditions Min Typ θJA Junction to Ambient 0 LFPM Air Flow (Note 3) LLP-6 and eMSOP-8 Packages 80 θJC Junction to Case (Note 3) LLP-6 and eMSOP-8 Packages 18 TSD Thermal Shutdown Temperature 165 Max Units ˚C/W ˚C/W ˚C Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating Range indicates conditions for which the device is intended to be functional, but does not guarantee specfic performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. 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 3” x 3” PC board with 2oz. copper on 4 layers in still air. 5 www.national.com LM2832 Electrical Characteristics VIN = 5V unless otherwise indicated under the Conditions column. 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 at TJ = 25˚C, and are provided for reference purposes only. (Continued) LM2832 Typical Performance Characteristics All curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. η vs Load "X, Y and Z" Vin = 3.3V, Vo = 1.8V η vs Load "X" Vin = 5V, Vo = 1.8V & 3.3V 20197587 20197539 η vs Load - "Y" Vin = 5V, Vo = 3.3V & 1.8V η vs Load "Z" Vin = 5V, Vo = 3.3V & 1.8V 20197590 20197542 Load Regulation Vin = 3.3V, Vo = 1.8V (All Options) Load Regulation Vin = 5V, Vo = 1.8V (All Options) 20197583 www.national.com 20197584 6 Load Regulation Vin = 5V, Vo = 3.3V (All Options) Oscillator Frequency vs Temperature - "X" 20197524 20197585 Oscillator Frequency vs Temperature - "Y" Oscillator Frequency vs Temperature - "Z" 20197536 20197525 Current Limit vs Temperature Vin = 3.3V RDSON vs Temperature (LLP-6 Package) 20197588 20197586 7 www.national.com LM2832 Typical Performance Characteristics All curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. (Continued) LM2832 Typical Performance Characteristics All curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. (Continued) RDSON vs Temperature (eMSOP-8 Package) LM2832X IQ (Quiescent Current) 20197589 20197528 LM2832Y IQ (Quiescent Current) LM2832Z IQ (Quiescent Current) 20197529 20197537 www.national.com 8 Line Regulation Vo = 1.8V, Io = 500mA VFB vs Temperature 20197527 20197553 Phase Plot vs Frequency (Vin = 5V, Vo = 1.2V @ 1A) Gain vs Frequency (Vin = 5V, Vo = 1.2V @ 1A) 20197556 20197557 9 www.national.com LM2832 Typical Performance Characteristics All curves taken at VIN = 5.0V with configuration in typical application circuit shown in Application Information section of this datasheet. TJ = 25˚C, unless otherwise specified. (Continued) LM2832 Simplified Block Diagram 20197504 FIGURE 1. www.national.com 10 LM2832 Applications Information THEORY OF OPERATION SOFT-START This function forces VOUT to increase at a controlled rate during start up. During soft-start, the error amplifier’s reference voltage ramps from 0V to its nominal value of 0.6V in approximately 600 µs. This forces the regulator output to ramp up in a controlled fashion, which helps reduce inrush current. The LM2832 is a constant frequency PWM buck regulator IC that delivers a 2.0A load current. The regulator has a preset switching frequency of 1.6MHz or 3.0MHz. This high frequency allows the LM2832 to operate with small surface mount capacitors and inductors, resulting in a DC/DC converter that requires a minimum amount of board space. The LM2832 is internally compensated, so it is simple to use and requires few external components. The LM2832 uses current-mode control to regulate the output voltage. The following operating description of the LM2832 will refer to the Simplified Block Diagram (Figure 1) and to the waveforms in Figure 2. The LM2832 supplies a regulated output voltage by switching the internal PMOS control switch at constant frequency and variable duty 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 control switch. During this ontime, the SW pin voltage (VSW) swings up to approximately VIN, and the inductor current (IL) increases with a linear slope. IL is measured by the current sense amplifier, which generates an output proportional 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 between the feedback voltage and VREF. When the PWM comparator output goes high, the output switch turns off until the next switching cycle begins. During