LTM8020EV#PBF

LTM8020 200mA, 36V DC/DC µModule Regulator FEATURES DESCRIPTION Complete Step-Down Switch Mode Power Supply n Wide Input Voltage Range: 4V to 36V n 1.25V to 5V Output Voltage n EN55022 Class B Compliant n 200mA Output Current n Current Mode Control n –55°C to 125°C Operating Temperature (LTM8020MPV) n Pb-Free (e4) RoHS Compliant Package with Gold Pad Finish n Tiny, Low Profile (6.25mm × 6.25mm × 2.32mm) Surface Mount LGA Package The LTM®8020 is a complete 200mA, DC/DC step-down power supply. Included in the package are the switching controller, power switches, inductor, and all support components. Operating over an input voltage range of 4V to 36V, the LTM8020 supports an output voltage range of 1.25V to 5V, set by a single resistor. Only bulk capacitors are needed to finish the design. The LTM8020 meets the radiated emissions requirements of EN55022. Conducted emission requirements can be met by adding standard filter components. n APPLICATIONS The low profile (2.32mm) tiny package enables utilization of unused space on the bottom of PC boards for high density point of load regulation. The LTM8020 is packaged in a thermally enhanced, compact (6.25mm × 6.25mm) and low profile (2.32mm) overmolded land grid array (LGA) package suitable for automated assembly by standard surface mount equipment. The LTM8020 is Pb-free and RoHS compliant. Automotive Battery Regulation Power for Portable Products n Distributed Supply Regulation n Industrial Supplies n Wall Transformer Regulation n n All registered trademarks and trademarks are the property of their respective owners. TYPICAL APPLICATION 6.5VIN to 36VIN, 5V at 200mA DC/DC µModule® Regulator VIN 2.2µF VOUT LTM8020 SHDN 80 BIAS 70 10µF ADJ 165k 1% 100 60 50 10 40 1 30 8020 TA01 *RUNNING VOLTAGE RANGE. PLEASE REFER TO APPLICATIONS INFORMATION FOR START-UP DETAILS POWER LOSS (mW) GND 1000 90 VOUT 5V 200mA EFFICIENCY (%) VIN *6.5V TO 36V Efficiency and Power Loss vs Load Current 20 10 0.1 1 10 LOAD CURRENT (mA) 100 0.1 3470 TA01b Rev. F Document Feedback For more information www.analog.com 1 LTM8020 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW VIN, SHDN Voltage.....................................................40V ADJ Voltage.................................................................5V BIAS Voltage..............................................................25V VIN + BIAS Voltage.....................................................47V VOUT Voltage..............................................................10V Internal Operating Temperature Range.... –40°C to 125°C Storage Temperature Range................... –55°C to 125°C Maximum Solder Temperature............................... 260°C 5 VOUT 4 GND 3 BIAS 2 VIN 1 ADJ SHDN A B C D E LGA PACKAGE 21-LEAD (6.25mm × 6.25mm × 2.32mm) TJMAX = 125°C, θJA = 23.1°C/W θJA DERIVED FROM 5cm × 5cm PCB WITH 4 LAYERS WEIGHT = 0.25g ORDER INFORMATION PART MARKING* PART NUMBER PAD OR BALL FINISH LTM8020EV#PBF LTM8020IV#PBF DEVICE FINISH CODE PACKAGE TYPE MSL RATING TBD LGA TBD LTM8020V Au (RoHS) LTM8020MPV#PBF LTM8020V LTM8020MPV TEMPERATURE RANGE (SEE NOTE 2) –40°C to 85°C –55°C to 125°C • Contact the factory for parts specified with wider operating temperature • Recommended LGA and BGA PCB Assembly and Manufacturing ranges. *Pad or ball finish code is per IPC/JEDEC J-STD-609. Procedures • Device temperature grade is indicated by a label on the shipping container. • LGA and BGA Package and Tray Drawings ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VSHDN = 10V, VBIAS = 3V, External CIN = 2.2µF, COUT = 4.7µF. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VIN Input DC Voltage 4 36 V VOUT Output DC Voltage 0 < IOUT ≤ 200mA; 167kΩ < RADJ < ∞ 1.2 5 V RADJ(MIN) Minimum Allowable RADJ (Note 3) 163 ILK Leakage from IN to OUT VSHDN = 0V, BIAS = 0V IOUT Continuous Output DC Current 5.5V ≤ VIN ≤ 36V, RADJ = 301k, VO = 3.3V IQ(VIN) Quiescent Current into IN SHDN = 0.2V, BIAS Open BIAS = 3V, Not Switching BIAS = 0V, Not Switching l 10 35 SHDN = 0.2V, BIAS = 0V BIAS = 3V, Not Switching BIAS = 0V, Not Switching l 25 IQ(BIAS) Quiescent Current into BIAS l kΩ 1.2 0 6 µA 200 mA 1 18 50 µA µA µA 0.5 60 1.5 µA µA µA ∆VOUT/VOUT Line Regulation 5V ≤ VIN ≤ 36V, IOUT = 200mA, RADJ Open 1 % ∆VOUT/VOUT Load Regulation VIN = 24V, 0 ≤ IOUT ≤ 200mA, VOUT = 3.3V 2 % Rev. F 2 For more information www.analog.com LTM8020 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VSHDN = 10V, VBIAS = 3V, External CIN = 2.2µF, COUT = 4.7µF. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VOUT(AC_RMS) Output Ripple (RMS) IOUT = 100mA, VOUT = 3.3V, VIN = 24V 7.5 mV fSW Switching Frequency IOUT = 200mA 450 kHz ISC Output Short-Circuit Current VIN = 36V, VOUT = 0V 350 mA VADJ Voltage at ADJ Pin l 1.228 VBIAS(MIN) Minimum BIAS Voltage for Proper Operation l 3 IADJ Current Out of ADJ Pin ADJ = 0V, VOUT = 5V, VSHDN = 0V l 9.65 ISHDN SHDN Pin Current VSHDN = 2.5V VIH(SHDN) SHDN Input High Voltage VIL(SHDN) SHDN Input Low Voltage 10.35 µA 5 µA V 0.2 3.3VOUT Efficiency V LTM8020I is guaranteed to meet specifications over the full –40°C to 85°C ambient operating temperature range. The LTM8020MP is guaranteed to meet specifications over the full –55°C to 125°C internal operating temperature range. Note that the maximum internal temperature is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. Note 3: Guaranteed by design. TA = 25°C unless otherwise noted. 3.3VOUT Power Loss 5VOUT Efficiency 90 1000 80 80 70 70 60 50 40 30 5VIN 12VIN 24VIN 36VIN 20 10 1 10 ILOAD (mA) 100 1000 8020 G01 EFFICIENCY (%) 100 POWER LOSS (mW) EFFICIENCY (%) V 1 TYPICAL PERFORMANCE CHARACTERISTICS 0 0.1 V 2.5 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTM8020E is guaranteed to meet performance specifications from 0°C to 85°C ambient. Specifications over the full –40°C to 85°C ambient operating temperature range are assured by design, characterization and correlation with statistical process controls. The 90 1.265 10 1 0.1 0.1 5VIN 12VIN 24VIN 36VIN 1 10 IOUT (mA) 100 1000 8020 G02 60 50 40 30 20 12VIN 24VIN 36VIN 10 0 0.1 1 10 ILOAD (mA) 100 1000 8020 G03 Rev. F For more information www.analog.com 3 LTM8020 TYPICAL PERFORMANCE CHARACTERISTICS Input Current vs Output Current (5VIN) 5VOUT Power Loss 1000 0.18 INPUT CURRENT (A) 1 10 IOUT (mA) 100 0.10 0.08 0.06 0 0.060 0.035 0.030 0.020 0 4356 G05 0.05 0.10 0.15 OUTPUT CURRENT (A) 0.20 4356 G06 Input Quiescent Current vs Input Voltage 5 0.030 0.025 0.020 0.015 4 3 2 1 0.005 0 0.05 0.10 0.15 OUTPUT CURRENT (A) 0 0.20 INPUT VOLTAGE (V) 80 60 40 20 10 20 30 INPUT VOLTAGE (V) 0.05 0.10 0.15 OUTPUT CURRENT (A) 0 0.20 40 4356 G10 7.0 6.5 6.5 6.0 6.0 5.5 TO RUN TO START RUN/SS ENABLED 4.5 5.0 3.5 3.5 50 100 150 LOAD CURRENT (mA) 200 8020 G11 40 4356 G09 TO RUN TO START RUN/SS ENABLED 4.5 4.0 0 20 30 INPUT VOLTAGE (V) 5.5 4.0 3.0 10 Minimum Required Input Voltage vs Load (VOUT = 3.3V, TA = –40°C) 7.0 5.0 0 4356 G08 Minimum Required Input Voltage vs Load (VOUT = 3.3V, TA = –55°C) 100 0 0 4356 G07 Input Current vs Input Voltage (Output Short) INPUT CURRENT (mA) 0 0.20 0.010 0.010 0 0.05 0.10 0.15 OUTPUT CURRENT (A) 1.8VOUT 2.5VOUT 3.3VOUT 5VOUT 0.040 INPUT CURRENT (A) INPUT CURRENT (A) 0.045 0.040 0 0.040 Input Current vs Output Current (36VIN) 1.8VOUT 2.5VOUT 3.3VOUT 5VOUT 0.050 0 8020 G04 Input Current vs Output Current (24VIN) 0.060 0.020 0.02 1000 0.080 QUIESCENT CURRENT (µA) 1 0.12 0.04 12VIN 24VIN 36VIN 1.8VOUT 2.5VOUT 3.3VOUT 5VOUT 0.100 INPUT VOLTAGE (V) POWER LOSS (mW) 10 0.120 INPUT CURRENT (A) 0.14 100 Input Current vs Output Current (12VIN) 1.8VOUT 2.5VOUT 3.3VOUT 0.16 0.1 0.1 TA = 25°C unless otherwise noted. 