LTM8031 Ultralow Noise EMC 36V, 1A DC/DC µModule Regulator Features n n n n n n n n n n n Description Complete Step-Down Switch Mode Power Supply Wide Input Voltage Range: 3.6V to 36V 1A Output Current 0.8V to 10V Output Voltage Switching Frequency from 200kHz to 2.4MHz EN55022 Class B Compliant with Margin Current Mode Control (e4) RoHS Compliant Package with Gold Pad Finish Programmable Soft-Start Pin Compatible with the LTM8032 Low Profile (9mm × 15mm × 2.82mm) Surface Mount LGA Package Applications n n n n n The LTM®8031 is an electromagnetic compatible (EMC) 36V, 1A DC/DC µModule® buck converter designed to meet the radiated emissions requirements of EN55022. Conducted emission requirements can be met by adding standard filter components. Included in the package are the switching controller, power switches, inductor, filters and all support components. Operating over an input voltage range of 3.6V to 36V, the LTM8031 supports an output voltage range of 0.8V to 10V, and a switching frequency range of 200kHz to 2.4MHz, each set by a single resistor. Only the bulk input and output filter capacitors are needed to finish the design. The low profile package (2.82mm) enables utilization of unused space on the bottom of PC boards for high density point of load regulation. The LTM8031 is packaged in a thermally enhanced, compact (9mm ×15mm) and low profile (2.82mm) overmolded land grid array (LGA) package suitable for automated assembly by standard surface mount equipment. The LTM8031 is RoHS compliant. Automotive Battery Regulation Power for Portable Products Distributed Supply Regulation Industrial Supplies Wall Transformer Regulation L, LT, LTC, LTM, µModule, Burst Mode, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical Application Ultralow Noise 5V/1A DC/DC µModule Regulator OUT VIN 10µF FIN LTM8031 RUN/SS AUX BIAS 1µF SHARE PGOOD RT SYNC GND ADJ 44.2k 47.5k 8031 TA01a VOUT 5V 1A 80 EMISSIONS LEVEL (dBµV/m) VIN* 7VDC TO 36VDC LTM8031 EMI Performance VIN = 36V 70 60 50 EN55022 CLASS B LIMIT 40 30 20 10 0 *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS –10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) 8031 TA01b 8031fb 1 LTM8031 Absolute Maximum Ratings (Note 1) VIN, FIN, RUN/SS Voltage...........................................40V ADJ, RT, SHARE Voltage..............................................5V VOUT, AUX..................................................................10V Current from AUX.................................................100mA PGOOD, SYNC...........................................................30V BIAS...........................................................................25V VIN + BIAS..................................................................56V Maximum Junction Temperature (Note 2)............. 125°C Solder Temperature (Note 3).................................. 245°C Pin Configuration 1 2 TOP VIEW 3 4 5 VOUT 6 GND 7 A BANK 1 B C D E BANK 2 F G RT H SHARE BIAS J BANK 3 ADJ AUX K PGOOD L VIN FIN RUN/SS SYNC LGA PACKAGE 71-LEAD (9mm × 15mm × 2.82mm) TJMAX = 125°C, θJA = 20.7°C/W, θJC(BOTTOM) = 8.4°C/W, θJC(TOP) = 25.6°C/W, θJBOARD = 13.8°C/W θ VALUES DETERMINED PER JESD 51-9 WEIGHT = 1.2g order information LEAD FREE FINISH TRAY PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTM8031EV#PBF LTM8031EV#PBF LTM8031V 71-Lead (9mm × 15mm × 2.82mm) LGA –40°C to 125°C LTM8031IV#PBF LTM8031IV#PBF LTM8031V 71-Lead (9mm × 15mm × 2.82mm) LGA –40°C to 125°C LTM8031MPV#PBF LTM8031MPV#PBF LTM8031V 71-Lead (9mm × 15mm × 2.82mm) LGA –55°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://www.linear.com/packaging/ 8031fb 2 LTM8031 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBIAS = 3V, unless otherwise specified. SYMBOL PARAMETER VIN Input DC Voltage VOUT Output DC Voltage 0.2A < IOUT ≤ 1A, RADJ Open 0.2A < IOUT ≤ 1A, RADJ = 21.6k IOUT Continuous Output DC Current VIN = 24V IQ(VIN) VIN Quiescent Current VRUN/SS = 0.2V VBIAS = 3V, Not Switching VBIAS = 0V, Not Switching l VRUN/SS = 0.2V VBIAS = 3V, Not Switching VBIAS = 0V, Not Switching l IQ(BIAS) ∆VOUT VOUT BIAS Quiescent Current Line Regulation Load Regulation VOUT(AC_RMS) Output Ripple (RMS) CONDITIONS MIN l TYP 3.6 MAX 36 0.8 10 UNITS V V V 1 A 0.6 25 88 60 120 µA µA µA 0.03 60 1 120 5 µA µA µA 10V ≤ VIN ≤ 36V, IOUT = 1A, VOUT = 3.3V 0.1 VIN = 24V, 0.2A ≤ IOUT ≤ 1A, VOUT = 3.3V 0.3 % 6 mV VIN = 24V, IOUT = 1A, VOUT = 3.3V