LMZ10500 LMZ10500 650mA SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage Literature Number: SNVS723A LMZ10500 650mA SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage 8 Pin LLP-Footprint Package System Performance (Quick Overview Links: VOUT = 1.2V, 1.8V, 2.5V, 3.3V) Typical Efficiency at VIN = 3.6V 100 90 SE08A 8 Pin Package 3.0 x 2.5 x 1.2 mm (0.118 x 0.098 x 0.047 in) RoHS Compliant Electrical Specifications ■ ■ ■ ■ EFFICIENCY (%) 30161631 Up to 650mA output current Input voltage range 2.7V to 5.5V Output voltage range 0.6V to 3.6V Efficiency up to 95% 80 70 60 50 VOUT = 1.2V VOUT = 1.8V VOUT = 2.5V VOUT = 3.3V 40 30 20 0.0 Key Features 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 30161630 Integrated inductor Miniature form factor (3.0 mm x 2.5 mm x 1.2 mm) 8-pin LLP footprint -40°C to 125°C junction temperature range Adjustable output voltage 2.0MHz fixed PWM switching frequency Integrated compensation Soft start function Current limit protection Thermal shutdown protection Input voltage UVLO for power-up, power-down, and brown-out conditions ■ Only 5 external components — resistor divider and 3 ceramic capacitors Applications ■ Point of load conversions from 3.3V and 5V rails ■ Space constrained applications ■ Low output noise applications Performance Benefits Small solution size Low output voltage ripple Easy component selection and simple PCB layout High efficiency reduces system heat generation Output Voltage Ripple VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA 30161633 Radiated EMI (CISPR22) VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA 80 RADIATED EMISSIONS (dBμV/m) ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 0.1 Emissions CISPR 22 Class B Limit CISPR 22 Class A Limit 70 60 50 40 30 20 10 0 0 200 400 600 800 FREQUENCY (MHz) 1000 30161632 © 2011 National Semiconductor Corporation 301616 www.national.com 650mA SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage October 5, 2011 LMZ10500 Connection Diagram 30161620 NS Package Number SE08A Order Information Order Number Package Marking (Note) Supplied As LMZ10500SEE XVS SX 250 units, Tape-and-Reel LMZ10500SE XVS SX 1000 units, Tape-and-Reel LMZ10500SEX XVS SX 3000 units, Tape-and-Reel Note: The actual physical placement of the package marking will vary from part to part. The package marking “X” designates the date code. “V” is a NSC internal code for die traceability. Both will vary in production. “S” designates device type as switcher and “SX” identifies the device (part number). Pin Descriptions Pin # Name 1 EN Enable Input. Set this digital input higher than 1.2V for normal operation. For shutdown, set low. Pin is internally pulled up to VIN and can be left floating for always-on operation. Description 2 VCON Output voltage control pin. Connect to analog voltage from resisitve divider or DAC/controller to set the VOUT voltage. VOUT = 2.5 x VCON. Connect a small (470pF) capacitor from this pin to SGND to provide noise filtering. 3 FB 4 SGND Ground for analog and control circuitry. Connect to PGND at a single point. 5 VOUT Output Voltage. Connected to one terminal of the integrated inductor. Connect output filter capacitor between VOUT and PGND. 6 PGND Power ground for the power MOSFETs and gate-drive circuitry. 7 VIN 8 VREF PAD www.national.com Feedback of the error amplifier. Connect directly to output capacitor to sense VOUT. Voltage supply input. Connect ceramic capacitor between VIN and PGND as close as possible to these two pins. Typical capacitor values are between 4.7µF and 22µF. 2.35V voltage reference output. Typically connected to VCON pin through a resistive divider to set the output voltage. The 3 pads underneath the module are not internally connected to any node. These pads should be connected to the ground plane for improved thermal performance. 