LTM8021 36VIN, 500mA Step-Down DC/DC µModule FEATURES DESCRIPTION n The LTM®8021 is a 36VIN 500mA, step-down DC/DC μModuleTM. Included in the package are the switching controller, power switches, inductor, and all support components. Operating over an input voltage range of 3V to 36V, the LTM8021 supports an output voltage range of 0.8V to 5V, set by a single resistor. Only an output and bulk input capacitor are needed to finish the design. n n n n n n n n Complete Switch Mode Power Supply Wide Input Voltage Range: 3V to 36V 500mA Output Current 0.8V to 5V Output Voltage Fixed 1.1MHz Switching Frequency Current Mode Control (e4) RoHS Compliant Package with Gold Pad Finish Programmable Soft-Start Tiny, Low Profile (11.25mm × 6.25mm × 2.82mm) Surface Mount LGA Package APPLICATIONS n n n n n The low profile package (2.82mm) enables utilization of unused space on the bottom of PC boards for high density point of load regulation. A built-in soft-start timer is adjustable with just a resistor and capacitor. The LTM8021 is packaged in a thermally enhanced, compact (11.25mm × 6.25mm) and low profile (2.82mm) overmolded Land Grid Array (LGA) package suitable for automated assembly by standard surface mount equipment. The LTM8021 is RoHS compliant. Automotive Battery Regulation Power for Portable Products Distributed Supply Regulation Industrial Supplies Wall Transformer Regulation , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. μModule is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Efficiency and Power Loss 7VIN to 36VIN, 5V/500mA μModule Regulator 90 LTM8021 RUN/SS GND 1μF BIAS ADJ 19.1k 2.2μF 8021 TA01a 400 80 VOUT 5V AT 500mA OUT 350 EFFICIENCY EFFICIENCY (%) IN 70 300 250 60 200 50 150 POWER LOSS 40 POWER LOSS (mW) VIN* 7V TO 36V 450 100 50 *RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS. 30 1.00 10.00 100.00 LOAD CURRENT (mA) 0 1000.00 8021 TA01b 8021fb 1 LTM8021 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VIN, RUN/SS Voltage .................................................40V RUN/SS Above VIN ......................................................3V ADJ Voltage ................................................................5V BIAS Voltage ...............................................................7V VOUT Voltage .............................................................10V Internal Operating Temperature Range (Note 2) ..................................–40°C to 125°C Maximum Solder Temperature .............................. 260°C Storage Temperature Range...................–55°C to 125°C TOP VIEW VIN BANK 1 5 VOUT BANK 2 4 3 BIAS ADJ 2 GND BANK 3 RUN/SS 1 A B C D E F G H LGA PACKAGE 35-LEAD (11.25mm s 6.25mm s 2.82mm) TJMAX = 125°C, θJA = 24.9°C/W, WEIGHT = 0.49g θJA DERIVED FROM 6.35cm × 6.35cm; 4-LAYER PCB ORDER INFORMATION LEAD FREE FINISH PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE (NOTE 2) LTM8021EV#PBF LTM8021V 35-Lead (11.25mm × 6.25mm × 2.82mm) –40°C to 125°C LTM8021IV#PBF LTM8021V 35-Lead (11.25mm × 6.25mm × 2.82mm) –40°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/ 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, RADJ = 31.6k. SYMBOL PARAMETER CONDITIONS VIN Input DC Voltage VRUN/SS = 5V, RADJ = Open MIN TYP VOUT Output DC Voltage 0 < IOUT < 500mA; RADJ Open 0 < IOUT < 500mA; RADJ = 19.1k, 0.1% RADJ(MIN) Minimum Allowable RADJ Note 3 ILK Leakage from IN to OUT RUN/SS = VBIAS = 0V, RADJ Open IOUT Continuous Output DC Current 5V ≤ VIN ≤ 36V, VBIAS = VOUT IQVIN Quiescent Current into VIN RUN/SS = 0.2V, VBIAS , RADJ Open Not Switching 0.1 1.5 IQBIAS Quiescent Current into BIAS Not Switching 0.15 μA ΔVOUT/VOUT Line Regulation 5V ≤ VIN ≤ 36V, IOUT = 500mA RADJ = Open 0.5 % ΔVOUT/VOUT Load Regulation VIN = 24V, 0 ≤ IOUT ≤ 500mA, VBIAS = VOUT 0.35 % 3 MAX 36 0.8 5 UNITS V V V 18 kΩ 2.7 0 6 μA 500 mA 1 2.5 μA mA 8021fb 2 LTM8021 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, RADJ = 31.6k. SYMBOL PARAMETER CONDITIONS VOUT(DC) DC Output Voltage VIN = 24V, 0 ≤ IOUT ≤ 500mA RADJ = 31.6k, 0.1% MIN TYP MAX VOUT(AC_RMS) Output Voltage Ripple (RMS) VIN = 24V, IOUT = 250mA COUT = 2.2μF, VBIAS = VOUT fSW Switching Frequency IOUT = 500mA IOSC Short-Circuit Output Current VIN = 36V, VBIAS = VOUT = 0V 900 mA IISC Short-Circuit Input Current VIN = 36V, VBIAS = VOUT = 0V 25 mA ADJ Voltage at ADJ Pin RADJ Open VBIAS(MIN) Minimum BIAS Voltage for Proper Operation IADJ 3.3 V 1 0.9 l mV 1.3 MHz 0.80 0.83 V IOUT = 500mA 2.2 3 V Current Out of ADJ Pin VOUT = 5V, VADJ = 0V, RUN/SS = 0V 50 μA IRUN/SS RUN/SS Pin Current VRUN/SS = 2.5V, RADJ Open 23 μA VIH(RUN/SS) RUN/SS Input High Voltage RADJ Open, IOUT = 500mA VIL(RUN/SS) RUN/SS Input Low Voltage RADJ Open, IOUT = 500mA RFB Internal Feedback Resistor RUN/SS = VBIAS = VADJ = 0V 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 LTM8021E is guaranteed to meet performance specifications from 0°C to 125°C internal. Specifications over the full –40°C to 125°C internal operating temperature range are assured by design, characteriza- 0.79 1.1 UNITS 1.6 V 0.5 100 V kΩ tion and correlation with statistical process controls. The LTM8021I is guaranteed to meet specifications over the full –40°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. 8021fb 3 LTM8021 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current VOUT = 1.8V 80 VIN = 5V 75 VIN = 12V 70 VIN = 24V 65 VIN = 36V 60 VOUT = 2.5V 85 EFFICIENCY (%) 85 EFFICIENCY (%) Efficiency vs Load Current 90 Efficiency vs Load Current 90 VIN = 5V 80 VIN = 12V 75 VIN = 24V 70 VIN = 36V 65 0 0 IBIAS vs Load Current IBIAS vs Load Current 9 VOUT = 0.8V VIN = 12V VOUT = 1.8V VIN = 3.4V 8 VIN = 3.4V 5 VIN = 24V 75 70 BIAS CURRENT (mA) 7 VIN = 36V 80 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 8021 G03 6 BIAS CURRENT (mA) EFFICIENCY (%) 85 0 8021 G02 Efficiency vs Load Current VOUT = 5V 70 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 8021 G01 90 VIN = 36V 55 50 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 75 60 55 40 VIN = 24V 65 60 45 VIN = 5V VIN = 12V 80 55 50 VOUT = 3.3V 85 EFFICIENCY (%) 90 TA = 25°C, unless otherwise noted 4 VIN = 5V 3 2 VIN = 12V 6 VIN = 5V 5 4 3 VIN = 12V 2 1 65 60 0 0 0 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 0 100 300 400 200 LOAD CURRENT (mA) 500 8021 G04 500 600 VOUT = 3.3V VIN = 5V 8 6 BIAS CURRENT (mA) BIAS CURRENT (mA) 300 400 200 LOAD CURRENT (mA) 8021 G06 9 VIN = 5V 5 4 VIN = 12V 3 VIN = 24V 2 100 IBIAS vs Load Current 10 VOUT = 2.5V 7 0 600 8021 G05 IBIAS vs Load Current 8 VIN = 24V 1 VIN = 24V 7 6 5 VIN = 12V 4 3 VIN = 24V 2 1 1 0 0 0 100 300 400 200 LOAD CURRENT (mA) 500 600 8021 G07 0 100 300 400 200 LOAD CURRENT (mA) 500 600 8021 G08 8021fb 4 LTM8021 TYPICAL PERFORMANCE CHARACTERISTICS Input Current vs Output Current VIN = 5V INPUT CURRENT (mA) INPUT