LT8610 42V, 2.5A Synchronous Step-Down Regulator with 2.5µA Quiescent Current DESCRIPTION FEATURES Wide Input Voltage Range: 3.4V to 42V n Ultralow Quiescent Current Burst Mode® Operation: 2.5μA IQ Regulating 12VIN to 3.3VOUT Output Ripple < 10mVP-P n High Efficiency Synchronous Operation: 96% Efficiency at 1A, 5VOUT from 12VIN 94% Efficiency at 1A, 3.3VOUT from 12VIN n Fast Minimum Switch-On Time: 50ns n Low Dropout Under All Conditions: 200mV at 1A n Allows Use Of Small Inductors n Low EMI n Adjustable and Synchronizable: 200kHz to 2.2MHz n Current Mode Operation n Accurate 1V Enable Pin Threshold n Internal Compensation n Output Soft-Start and Tracking n Small Thermally Enhanced 16-Lead MSOP Package n APPLICATIONS Automotive and Industrial Supplies General Purpose Step-Down n GSM Power Supplies n The LT®8610 is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 2.5µA of quiescent current. Top and bottom power switches are included with all necessary circuitry to minimize the need for external components. Low ripple Burst Mode operation enables high efficiency down to very low output currents while keeping the output ripple below 10mVP-P. A SYNC pin allows synchronization to an external clock. Internal compensation with peak current mode topology allows the use of small inductors and results in fast transient response and good loop stability. The EN/UV pin has an accurate 1V threshold and can be used to program VIN undervoltage lockout or to shut down the LT8610 reducing the input supply current to 1µA. A capacitor on the TR/SS pin programs the output voltage ramp rate during start-up. The PG flag signals when VOUT is within ±9% of the programmed output voltage as well as fault conditions. The LT8610 is available in a small 16-lead MSOP package with exposed pad for low thermal resistance. L, LT, LTC, LTM, 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. n TYPICAL APPLICATION 5V 2.5A Step-Down Converter 100 4.7µF VIN EN/UV PG SYNC 10nF 1µF BST LT8610 0.1µF 4.7µH SW BIAS TR/SS FB 1M 10pF INTVCC RT PGND GND 60.4k fSW = 700kHz 95 VOUT 5V 47µF 2.5A 90 EFFICIENCY (%) VIN 5.5V TO 42V 12VIN to 5VOUT Efficiency 85 80 75 70 65 fSW = 700kHz VIN = 12V VIN = 24V 60 243k 55 50 8610 TA01a 0 0.5 1.5 1 LOAD CURRENT (A) 2 2.5 8610 G01 8610fa For more information www.linear.com/LT8610 1 LT8610 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION VIN, EN/UV, PG...........................................................42V BIAS...........................................................................30V BST Pin Above SW Pin................................................4V FB, TR/SS, RT, INTVCC ................................................4V SYNC Voltage ..............................................................6V Operating Junction Temperature Range (Note 2) LT8610E.................................................. –40 to 125°C LT8610I................................................... –40 to 125°C LT8610H................................................. –40 to 150°C Storage Temperature Range.......................–65 to 150°C TOP VIEW SYNC TR/SS RT EN/UV VIN VIN PGND PGND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 17 GND FB PG BIAS INTVCC BST SW SW SW MSE PACKAGE 16-LEAD PLASTIC MSOP θJA = 40°C/W, θJC(PAD) = 10°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8610EMSE#PBF LT8610EMSE#TRPBF 8610 16-Lead Plastic MSOP –40°C to 125°C LT8610IMSE#PBF LT8610IMSE#TRPBF 8610 16-Lead Plastic MSOP –40°C to 125°C LT8610HMSE#PBF LT8610HMSE#TRPBF 8610 16-Lead Plastic MSOP –40°C to 150°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS MIN Minimum Input Voltage VIN Quiescent Current TYP MAX l 2.9 3.4 V l 1.0 1.0 3 8 µA µA l 1.7 1.7 4 10 µA µA 0.24 0.5 mA 24 210 50 350 µA µA 0.970 0.970 0.976 0.982 V V 0.004 0.02 %/V 20 nA VEN/UV = 0V, VSYNC = 0V VEN/UV = 2V, Not Switching, VSYNC = 0V VEN/UV = 2V, Not Switching, VSYNC = 2V VIN Current in Regulation VOUT = 0.97V, VIN = 6V, Output Load = 100µA VOUT = 0.97V, VIN = 6V, Output Load = 1mA l l Feedback Reference Voltage VIN = 6V, ILOAD = 0.5A