2 Operating Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Voltage Range Recommended Load Current Junction Temperature (TJ) Range VIN, VREF to SGND PGND to SGND EN, FB, VCON VOUT Junction Temperature (TJ-MAX) Storage Temperature Range Maximum Lead Temperature ESD Susceptibility(Note 2) −0.2V to +6.0V −0.2V to +0.2V (SGND −0.2V) to (VIN +0.2V) w/6.0V max (PGND −0.2V) to (VIN +0.2V) w/6.0V max +150°C −65°C to +150°C +260°C ±2kV (Note 1) 2.7V to 5.5V 0 mA to 650mA −40°C to +125°C Thermal Properties Junction-to-Ambient Thermal 120°C/W Resistance (θJA), SE08A Package (Note 3) Electrical Characteristics (Note 4) Specifications with standard typeface are for TJ = 25°C only; Limits in bold face type apply over the operating junction temperature range TJ 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. Unless otherwise stated the following conditions apply: VIN = 3.6V, VEN = 1.2V. Symbol Parameter Conditions Min Typ (Note 4) (Note 5) Max (Note 4) Units SYSTEM PARAMETERS VREF x GAIN Reference voltage x VCON to VIN = VEN = 5.5V, VCON = 1.44V FB Gain 5.7575 5.875 5.9925 V GAIN VCON to FB Gain 2.4375 2.5 2.5750 V/V VINUVLO VIN rising threshold 2.4 V VINUVLO VIN falling theshold 2.25 V ISHDN Shutdown supply current VIN = 3.6V, VEN = 0.5V (Note 6) 11 18 µA Iq DC bias current into VIN VIN = 5.5V, VCON = 1.6V, IOUT = 0A 6.5 8.5 mA RDROPOUT VIN to VOUTresistance IOUT = 200 mA 285 425 mΩ I LIM DC Output Current Limit VCON = 0.24V (Note 7) FOSC VIN = 5.5V, VCON = 1.44V 800 1000 mA Internal oscillator frequency 1.75 2.0 VIH,ENABLE Enable logic HIGH voltage 1.2 VIL,ENABLE Enable logic LOW voltage TSD Thermal shutdown 150 °C TSD-HYST Thermal shutdown hysteresis 20 °C DMAX Maximum duty cycle 100 % TON-MIN Minimum on-time 50 ns θJA Package Thermal Resistance 20mm x 20mm board 2 layers, 2 oz copper, 0.5W, no airlow 118 15mm x 15mm board 2 layers, 2 oz copper, 0.5W, no airlow 132 10mm x 10mm board 2 layers, 2 oz copper, 0.5W, no airlow 157 2.25 V 0.5 Rising Threshold 3 MHz V °C/W www.national.com LMZ10500 Absolute Maximum Ratings (Note 1) LMZ10500 System Characteristics The following specifications are guaranteed by design providing the component values in the Typical Application Circuit are used (CIN = COUT = 10 µF, 6.3V, 0603, TDK C1608X5R0J106K). These parameters are not guaranteed by production testing. Unless otherwise stated the following conditions apply: TA = 25°C. Symbol Parameter Conditions ΔVOUT/VOUT Output Voltage Regulation Over VOUT = 0.6V Line Voltage and Load Current ΔVIN =2.7V to 4.2V Min Typ Max Units ±1.23 % ±0.56 % ±0.24 % EN = Low to High, VIN = 4.2V VOUT = 2.7V, IOUT = 650 mA 10 µs VIN = 5.0V, VOUT = 3.3V IOUT = 200 mA 95 VIN = 5.0V, VOUT = 3.6V IOUT = 650 mA 93 VIN = 5.0V, VOUT = 1.8V IOUT = 650 mA (Note 8) 8 mV pk-pk Line transient response VIN = 2.7V to 5.5V, TR = TF= 10 µs, VOUT = 1.8V, IOUT = 650 mA 25 mV pk-pk Load transient response VIN = 5.0V TR = TF = 40 µs, VOUT = 1.8V IOUT = 65mA to 650mA 25 mV pk-pk ΔIOUT = 0A to 650mA ΔVOUT/VOUT Output Voltage Regulation Over VOUT = 1.5V Line Voltage and Load Current ΔVIN = 2.7V to 5.5V ΔIOUT = 0A to 650mA ΔVOUT/VOUT Output Voltage Regulation Over VOUT = 3.6V Line Voltage and Load Current ΔVIN = 4.0V to 5.5V ΔIOUT = 0A to 650 mA VREF TRISE Rise time of reference voltage Peak Efficiency η Full Load Efficiency VOUT Ripple Output voltage ripple Line Transient Load Transient www.national.com 4 % Note 2: The human body model is a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin. Test method is per JESD-22-114. Note 3: Junction-to-ambient thermal resistance (θJA) is based on 4 layer board thermal measurements, performed under the conditions and guidelines set forth in the JEDEC standards JESD51-1 to JESD51-11. θJA varies with PCB copper area, power dissipation, and airflow. Note 4: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. Limits are used to calculate National’s Average Outgoing Quality Level (AOQL). Note 5: Typical numbers are at 25°C and represent the most likely parametric norm. Note 6: Shutdown current includes leakage current of the high side PFET. Note 7: Current limit is built-in, fixed, and not adjustable. Note 8: Ripple voltage should be measured across COUT on a well-designed PC board using the suggested capacitors. 