CURRENT (mA) 250 VOUT = 2.5V 200 150 VOUT = 1.8V 100 200 VOUT = 3.3V 150 VOUT = 2.5V 100 VOUT = 1.8V 50 100 150 200 250 300 350 400 450 500 OUTPUT CURRENT (mA) 0 1000 5 4 3 2 500 1 0 0 10 15 20 25 30 INPUT VOLTAGE (V) 35 40 8021 G12 50 100 150 200 250 300 350 400 450 500 OUTPUT CURRENT (mA) VOUT = 3.3V 880 OUTPUT CURRENT (mA) 2500 INPUT VOLTAGE (V) INPUT QUIESCENT CURRENT (μA) 900 IOUT = 500mA 1500 0 Output Short-Circuit Current vs Input Voltage 7 2000 VOUT = 1.8V 8021 G11 6 5 40 Minimum Input Running Voltage vs Output Voltage VO = 3.3V 0 VOUT = 2.5V 60 8021 G10 Input Quiescent Current vs Input Voltage 3000 VOUT = 3.3V 80 0 50 100 150 200 250 300 350 400 450 500 OUTPUT CURRENT (mA) 8021 G09 100 20 0 0 VOUT = 5V VOUT = 5V 50 50 VIN = 24V 120 250 300 0 140 VIN = 12V VOUT = 3.3V 350 Input Current vs Output Current Input Current vs Output Current 300 INPUT CURRENT (mA) 400 TA = 25°C, unless otherwise noted 860 840 820 800 780 760 740 720 0 1 3 4 2 OUTPUT VOLTAGE (V) 5 6 4 8 12 16 20 24 28 32 36 INPUT VOLTAGE (V) 8021 G13 8021 G14 8021fb 5 LTM8021 PIN FUNCTIONS VIN (Bank 1): The VIN pin supplies current to the LTM8021’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. VOUT (Bank 2): Power Output Pins. An external capacitor is connected from VOUT to GND in most applications. Apply output load between these pins and GND pins. BIAS (Pin H3): 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. RUN/SS (Pin A1): Tie RUN/SS pin to ground to shut down the LTM8021. Tie to 1.6V or more for normal operation. If the shutdown feature is not used, tie this pin to the VIN pin. The RUN/SS also provides soft-start and frequency foldback. To use the soft-start function, connect a resistor and capacitor to this pin. Do not allow the RUN/SS pin to rise above VIN. See the Applications Information section. GND (Bank 3): The GND connections serve as the main signal return and the primary heatsink for the LTM8021. Tie the GND pins to a local ground plane below the LTM8021 and the circuit components. Return the feedback divider to this signal. ADJ (Pin A2): The LTM8021 regulates its ADJ pin to 0.8V. Connect the adjust resistor from this pin to ground. The value of RADJ is given by the equation, RADJ = 80/(VOUT – 0.8), where RADJ is in k. BLOCK DIAGRAM VIN VOUT 10μH 0.1μF 15pF 100k 1% 10μF BIAS RUN/SS CURRENT MODE CONTROLLER GND ADJ 8021 BD 8021fb 6 LTM8021 OPERATION The LTM8021 is a stand alone non-isolated step down switching DC/DC power supply. It can deliver up to 500mA 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 5VDC . The input voltage range is 3V to 36V. Given that the LTM8021 is a step down converter, make sure that the input voltage is high enough to support the desired output voltage and load current. Please refer to the simplified Block Diagram. The LTM8021 contains a current mode controller, power switching element, power inductor, power Schottky diode and a modest amount of input and output capacitance. With its high performance current mode controller and internal feedback loop compensation, the LTM8021 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-by-cycle fast current limit, and automatic current limiting protects the module in the event of a short-circuit or overload fault. The LTM8021 is based upon a 1.1MHz fixed frequency PWM current mode controller, equipped with cycle skip capability for low voltage outputs or light loads. A frequency foldback scheme helps to protect internal components from overstress under heavy and short-circuit output loads. The drive circuit for the internal power switching element is powered through the BIAS pin. Power this pin with at least 3V. APPLICATIONS INFORMATION For most applications, the design process is straight forward, summarized as follows: 1. Refer to Table 1 for the row that has the desired input range and output voltage. 