the switch off-time, inductor current discharges through the Schottky catch diode, which forces the SW pin to swing below ground by the forward voltage (VD) of the Schottky catch diode. The regulator loop adjusts the duty cycle (D) to maintain a constant output voltage. OUTPUT OVERVOLTAGE PROTECTION The over-voltage comparator compares the FB pin voltage to a voltage that is 15% higher than the internal reference VREF. Once the FB pin voltage goes 15% above the internal reference, the internal PMOS control switch is turned off, which allows the output voltage to decrease toward regulation. UNDERVOLTAGE LOCKOUT Under-voltage lockout (UVLO) prevents the LM2832 from operating until the input voltage exceeds 2.73V (typ). The UVLO threshold has approximately 430 mV of hysteresis, so the part will operate until VIN drops below 2.3V (typ). Hysteresis prevents the part from turning off during power up if VIN is non-monotonic. CURRENT LIMIT The LM2832 uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a current limit comparator detects if the output switch current exceeds 3.25A (typ), and turns off the switch until the next switching cycle begins. THERMAL SHUTDOWN Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature exceeds 165˚C. After thermal shutdown occurs, the output switch doesn’t turn on until the junction temperature drops to approximately 150˚C. 20197566 FIGURE 2. Typical Waveforms 11 www.national.com LM2832 capacitor section for more details on calculating output voltage ripple. Now that the ripple current is determined, the inductance is calculated by: Design Guide INDUCTOR SELECTION The Duty Cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN): Where 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: When selecting an inductor, make sure that it is capable of supporting the peak output current without saturating. Inductor saturation will result in a sudden reduction in inductance and prevent the regulator from operating correctly. Because of the speed of the internal current limit, the peak current of the inductor need only be specified for the required maximum output current. For example, if the designed maximum output current is 1.0A and the peak current is 1.25A, then the inductor should be specified with a saturation current limit of > 1.25A. There is no need to specify the saturation or peak current of the inductor at the 3.25A typical switch current limit. The difference in inductor size is a factor of 5. Because of the operating frequency of the LM2832, ferrite based inductors are preferred to minimize core losses. This presents little restriction since the variety of ferrite-based inductors is huge. Lastly, inductors with lower series resistance (RDCR) will provide better operating efficiency. For recommended inductors see Example Circuits. VSW can be approximated by: VSW = IOUT x RDSON 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 efficiency of the converter. The inductor value determines the output ripple current. 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. One must ensure that the minimum current limit (2.4A) is not exceeded, so the peak current in the inductor must be calculated. The peak current (ILPK) in the inductor is calculated by: ILPK = IOUT + ∆iL INPUT CAPACITOR An input capacitor is necessary to ensure that VIN does not drop excessively during switching transients. The primary specifications of the input capacitor are capacitance, voltage, RMS current rating, and ESL (Equivalent Series Inductance). The recommended input capacitance is 22 µF.The input voltage rating is specifically stated by the capacitor manufacturer. Make sure to check any recommended 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: 20197505 FIGURE 3. Inductor Current Neglecting inductor ripple simplifies the above equation to: In general, 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 effective cross sectional area of the current path. A large leaded capacitor will have high ESL and a 0805 ceramic chip capacitor will have very low ESL. At the operating frequencies of the LM2832, leaded capacitors may have an ESL so large that the