5 www.national.com LMZ10500 Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics. Unless otherwise specified the following conditions apply: VIN = 3.6V, TA = 25°C Thermal Derating VOUT = 1.2V, θJA = 120°C/W Dropout Voltage vs Load Current and Input Voltage 0.7 VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 4.0V 0.30 0.25 0.6 OUTPUT CURRENT (A) DROPOUT VOLTAGE (V) 0.35 0.20 0.15 0.10 0.05 0.0 0.5 0.4 0.3 VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 0.2 0.1 0.00 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 60 70 80 90 100 110 120 130 AMBIENT TEMPERATURE (°C) 30161649 30161644 Thermal Derating VOUT = 1.8V, θJA = 120°C/W Thermal Derating VOUT = 2.5V, θJA = 120°C/W 0.7 0.7 0.6 0.6 OUTPUT CURRENT (A) OUTPUT CURRENT (A) LMZ10500 Typical Performance Characteristics 0.5 0.4 0.3 VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 0.2 0.1 0.4 0.3 VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 0.2 0.1 0.0 0.0 60 70 80 90 100 110 120 130 AMBIENT TEMPERATURE (°C) 60 30161643 www.national.com 0.5 70 80 90 100 110 120 130 AMBIENT TEMPERATURE (°C) 30161642 6 Radiated EMI (CISPR22) VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA Default evaluation board BOM 0.7 80 RADIATED EMISSIONS (dBμV/m) OUTPUT CURRENT (A) 0.6 0.5 0.4 0.3 VIN = 4.0V VIN = 4.5V VIN = 5.0V VIN = 5.5V 0.2 0.1 0.0 60 LMZ10500 Thermal Derating VOUT = 3.3V, θJA = 120°C/W 70 80 90 100 110 120 130 AMBIENT TEMPERATURE (°C) Emissions CISPR 22 Class B Limit CISPR 22 Class A Limit 70 60 50 40 30 20 10 0 0 30161641 200 400 600 800 FREQUENCY (MHz) 1000 30161632 Conducted EMI VIN = 5.0V, VOUT = 1.8V, IOUT = 650mA Default evaluation board BOM with additional 1µH 1µF LC input filter CONDUCTED EMISSIONS (dBμV) 80 70 Startup Conducted Emissions CISPR 22 Quasi Peak CISPR 22 Average 60 50 40 30 20 10 30161634 0 100m 1 10 FREQUENCY (MHz) 100 30161650 7 www.national.com Schematic VOUT = 1.2V Efficiency VOUT = 1.2V 100 EFFICIENCY (%) 90 80 70 60 50 VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 40 30 20 30161622 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 30161627 Output Ripple VOUT = 1.2V Load Transient VOUT = 1.2V 30161657 30161655 Line and Load Regulation VOUT = 1.2V DC Current Limit VOUT = 1.2V 1.1 DC CURRENT LIMIT (A) 1.24 OUTPUT VOLTAGE (V) LMZ10500 1.2V 1.23 1.22 VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 1.21 1.20 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.9 TA = 85°C 0.8 0.7 0.6 0.7 2.5 30161637 www.national.com 1.0 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 5.5 30161651 8 LMZ10500 1.8V Schematic VOUT = 1.8V Efficiency VOUT = 1.8V 100 EFFICIENCY (%) 90 80 70 60 50 VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 40 30 20 30161623 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 30161626 Output Ripple VOUT = 1.8V Load Transient VOUT = 1.8V 30161658 30161633 Line and Load Regulation VOUT = 1.8V DC Current Limit VOUT = 1.8V 1.3 DC CURRENT LIMIT (A) OUTPUT VOLTAGE (V) 1.81 1.80 1.79 VIN = 2.7V VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 1.78 1.77 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 1.2 1.1 1.0 0.9 0.7 2.5 0.7 30161638 TA = 85°C 0.8 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 5.5 30161652 9 www.national.com Schematic VOUT = 2.5V Efficiency VOUT = 2.5V 100 EFFICIENCY (%) 90 80 70 60 50 VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 40 30 20 30161624 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 30161628 Output Ripple VOUT = 2.5V Load Transient VOUT = 2.5V 30161647 30161646 Line and Load Regulation VOUT = 2.5V DC Current Limit VOUT = 2.5V 1.3 DC CURRENT LIMIT (A) 2.53 OUTPUT VOLTAGE (V) LMZ10500 2.5V 2.52 2.51 2.50 VIN = 3.3V VIN = 3.6V VIN = 5.0V VIN = 5.5V 2.50 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 1.1 1.0 0.9 TA = 85°C 0.8 