3.0 0 50 100 150 LOAD CURRENT (mA) 200 8020 G12 Rev. F 4 For more information www.analog.com LTM8020 TYPICAL PERFORMANCE CHARACTERISTICS Minimum Required Input Voltage vs Load (VOUT = 3.3V, TA = 25°C) 8.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 5.5 5.0 4.5 4.0 Minimum Required Input Voltage vs = 5V, TA == –55°C) vs Load Load (V (VOUT –55°C) OUT = 5V, TA Minimum Required Input Voltage vs Load (VOUT = 5V, TA = –40°C) 8.0 7.5 7.5 7.0 7.0 INTPUT VOLTAGE (V) 6.0 TA = 25°C unless otherwise noted. 6.5 6.0 5.5 5.0 TO RUN TO START RUN/SS ENABLED 3.5 3.0 0 50 100 150 LOAD CURRENT (mA) 200 TO RUN TO START RUN/SS ENABLED 4.5 4.0 0 8020 G13 50 100 150 LOAD CURRENT (mA) 5.5 5.0 8 7.5 4.0 200 IOUT = 200mA 25 6 TO RUN 5 4 5.0 TO RUN TO START RUN/SS ENABLED 4.5 50 100 150 LOAD CURRENT (mA) 200 3 2 1 8020 G16 2 3 4 OUTPUT VOLTAGE (V) 15 3.3VOUT 10 5 0 10 20 30 INPUT VOLTAGE (V) 4356 G17 Turn-On Behavior (6VIN, 3.3VOUT, No Load) 40 50 8020 G18 Radiated Emissions 90 36VIN 5VOUT FULL LOAD 80 INPUT CURRENT 100mA/DIV VOUT 2V/DIV SHDN 5V/DIV 50µs/DIV 5VOUT 20 0 5 EMISSIONS LEVEL (dBµV/m) 0 200 TO START TEMPERATURE RISE (°C) INPUT VOLTAGE (V) 5.5 50 100 150 LOAD CURRENT (mA) 8020 G15 7 6.0 0 Temperature Rise vs Input Voltage (Full Load, TA = 25°C) 7.0 6.5 TO RUN TO START RUN/SS ENABLED 4.5 Minimum Required Input Voltage vs Output Voltage 8.0 INPUT VOLTAGE (V) 6.0 8020 G14 Minimum Required Input Voltage vs Load (VOUT = 5V, TA = 25°C) 4.0 6.5 8020 G19 70 60 50 EN55022 CLASS B LIMIT 40 30 20 10 0 –10 0 200 600 800 400 FREQUENCY (MHz) 1000 8020 G20 Rev. F For more information www.analog.com 5 LTM8020 PIN FUNCTIONS VIN (Pins A1, A2): The VIN pins supply current to the LTM8020’s internal regulator and to the internal power switch. These pins must be locally bypassed with an external, low ESR capacitor of at least 1µF. SHDN (Pin C1): The SHDN pin is used to put the LTM8020 in shutdown mode. Tie to ground to shut down the LTM8020. Apply 2V or more for normal operation. If the shutdown feature is not used, tie this pin to VIN. VOUT (Pins A4, A5, B4, B5, C4, C5): Power Output Pins. An external capacitor is connected from VOUT to GND in most applications. Apply output load between these pins and GND. GND (Pins C2, D1, D2, D3, D4, D5, E2, E3, E4, E5): The GND connections serve as the main signal return and the primary heat sink for the LTM8020. Tie the GND pins to a local ground plane below the LTM8020 and the circuit components. Return the feedback divider to this signal. BIAS (Pin C3): The BIAS pin connects to the internal boost Schottky diode and to the internal regulator. Tie to VOUT when VOUT > 3V or to another DC voltage greater than 3V otherwise. When BIAS > 3V the internal circuitry will be powered from this pin to improve efficiency. Main regulator power will still come from VIN. ADJ (Pin E1): The LTM8020 regulates its ADJ pin to 1.25V. Connect the adjust resistor from this pin to GND. The value of this adjust resistor is determined by the equation RADJ = 623.75/(VOUT – 1.25), where RADJ is in kΩ. Note that the ADJ pin is open circuit if VOUT = 1.25V. Rev. F 6 For more information www.analog.com LTM8020 BLOCK DIAGRAM 22µH VIN 0.1µF VOUT 15pF 499k ±1% 10µF BIAS SHDN CURRENT MODE CONTROLLER ADJ GND 8020 BD Rev. F For more information www.analog.com 7 LTM8020 OPERATION The LTM8020 is a standalone nonisolated step-down switching DC/DC power supply. It can deliver up to 200mA of DC output current with only bulk external input and output capacitors. This module provides a precisely regulated output voltage programmable via one external resistor from 1.25VDC to 5VDC. The input voltage range is 4V to 36V. Given