fSW Switching Frequency VADJ Voltage at ADJ Pin RT = 113k VBIAS(MIN) Minimum BIAS Voltage for Proper Operation IADJ Current Out of ADJ Pin VRUN/SS = 0V, VADJ = 0V, VOUT = 1V 4 IRUN/SS RUN/SS Pin Current VRUN/SS = 2.5V 5 VIH(RUN/SS) RUN/SS Input High Voltage VIL(RUN/SS) RUN/SS Input Low Voltage VPG(TH) ADJ Voltage Threshold for PGOOD to Switch % 325 l 765 kHz 790 815 mV 1.9 2.8 V 10 µA µA 2.5 V 0.2 730 IPGO PGOOD Leakage VPG = 30V IPGSINK PGOOD Sink Current VPG = 0.4V VSYNCIL SYNC Input Low Threshold fSYNC = 550kHz 0.1 200 1 800 µA µA 0.5 V VSYNCIH SYNC Input High Threshold fSYNC = 550kHz ISYNC(BIAS) SYNC Pin Bias Current VSYNC = 0V, VBIAS = 0V 0.1 µA VIN(RIPPLE) 550kHz Narrowband Conducted Emission 1MHz Narrowband Conducted Emission 3MHz Narrowband Conducted Emission VIN = 24V, VOUT = 3.3V, IOUT = 1A, fSW = 550kHz, 5µH LISN 83 63 51 dBµV dBµV dBµV 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 LTM8031E is guaranteed to meet performance specifications from 0°C to 125°C internal. Specifications over the –40°C to 125°C internal temperature range are assured by design, characterization and correlation with statistical process controls. The LTM8031I is guaranteed 0.7 V mV V to meet specifications over the full –40°C to 125°C internal operating temperature range. The LTM8031MP 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: See Linear Technology Application Note 100. 8031fb 3 LTM8031 Typical Performance Characteristics TA = 25°C, unless otherwise noted. 3.3VOUT Efficiency 100 5VOUT Efficiency 90 80 80 80 70 60 5VIN 12VIN 24VIN 36VIN 40 0 200 400 600 800 OUTPUT CURRENT (mA) EFFICIENCY (%) 90 50 70 60 12VIN 24VIN 36VIN 50 40 1000 0 200 400 600 800 OUTPUT CURRENT (mA) 8031 G01 500 400 500 400 300 200 200 400 800 600 OUTPUT CURRENT (mA) 800 350 300 250 200 150 0 1000 400 600 800 OUTPUT CURRENT (mA) 600 400 300 200 100 0 200 600 800 400 OUTPUT CURRENT (mA) 0 1000 0 200 400 800 600 OUTPUT CURRENT (mA) 1000 8031 G06 Minimum VIN vs Output Current 3.3V VOUT Minimum VIN vs Output Current 5V VOUT 6.1 5.0 1000 500 8031 G05 Minimum VIN vs Output Current 2.5V VOUT 7.6 4.8 7.1 5.6 RUN/SS = VIN OR TOGGLED VIN (V) 4.4 4.2 4.0 3.8 0 200 400 800 600 OUTPUT CURRENT (mA) 4.6 RUN/SS = VIN 6.1 5.1 5.6 RUNNING OR RUN/SS TOGGLED 5.1 RUN/SS TOGGLED 4.6 RUNNING 4.1 RUNNING 3.6 6.6 RUN/SS = VIN VIN (V) 4.6 VIN (V) 200 12VIN 24VIN 36VIN 700 8031 G04 3.4 0 Input Current vs Output Current, 8VOUT 50 0 12VIN 24VIN 36VIN 8031 G03 100 100 0 40 1000 12VIN 24VIN 36VIN 450 INPUT CURRENT (mA) 600 60 Input Current vs Output Current, 5VOUT 5VIN 12VIN 24VIN 36VIN 700 70 50 INPUT CURRENT (mA) 800 8VOUT Efficiency 8031 G02 Input Current vs Output Current, 3.3VOUT INPUT CURRENT (mA) 100 90 EFFICIENCY (%) EFFICIENCY (%) 100 4.1 1000 8031 G07 3.6 0 200 600 800 400 OUTPUT CURRENT (mA) 1000 8031 G08 3.6 0 200 400 800 600 OUTPUT CURRENT (mA) 1000 8031 G09 8031fb 4 LTM8031 Typical Performance Characteristics TA = 25°C, unless otherwise noted. Minimum VIN vs Output Current 8V VOUT Minimum Input Running Voltage vs Output Voltage, IOUT = 1A 12 11 RUN/SS = VIN 14 30 VIN (V) 10 8 8 7 6 6 4 5 2 200 800 600 OUTPUT CURRENT (mA) 0 BIAS CURRENT (mA) RUNNING OR RUN/SS TOGGLED 9 VIN (V) 35 12 10 4 400 0 1000 20 15 10 0 2 4 8 6 VOUT (V) 0 10 30 2.70 1.2 25 2.50 2.45 1.0 0.8 0.6 0.4 0 4 8 12 16 20 24 28 32 0 36 0 10 VIN (V) 20 30 30 36VIN 24VIN 12VIN 15 10 5 30 36VIN 24VIN 12VIN 200 400 600 800 OUTPUT CURRENT (mA) 0 200 1000 8031 G16 400 600 800 OUTPUT CURRENT (mA) 20 15 10 0 1000 Temperature Rise vs Load Current, VOUT = 10V 36VIN 24VIN 25 5 1 10 8031 G15 TEMPERATURE RISE (°C) 20 0 15 0 40 Temperature Rise vs Load Current, VOUT = 8V 25 TEMPERATURE RISE (°C) 25 20 8031 G14 Temperature Rise vs Load Current, VOUT = 5V 1000 36VIN 24VIN 12VIN 5VIN VIN (V) 8031 G13 30 400 600 800 OUTPUT CURRENT (mA) 5 0.2 2.40 2.35 TEMPERATURE RISE (°C) 1.4 2.55 200 Temperature Rise vs Load Current, VOUT = 3.3V 2.75 2.60 0 8031 G12 Input Current vs Input Voltage (Output Shorted) INPUT CURRENT (A) OUTPUT CURRENT (A) 25 8031 G11 Output Current vs Input Voltage (Output Shorted) 2.65 8VOUT 5VOUT 3.3VOUT 5 8031 G10 TEMPERATURE RISE (°C) Bias Current vs Output Current 16 20 15 10 5 1 200 400 600 800 OUTPUT CURRENT (mA) 1000 8031 G17 0 1 200 400 600 800 OUTPUT CURRENT (mA) 1000 8031 G18 8031fb 5 LTM8031 Typical Performance Characteristics TA = 25°C, unless otherwise noted. Radiated Emissions EMISSIONS LEVEL (dBµV/m) 