VIN = 6V, ILOAD = 0.5A l l 0.964 0.958 UNITS Feedback Voltage Line Regulation VIN = 4.0V to 42V, ILOAD = 0.5A Feedback Pin Input Current VFB = 1V –20 INTVCC Voltage ILOAD = 0mA, VBIAS = 0V ILOAD = 0mA, VBIAS = 3.3V 3.23 3.25 3.4 3.29 3.57 3.35 V V 2.5 2.6 2.7 V INTVCC Undervoltage Lockout BIAS Pin Current Consumption VBIAS = 3.3V, ILOAD = 1A, 2MHz Minimum On-Time ILOAD = 1A, SYNC = 0V ILOAD = 1A, SYNC = 3.3V Minimum Off-Time 8.5 l l mA 30 30 50 45 70 65 50 80 110 ns ns ns 8610fa 2 For more information www.linear.com/LT8610 LT8610 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS Oscillator Frequency RT = 221k, ILOAD = 1A RT = 60.4k, ILOAD = 1A RT = 18.2k, ILOAD = 1A Top Power NMOS On-Resistance ISW = 1A MIN TYP MAX UNITS l l l 180 665 1.85 210 700 2.00 240 735 2.15 kHz kHz MHz l 3.5 4.8 2.5 3.3 120 Top Power NMOS Current Limit Bottom Power NMOS On-Resistance VINTVCC = 3.4V, ISW = 1A Bottom Power NMOS Current Limit VINTVCC = 3.4V SW Leakage Current VIN = 42V, VSW = 0V, 42V EN/UV Pin Threshold EN/UV Rising mΩ 5.8 65 –1.5 l 0.94 EN/UV Pin Hysteresis 1.0 mΩ 4.8 A 1.5 µA 1.06 40 –20 A V mV EN/UV Pin Current VEN/UV = 2V 20 nA PG Upper Threshold Offset from VFB VFB Falling l 6 9.0 12 % PG Lower Threshold Offset from VFB VFB Rising l –6 –9.0 –12 % 40 nA 680 2000 Ω 1.1 2.0 1.4 2.4 V V 40 nA 2.2 3.2 µA PG Hysteresis 1.3 PG Leakage VPG = 3.3V PG Pull-Down Resistance VPG = 0.1V SYNC Threshold SYNC Falling SYNC Rising SYNC Pin Current VSYNC = 2V –40 l 0.8 1.6 –40 TR/SS Source Current TR/SS Pull-Down Resistance l Fault Condition, TR/SS = 0.1V 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 LT8610E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LT8610I is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT8610H is guaranteed over the full –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction 1.2 % 230 Ω temperatures greater than 125°C. Note 3: This IC includes overtemperature protection that is intended to protect the device during overload conditions. Junction temperature will exceed 150°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature will reduce lifetime. 8610fa For more information www.linear.com/LT8610 3 LT8610 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency at 5VOUT Efficiency at 3.3VOUT 95 95 90 90 90 80 85 85 80 75 70 65 fSW = 700kHz VIN = 12V VIN = 24V 60 55 50 0.5 0 1.5 1 LOAD CURRENT (A) 2 EFFICIENCY (%) 100 EFFICIENCY (%) 100 EFFICIENCY (%) 100 80 75 70 65 55 50 2.5 0.5 0 1.5 1 LOAD CURRENT (A) 2 Efficiency at 3.3VOUT 90 30 0 0.001 0.01 2.5 Reference Voltage VOUT = 3.3V 0.982 EFFICIENCY (%) 92 50 40 30 0.1 1 10 100 1000 10000 LOAD CURRENT (mA) 0.985 REFERENCE VOLTAGE (V) 70 60 fSW = 700kHz VIN = 12V VIN = 24V 10 94 80 EFFICIENCY (%) 40 Efficiency vs Frequency 96 0 0.001 0.01 50 8610 G02 100 90 88 86 fSW = 700kHz VIN = 12V VIN = 24V 10 60 8610 G03 8610 G01 20 70 20 fSW = 700kHz VIN = 12V VIN = 24V 60 Efficiency at 5VOUT 84 10 100 1000 10000 0.1 1 LOAD CURRENT (mA) 82 0.25 8610 G04 VIN = 12V VIN = 24V 0.75 0.979 0.976 0.973 0.970 0.967 0.964 0.961 0.958 1.25 2.25 1.75 SWITCHING FREQUENCY (MHz) 0.955 –55 65 35 5 95 TEMPERATURE (°C) –25 Load Regulation 1.03 0.20 1.02 0.15 1.01 EN RISING 1.00 0.99 Line Regulation 0.10 VOUT = 3.3V VIN = 12V 0.06 0.10 0.05 0 –0.05 0.98 0.04 0.02 0 –0.02 –0.10 EN FALLING 0.97 –0.04 –0.15 –0.06 0.96 –0.20 –0.08 0.95 –55 –0.25 –25 5 35 65 95 TEMPERATURE (°C) 125 155 8610 G07 VOUT = 3.3V ILOAD = 0.5A 0.08 CHANGE IN VOUT (%) 0.25 CHANGE IN VOUT (%) EN THRESHOLD (V) EN Pin Thresholds 155 8610 G06 8610 G05 1.04 125 0 0.5 1.5 2 1 LOAD CURRENT (A) 3 2.5 8610 G08 –0.10 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 45 8610 G09 8610fa 4 For more information www.linear.com/LT8610 LT8610 TYPICAL PERFORMANCE CHARACTERISTICS No Load Supply Current 25 VOUT = 3.3V IN REGULATION 4.5 20 INPUT CURRENT (µA) INPUT CURRENT (µA) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Top FET Current Limit vs Duty Cycle 6.0 VOUT = 3.3V VIN = 12V IN REGULATION 5.5 CURRENT LIMIT (A) No Load Supply Current 5.0 15 10 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 