0.7 2.5 0.7 30161639 www.national.com 1.2 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 5.5 30161653 10 LMZ10500 3.3V Schematic VOUT = 3.3V Efficiency VOUT = 3.3V 100 EFFICIENCY (%) 90 80 70 60 50 VIN = 3.6V VIN = 4.0V VIN = 4.5V VIN = 5.0V VIN = 5.5V 40 30 20 30161625 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 0.7 30161629 Output Ripple VOUT = 3.3V Load Transient VOUT = 3.3V 30161659 30161656 Line and Load Regulation VOUT = 3.3V DC Current Limit VOUT = 3.3V 1.1 DC CURRENT LIMIT (A) OUTPUT VOLTAGE (V) 3.30 3.28 3.26 VIN = 3.6V VIN = 4.0V VIN = 4.5V VIN = 5.0V VIN = 5.5V 3.24 3.22 0.0 0.1 0.2 0.3 0.4 0.5 LOAD CURRENT (A) 0.6 1.0 0.9 TA = 85°C 0.8 0.7 0.6 0.7 2.5 30161640 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 5.5 30161654 11 www.national.com LMZ10500 Block Diagram 30161604 FIGURE 1. Functional Block Diagram The LMZ10500 SIMPLE SWITCHER® nano module is an easy-to-use step-down DC-DC solution capable of driving up to 650mA load in space-constrained applications. Only an input capacitor, an output capacitor, a small VCON filter capacitor, and two resistors are required for basic operation. The nano module comes in 8-pin LLP footprint package with an integrated inductor. The LMZ10500 operates in fixed 2.0MHz PWM (Pulse Width Modulation) mode, and is designed to deliver power at maximum efficiency. The output voltage is typically set by using a resistive divider between the built-in reference voltage VREF and the control pin VCON. The VCON pin is the positive input to the error amplifier. The output voltage of the LMZ10500 can also be dynamically adjusted between 0.6V and 3.6V by driving the VCON pin externally. Internal current limit based softstart function, current overload protection, and thermal shutdown are also provided. to the average of the duty-cycle modulated rectangular signal. In PWM mode, the switching frequency is constant. The energy per cycle to the load is controlled by modulating the PFET on-time, which controls the peak inductor current. In current mode control architecture, the inductor current is compared with the slope compensated output of the error amplifier. At the rising edge of the clock, the PFET is turned ON, ramping up the inductor current with a slope of (VIN - VOUT)/ L. The PFET is ON until the current signal equals the error signal. Then the PFET is turned OFF and NFET is turned ON, ramping down the inductor current with a slope of VOUT /L. At the next rising edge of the clock, the cycle repeats. An increase of load pulls the output voltage down, resulting in an increase of the error signal. As the error signal goes up, the peak inductor current is increased, elevating the average inductor current and responding to the heavier load. To ensure stability, a slope compensation ramp is subtracted from the error signal and internal loop compensation is provided. CIRCUIT OPERATION The LMZ10500 is a synchronous Buck power module using a PFET for the high side switch and an NFET for the synchronous rectifier switch. The output voltage is regulated by modulating the PFET switch on-time. The circuit generates a duty-cycle modulated rectangular signal. The rectangular signal is averaged using a low pass filter formed by the integrated inductor and an output capacitor. The output voltage is equal INPUT UNDER VOLTAGE DETECTION The LMZ10500 implements an under voltage lock out (UVLO) circuit to ensure proper operation during startup, shutdown and input supply brownout conditions. The circuit monitors the voltage at the VIN pin to ensure that sufficient voltage is present to bias the regulator. If the under voltage threshold is not met, all functions of the controller are disabled and the controller remains in a low power standby state. Overview www.national.com 12 LMZ10500 SHUTDOWN MODE To shutdown the LMZ10500, pull the EN pin low (<0.5V). In the shutdown mode all internal circuits are turned OFF. EN PIN OPERATION The EN pin is internally pulled up to VIN through a 790kΩ (typ.) resistor. This allows the nano module to be enabled by default when the EN pin is left floating. In such cases VIN will set EN high when VIN reaches 1.2V. As the input voltage continues to rise, operation will start once VIN exceeds the undervoltage lockout (UVLO) threshold. To set EN high externally, pull it up to 1.2V or higher. Note that the voltage on EN must remain at less than VIN+ 0.2V due to absolute maximum ratings of the device. 