80 Radiated Emissions 90 VIN = 36V VOUT = 10V AT 1A 80 70 60 50 EN55022 CLASS B LIMIT 40 30 20 10 EMISSIONS LEVEL (dBµV/m) 90 70 60 50 30 20 10 0 –10 –10 8031 G19 EN55022 CLASS B LIMIT 40 0 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) VIN = 36V VOUT = 2.5V AT 1A 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) 8031 G20 Pin Functions VIN (Bank 3): The VIN pin supplies current to the LTM8031’s internal regulator and to the internal power switch. This pin must be locally bypassed with an external, low ESR capacitor of at least 1µF . FIN (K3, L3): Filtered Input. This is the node after the input EMI filter. Use this only if there is a need to modify the behavior of the integrated EMI filter or if VIN rises or falls rapidly; otherwise, leave these pins unconnected. See the Applications Information section for more details. GND (Bank 2): Tie these GND pins to a local ground plane below the LTM8031 and the circuit components. Return the feedback divider (RADJ) to this net. VOUT (Bank 1): Power Output Pins. Apply the output filter capacitor and the output load between these pins and GND pins. AUX (Pin H5): Low Current Voltage Source for BIAS. In many designs, the BIAS pin is simply connected to VOUT . The AUX pin is internally connected to VOUT and is placed adjacent to the BIAS pin to ease printed circuit board routing. Although this pin is internally connected to VOUT , do not connect this pin to the load. If this pin is not tied to BIAS, leave it floating. BIAS (Pin H4): The BIAS pin connects to the internal power bus. Connect to a power source greater than 2.8V. If the output is greater than 2.8V, connect this pin to AUX. If the output voltage is less, connect this to a voltage source between 2.8V and 25V. Also, make sure that BIAS + VIN is less than 56V. RUN/SS (Pin L5): Pull RUN/SS pin to less than 0.2V to shut down the LTM8031. Tie to 2.5V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. RUN/SS also provides a soft-start function; see the Applications Information section. RT (Pin G7): The RT pin is used to program the switching frequency of the LTM8031 by connecting a resistor from this pin to ground. The Applications Information section of the data sheet includes a table to determine the resistance value based on the desired switching frequency. Minimize capacitance at this pin. SHARE (Pin H7): Tie this to the SHARE pin of another LTM8031 when paralleling the outputs. 8031fb 6 LTM8031 Pin Functions SYNC (Pin L6): This is the external clock synchronization input. Ground this pin for low ripple Burst Mode® operation at low output loads. Tie to a stable voltage source greater than 0.7V to disable Burst Mode operation. Do not leave this pin floating. Tie to a clock source for synchronization. Clock edges should have rise and fall times faster than 1µs. See Synchronization section in Applications Information. The PGOOD output is valid when VIN is above 3.6V and RUN/SS is high. If this function is not used, leave this pin floating. PGOOD (Pin K7): The PGOOD pin is the open-collector output of an internal comparator. PGOOD remains low until the ADJ pin is within 10% of the final regulation voltage. ADJ (Pin J7): The LTM8031 regulates its ADJ pin to 0.79V. Connect the adjust resistor from this pin to ground. The value of RADJ is given by the equation: R ADJ = 196.71 VOUT – 0.79 where RADJ is in kΩ. Block Diagram FIN VIN EMI FILTER 4.7µH VOUT 22pF 249k GND 10µF AUX GND BIAS SHARE CURRENT MODE CONTROLLER RUN/SS SYNC RT PGOOD ADJ 8031 BD 8031fb 7 LTM8031 Operation The LTM8031 is a standalone nonisolated step-down switching DC/DC power supply. It can deliver up to 1A 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 0.8VDC to 10VDC. The input voltage range is 3.6V to 36V. Given that the LTM8031 is a step-down converter, make sure that the input voltage is high enough to support the desired output voltage and load current. A simplified Block Diagram is given on the previous page. The LTM8031 is designed with an input EMI filter and other features to make its radiated emissions compliant with several EMC specifications including EN55022 class B. Compliance with conducted emissions requirements may be obtained by adding a standard input filter. The LTM8031 contains a current mode controller, power switching element, power inductor, power Schottky diode and a modest amount of input and output capacitance. The LTM8031 is