0 –55 45 Top FET Current Limit 65 5 95 35 TEMPERATURE (°C) –25 125 2.0 155 250 3.4 3.5 3.0 3.2 3.0 2.8 5 35 65 TEMPERATURE (°C) 95 2.4 –55 125 –25 5 35 65 TEMPERATURE (°C) Switch Drop 80 400 75 MINIMUM ON-TIME (ns) 300 TOP SW BOT SW 150 100 50 1 1.5 2 SWITCH CURRENT (A) 2.5 3 8610 G41 BOT SW –25 65 5 95 35 TEMPERATURE (°C) 65 155 8610 G40 95 60 55 50 45 30 –55 125 Minimum Off-Time VIN = 3.3V ILOAD = 0.5A 90 85 80 75 70 65 35 0.5 100 100 40 0 TOP SW 0 –55 125 ILOAD = 1A, VSYNC = 0V ILOAD = 1A, VSYNC = 3V ILOAD = 2.5A, VSYNC = 0V ILOAD = 2.5A, VSYNC = 3V 70 200 150 Minimum On-Time 450 350 SWITCH CURRENT = 1A 8610 G15 8610 G14 250 95 MINIMUM OFF-TIME (ns) –25 1.0 50 2.6 2.5 –55 0.8 200 SWITCH DROP (mV) CURRENT LIMIT (A) 70% DC 0.4 0.6 DUTY CYCLE Switch Drop Bottom FET Current Limit 30% DC 4.0 0.2 0 8610 G13 3.6 4.5 CURRENT LIMIT (A) 3.5 8610 G11 5.0 SWITCH DROP (mV) 4.0 2.5 8610 G10 0 4.5 3.0 5 0.5 0 5.0 –25 65 35 5 95 TEMPERATURE (°C) 125 155 8610 G17 60 –50 –25 95 65 35 TEMPERATURE (°C) 5 125 155 8610 G18 8610fa For more information www.linear.com/LT8610 5 LT8610 TYPICAL PERFORMANCE CHARACTERISTICS Switching Frequency 700 730 600 500 400 300 200 RT = 60.4k 720 710 700 690 680 670 100 0 Burst Frequency 800 SWITCHING FREQUENCY (kHz) 740 SWITCHING FREQUENCY (kHz) DROPOUT VOLTAGE (mV) Dropout Voltage 800 0 1 0.5 1.5 2 2.5 LOAD CURRENT (A) 95 65 35 TEMPERATURE (°C) 5 125 8610 G19 VOUT = 5V fSW = 700kHz SWITCHING FREQUENCY (kHz) 20 600 25 30 35 INPUT VOLTAGE (V) 40 1.0 500 400 300 0 45 0.2 0 0.2 0.4 0.6 FB VOLTAGE (V) SS PIN CURRENT (µA) 0.8 0 1 11.5 –7.5 10.5 2.1 FB RISING 10.0 2.0 1.9 1.8 1.7 125 155 8610 G24 0.2 1.0 0.4 0.6 0.8 TR/SS VOLTAGE (V) FB FALLING 9.5 9.0 1.4 –8.0 –8.5 –9.0 FB RISING –9.5 FB FALLING –10.0 8.5 –10.5 8.0 –11.0 7.5 7.0 –55 1.2 PG Low Thresholds –7.0 11.0 2.2 0 8610 G23 12.0 PG THRESHOLD OFFSET FROM VREF (%) VSS = 0.5V 95 65 35 TEMPERATURE (°C) 0.4 PG High Thresholds 2.3 5 0.6 8610 G22 Soft-Start Current 1.6 –50 –25 0.8 200 8610 G39 2.4 200 Soft-Start Tracking PG THRESHOLD OFFSET FROM VREF (%) 20 100 50 150 LOAD CURRENT (mA) 0 1.2 100 15 200 8610 G21 FB VOLTAGE (V) LOAD CURRENT (mA) 40 10 300 0 155 VOUT = 3.3V VIN = 12V VSYNC = 0V RT = 60.4k 700 60 5 400 Frequency Foldback 800 80 0 500 8610 G20 Minimum Load to Full Frequency (SYNC DC High) 100 600 100 660 –55 –25 3 VIN = 12V VOUT = 3.3V 700 –11.5 –25 65 35 5 95 TEMPERATURE (°C) 125 155 8610 G25 –12.0 –55 –25 65 35 5 95 TEMPERATURE (°C) 125 155 8610 G26 8610fa 6 For more information www.linear.com/LT8610 LT8610 TYPICAL PERFORMANCE CHARACTERISTICS RT Programmed Switching Frequency Bias Pin Current 3.6 225 3.4 4.75 3.2 4.50 INPUT VOLTAGE (V) 175 150 125 100 75 5.00 BIAS PIN CURRENT (mA) 200 RT PIN RESISTOR (kΩ) VIN UVLO 250 3.0 2.8 2.6 2.4 50 2.2 25 0 0.2 0.6 1.4 1.8 1 SWITCHING FREQUENCY (MHz) 2.2 2.0 –55 –25 BIAS PIN CURRENT (mA) 4.00 3.75 3.50 95 65 35 TEMPERATURE (°C) 5 125 155 3.00 5 15 20 25 30 35 INPUT VOLTAGE (V) 40 45 8610 G29 Switching Waveforms VBIAS = 5V VOUT = 5V VIN = 12V ILOAD = 1A 10 8610 G28 Bias Pin Current 10 4.25 3.25 8610 G27 12 VBIAS = 5V VOUT = 5V ILOAD = 1A fSW = 700kHz Switching Waveforms IL 200mA/DIV IL 1A/DIV 8 VSW 5V/DIV 6 4 VSW 5V/DIV 500ns/DIV 12VIN TO 5VOUT AT 1A 500µs/DIV 12VIN TO 5VOUT AT 10mA VSYNC = 0V 8610 G31 2 0 0 0.5 1 1.5 2 SWITCHING FREQUENCY (MHz) 8610 G32 2.5 8610 G30 Transient Response Switching Waveforms IL 1A/DIV Transient Response ILOAD 1A/DIV ILOAD 1A/DIV VOUT 100mV/DIV VSW 10V/DIV 500ns/DIV 36VIN TO 5VOUT AT 1A 8610 G33 VOUT 200mV/DIV 50µs/DIV 0.5A TO 1.5A TRANSIENT 12VIN, 5VOUT COUT = 47µF 8610 G34 50µs/DIV 0.5A TO 2.5A TRANSIENT 12VIN, 5VOUT COUT = 47µF 8610 G35 8610fa For more information www.linear.com/LT8610 7 LT8610 TYPICAL PERFORMANCE CHARACTERISTICS Transient Response Start-Up Dropout Performance ILOAD 1A/DIV VIN VIN 2V/DIV VOUT 200mV/DIV 50µs/DIV 50mA TO 1A TRANSIENT 12VIN, 5VOUT COUT = 47µF 8610 G36 VIN 2V/DIV VOUT VOUT 2V/DIV 100ms/DIV 2.5Ω LOAD (2A IN REGULATION) Start-Up Dropout Performance VOUT 2V/DIV 8610 G37 VIN VOUT 100ms/DIV 20Ω LOAD (250mA