30161634 INTERNAL SYNCHRONOUS RECTIFICATION The LMZ10500 uses an internal NFET as a synchronous rectifier to minimize the switch voltage drop and increase efficiency. The NFET is designed to conduct through its intrinsic body diode during the built-in dead time between the PFET on-time and the NFET on-time. This eliminates the need for an external diode. The dead time between the PFET and NFET connection prevents shoot through current from VIN to PGND during the switching transitions. FIGURE 2. Startup behavior of current limit based softstart. The soft start rate is also limited by the VCON ramp up rate. The VCON pin is discharged internally through a pull down device before startup occurs. This is done to deplete any residual charge on the VCON filter capacitor and allow the VCON voltage to ramp up from 0V when the part is started. The events that cause VCON discharge are thermal shutdown, UVLO, EN low, or output short circuit detection. The minimum recommended capacitance on VCON is 220pF and the maximum is 1nF. The duration of startup current limiting sequence takes approximately 75µs. After the sequence is completed, the feedback voltage is monitored for output short circuit events. CURRENT LIMIT The LMZ10500 current limit feature protects the module during an overload condition. The circuit employs positive peak current limit in the PFET and negative peak current limit in the NFET switch. The positive peak current through the PFET is limited to 1.2A (typ.). When the current reaches this limit threshold the PFET switch is immediately turned off until the next switching cycle. This behavior continues on a cycle-bycycle basis until the overload condition is removed from the output. The typical negative peak current limit through the NFET switch is -0.6A (typ.). The ripple of the inductor current depends on the input and output voltages. This means that the DC level of the output current when the peak current limiting occurs will also vary over the line voltage and the output voltage level. Refer to the DC Output Current Limit plots in the Typical Performance Characteristics section for more information. OUTPUT SHORT CIRCUIT PROTECTION In addition to cycle by cycle current limit, the LMZ10500 features a second level of short circuit protection. If the load pulls the output voltage down and the feedback voltage falls to 0.375V, the output short circuit protection will engage. In this mode the internal PFET switch is turned OFF after the current limit comparator trips and the beginning of the next cycle is inhibited for approximately 230µs. This forces the inductor current to ramp down and limits excessive current draw from the input supply when the output of the regulator is shorted. The synchronous rectifier is always OFF in this mode. After 230µs of non-switching a new startup sequence is initiated. During this new startup sequence the current limit is gradually stepped up to the nominal value as illustrated in the STARTUP BEHAVIOR AND SOFTSTART section. After the startup sequence is completed again, the feedback voltage is monitored for output short circuit. If the short circuit is still persistent after the new startup sequence, switching will be stopped again and there will be another 230µs off period. A persistent output short condition results in a hiccup behavior where the LMZ10500 goes through the normal startup sequence, then detects the output short at the end of startup, terminates switching for 230µs, and repeats this cycle until