that the LTM8020 is a step-down converter, make sure that the input voltage is high enough to support the desired output voltage and load current. See Block Diagram The LTM8020 contains a current mode controller, power switching element, power inductor, power Schottky diode and a modest amount of input and output capacitance. For some applications, as shown in Table 1, no output capacitor is necessary. With its high performance current mode controller and internal feedback loop compensation, the LTM8020 module has sufficient stability margin and good transient performance under a wide range of operating conditions with a wide range of output capacitors, even all ceramic ones (X5R or X7R). Current mode control provides cycle-bycycle fast current limit, and automatic current limiting protects the module in the event of a short circuit or overload fault. The LTM8020 is built upon a variable frequency controller. The on time, off time and switching frequency are dependent upon the input voltage, output voltage and load current. The drive circuit for the internal power switching element is powered through the BIAS pin. Power this pin with at least 3V. The LTM8020 is equipped with two operating modes, dependant upon the load current. When the load current is sufficiently high, the LTM8020 will switch continuously (see Figure 1a). If the load is very light, or if the input voltage is high relative to the output voltage, the part will operate in Burst Mode® operation, alternating between its micropower and switching states to keep the output in regulation and hold the power dissipation to a minimum (See Figure 1b). If the SHDN pin is grounded, all internal circuits are turned off and VIN current reduces to the device leakage current, typically a few nanoamps. 200mA LOAD NO LOAD VOUT 20mV/DIV VOUT 20mV/DIV IL 100mA/DIV IL 100mA/DIV 1µs/DIV 1ms/DIV 150mA LOAD 10mA LOAD VOUT 20mV/DIV VOUT 20mV/DIV IL 100mA/DIV IL 100mA/DIV 8020 F1a 1µs/DIV (1a) Continuous Operation 5µs/DIV 8020 F01b (1b) Burst Mode Operation Figure 1. Output Voltage and Internal Inductor Current Rev. F 8 For more information www.analog.com LTM8020 APPLICATIONS INFORMATION For most applications, the design process is straight forward, summarized as follows: 1. Look at Table 1 and find the row that has the desired input range and output voltage. 2. Apply the CIN, COUT, RADJ and BIAS connection indicated on that row. While these component combinations have been tested for proper operation, it is incumbent upon the user to verify proper operation over the intended system’s line, load and environmental conditions. If an output voltage other than those listed in Table 1 is desired, use the equation RADJ = 623.75/(VOUT – 1.25), where RADJ is in kΩ. As a starting point, use values for CIN and COUT that correspond to the input voltage and output voltage that most closely matches the intended application, and verify proper operation over the system’s line, load and environmental conditions. Capacitor Selection Considerations The CIN and COUT capacitor values in Table 1 are the minimum recommended values for the associated operating conditions. Applying capacitor values below those indicated in Table 1 is not recommended, and may result in undesirable operation. An input system bulk capacitor is assumed. Using larger values is generally acceptable, and can yield improved dynamic response, if it is necessary. Again, it is incumbent upon the user to verify proper operation over the intended system’s line, load and environmental conditions. Ceramic capacitors are small, robust and have very low ESR. However, not all ceramic capacitors are suitable. X5R and X7R types are stable over temperature and applied voltage and give dependable service. Other types, including