a fixed frequency PWM regulator. The switching frequency is set by simply connecting the appropriate resistor value from the RT pin to GND. An internal regulator provides power to the control circuitry. The bias regulator can draw power from the VIN pin, but if the BIAS pin is connected to an external voltage higher than 2.8V, bias power will be drawn from the external source (typically the regulated output voltage). This improves efficiency. The RUN/SS pin is used to place the LTM8031 in shutdown, disconnecting the output and reducing the input current to less than 1µA. To further optimize efficiency, the LTM8031 automatically switches to Burst Mode operation in light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down reducing the input supply current to 50µA in a typical application. The oscillator reduces the LTM8031’s operating frequency when the voltage at the ADJ pin is low. This frequency foldback helps to control the output current during start-up and overload. The LTM8031 contains a power good comparator which trips when the ADJ pin is at 90% of its regulated value. The PGOOD output is an open-collector transistor that is off when the output is in regulation, allowing an external resistor to pull the PGOOD pin high. Power good is valid when the LTM8031 is enabled and VIN is above 3.6V. 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 recommended CIN, COUT, RADJ and RT values. 3.Connect BIAS as indicated. As the integrated input EMI filter may ring in response to an application of a step input voltage, a bulk capacitance, series resistance or some clamping mechanism may be required. See the Hot-Plugging Safely section for details. 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. 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. 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 8031fb 8 LTM8031 Applications Information Table 1. Recommended Component Values and Configuration (See Typical Performance Characteristics for Load Conditions) VIN VOUT CIN COUT RADJ BIAS fOPTIMAL RT(OPTIMAL) fMAX RT(MIN) 3.6V to 36V 0.82V 1µF 0805 50V 2 × 100µF 1206 6.3V 5.11M ≥2.8V, <25V 250kHz 150k 250kHz 150k 3.6V to 36V 1.20V 1µF 0805 50V 100µF//47µF 1206 6.3V 475k ≥2.8V, <25V 300kHz 124k 325kHz 113k 3.6V to 36V 1.80V 1µF 0805 50V 100µF 1206 191k ≥2.8V, <25V 420kHz 84.5k 450kHz 78.7k 3.6V to 36V 2.00V 1µF 0805 50V 100µF 1206 162k ≥2.8V, <25V 450kHz 78.7k 475kHz 73.2k 3.6V to 36V 2.50V 1µF 0805 50V 47µF 0805 6.3V 115k ≥2.8V, <25V 550kHz 61.9k 575kHz 59.0k 4.75V to 36V 3.30V 1µF 0805 50V 22µF 1206 6.3V 78.7k AUX 675kHz 48.7k 725kHz 44.2k 6.8V to 36V 5.00V 1µF 0805 50V 10µF 1206 6.3V 46.4k AUX 975kHz 29.4k 1000kHz 28.0k 10.5V to 36V 8.00V 1µF 0805 50V 4.7µF 1206 10V 26.7k AUX 1200kHz 23.7k 1600kHz 15.8k 13V to 36V 10.00V 1µF 0805 50V 4.7µF 0805 16V 21.0k AUX 1250kHz 22.6k 2050kHz 10.5k 3.6V to 15V 0.82V 1µF 0805 50V 2 × 100µF 1206 6.3V 5.11M VIN 500kHz 69.8k 600kHz 56.2k 3.6V to 15V 1.20V 1µF 0805 50V 100µF 1206 6.3V 475k VIN 600kHz 56.2k 750kHz 42.2k 3.6V to 15V 1.80V 1µF 0805 50V 100µF 1206 191k VIN 650kHz 51.1k 1000kHz 28.0k 3.6V to 15V 2.00V 1µF 0805 50V 100µF 1206 162k VIN 650kHz 51.1k 1100kHz 26.7k 3.6V to 15V 2.50V 1µF 0805 50V 47µF 0805 6.3V 115k VIN 700kHz 47.5k 1350kHz 20.5k 4.75V to 15V 3.30V 1µF 0805 50V 22µF 1206 6.3V 78.7k AUX 950kHz 32.4k 1650kHz 15.0k 6.8V to 15V 5.00V 1µF 0805 50V 10µF 1206 6.3V 46.4k AUX 1150kHz 25.5k 2400kHz 7.87k 10.5V to 15V 8.00V 1µF 0805 50V 4.7µF 1206 10V 26.7k AUX 1200kHz 23.7k 2400kHz 7.87k 9V to 24V 0.82V 1µF 0805 50V 2 × 100µF 1206 6.3V 5.11M ≥2.8V, <25V 350kHz 105k 375kHz 93.1k 9V to 24V 1.20V 1µF 0805 50V 100µF//47µF 1206 6.3V 475k ≥2.8V, <25V 450kHz 78.7k 475kHz 73.2k 9V to 24V 1.80V 1µF 0805 50V 100µF 1206 191k ≥2.8V, <25V 600kHz 56.2k 650kHz 51.1k 9V to 24V 2.00V 1µF 0805 50V 100µF 1206 162k ≥2.8V, <25V 650kHz 51.1k 700kHz 47.5k 9V to 24V 2.50V 1µF 0805 50V 47µF 0805 6.3V 115k ≥2.8V, <25V 700kHz 47.5k 850kHz 37.4k 9V to 24V 3.30V 1µF 0805 50V 22µF 1206 6.3V 78.7k AUX 950kHz 32.4k 1050kHz 28.0k 9V to 24V 5.00V 1µF 0805 50V 10µF 1206 6.3V 46.4k AUX 1150kHz 25.5k 1550kHz 16.5k 10.5V to 24V 8.00V 1µF 0805 50V 4.7µF 1206 10V 26.7k AUX 1200kHz 23.7k 2400kHz 7.87k 13V to 24V 10.00V 1µF 0805 50V 4.7µF 0805 16V 21.0k AUX 1250kHz 22.6k 2400kHz 7.87k Note: An input bulk capacitor is required. 