2. Apply the recommended CIN, COUT, and RADJ values. 3. Connect BIAS as indicated. 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 the desired output voltage is not listed in Table 1, set the output by applying an RADJ resistor whose value is given by the equation, RADJ = 80/(VOUT – 0.80), where RADJ is in k and VOUT is in volts. Verify the LTM8021’s operation over the system’s intended line, load and environmental conditions. Minimum Duty Cycle The LTM8021 has a fixed 1.1MHz switching frequency. For any given output voltage, the duty cycle falls as the input voltage rises. At very large VIN to VOUT ratios, the duty cycle can be very small. Because the LTM8021’s internal controller IC has a minimum on-time, the regulator will skip cycles in order to maintain output voltage regulation. This will result in a larger output voltage ripple and possible disturbances during recovery from a transient load step. The component values provided in Table 1 allow for skip cycle operation, but hold the resultant output ripple to around 50mV, or less. If even less ripple is desired, then more output capacitance may be necessary. Adding a feedforward capacitor has been empirically shown to modestly extend the input voltage range to where the LTM8021 does not skip cycles. Apply the feedforward capacitor between the VOUT pins and ADJ. This injects perturbations into the control loop, therefore, values larger than 50pF are not recommended. A good value to start with is 12pF. 8021fb 7 LTM8021 APPLICATIONS INFORMATION Table 1. Recommended Component Values and Configuration VIN RANGE VOUT CIN COUT RADJ BIAS 3.4V to 36V 0.8V 4.7μF 100μF 1210 8.2M 3V to 7V 3.4V to 36V 1.2V 4.7μF 100μF 1210 200k 3V to 7V 3.4V to 36V 1.5V 4.7μF 100μF 1210 115k 3V to 7V 3.4V to 36V 1.8V 2.2μF 100μF 1210 78.7k 3V to 7V 3.5V to 36V 2V 2.2μF 100μF 1210 66.5k 3V to 7V 4V to 36V 2.2V 1μF 22μF 1206 57.6k 3V to 7V 4V to 36V 2.5V 1μF 10μF 0805 47.5k 3V to 7V 5V to 36V 3.3V 1μF 4.7μF 0805 32.4k VOUT 7V to 36V 5V 1μF 2.2μF 0805 19.1k VOUT 3.5V to 32V –3.3V 1μF 4.7μF 0805 32.4k GND 3.75V to 31V –5V 1μF 4.7μF 0805 19.1k GND 3.4V to 15V 0.8V 4.7μF 100μF 1210 8.2M 3V to 7V 3.4V to 15V 1.2V 4.7μF 100μF 1210 200k 3V to 7V 3.4V to 15V 1.5V 4.7μF 47μF 1206 115k 3V to 7V 3.4V to 15V 1.8V 2.2μF 47μF 1206 78.7k 3V to 7V 3.5V to 15V 2V 2.2μF 22μF 1206 66.5k 3V to 7V 4V to 15V 2.2V 1μF 22μF 1206 57.6k 3V to 7V 4V to 15V 2.5V 1μF 10μF 0805 47.5k 3V to 7V 5V to 15V 3.3V 1μF 2.2μF 0805 32.4k VOUT 7V to 15V 5V 1μF 1μF 0805 19.1k VOUT 9V to 24V 0.8V 1μF 100μF 1210 Open 3V to 7V 9V to 24V 1.2V 1μF 100μF 1210 200k 3V to 7V 9V to 24V 1.5V 1μF 47μF 1206 115k 3V to 7V 9V to 24V 1.8V 1μF 47μF 1206 78.7k 3V to 7V 9V to 24V 2V 1μF 22μF 1206 66.5k 3V to 7V 9V to 24V 2.2V 1μF 22μF 1206 57.6k 3V to 7V 9V to 24V 2.5V 1μF 10μF 0805 47.5k 3V to 7V 9V to 24V 3.3V 1μF 2.2μF 0805 32.4k VOUT 9V to 24V 5V 1μF 1μF 0805 19.1k VOUT 18V to 36V 0.8V 1uF 100μF 1210 Open 3V to 7V 18V to 