Y5V and Z5U have very large temperature and voltage coefficients of capacitance. In an application circuit they may have only a small fraction of their nominal capacitance resulting in much higher output voltage ripple than expected. frequencies, generating audible noise. Since the LTM8020 operates at a lower current limit during Burst Mode operation, the noise is typically very quiet to a casual ear. If this audible noise is unacceptable, use a high performance electrolytic capacitor at the output. The input capacitor can be a parallel combination of a 2.2µF ceramic capacitor and a low cost electrolytic capacitor. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LTM8020. A ceramic input capacitor combined with trace or cable inductance forms a high Q (under damped) tank circuit. If the LTM8020 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the device’s rating. This situation is easily avoided; see the Hot-Plugging Safely section. Shorted Input Protection Care needs to be taken in systems where the output will be held high when the input to the LTM8020 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ORed with the LTM8020’s output. If the VIN pin is allowed to float and the SHDN pin is held high (either by a logic signal or because it is tied to VIN), then the LTM8020’s internal circuitry will pull its quiescent current from its output. This is fine if your system can tolerate a few milliamps in this state. If you ground the SHDN pin, this quiescent current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LTM8020 can pull large currents from the output through the internal power switch, possibly damaging the device. Figure 2 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. D1 VIN VIN 100k 1M LTM8020 SHDN GND 8020 F02 Ceramic capacitors are also piezoelectric. The LTM8020’s switching frequency depends on the load current, and at light loads it can excite a ceramic capacitor at audio Figure 2. Diode D1 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output, as Well as Protecting the LTM8020 from a Reversed Input Rev. F For more information www.analog.com 9 LTM8020 APPLICATIONS INFORMATION PCB Layout Positive-to-Negative Voltage Regulation Most of the headaches associated with PCB layout have been alleviated or even eliminated by the high level of integration of the LTM8020. The LTM8020 is never-theless a switching power supply, and care must be taken to minimize EMI and ensure proper operation. Even with the high level of integration, you may fail to achieve specified operation with a haphazard or poor layout. See Figure 3 for a suggested layout. The LTM8020 can generate a negative output by tying the VOUT pads to system ground and connecting GND as shown in the Typical Application section. In this configuration, SHDN must be level shifted or referenced to GND, and the available output current may be reduced. Ensure that the grounding and heat sinking are acceptable. A few rules to keep in mind are: 1. Place the CIN capacitor as close as possible to the VIN and GND connection of the LTM8020. 2. Place the COUT capacitor as close as possible to the VOUT and GND connection of the LTM8020. 3. Place the CIN and COUT capacitors such that their ground current flows directly adjacent or underneath the LTM8020. 4. Connect all of the GND connections to as large a copper pour or plane area as possible on the top layer. Avoid breaking the ground connection between the external components and the LTM8020. 