IN REGULATION) 8610 G38 PIN FUNCTIONS SYNC (Pin 1): External Clock Synchronization Input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a clock source for synchronization to an external frequency. Apply a DC voltage of 3V or higher or tie to INTVCC for pulse-skipping mode. When in pulseskipping mode, the IQ will increase to several hundred µA. Do not float this pin. TR/SS (Pin 2): Output Tracking and Soft-Start Pin. This pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.97V forces the LT8610 to regulate the FB pin to equal the TR/SS pin voltage. When TR/SS is above 0.97V, the tracking function is disabled and the internal reference resumes control of the error amplifier. An internal 2.2μA pull-up current from INTVCC on this pin allows a capacitor to program output voltage slew rate. This pin is pulled to ground with an internal 230Ω MOSFET during shutdown and fault conditions; use a series resistor if driving from a low impedance output. This pin may be left floating if the tracking function is not needed. RT (Pin 3): A resistor is tied between RT and ground to set the switching frequency. EN/UV (Pin 4): The LT8610 is shut down when this pin is low and active when this pin is high. The hysteretic threshold voltage is 1.00V going up and 0.96V going down. Tie to VIN if the shutdown feature is not used. An external resistor divider from VIN can be used to program a VIN threshold below which the LT8610 will shut down. VIN (Pins 5, 6): The VIN pins supply current to the LT8610 internal circuitry and to the internal topside power switch. These pins must be tied together and be locally bypassed. Be sure to place the positive terminal of the input capacitor as close as possible to the VIN pins, and the negative capacitor terminal as close as possible to the PGND pins. PGND (Pins 7, 8): Power Switch Ground. These pins are the return path of the internal bottom-side power switch and must be tied together. Place the negative terminal of the input capacitor as close to the PGND pins as possible. SW (Pins 9, 10, 11): The SW pins are the outputs of the internal power switches. Tie these pins together and connect them to the inductor and boost capacitor. This node should be kept small on the PCB for good performance. BST (Pin 12): This pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. Place a 0.1µF boost capacitor as close as possible to the IC. INTVCC (Pin 13): Internal 3.4V Regulator Bypass Pin. The internal power drivers and control circuits are powered from this voltage. INTVCC maximum output current is 20mA. Do not load the INTVCC pin with external circuitry. INTVCC current will be supplied from BIAS if VBIAS > 3.1V, otherwise current will be drawn from VIN. Voltage on INTVCC will vary between 2.8V and 3.4V when VBIAS is between 3.0V and 3.6V. Decouple this pin to power ground with at least a 1μF low ESR ceramic capacitor placed close to the IC. 8610fa 8 For more information www.linear.com/LT8610 LT8610 PIN FUNCTIONS BIAS (Pin 14): The internal regulator will draw current from BIAS instead of VIN when BIAS is tied to a voltage higher than 3.1V. For output voltages of 3.3V and above this pin should be tied to VOUT. If this pin is tied to a supply other than VOUT use a 1µF local bypass capacitor on this pin. PG (Pin 15): The PG pin is the open-drain output of an internal comparator. PG remains low until the FB pin is within ±9% of the final regulation voltage, and there are no fault conditions. PG is valid when VIN is above 3.4V, regardless of EN/UV pin state. FB (Pin 16): The LT8610 regulates the FB pin to 0.970V. Connect the feedback resistor divider tap to this pin. Also, connect a phase lead capacitor between FB and VOUT. Typically, this capacitor is 4.7pF to 10pF. GND (Exposed Pad Pin 17): Ground. The exposed pad must be connected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the thermal resistance. BLOCK DIAGRAM VIN VIN 5, 6 CIN R3 OPT 4 R4 OPT 15 EN/UV PG 1V + – SHDN ±9% R2 R1 16 CSS OPT 2 RT 3 1 FB TR/SS ERROR AMP INTVCC OSCILLATOR 200kHz TO 2.2MHz VC BST BURST DETECT SHDN