36V 1.2V 1uF 100μF 1210 200k 3V to 7V 18V to 36V 1.5V 1uF 100μF 1210 115k 3V to 7V 18V to 36V 1.8V 1uF 100μF 1210 78.7k 3V to 7V 18V to 36V 2V 1uF 100μF 1210 66.5k 3V to 7V 18V to 36V 2.2V 1uF 22μF 1206 57.6k 3V to 7V 18V to 36V 2.5V 1uF 10μF 0805 47.5k 3V to 7V 18V to 36V 3.3V 1uF 4.7μF 0805 32.4k VOUT 18V to 36V 5V 1uF 2.2μF 0805 19.1k VOUT 8021fb 8 LTM8021 APPLICATIONS INFORMATION If this audible noise is unacceptable, use a high performance electrolytic capacitor at the output. This output capacitor can be a parallel combination of a 1μF ceramic capacitor and a low cost electrolytic capacitor. 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 or fault recovery, 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. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LTM8021. A ceramic input capacitor combined with trace or cable inductance forms a high Q (under damped) tank circuit. If the LTM8021 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. 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. Minimum Input Voltage The LTM8021 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 must be about 1.5V above the desired output. In addition, it takes more input voltage to turn on than is required for continuous operation. This is shown in Figure 1. Ceramic capacitors are also piezoelectric. At light loads, the LTM8021 skips switching cycles in order to maintain regulation. The resulting bursts of current can excite a ceramic capacitor at audio frequencies, generating audible noise. 8 6.0 VOUT = 5V VOUT = 3.3V 5.5 7 TO START TO START 6 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 5.0 RUN/SS ENABLED 5 TO RUN 4 4.5 4.0 RUN/SS ENABLED 3.5 TO RUN 3.0 3 2 0.001 2.5 0.01 0.1 LOAD CURRENT (A) 1 2.0 0.001 0.01 0.1 LOAD CURRENT (A) 1 8021 F01 Figure 1. The LTM8021 Requires More Voltage to Start Than to Run 8021fb 9 LTM8021 APPLICATIONS INFORMATION Soft-Start Shorted Input Protection The RUN/SS pin can be used to soft-start the LTM8021, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC filter to create a voltage ramp at this pin. Figure 2 shows the soft-start circuit. By choosing a large 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 80μA when the RUN/SS pin reaches 2V. Care needs to be taken in systems where the output will be held high when the input to the LTM8021 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 LTM8021’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 LTM8021’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 the RUN/SS pin is grounded, the internal power 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 LTM8021 can pull large currents from the output through the internal power switch and the VIN pin. Figure 3 shows a circuit that will run only when the input voltage is present and that protects against a shorted or reversed input. RUN 15k RUN/SS 0.22μF GND 8021 F02 Figure 2. To Soft-Start the LTM8021, Add a Resisitor and Capacitor to the RUN/SS Pin LTM8021 VIN 4V TO 36V VIN VOUT RUN/SS BIAS GND CIN VOUT RT COUT RADJ 8021 F03 Figure 3. The Input Diode Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output. It Also Protects the Circuit from a Reversed Input. The LTM8021 Runs Only When the Input is Present 8021fb 10 LTM8021 APPLICATIONS INFORMATION PCB Layout Hot-Plugging Safely Most of the problems associated with the PCB layout have been alleviated or eliminated by the high