8031fb 9 LTM8031 Applications Information may have only a small fraction of their nominal capacitance resulting in much higher output voltage ripple than expected. Ceramic capacitors are also piezoelectric. In Burst Mode operation, the LTM8031’s switching frequency depends on the load current, and can excite a ceramic capacitor at audio frequencies, generating audible noise. Since the LTM8031 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 1µF ceramic capacitor and a low cost electrolytic capacitor. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LTM8031. A ceramic input capacitor combined with trace or cable inductance forms a high Q (under damped) tank circuit. If the LTM8031 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. Electromagnetic Compliance The LTM8031 is compliant with the radiated emissions requirements of EN55022 class B. Graphs of the LTM8031’s EMC performance are given in the Typical Performance Characteristics section. Further data, operating conditions and test setup are detailed in an EMI Test report available from Linear Technology. Frequency Selection The LTM8031 uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.4MHz by using a resistor tied from the RT pin to ground. Table 2 provides a list of RT resistor values and their resultant frequencies. Table 2. Switching Frequency vs RT Value SWITCHING FREQUENCY (MHz) 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.5 1.8 2 2.2 2.4 RT VALUE (kΩ) 187 124 88.7 69.8 56.2 47.5 39.2 34 28.0 23.7 19.1 16.2 13.3 11.5 9.76 8.66 Operating Frequency Trade-Offs It is recommended that the user apply the optimal RT value given in Table 1 for the input and output operating condition. System level or other considerations, however, may necessitate another operating frequency. While the LTM8031 is flexible enough to accommodate a wide range of operating frequencies, a haphazardly chosen one may result in undesirable operation under certain operating or fault conditions. A frequency that is too high can reduce efficiency, generate excessive heat or even damage the LTM8031 if the output is overloaded or short-circuited. A frequency that is too low can result in a final design that has too much output ripple or unnecessarily large output capacitor. The maximum frequency (and attendant RT value) at which the LTM8031 should be allowed to switch is given in Table 1 in the fMAX column, while the recommended frequency (and RT value) for optimal efficiency over the given input condition is given in the fOPTIMAL column. There are additional conditions that must be satisfied if the synchronization function is used. Please refer to the Synchronization section for details. 8031fb 10 LTM8031 Applications Information 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 2.8V. If the output voltage is programmed to be 2.8V or higher, simply tie BIAS to AUX. If VOUT is less than 2.8V, 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 56V. If BIAS power is applied from a remote or noisy voltage source, it may be necessary to apply a decoupling capacitor locally to the LTM8031. Load Sharing Two or more LTM8031s may be paralleled to produce higher currents. This may, however, alter the EMI performance of the LTM8031s. To do this, tie the VIN, ADJ, VOUT and SHARE pins of all the paralleled LTM8031s together. To ensure that paralleled modules start up together, the RUN/SS pins may be tied together, as well. Synchronize the LTM8031s to an external clock to eliminate beat frequencies, if required. If the RUN/SS pins are not tied together, make sure that the same valued soft-start capacitors are used for each module. An example of two LTM8031 modules configured for load sharing is given in the Typical Applications section. For 2A applications also see the LTM8032, 2A EMC DC/DC µModule regulator Burst Mode Operation To enhance efficiency at light loads, the LTM8031 automatically switches to Burst Mode operation which keeps the output capacitor charged to the proper voltage while minimizing the input quiescent current. During Burst Mode operation, the LTM8031 delivers single cycle bursts of current to the output capacitor followed by sleep periods where the output power is delivered to the load by the output capacitor. In addition, VIN and BIAS quiescent currents are reduced to typically 25µA and 60µA respectively during the sleep time. As the load current decreases towards a no-load condition, the percentage of time that the LTM8031 operates in sleep mode increases and