TSD INTVCC UVLO VIN UVLO 2.2µA BIAS 3.4V REG SLOPE COMP + + – VOUT C1 – + INTERNAL 0.97V REF SWITCH LOGIC AND ANTISHOOT THROUGH 14 13 CVCC 12 CBST M1 L SW 9-11 VOUT COUT M2 PGND SHDN TSD VIN UVLO 7, 8 RT SYNC GND 17 8610 BD 8610fa For more information www.linear.com/LT8610 9 LT8610 OPERATION The LT8610 is a monolithic, constant frequency, current mode step-down DC/DC converter. An oscillator, with frequency set using a resistor on the RT pin, turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. The peak inductor current at which the top switch turns off is controlled by the voltage on the internal VC node. The error amplifier servos the VC node by comparing the voltage on the VFB pin with an internal 0.97V reference. When the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the VC voltage until the average inductor current matches the new load current. When the top power switch turns off, the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. If overload conditions result in more than 3.3A flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. If the EN/UV pin is low, the LT8610 is shut down and draws 1µA from the input. When the EN/UV pin is above 1V, the switching regulator will become active. To optimize efficiency at light loads, the LT8610 operates in 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 1.7μA. In a typical application, 2.5μA will be consumed from the input supply when regulating with no load. The SYNC pin is tied low to use Burst Mode operation and can be tied to a logic high to use pulse-skipping mode. If a clock is applied to the SYNC pin the part will synchronize to an external clock frequency and operate in pulse-skipping mode. While in pulse-skipping mode the oscillator operates continuously and positive SW transitions are aligned to the clock. During light loads, switch pulses are skipped to regulate the output and the quiescent current will be several hundred µA. To improve efficiency across all loads, supply current to internal circuitry can be sourced from the BIAS pin when biased at 3.3V or above. Else, the internal circuitry will draw current from VIN. The BIAS pin should be connected to VOUT if the LT8610 output is programmed at 3.3V or above. Comparators monitoring the FB pin voltage will pull the PG pin low if the output voltage varies more than ±9% (typical) from the set point, or if a fault condition is present. The oscillator reduces the LT8610’s operating frequency when the voltage at the FB pin is low. This frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up or overcurrent conditions. When a clock is applied to the SYNC pin or the SYNC pin is held DC high, the frequency foldback is disabled and the switching frequency will slow down only during overcurrent conditions. 8610fa 10 For more information www.linear.com/LT8610 LT8610 APPLICATIONS INFORMATION Achieving Ultralow Quiescent Current To enhance efficiency at light loads, the LT8610 operates in low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimizing output voltage ripple. In Burst Mode operation the LT8610 delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor. While in sleep mode the LT8610 consumes 1.7μA. As the output load decreases, the frequency of single current pulses decreases (see Figure 1a) and the percentage of time the LT8610 is in sleep mode increases, resulting in Burst Frequency SWITCHING FREQUENCY (kHz) 800 VIN = 12V VOUT = 3.3V 700 600 500 400 300 200 100 0 100 50 150 LOAD CURRENT (mA) 0 (1a) 200 8610 F01a Minimum Load to Full Frequency (SYNC DC High) 100 much higher light load efficiency than for typical converters. By maximizing the time between pulses, the converter quiescent current approaches 2.5µA for a typical application when there is no output load. Therefore, to optimize the quiescent current performance at light loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. While in Burst Mode operation the current limit of the top switch is approximately 400mA resulting in output voltage ripple shown in Figure 2. Increasing the output capacitance