level of integration of the LTM8021. The LTM8021 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, one may fail to achieve a specified operation with a haphazard or poor layout. See Figure 4 for a suggested layout. The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LTM8021. However, these capacitors can cause problems if the LTM8021 is plugged into a live supply (see the 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 LTM8021 can ring to twice the nominal input voltage, possibly exceeding the LTM8021’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LTM8021 into an energized supply, the input network should be designed to prevent this overshoot. Figure 5 shows the waveforms that result when an LTM8021 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 5b 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 5c. 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. 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. Ensure that the grounding and heatsinking 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 LTM8021. 2. Place the COUT capacitor as close as possible to the VOUT and GND connection of the LTM8021. 3. Place the CIN and COUT capacitors such that their ground currents flow directly adjacent to, or underneath, the LTM8021. 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 LTM8021. VIN PLANE VOUT COUT BIAS CIN GND RADJ FB RUN/SS 8021 F04 Figure 4. Layout Showing Suggested External Components, GND Plane and Thermal Vias 8021fb 11 LTM8021 APPLICATIONS INFORMATION CLOSING SWITCH SIMULATES HOT PLUG IIN VIN DANGER VIN 20V/DIV RINGING VIN MAY EXCEED ABSOLUTE MAXIMUM RATING LTM8021 + 4.7μF LOW IMPEDANCE ENERGIZED 24V SUPPLY IIN 10A/DIV STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR 20μs/DIV (5a) LTM8021 + + 22μF AI.EI. VIN 20V/DIV 4.7μF IIN 10A/DIV (5b) 0.7Ω LTM8021 20μs/DIV VIN 20V/DIV + 0.1μF 4.7μF IIN 10A/DIV (5c) 20μs/DIV 8021 F05 Figure 5. Ensures Reliable Operation When the LTM8021 is Connected to a Live Supply High Temperature Considerations The die temperature of the LTM8021 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 LTM8021. To estimate the junction temperature, approximate the power dissipation within the LTM8021 by applying the typical efficiency stated in this datasheet to the desired output power, or, if one has an actual module, by taking a power measurement. Then, calculate the temperature rise of the LTM8021 junction 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 LTM8021 to the printed circuit board depends on the layout of the circuit board, but the thermal resistance given on page 2, which is based upon a 40.3cm2 4-layer FR4 PC board, can be used a guide. Finally, be aware that at high ambient temperatures the internal Schottky diode will have significant leakage current (see the Typical Performance Characteristics) increasing the quiescent current of the LTM8021. 