the average input current is greatly reduced, resulting in higher efficiency. Burst Mode operation is enabled by tying SYNC to GND. To disable Burst Mode operation, tie SYNC to a stable voltage above 0.7V. Do not leave the SYNC pin floating. Minimum Input Voltage The LTM8031 is a step-down converter, so a minimum amount of headroom is required to keep the output in regulation. In addition, the input voltage required to turn on is higher than that required to run, and depends upon whether the RUN/SS is used. As shown in the Typical Performance Characteristics section, it takes only about 3.6VIN for the LTM8031 to run a 3.3V output at light load. If RUN/SS is pulled up to VIN, it takes 5.7VIN to start. If the LTM8031 is enabled via the RUN/SS pin, the minimum voltage to start at light loads is lower, about 4.4V. Similar curves for 2.5VOUT , 5VOUT and 8VOUT operation are also provided in the Typical Performance Characteristics section. Soft-Start The RUN/SS pin can be used to soft-start the LTM8031, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC network to create a voltage ramp at this pin. Figure 1 shows the startup and shutdown waveforms with the soft-start circuit. By choosing an appropriate RC time constant, the peak start-up current can be reduced to the current that is required to regulate the output, with no overshoot. Choose the value of the resistor so that it can supply at least 20µA when the RUN/SS pin reaches 2.5V. 8031fb 11 LTM8031 Applications Information VIN 15k RUN/SS VOUT 2V/DIV 2ms/DIV 8031 F01 Figure 1. To Soft-Start the LTM8031, Add a Resistor and Capacitor to the RUN/SS Pin Synchronization The internal oscillator of the LTM8031 can be synchronized by applying an external 250kHz to 2MHz clock to the SYNC pin. Do not leave this pin floating. The resistor tied from the RT pin to ground should be chosen such that the LTM8031 oscillates 20% lower than the intended synchronization frequency (see the Frequency Selection section). The LTM8031 will not enter Burst Mode operation while synchronized to an external clock, but will instead skip pulses to maintain regulation. Shorted Input Protection Care needs to be taken in systems where the output will be held high when the input to the LTM8031 is absent. This may occur in battery charging applications or in battery back-up systems where a battery or some other supply is diode ORed with the LTM8031’s output. If the VIN pin is allowed to float and the RUN/SS pin is held high (either by a logic signal or because it is tied to VIN), then the LTM8031’s internal circuitry will pull its quiescent current through its internal power switch. This is fine if your system can tolerate a few milliamps in this state. If you ground the RUN/SS pin, the internal switch current will drop to essentially zero. However, if the VIN pin is grounded while the output is held high, then parasitic diodes inside the LTM8031 can pull large currents from the output through the VIN pin, potentially damaging the VOUT ADJ RT SYNC GND VRUN/SS 2V/DIV GND 0.22µF VOUT RUN/SS AUX LTM8031 BIAS IL 0.5A/DIV RUN VIN 8031 F02 Figure 2. The Input Diode Prevents a Shorted Input from Discharging a Back-Up Battery Tied to the Output. It Also Protects the Circuit from a Reversed Input. The LTM8031 Runs Only When the Input is Present 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. PCB Layout Most of the headaches associated with PCB layout have been alleviated or even eliminated by the high level of integration of the LTM8031. The LTM8031 is nevertheless 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. Ensure that the grounding and heat sinking are acceptable. A few rules to keep in mind are: 1.Place the RADJ and RT resistors as close as possible to their respective pins. 2.Place the CIN capacitor as close as possible to the VIN and GND connection of the LTM8031. If a capacitor is connected to the FIN terminals, place it as close as possible to the FIN terminals, such that its ground connection is as close as possible to that of the CIN capacitor. 3.Place the COUT capacitor as close as possible to the VOUT and GND connection of the LTM8031. 8031fb 12 LTM8031 PGOOD RT GND RADJ Applications Information COUT SYNC AUX BIAS RUN/SS FIN VIN OPTIONAL FIN CAPACITOR VOUT CIN GND 8031 F03 Figure 3. Layout Showing Suggested External Components, GND Plane and Thermal Vias 4.Place the CIN and COUT capacitors such that their ground currents flow directly adjacent or underneath the LTM8031. 