5. The copper pours also serve as the heat sink for the LTM8020. Place several vias in the GND plane to act as heat pipes to other layers of the printed circuit board. VIN SHDN VOUT CIN BIAS COUT ADJ GND COPPER RADJ VIAs TO GND PLANE 8020 F03 Figure 3. Layout Showing Suggested External Components, GND Plane and Thermal Vias Hot-Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LTM8020. However, these capacitors can cause problems if the LTM8020 is plugged into a live supply (see Analog Devices Application Note 88 for a complete discussion). The low loss ceramic capacitor combined with stray inductance in series with the power source forms an under damped tank circuit, and the voltage at the VIN pin of the LTM8020 can ring to twice the nominal input voltage, possibly exceeding the LTM8020’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LTM8020 into an energized supply, the input network should be designed to prevent this overshoot. Figure 4 shows the waveforms that result when an LTM8020 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The first plot is the response with a 2.2µF ceramic capacitor at the input. The input voltage rings as high as 35V and the input current peaks at 20A. One method of damping the tank circuit is to add another capacitor with a series resistor to the circuit. In Figure 4b an aluminum electrolytic capacitor has been added. This capacitor’s high equivalent series resistance damps the circuit and eliminates the voltage overshoot. The extra capacitor improves low frequency ripple filtering and can slightly improve the efficiency of the circuit, though it is likely to be the largest component in the circuit. An alternative solution is shown in Figure 4c. A 1Ω resistor is added in series with the input to eliminate the voltage overshoot (it also reduces the peak input current). A 0.1µF capacitor improves high frequency filtering. This solution is smaller and less expensive than the electrolytic capacitor. For high input voltages its impact on efficiency is minor, reducing efficiency less than one-half percent for a 5V output at full load operating from 24V. Rev. F 10 For more information www.analog.com LTM8020 APPLICATIONS INFORMATION High Temperature Considerations The die temperature of the LTM8020 must be lower than the maximum rating of 125°C, so care should be taken in the layout of the circuit to ensure good heat sinking of the LTM8020. To estimate the junction temperature, approximate the power dissipation within the LTM8020 by applying the typical efficiency stated in this data sheet to the desired output power, or, if you have an actual module, by taking a power measurement. Then calculate the internal temperature rise of the LTM8020 above the surface of the printed circuit board by multiplying the module’s power dissipation by the thermal resistance. The actual thermal resistance of the LTM8020 to the printed circuit board depends upon the layout of the circuit board, but the thermal resistance given in the Pin Configuration, which is based upon a 25cm2 4-layer FR4 PC board, and the Typical Performance Characteristics can be used a guide. CLOSING SWITCH SIMULATES HOT PLUG IIN VIN + LOW IMPEDANCE ENERGIZED 24V SUPPLY LTM8020 Finally, be aware that at high ambient temperatures the internal Schottky diode will have significant leakage current increasing the quiescent current of the LTM8020. BIAS Pin Considerations The BIAS pin is used to provide drive power for the internal power switching stage and operate internal circuitry. For proper operation, it must be powered by at least 3V. If the output voltage is programmed to be 3V or higher, simply tie BIAS to VOUT. If VOUT is less than 3V, BIAS can be tied to VIN or some other voltage source. In all cases, ensure that the maximum voltage at the BIAS pin is both less than 25V and the sum of VIN and BIAS is less than 47V. If BIAS power is applied from a remote or noisy voltage source, it may be necessary to apply a decoupling capacitor locally to the LTM8020. VIN 10V/DIV 2.2µF IIN 10A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 10µF 35V AI.EI. 10µs/DIV (4a) LTM8020 + 2.2µF VIN 10V/DIV IIN 10A/DIV (4b) 1Ω 0.1µF LTM8020 2.2µF 10µs/DIV VIN 10V/DIV IIN 10A/DIV (4c) 10µs/DIV 8020 F04 Figure 4. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LTM8020 is Connected to a Live Supply Rev. F For more information www.analog.com 11 LTM8020 APPLICATIONS INFORMATION Minimum Input Voltage The LTM8020 is a step-down converter, so a minimum amount of headroom is required to keep the output in regulation. For most applications at full load, the input needs to be at least 1.5V above the desired output at room temperature. This headroom may increase over the full operating temperature range. In addition, the input voltage required to turn on depends upon how the SHDN pin is tied. It takes more input voltage to turn on if SHDN is tied to VIN than if the turn-on is controlled by raising SHDN when VIN is in the required operating range. For a typical part at room temperature, a sample graph of the input voltage required to turn on the LTM8020 when SHDN is tied to VIN or when SHDN is toggled high is given in the Typical Performance Characteristics section. given in the Typical Performance Characteristics section, while further data, operating conditions and test setup are detailed in the electromagnetic compatibility test report, available here. Conducted emissions requirements may be met by adding an appropriate input power line filter. The proper implementation of this filter depends upon the system operating and performance conditions as a whole, of which the LTM8020 is typically only a component, so conducted emissions are not addressed at this level. Note: To RUN = Minimum VIN required to maintain output regulation after meeting the TO START requirement. VIN is lowered after output is in regulation. Electromagnetic Compliance To START = Minimum VIN required to cause the part to overcome the headroom and regulate the output voltage. SHDN pin remains high prior to applying VIN. The LTM8020 was evaluated by an independent nationally recognized test lab and found to be compliant with EN55022 class B: 2006 by a wide margin. A sample graph of the LTM8020’s radiated EMC performance is SHDN CONTROLLED = With VIN applied, minimum VIN required to cause the part to overcome the headroom and regulate the output voltage when the SHDN pin is toggled high. Rev. F 12 For more information www.analog.com LTM8020 APPLICATIONS INFORMATION Table 1. Recommended External Component Values and Configuration, TA = 25°C VIN RANGE VOUT CIN COUT RADJ BIAS CONNECTION 4.5V - 36V 1.25V 2.2µF 50V 1206 X7R 47µF 6.3V 1206 X5R Open >2V, < 25V 4.5V - 36V 1.5V 2.2µF 50V 1206 X7R 47µF 6.3V 1206 X5R 2.43M >2V, < 25V 4.5V - 36V 1.8V 2.2µF 50V 1206 X7R 47µF 6.3V 1206 X5R 1.1M >2V, < 25V 4.5V - 36V 2.5V 2.2µF 50V 1206 X7R 22µF 6.3V 1206 X7R 499k VOUT 4.5V - 36V 3.3V 2.2µF 50V 1206 X7R 10µF 6.3V 1206 X7R 301k VOUT 6.5V - 36V 5V 2.2µF 50V 1206 X7R 10µF 6.3V 1206 X7R 165k VOUT 4.5V - 15V 1.25V 2.2µF 16V 0805 X7R 22µF 6.3V 1206 X7R Open VIN 4.5V - 15V 1.5V 2.2µF 16V 0805 X7R 10µF 6.3V 0805 X7R 2.43M VIN 4.5V - 15V 1.8V 2.2µF 16V 0805 X7R 10µF 6.3V 0805 X7R 1.1M VIN 4.5V - 15V 2.5V 2.2µF 16V 0805 X7R 10µF 6.3V 0805 X7R 499k VIN 4.5V - 15V 3.3V 2.2µF 16V 0805 X7R 10µF 6.3V 0805 X7R 301k VOUT 6.5V - 15V 5V 2.2µF 16V 0805 X7R None 165k VOUT 9V - 24V 1.25V 1µF 25V 0805 X7R 47µF 6.3V 0805 X5R Open VIN 9V - 24V 1.5V 1µF 25V 0805 X7R 47µF 6.3V 0805 X7R 2.43M VIN 9V - 24V 1.8V 1µF 25V 0805 X7R 10µF 6.3V 0805 X7R 1.1M VIN 9V - 24V 2.5V 1µF 25V 0805 X7R 10µF 6.3V 0805 X7R 499k VIN 9V - 24V 3.3V 1µF 25V 0805 X7R 10µF 6.3V 0805 X7R 301k VOUT 9V - 24V 5V 4.7µF 25V 0805 X7R 10µF 6.3V 0805 X5R 165k VOUT 18V - 36V 1.25V 2.2µF 50V 1206 X7R 47µF 6.3V 1206 X5R Open >2V, 2V, 2V,