will decrease the output ripple proportionally. As load ramps upward from zero the switching frequency will increase but only up to the switching frequency programmed by the resistor at the RT pin as shown in Figure 1a. The output load at which the LT8610 reaches the programmed frequency varies based on input voltage, output voltage, and inductor choice. For some applications it is desirable for the LT8610 to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. In this mode much of the internal circuitry is awake at all times, increasing quiescent current to several hundred µA. Second is that full switching frequency is reached at lower output load than in Burst Mode operation (see Figure 1b). To enable pulse-skipping mode, the SYNC pin is tied high either to a logic output or to the INTVCC pin. When a clock is applied to the SYNC pin the LT8610 will also operate in pulse-skipping mode. 5VOUT 700kHz LOAD CURRENT (mA) 80 IL 200mA/DIV 60 40 VOUT 10mV/DIV 20 0 VSYNC = 0V 5 10 15 20 25 30 35 INPUT VOLTAGE (V) (1b) 40 45 5µs/DIV 8610 F02 Figure 2. Burst Mode Operation 8610 F01b Figure 1. SW Frequency vs Load Information in Burst Mode Operation (1a) and Pulse-Skipping Mode (1b) For more information www.linear.com/LT8610 8610fa 11 LT8610 APPLICATIONS INFORMATION FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the resistor values according to: V R1= R2 OUT – 1 0.970V where RT is in kΩ and fSW is the desired switching frequency in MHz. Table 1. SW Frequency vs RT Value (1) Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain output voltage accuracy. If low input quiescent current and good light-load efficiency are desired, use large resistor values for the FB resistor divider. The current flowing in the divider acts as a load current, and will increase the no-load input current to the converter, which is approximately: V V 1 IQ = 1.7µA + OUT OUT R1+R2 VIN n (2) where 1.7µA is the quiescent current of the LT8610 and the second term is the current in the feedback divider reflected to the input of the buck operating at its light load efficiency n. For a 3.3V application with R1 = 1M and R2 = 412k, the feedback divider draws 2.3µA. With VIN = 12V and n = 80%, this adds 0.8µA to the 1.7µA quiescent current resulting in 2.5µA no-load current from the 12V supply. Note that this equation implies that the no-load current is a function of VIN; this is plotted in the Typical Performance Characteristics section. When using large FB resistors, a 4.7pF to 10pF phase-lead capacitor should be connected from VOUT to FB. Setting the Switching Frequency The LT8610 uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.2MHz by using a resistor tied from the RT pin to ground. A table showing the necessary RT value for a desired switching frequency is in Table 1. The RT resistor required for a desired switching frequency can be calculated using: RT = 46.5 – 5.2 fSW (3) fSW (MHz) RT (kΩ) 0.2 232 0.3 150 0.4 110 0.5 88.7 0.6 71.5 0.7 60.4 0.8 52.3 1.0 41.2 1.2 33.2 14 28.0 1.6 23.7 1.8 20.5 2.0 18.2 2.2 15.8 Operating Frequency Selection and Trade-Offs Selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. The advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvantages are lower efficiency and a smaller input voltage range. The highest switching frequency (fSW(MAX)) for a given application can be calculated as follows: fSW(MAX) = ( VOUT + VSW(BOT) tON(MIN) VIN – VSW(TOP) + VSW(BOT) ) (4) where VIN is the typical input voltage, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~0.3V, ~0.15V, respectively at maximum load) and tON(MIN) is the minimum top switch on-time (see the Electrical Characteristics). This equation shows that a slower switching frequency is necessary to accommodate a high VIN/VOUT ratio. For transient operation, VIN may go as high as the absolute maximum rating of 42V regardless of the RT value, however the LT8610 will reduce switching frequency as necessary to maintain control of inductor current to assure safe operation. 