5. 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 LTM8031. 6. Use vias to connect the GND copper area to the board’s internal ground plane. Liberally distribute these GND vias to provide both a good ground connection and thermal path to the internal planes of the printed circuit board. Hot-Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LTM8031. However, these capacitors can cause problems if the LTM8031 is plugged into a live or fast rising or falling supply (see Linear Technology 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 LTM8031 can ring to twice the nominal input voltage, possibly exceeding the LTM8031’s rating and damaging the part. A similar phenomenon can occur inside the LTM8031 module, at the output of the integrated EMI filter, with the same potential of damaging the part. If the input supply is poorly controlled or the user will be plugging the LTM8031 into an energized supply, the input network should be designed to prevent this overshoot. Figure 4 shows the waveforms that result when an LTM8031 circuit is connected to a 24V supply through six feet of 24gauge twisted pair. The first plot (4a) is the response with a 2.2µF ceramic capacitor at the input. The input voltage 8031fb 13 LTM8031 Applications Information 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, as shown in Figure 4b. A 0.7Ω 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. 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. By far the most popular method of controlling overshoot is shown in Figure 4c, where an aluminum electrolytic capacitor has been connected to FIN. 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. Placing the electrolytic capacitor at the FIN terminals can also improve the LTM8031’s EMI filtering as well as guard against overshoots caused by the Q of the integrated filter. Thermal Considerations The LTM8031 output current may need to be derated if it is required to operate in a high ambient temperature or deliver a large amount of continuous power. The amount of current derating is dependent upon the input voltage, output power and ambient temperature. The temperature rise curves given in the Typical Performance Characteristics section can be used as a guide. These curves were generated by a LTM8031 mounted to a 35cm2 4-layer FR4 printed circuit board. Boards of other sizes and layer count can exhibit different thermal behavior, so it is incumbent upon the user to verify proper operation over the intended system’s line, load and environmental operating conditions. The junction-to-air and junction-to-board thermal resistances given in the Pin Configuration diagram may also be used to estimate the LTM8031 internal temperature. These thermal coefficients are determined per JESD 51‑9 (JEDEC standard, test boards for area array surface mount package thermal measurements) through analysis and physical correlation. Bear in mind that the actual thermal resistance of the LTM8031 to the printed circuit board depends upon the design of the circuit board. The die temperature of the LTM8031 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 LTM8031. The bulk of the heat flow out of the LTM8031 is through the bottom of the module and the LGA pads into the printed circuit board. Consequently a poor printed circuit board design can cause excessive heating, resulting in impaired performance or reliability. Please refer to the PCB Layout section for printed circuit board design suggestions. Finally, be aware that at high ambient temperatures the internal Schottky diode will have significant leakage current increasing the quiescent current of the LTM8031. 8031fb 14 LTM8031 Typical applications CLOSING SWITCH SIMULATES HOT PLUG IIN + LOW IMPEDANCE ENERGIZED 24V SUPPLY DANGER RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING 4.7µF IIN 10A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 0.7Ω + LTM8031 VIN VIN 20V/DIV 0.1µF 20µs/DIV (4a) LTM8031 VIN VIN 20V/DIV 4.7µF IIN 10A/DIV (4b) + 22µF 35V AI.EI. + FIN LTM8031 VIN 20µs/DIV VIN 20V/DIV 4.7µF IIN 10A/DIV (4c) 20µs/DIV 8031 F04 Figure 4. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LTM8031 is Hot-Plugged to a Live Supply 8031fb 15 LTM8031 Typical applications 0.82V Step-Down Converter VIN* 3.6V TO 15V OUT VIN 1µF FIN LTM8031 VOUT 0.82V 200µF 1A AUX RUN/SS BIAS SHARE PGOOD RT SYNC GND ADJ 5.11M 69.8k *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS 8031 TA02 1.8V Step-Down Converter VIN* 9V TO 24V OUT VIN 1µF FIN LTM8031 RUN/SS VOUT 1.8V 100µF 1A AUX BIAS SHARE PGOOD RT SYNC GND ADJ 56.2k *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS 191k 8031 TA03 8031fb 16 LTM8031 Typical applications 2.5V Step-Down Converter VIN* 3.6V TO 36V 1µF FIN LTM8031 22µF VOUT 3.3V 1A 10µF VOUT 5V 1A AUX RUN/SS 3.3V 47µF VOUT 2.5V 1A OUT VIN BIAS SHARE PGOOD RT SYNC GND ADJ 115k 61.9k 8031 TA04 *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS 3.3V Step-Down Converter VIN* 4.75V TO 36V OUT VIN LTM8031 FIN AUX RUN/SS 1µF BIAS SHARE PGOOD RT SYNC GND ADJ 48.7k 78.7k *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS 8031 TA08 5V Step-Down Converter VIN* 6.8V TO 36V OUT VIN FIN LTM8031 RUN/SS 1µF AUX BIAS SHARE PGOOD RT SYNC GND ADJ 29.4k *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS 46.4k 8031 TA05 8031fb 17 LTM8031 Typical applications Two LTM8031s Operating in Parallel (Also See the LTM8032, 2A Pin Compatible) VIN* 11.5V TO 36V FIN VOUT 8V 1.9A OUT VIN LTM8031 AUX RUN/SS BIAS 1µF SHARE PGOOD RT SYNC GND ADJ 23.7k 13.7k OPTIONAL SYNC TIE TO GND IF NOT USED OUT VIN FIN 10µF LTM8031 RUN/SS AUX BIAS 1µF SHARE PGOOD RT SYNC GND ADJ 23.7k 8031 TA07 *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS package photograph 8031fb 18 LTM8031 Package Description LGA Package 71-Lead (15mm × 9mm × 2.82mm) (Reference LTC DWG # 05-08-1823 Rev Ø) 2.670 – 2.970 7 aaa Z 6 5 4 3 2 1 PAD 1 Ø (0.635) A PAD 1 CORNER B 4 C D E 15.00 BSC 12.700 BSC F G H MOLD CAP SUBSTRATE J 0.27 – 0.37 K 1.270 BSC Z bbb Z 2.40 – 2.60 DETAIL A PADS SEE NOTES X 9.00 BSC Y DETAIL A PACKAGE SIDE VIEW aaa Z PACKAGE TOP VIEW 3 L 1.27 BSC 7.620 BSC DETAIL A PACKAGE BOTTOM VIEW 0.635 ±0.025 SQ. 71x 3.810 2.540 1.270 0.000 1.270 2.540 3.810 eee S X Y 6.350 DETAIL A 5.080 3.810 2.540 1.270 0.000 1.270 2.540 3.810 5.080 NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994 2. ALL DIMENSIONS ARE IN MILLIMETERS 3 LAND DESIGNATION PER JESD MO-222, SPP-010 AND SPP-020 4 DETAILS OF PAD #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE PAD #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE LTMXXXXXX µModule COMPONENT PIN 1 TRAY PIN 1 BEVEL PACKAGE IN TRAY LOADING ORIENTATION LGA 71 0108 REV Ø 5. PRIMARY DATUM -Z- IS SEATING PLANE 6. THE TOTAL NUMBER OF PADS: 71 SYMBOL TOLERANCE aaa 0.15 bbb 0.10 eee 0.05 6.350 SUGGESTED PCB LAYOUT TOP VIEW 8031fb 19 LTM8031 Package Description Table 3. LTM8031 Pinout (Sorted by Pin Number) PIN SIGNAL DESCRIPTION PIN SIGNAL DESCRIPTION A1 VOUT F1 GND A2 VOUT F2 GND A3 VOUT F3 GND A4 VOUT F4 GND A5 GND F5 GND A6 GND F6 GND A7 GND F7 GND B1 VOUT G1 GND B2 VOUT G2 GND B3 VOUT G3 GND B4 VOUT G4 GND B5 GND G5 GND B6 GND G6 GND B7 GND G7 RT C1 VOUT H1 GND C2 VOUT H2 GND C3 VOUT H3 GND C4 VOUT H4 BIAS C5 GND H5 AUX C6 GND H6 GND C7 GND H7 SHARE D1 VOUT J5 GND D2 VOUT J6 GND D3 VOUT J7 ADJ D4 VOUT K1 VIN D5 GND K2 VIN D6 GND K3 FIN D7 GND K5 GND E1 GND K6 GND E2 GND K7 PGOOD E3 GND L1 VIN E4 GND L2 VIN E5 GND L3 FIN E6 GND L5 RUN/SS E7 GND L6 SYNC L7 GND 8031fb 20 LTM8031 Revision History REV DATE DESCRIPTION PAGE NUMBER A 03/10 Addition to Features B 04/12 Changes to Applications Information Added MP-Grade part. Reflected throughout the data sheet 1 11 1-22 8031fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 21 LTM8031 Typical application 8V Step-Down Converter VIN* 10.5V TO 36V OUT VIN FIN 4.7µF LTM8031 RUN/SS 1µF VOUT 8V 1A AUX BIAS SHARE PGOOD RT SYNC GND ADJ 23.7k 26.7k *RUNNING VOLTAGE RANGE. SEE APPLICATIONS FOR START-UP DETAILS 8031 TA06 Related Parts PART NUMBER DESCRIPTION COMMENTS LTM4606 Ultralow Noise 6A DC/DC µModule Regulator 4.5V ≤ VIN ≤ 28V, 0.6V ≤ VOUT ≤ 5V, 15mm × 15mm × 2.8mm LGA LTM4612 Ultralow Noise High VOUT DC/DC µModule Regulator 5A, 5V ≤ VIN ≤ 36V, 3.3V ≤ VOUT ≤ 15V, 15mm × 15mm × 2.8mm LGA LTM8023 36V, 2A DC/DC µModule Regulator 3.6V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 10V, 9mm × 11.75mm × 2.8mm LGA LTM8025 36V, 3A DC/DC µModule Regulator 3.6V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 24V, 9mm × 15mm × 4.32mm LGA LTM8032 36V, 2A EMC DC/DC µModule Regulator EN55022 Class B, 9mm × 15mm × 2.8mm LGA. Pin Compatible with the LTM8031 8031fb 22 Linear Technology Corporation LT 0412 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2009