resulting impedance (2πfL) will be higher than that required to provide stable operation. As a result, surface mount capacitors are strongly recommended. ∆iL = 0.1 x (IOUT) → 0.2 x (IOUT) If ∆iL = 20% of 2A, the peak current in the inductor will be 2.4A. The minimum guaranteed current limit over all operating conditions is 2.4A. One can either reduce ∆iL, or make the engineering judgment that zero margin will be safe enough. The typical current limit is 3.25A. The LM2832 operates at frequencies allowing the use of ceramic output capacitors without compromising transient response. Ceramic capacitors allow higher inductor ripple without significantly increasing output ripple. See the output www.national.com 12 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 VO and the FB pin. A good value for R2 is 10kΩ. When designing a unity gain converter (Vo = 0.6V), R1 should be between 0Ω and 100Ω, and R2 should be equal or greater than 10kΩ. (Continued) Sanyo POSCAP, Tantalum or Niobium, Panasonic SP, and multilayer ceramic capacitors (MLCC) are all good choices for both input and output capacitors and have very low ESL. For MLCCs it is recommended to use X7R or X5R type capacitors due to their tolerance and temperature characteristics. Consult capacitor manufacturer datasheets to see how rated capacitance varies over operating conditions. OUTPUT CAPACITOR The output capacitor is selected based upon the desired output ripple and transient response. The initial current of a load transient is provided mainly by the output capacitor. The output ripple of the converter is: VREF = 0.60V PCB LAYOUT CONSIDERATIONS When planning layout there are a few things to consider when trying to achieve a clean, regulated output. The most important consideration is the close coupling of the GND connections of the input capacitor and the catch diode D1. These ground ends should be close to one another and be connected to the GND plane with at least two through-holes. Place these components as close to the IC as possible. Next in importance is the location of the GND connection of the output capacitor, which should be near the GND connections of CIN and D1. There should be a continuous ground plane on the bottom layer of a two-layer board except under the switching node island. The FB pin is a high impedance node and care should be taken to make the FB trace short to avoid noise pickup and inaccurate regulation. The feedback resistors should be placed as close as possible to the IC, with the GND of R1 placed as close as possible to the GND of the IC. The VOUT trace to R2 should be routed away from the inductor and any other traces that are switching. High AC currents flow through the VIN, SW and VOUT traces, so they should be as short and wide as possible. However, making the traces wide increases radiated noise, so the designer must make this trade-off. Radiated noise can be decreased by choosing a shielded inductor. The remaining components should also be placed as close as possible to the IC. Please see Application Note AN-1229 for further considerations and the LM2832 demo board as an example of a four-layer layout. When using MLCCs, the ESR is typically so low that the capacitive 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 LM2832, 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 capacitances 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 22 µF of output capacitance. Capacitance often, but not always, can be increased significantly with little detriment to the regulator stability. Like the input capacitor, recommended multilayer ceramic capacitors are X7R or X5R types. CATCH DIODE The catch diode (D1) conducts during the switch off-time. A Schottky diode is recommended for its fast switching times and low forward voltage drop. The catch diode should be chosen so that its current rating is greater than: ID1 = IOUT x (1-D) The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin. To improve efficiency, choose a Schottky diode with a low forward voltage drop. 13 www.national.com LM2832 Design Guide LM2832 PCOND = IOUT2 x RDSON x D Calculating Efficiency, and Junction Temperature Switching