the output short is released. This behavior is illustrated in the following figure. STARTUP BEHAVIOR AND SOFTSTART The LMZ10500 features a current limit based soft start circuit in order to prevent large in-rush current and output overshoot as VOUT is ramping up. This is achieved by gradually increasing the PFET current limit threshold to the final operating value as the output voltage ramps during startup. The maximum allowed current in the inductor is stepped up in a staircase profile for a fixed number of switching periods in each step. Additionally, the switching frequency in the first step is set at 450kHz and is then increased for each of the following steps until it reaches 2MHz at the final step of current limiting. This current limiting behavior is illustrated in the following figure and allows for a smooth VOUT ramp up. 13 www.national.com LMZ10500 regulation. If VIN is lowered even more, the off-time of the PFET will reach the 35ns mark again. The LMZ10500 will then reduce the frequency again, achieving less than 100% duty cycle operation and maintaining regulation. As VIN is lowered even more, the LMZ10500 will continue to scale down the frequency, aiming to maintain at least 35ns off time. Eventually, as the input voltage decreases further, 100% duty cycle is reached. This behavior of extending the VIN regulation range is illustrated in the following plot. 30161645 FIGURE 3. Hiccup behavior with persistent output short circuit. Since the output current is limited during normal startup by the softstart function, the current charging the output capacitor is also limited. This results in a smooth VOUT ramp up to nominal voltage. However, using excessively large output capacitance or VCON capacitance under normal conditions can prevent the output voltage from reaching 0.375V at the end of the startup sequence. In such cases the module will maintain the described above hiccup mode and the output voltage will not ramp up to final value. To cause this condition, one would have to use unnecessarily large output capacitance for 650mA load applications. See the INPUT AND OUTPUT CAPACITOR SELECTION section for guidance on maximum capacitances for different output voltage settings. 30161660 FIGURE 4. High duty cycle operation and switching frequency reduction. THERMAL OVERLOAD PROTECTION The junction temperature of the LMZ10500 should not be allowed to exceed its maximum operating rating of 125°C. Thermal protection is implemented by an internal thermal shutdown circuit which activates at 150°C (typ). When this temperature is reached, the device enters a low power standby state. In this state switching remains off causing the output voltage to fall. Also, the VCON capacitor is discharged to SGND. When the junction temperature falls back below 130 °C (typ) normal startup occurs and VOUT rises smoothly from 0V. Applications requiring maximum output current may require derating at elevated ambient temperature. See the Typical Performance Characteristics section for thermal derating plots for various output voltages. HIGH DUTY CYCLE OPERATION The LMZ10500 features a transition mode designed to extend the output regulation range to the minimum possible input voltage. As the input voltage decreases closer and closer to VOUT, the off-time of the PFET gets smaller and smaller and the duty cycle eventually needs to reach 100% to support the output voltage. The input voltage at which the duty cycle reaches 100% is the edge of regulation. When the LMZ10500 input voltage is lowered, such that the off-time of the PFET reduces to less than 35ns, the LMZ10500 doubles the switching period to extend the off-time for that VIN and maintain www.national.com 14 LMZ10500 Application Information 30161636 FIGURE 5. Typical Application Circuit trimmed so that this product is as close to the ideal 5.875V value as possible, achieving high VOUT accuracy. See the Electrical Specifications section for the VREF x GAIN product