8021fb 12 LTM8021 TYPICAL APPLICATIONS 1.8V Step-Down Converter 0.8V Step-Down Converter LTM8021 VIN* 3.4V TO 36V VIN 5V VIN 5V BIAS RUN/SS 1μF LTM8021 VIN* 3.4V TO 36V VOUT 0.8V AT 500mA VOUT GND VOUT 1.8V AT 500mA VOUT BIAS RUN/SS 100μF GND ADJ 100μF ADJ 1μF 78.7k 8021 TA02 8021 TA03 *RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS. *RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS. 5V Step-Down Converter LTM8021 VIN* 7V TO 36V VIN VOUT RUN/SS BIAS GND 1μF VOUT 5V AT 500mA ADJ 2.2μF 19.1k 8021 TA04 *RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS. –5V Positive-to-Negative Converter Load Current vs Input Voltage 600 LTM8021 VIN VOUT RUN/SS BIAS 500 400 4.7μF GND 1μF ADJ OPTIONAL SCHOTTKY CLAMP 300 200 19.1k –5V 8021 TA05 *RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS. ILOAD (mA) VIN* 3.75V TO 31V 100 0 0 5 10 15 20 25 VIN (V) 8021 TA05b 8021fb 13 LTM8021 PACKAGE DESCRIPTION LGA Package 35-Lead (11.25mm × 6.25mm × 2.82mm) (Reference LTC DWG # 05-08-1805 Rev A) 11.250 BSC aaa Z X 2.72 – 2.92 Y MOLD CAP 6.250 BSC SUBSTRATE 0.27 – 0.37 PAD 1 CORNER Z bbb Z 2.40 – 2.60 DETAIL A aaa Z PACKAGE TOP VIEW 4 4.445 3.175 1.905 0.635 0.0000 0.635 1.905 3.175 4.445 DETAIL A PACKAGE SIDE VIEW 8.890 BSC 0.605 – 0.665 PADS SEE NOTES 3 5 2.540 1.270 4 0.605 – 0.665 5.080 BSC 0.0000 0.9525 1.270 1.5875 3 2 1.270 BSC 1 0.9525 0.635 0.3175 2.540 H G F E D C B A PAD 1 C (0.30) PACKAGE BOTTOM VIEW SUGGESTED PCB LAYOUT TOP VIEW 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 A MARKED FEATURE LTMXXXXXX MModule 5. PRIMARY DATUM -Z- IS SEATING PLANE 6. THE TOTAL NUMBER OF PADS: 35 COMPONENT PIN “A1” 8021fb 14 LTM8021 PACKAGE DESCRIPTION LTM8021 Pinout (Sorted by Pin Number) PIN SIGNAL DESCRIPTION A1 RUN/SS A2 ADJ A4 VIN A5 VIN B1 GND B2 GND B4 VIN B5 VIN C1 GND C2 GND D1 GND D2 GND D3 GND D4 GND D5 GND E1 GND E2 GND E3 GND E4 GND E5 GND F1 GND F2 GND F3 VOUT F4 VOUT F5 VOUT G1 GND G2 GND G3 VOUT G4 VOUT G5 VOUT H1 GND H2 GND H3 BIAS H4 VOUT H5 VOUT 8021fb 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. 15 LTM8021 TYPICAL APPLICATION 3.3V Step-Down Converter LTM8021 VIN* 5.5V TO 36V VIN VOUT RUN/SS BIAS GND 1μF VOUT 3.3V AT 500mA ADJ 32.4k 4.7μF 8021 TA06 *RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS. RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTM4600 10A DC/DC μModule Basic 10A DC/DC μModule, 15mm × 15mm × 2.8mm LGA LTM4600HVMPV Military Plastic 10A DC/DC μModule –55°C to 125°C Operation, 15mm × 15mm × 2.8mm LGA LTM4601/ LTM4601A 12A DC/DC μModule with PLL, Output Tracking/Margining and Remote Sensing Synchronizable, PolyPhase® Operation, LTM4601-1 Version Has No Remote Sensing LTM4602 6A DC/DC μModule Pin-Compatible with the LTM4600 LTM4603 6A DC/DC μModule with PLL and Output Tracking/ Margining and Remote Sensing Synchronizable, PolyPhase Operation, LTM4603-1 Version Has No Remote Sensing, Pin-Compatible with the LTM4601 LTM4604 4A Low VIN DC/DC μModule 2.375V ≤ VIN ≤ 5V, 0.8V ≤ VOUT ≤ 5V, 9mm × 15mm × 2.3mm LGA LTM4605 5A to 12A Buck-Boost μModule High Efficiency, Adjustable Frequency, 4.5V ≤ VIN ≤ 20V, 0.8V ≤ VOUT ≤ 16V, 15mm × 15mm × 2.8mm LTM4607 5A to 12A Buck-Boost μModule High Efficiency, Adjustable Frequency, 4.5V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 25V, 15mm × 15mm × 2.8mm LTM4608 8A Low VIN DC/DC μModule 2.375V ≤ VIN ≤ 5V, 0.8V ≤ VOUT ≤ 5V, 9mm × 15mm × 2.8mm LGA LTM8020 36V, 200mA DC/DC μModule 4V ≤ VIN ≤ 36V, 1.25V ≤ VOUT ≤ 5V, 6.25mm × 6.25mm × 2.3mm LGA LTM8022 1A, 36V DC/DC μModule Adjustable Frequency, 0.8V ≤ VOUT ≤ 5V, 11.25mm × 9mm × 2.82mm, Pin-Compatible to the LTM8023 LTM8023 2A, 36V DC/DC μModule Adjustable Frequency, 0.8V ≤ VOUT ≤ 5V, 11.25mm × 9mm × 2.82mm, Pin-Compatible to the LTM8022 PolyPhase is a trademark of Linear Technology Corporation 8021fb 16 Linear Technology Corporation LT 1208 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 2008