losses are also associated with the internal PFET. They occur during the switch on and off transition periods, where voltages and currents overlap resulting in power loss. The simplest means to determine this loss is to empirically measuring the rise and fall times (10% to 90%) of the switch at the switch node. Switching Power Loss is calculated as follows: PSWR = 1/2(VIN x IOUT x FSW x TRISE) PSWF = 1/2(VIN x IOUT x FSW x TFALL) PSW = PSWR + PSWF Another loss is the power required for operation of the internal circuitry: PQ = IQ x VIN IQ is the quiescent operating current, and is typically around 2.5mA for the 0.55MHz frequency option. The complete LM2832 DC/DC converter efficiency can be calculated in the following manner. Or Calculations for determining the most significant power losses are shown below. Other losses totaling less than 2% are not discussed. Power loss (PLOSS) is the sum of two basic types of losses in the converter: switching and conduction. Conduction losses usually dominate at higher output loads, whereas switching losses remain relatively fixed and dominate at lower output loads. The first step in determining the losses is to calculate the duty cycle (D): Typical Application power losses are: Power Loss Tabulation VIN VSW is the voltage drop across the internal PFET when it is on, and is equal to: VSW = IOUT x RDSON VD is the forward voltage drop across the Schottky catch diode. It can be obtained from the diode manufactures Electrical Characteristics section. If the voltage drop across the inductor (VDCR) is accounted for, the equation becomes: 5.0V VOUT 3.3V IOUT 1.75A POUT 5.78W PDIODE 262mW VD 0.45V FSW 550kHz IQ 2.5mA PQ 12.5mW 10mW TRISE 4nS PSWR TFALL 4nS PSWF 10mW RDS(ON) 150mΩ PCOND 306mW INDDCR 50mΩ PIND 153mW D 0.667 PLOSS 753mW η 88% PINTERNAL 339mW ΣPCOND + PSW + PDIODE + PIND + PQ = PLOSS ΣPCOND + PSWF + PSWR + PQ = PINTERNAL PINTERNAL = 339mW Thermal Definitions TJ = Chip junction temperature TA = Ambient temperature RθJC = Thermal resistance from chip junction to device case RθJA = Thermal resistance from chip junction to ambient air Heat in the LM2832 due to internal power dissipation is removed through conduction and/or convection. Conduction: Heat transfer occurs through cross sectional areas of material. Depending on the material, the transfer of heat can be considered to have poor to good thermal conductivity properties (insulator vs. conductor). Heat Transfer goes as: Silicon → package → lead frame → PCB Convection: Heat transfer is by means of airflow. This could be from a fan or natural convection. Natural convection occurs when air currents rise from the hot device to cooler air. Thermal impedance is defined as: The conduction losses in the free-wheeling Schottky diode are calculated as follows: PDIODE = VD x IOUT x (1-D) Often this is the single most significant power loss in the circuit. Care should be taken to choose a Schottky diode that has 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 LM2832 conduction loss is mainly associated with the internal PFET: If the inductor ripple current is fairly small, the conduction losses can be simplified to: www.national.com 14 ambient temperature in the given working application until the circuit enters thermal shutdown. If the SW-pin is monitored, it will be obvious when the internal PFET stops switching, indicating a junction temperature of 165˚C. Knowing the internal power dissipation from the above methods, the junction temperature, and the ambient temperature RθJA can be determined. (Continued) Thermal impedance from the silicon junction to the ambient air is defined as: Once this is determined, the maximum ambient temperature allowed for a desired junction temperature can be found. An example of calculating RθJA for an application using the National Semiconductor LM2832 LLP demonstration board is shown below. The four layer PCB is constructed using FR4 with 1⁄2 oz copper traces. The copper ground plane is on the bottom layer. The ground plane is accessed by two vias. The board measures 3.0cm x 3.0cm. It was placed in an oven with no forced airflow. The ambient temperature was