tolerance limits. SETTING THE OUTPUT VOLTAGE The LMZ10500 provides a fixed 2.35V VREF voltage output. As shown in Figure 5 above, a resistive divider formed by RT and RB sets the VCON pin voltage level. The VOUT voltage tracks VCON and is governed by the following relationship: VOUT = GAIN x VCON DYNAMIC OUTPUT VOLTAGE SCALING The VCON pin on the LMZ10500 can be driven externally by a DAC to scale the output voltage dynamically. The output voltage VOUT = 2.5V/V x VCON. When driving VCON with a source different than VREF place a 1.5kΩ resistor in series with the VCON pin. Current limiting the external VCON helps to protect this pin and allows the VCON capacitor to be fully discharged to 0V after fault conditions. (1) where GAIN is 2.5V/V from VCON to VFB. This equation is valid for output voltages between 0.6V and 3.6V and corresponds to VCON voltage between 0.24V and 1.44V, respectively. RT and RB Selection for Fixed VOUT The parameters affecting the output voltage setting are the RT, RB, and the product of the VREF voltage x GAIN. The VREF voltage is typically 2.35V. Since VCON is derived from VREF via RT and RB, VCON = VREF x RB/ (RB + RT) INTEGRATED INDUCTOR The LMZ10500 uses a Low Temperature Co-fired Ceramic (LTCC) type 2.6 µH inductor with over 1.2A DC current rating and soft saturation profile for up to 2A. This inductor allows for the 1.2mm overall package height providing an easy to use, compact solution with reduced EMI. (2) After substitution, VOUT = VREF x GAIN x RB/ (RB + RT) (3) RT = ( GAIN x VREF / VOUT – 1 ) x RB (4) INPUT AND OUTPUT CAPACITOR SELECTION The LMZ10500 is designed for use with low ESR multi-layer ceramic capacitors (MLCC) for its input and output filters. Using a 10 µF 0603 or 0805 with 6.3V or 10V rating ceramic input capacitor typically provides sufficient VIN bypass. Use of multiple 4.7 µF or 2.2µF capacitors can also be considered. Ceramic capacitors with X5R and X7R temperature characteristics are recommended for both input and output filters. These provide an optimal balance between small size, cost, reliability, and performance for space sensitive applications. The DC voltage bias characteristics of the capacitors must be considered when selecting the DC voltage rating and case size of these components. The effective capacitance of an MLCC is typically reduced by the DC voltage bias applied across its terminals. For example, a typical 0805 case size X5R 6.3V 10 µF ceramic capacitor may only have 4.8 µF left in it when a 5.0V DC bias is applied. Similarly, a typical 0603 case size X5R 6.3V 10 µF ceramic capacitor may only have 2.4 µF at the same 5.0V DC. Smaller case size capacitors may have even larger percentage drop in value with DC bias. The optimum output capacitance value is application dependent. Too small output capacitance can lead to instability due to lower loop phase margin. On the other hand, if the output The ideal product of GAIN x VREF = 5.875V. Choose RT to be between 80kΩ and 300kΩ. Then, RB can be calculated using equation (5) below. RB = ( VOUT / (5.875V – VOUT) ) x RT (5) Note that the resistance of RT should be ≥ 80kΩ. This ensures that the VREF output current loading is not exceeded and the reference voltage is maintained. The current loading on VREF should not be greater than 30 µA. OUTPUT VOLTAGE ACCURACY OPTIMIZATION Each nano module is optimized to achieve high VOUT accuracy. Equation (1) shows that, by design, the output voltage is a function of the VCON voltage and the gain from VCON to VFB. The voltage at VCON is derived from VREF. Therefore, as shown in equation (3), the accuracy of the output voltage is a function of the VREF x GAIN product as well as the tolerance of the RT and RB resistors. The typical VREF x GAIN product by design is 5.875V. Each nano module's VREF voltage is 15 www.national.com LMZ10500 capacitor is too large, it may prevent the output voltage from reaching the 0.375V required voltage level at the end of the startup