raised to 126˚C, and at that temperature, the device went into thermal shutdown. From the previous example: The PCB size, weight of copper used to route traces and ground plane, and number of layers within the PCB can greatly effect RθJA. The type and number of thermal vias can also make a large difference in the thermal impedance. Thermal vias are necessary in most applications. They conduct heat from the surface of the PCB to the ground plane. Four to six thermal vias should be placed under the exposed pad to the ground plane if the LLP package is used. Thermal impedance also depends on the thermal properties of the application operating conditions (Vin, Vo, Io etc), and the surrounding circuitry. Silicon Junction Temperature Determination Method 1: To accurately measure the silicon temperature for a given application, two methods can be used. The first method requires the user to know the thermal impedance of the silicon junction to top case temperature. Some clarification needs to be made before we go any further. RθJC is the thermal impedance from all six sides of an IC package to silicon junction. RΦJC is the thermal impedance from top case to the silicon junction. In this data sheet we will use RΦJC so that it allows the user to measure top case temperature with a small thermocouple attached to the top case. RΦJC is approximately 30˚C/Watt for the 6-pin LLP package with the exposed pad. Knowing the internal dissipation from the efficiency calculation given previously, and the case temperature, which can be empirically measured on the bench we have: PINTERNAL = 339mW If the junction temperature was to be kept below 125˚C, then the ambient temperature could not go above 86˚C. Tj - (RθJA x PLOSS) = TA 125˚C - (115˚C/W x 339mW) = 86˚C LLP Package Therefore: 20197568 Tj = (RΦJC x PLOSS) + TC From the previous example: Tj = (RΦJC x PINTERNAL) + TC Tj = 30˚C/W x 0.339W + TC The second method can give a very accurate silicon junction temperature. The first step is to determine RθJA of the application. The LM2832 has over-temperature protection circuitry. When the silicon temperature reaches 165˚C, the device stops switching. The protection circuitry has a hysteresis of about 15˚C. Once the silicon temperature has decreased to approximately 150˚C, the device will start to switch again. Knowing this, the RθJA for any application can be characterized during the early stages of the design one may calculate the RθJA by placing the PCB circuit into a thermal chamber. Raise the FIGURE 4. Internal LLP Connection For certain high power applications, the PCB land may be modified to a "dog bone" shape (see Figure 6). By increasing the size of ground plane, and adding thermal vias, the RθJA for the application can be reduced. 15 www.national.com LM2832 Thermal Definitions LM2832 LLP Package (Continued) 20197506 FIGURE 5. 6-Lead LLP PCB Dog Bone Layout www.national.com 16 LM2832 LM2832X Design Example 1 20197507 FIGURE 6. LM2832X (1.6MHz): Vin = 5V, Vo = 1.2V @ 2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1 2.0A Buck Regulator NSC LM2832X C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M D1, Catch Diode 0.4Vf Schottky 2A, 20VR Diodes Inc. B220/A L1 2.2µH, 3.5A Coilcraft DS3316P-222 R2 15.0kΩ, 1% Vishay CRCW08051502F R1 15.0kΩ, 1% Vishay CRCW08051502F R3 100kΩ, 1% Vishay CRCW08051003F 17 www.national.com LM2832 LM2832X Design Example 2 20197560 FIGURE 7. LM2832X (1.6MHz): Vin = 5V, Vo = 0.6V @ 2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1 2.0A Buck Regulator NSC LM2832X C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M D1, Catch Diode 0.4Vf Schottky 2A, 20VR Diodes Inc. B220/A L1 3.3µH, 3.3A Coilcraft DS3316P-332 R2 10.0kΩ, 1% Vishay CRCW08051000F R1 0Ω R3 100kΩ, 1% Vishay CRCW08051003F www.national.com 18 LM2832 LM2832X Design Example 3 20197508 FIGURE 8. LM2832X (1.6MHz): Vin = 5V, Vo = 3.3V @ 2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1 2.0A Buck Regulator NSC LM2832X C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M D1, Catch Diode 0.4Vf Schottky 2A, 20VR Diodes Inc. B220/A L1 2.2µH, 2.8A Coilcraft ME3220-222 R2 10.0kΩ, 1% Vishay CRCW08051002F