sequence. In such cases, the output short circuit protection can be engaged and the nano module will enter a hiccup mode as described in the OUTPUT SHORT CIRCUIT PROTECTION section. The table below sets the minimum output capacitance for stability and maximum output capacitance for proper startup for various output voltage settings. Note that the maximum COUT value in Table 1 assumes that the filter capacitance on VCON is the maximum recommended value of 1nF and the RT resistor value is less than 300kΩ. Lower VCON capacitance can extend the maximum COUT range. There is no great performance benefit in using excessive COUT values. Use of multiple 4.7 µF or 2.2µF output capacitors can be considered for reduced effective ESR and smaller output voltage ripple. In addition to the main output capacitor, small 0.1µF – 0.01µF parallel capacitors can be used to reduce high frequency noise. PACKAGE CONSIDERATIONS The nano module package includes an LTCC inductor on the bottom and a micro SMD die mounted on top. The die has exposed edges and can be sensitive to ambient light. For applications with direct high intensity ambient red, infrared, LED, or natural light it is recommended to have the device shielded from the light source to avoid abnormal behavior. TABLE 1. Output Capacitance Range Output Voltage Minimum COUT Suggested COUT Maximum COUT 0.6V 4.7µF 10µF 33µF 1.0V 3.3µF 10µF 33µF 1.2V 3.3µF 10µF 33µF 1.8V 3.3µF 10µF 47µF 2.5V 3.3µF 10µF 68µF 3.3V 3.3µF 10µF 68µF www.national.com 16 LMZ10500 Board Layout Considerations 30161648 FIGURE 6. Example Top Layer Board Layout The board layout of any DC-DC switching converter is critical for the optimal performance of the design. Bad PCB layout design can disrupt the operation of an otherwise good schematic design. Even if the regulator still converts the voltage properly, the board layout can mean the difference between passing or failing EMI regulations. In a Buck converter, the most critical board layout path is between the input capacitor ground terminal and the synchronous rectifier ground. The loop formed by the input capacitor and the power FETs is a path for the high di/dt switching current during each switching period. This loop should always be kept as short as possible when laying out a board for any Buck converter. The LMZ10500 integrates the inductor and simplifies the DCDC converter board layout. Refer to the example layout in Figure 6. There are a few basic requirements to achieve a good LMZ10500 layout. 1. Place the input capacitor CIN as close as possible to the VIN and PGND terminals. VIN (pin 7) and PGND (pin 6) on the LMZ10500 are next to each other which makes the input capacitor placement simple. 2. Place the VCON filter capacitor CVC and the RB RT resistive divider as close as possible to the VCON and SGND terminals.The CVC capacitor (not RB) should be the component closer to the VCON pin, as shown in Figure 6. This allows for better bypass of the control voltage set at VCON. 3. Run the feedback trace (from VOUT to FB) away from noise sources. 4. Connect SGND to a quiet GND plane. 5. Provide enough PCB area for proper heatsinking. Refer to the Electrical Characteristics table for example θJA values for different board areas. Also, refer to AN-2020 for additional thermal design hints. Refer to the evaluation board application note (AN-2166) for a complete board layout example. 17 www.national.com LMZ10500 Physical Dimensions inches (millimeters) unless otherwise noted NS Package Number SE08A www.national.com 18 LMZ10500 Notes 19 www.national.com 650mA SIMPLE SWITCHER® Nano Module with 5.5V Maximum Input Voltage Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com 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 References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise® Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise® Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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