R1 45.3kΩ, 1% Vishay CRCW08054532F R3 100kΩ, 1% Vishay CRCW08051003F 19 www.national.com LM2832 LM2832Y Design Example 4 20197508 FIGURE 9. LM2832Y (550kHz): Vin = 5V, Vout = 3.3V @ 2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1 1.5A Buck Regulator NSC LM2832Y C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M D1, Catch Diode 0.3Vf Schottky 1.5A, 30VR TOSHIBA CRS08 L1 4.7µH 2.1A TDK SLF7045T-4R7M2R0-PF R1 10.0kΩ, 1% Vishay CRCW08051002F R2 10.0kΩ, 1% Vishay CRCW08051002F www.national.com 20 LM2832 LM2832Y Design Example 5 20197507 FIGURE 10. LM2832Y (550kHz): Vin = 5V, Vout = 1.2V @ 2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1 1.5A Buck Regulator NSC LM2832Y C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M D1, Catch Diode 0.3Vf Schottky 1.5A, 30VR TOSHIBA CRS08 L1 6.8µH 1.8A TDK SLF7045T-6R8M1R7 R1 10.0kΩ, 1% Vishay CRCW08051002F R2 10.0kΩ, 1% Vishay CRCW08051002F 21 www.national.com LM2832 LM2832Z Design Example 6 20197508 FIGURE 11. LM2832Z (3MHz): Vin = 5V, Vo = 3.3V @ 2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1 2.0A Buck Regulator NSC LM2832Z C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M D1, Catch Diode 0.4Vf Schottky 2A, 20VR Diodes Inc. B220/A L1 3.3µH, 3.3A Coilcraft DS3316P-332 R2 10.0kΩ, 1% Vishay CRCW08051002F R1 45.3kΩ, 1% Vishay CRCW08054532F R3 100kΩ, 1% Vishay CRCW08051003F www.national.com 22 LM2832 LM2832Z Design Example 7 20197507 FIGURE 12. LM2832Z (3MHz): Vin = 5V, Vo = 1.2V @ 2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1 2.0A Buck Regulator NSC LM2832Z C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M D1, Catch Diode 0.4Vf Schottky 2A, 20VR Diodes Inc. B220/A L1 4.7µH, 2.7A Coilcraft DS3316P-472 R2 10.0kΩ, 1% Vishay CRCW08051002F R1 10.0kΩ, 1% Vishay CRCW08051002F R3 100kΩ, 1% Vishay CRCW08051003F 23 www.national.com LM2832 LM2832X Dual Converters with Delayed Enabled Design Example 8 20197562 FIGURE 13. LM2832X (1.6MHz): Vin = 5V, Vo = 1.2V @ 2.0A & 3.3V @2.0A Bill of Materials Part ID Part Value Manufacturer Part Number U1, U2 2.0A Buck Regulator NSC LM2832X U3 Power on Reset NSC LP3470M5X-3.08 C1, C3 Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, C4 Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M C7 Trr delay capacitor TDK D1, D2 Catch Diode 0.4Vf Schottky 2A, 20VR Diodes Inc. B220/A L1, L2 3.3µH, 2.7A Coilcraft ME3220-102 R2, R4, R5 10.0kΩ, 1% Vishay CRCW08051002F R1, R6 45.3kΩ, 1% Vishay CRCW08054532F R3 100kΩ, 1% Vishay CRCW08051003F www.national.com 24 20197563 FIGURE 14. LM2832X (1.6MHz): Vin = 5V, Vo = 3.3V @ 2.0A & LP2986-5.0 @ 150mA Bill of Materials Part ID Part Value Manufacturer U1 2.0A Buck Regulator NSC Part Number LM2832X U2 200mA LDO NSC LP2986-5.0 C1, Input Cap 22µF, 6.3V, X5R TDK C3216X5ROJ226M C2, Output Cap 2x22µF, 6.3V, X5R TDK C3216X5ROJ226M C3 – C6 2.2µF, 6.3V, X5R TDK C1608X5R0J225M D1, Catch Diode 0.4Vf Schottky 2A, 20VR Diodes Inc. B220/A D2 0.4Vf Schottky 20VR, 500mA ON Semi MBR0520 L2 10µH, 800mA CoilCraft ME3220-103 L1 2.2µH, 3.5A CoilCraft DS3316P-222 R2 45.3kΩ, 1% Vishay CRCW08054532F R1 10.0kΩ, 1% Vishay CRCW08051002F 25 www.national.com LM2832 LM2832X Buck Converter & Voltage Double Circuit with LDO Follower Design Example 9 LM2832 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead eMSOP Package NS Package Number MUY08A 6-Lead LLP Package NS Package Number SDE06A www.national.com 26 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems 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. 2. A critical component is any component of 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. BANNED SUBSTANCE COMPLIANCE National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at: www.national.com/quality/green. Lead free products are RoHS compliant. National Semiconductor Americas Customer Support Center Email: [email protected] Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: [email protected] Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: [email protected] National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: [email protected] Tel: 81-3-5639-7560 LM2832 High Frequency 2.0A Load - Step-Down DC-DC Regulator Notes