8610fa 12 For more information www.linear.com/LT8610 LT8610 APPLICATIONS INFORMATION The LT8610 is capable of a maximum duty cycle of greater than 99%, and the VIN-to-VOUT dropout is limited by the RDS(ON) of the top switch. In this mode the LT8610 skips switch cycles, resulting in a lower switching frequency than programmed by RT. For applications that cannot allow deviation from the programmed switching frequency at low VIN/VOUT ratios use the following formula to set switching frequency: VIN(MIN) = VOUT + VSW(BOT) 1– fSW • tOFF(MIN) – VSW(BOT) + VSW(TOP) (5) where ∆IL is the inductor ripple current as calculated in Equation 9 and ILOAD(MAX) is the maximum output load for a given application. As a quick example, an application requiring 1A output should use an inductor with an RMS rating of greater than 1A and an ISAT of greater than 1.3A. During long duration overload or short-circuit conditons, the inductor RMS routing requirement is greater to avoid overheating of the inductor. To keep the efficiency high, the series resistance (DCR) should be less than 0.04Ω, and the core material should be intended for high frequency applications. where VIN(MIN) is the minimum input voltage without skipped cycles, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~0.3V, ~0.15V, respectively at maximum load), fSW is the switching frequency (set by RT), and tOFF(MIN) is the minimum switch off-time. Note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. The LT8610 limits the peak switch current in order to protect the switches and the system from overload faults. The top switch current limit (ILIM) is at least 3.5A at low duty cycles and decreases linearly to 2.8A at DC = 0.8. The inductor value must then be sufficient to supply the desired maximum output current (IOUT(MAX)), which is a function of the switch current limit (ILIM) and the ripple current. Inductor Selection and Maximum Output Current The LT8610 is designed to minimize solution size by allowing the inductor to be chosen based on the output load requirements of the application. During overload or short-circuit conditions the LT8610 safely tolerates operation with a saturated inductor through the use of a high speed peak-current mode architecture. The peak-to-peak ripple current in the inductor can be calculated as follows: A good first choice for the inductor value is: L= VOUT + VSW(BOT) fSW (6) where fSW is the switching frequency in MHz, VOUT is the output voltage, VSW(BOT) is the bottom switch drop (~0.15V) and L is the inductor value in μH. To avoid overheating and poor efficiency, an inductor must be chosen with an RMS current rating that is greater than the maximum expected output load of the application. In addition, the saturation current (typically labeled ISAT) rating of the inductor must be higher than the load current plus 1/2 of in inductor ripple current: 1 IL(PEAK) =ILOAD(MAX) + ∆IL 2 (7) IOUT(MAX) =ILIM – ∆IL = ∆IL 2 VOUT V • 1– OUT L • fSW VIN(MAX) (8) (9) where fSW is the switching frequency of the LT8610, and L is the value of the inductor. Therefore, the maximum output current that the LT8610 will deliver depends on the switch current limit, the inductor value, and the input and output voltages. The inductor value may have to be increased if the inductor ripple current does not allow sufficient maximum output current (IOUT(MAX)) given the switching frequency, and maximum input voltage used in the desired application. The optimum inductor for a given application may differ from the one indicated by this design guide. A larger value inductor provides a higher maximum load current and reduces the output voltage ripple. For applications requiring smaller load currents, the value of the inductor may be lower and the LT8610 may operate with higher ripple 8610fa For more information www.linear.com/LT8610 13 LT8610 APPLICATIONS INFORMATION current. This allows use of a physically smaller inductor, or one with a lower DCR resulting in higher efficiency. Be aware that low inductance may result in discontinuous mode operation, which further reduces maximum load current. For more information about maximum output current and discontinuous operation, see Linear Technology’s Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), a minimum inductance is required to avoid sub-harmonic oscillation. See Application Note 19. Input Capacitor Bypass the input of the LT8610 circuit with a ceramic capacitor of X7R or X5R type placed as close as possible to the VIN and PGND pins. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 4.7μF to 10μF ceramic capacitor is adequate to bypass the LT8610 and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used. If the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT8610 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7μF capacitor is capable of this task, but only if it is placed close to the LT8610 (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT8610. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8610 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8610’s voltage rating. This situation is easily avoided (see Linear Technology Application Note 88). Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT8610 to produce the DC output. In this role it determines the output ripple, thus low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT8610’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. For good starting values, see the Typical Applications section. Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between VOUT and FB. Increasing the output capacitance will also decrease the output voltage ripple. A lower value of output capacitor can be used to save space and cost but transient performance will suffer and may cause loop instability. See the Typical Applications in this data sheet for suggested capacitor values. When choosing a capacitor, special attention should be given to the data sheet to calculate the effective capacitance under the relevant operating conditions of voltage bias and temperature. A physically larger capacitor or one with a higher voltage rating may be required. Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT8610 due to their piezoelectric nature. When in Burst Mode operation, the LT8610’s switching frequency depends on the load current, and at very light loads the LT8610 can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT8610 operates at a lower current limit during Burst Mode operation, the noise is typically very quiet to a casual ear. If this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. Low noise ceramic capacitors are also available. 8610fa 14 For more information www.linear.com/LT8610 LT8610 APPLICATIONS INFORMATION A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LT8610. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (underdamped) tank circuit. If the LT8610 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8610’s rating. This situation is easily avoided (see Linear Technology Application Note 88). Enable Pin The LT8610 is in shutdown when the EN pin is low and active when the pin is high. The rising threshold of the EN comparator is 1.0V, with 40mV of hysteresis. The EN pin can be tied to VIN if the shutdown feature is not used, or tied to a logic level if shutdown control is required. Adding a resistor divider from VIN to EN programs the LT8610 to regulate the output only when VIN is above a desired voltage (see the Block Diagram). Typically, this threshold, VIN(EN), is used in situations where the input supply is current limited, or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. The VIN(EN) threshold prevents the regulator from operating at source voltages where the problems might occur. This threshold can be adjusted by setting the values R3 and R4 such that they satisfy the following equation: R3 VIN(EN) = +1 •1.0V R4 (10) where the LT8610 will remain off until VIN is above VIN(EN). Due to the comparator’s hysteresis, switching will not stop until the input falls slightly below VIN(EN). When operating in Burst Mode operation for light load currents, the current through the VIN(EN) resistor network can easily be greater than the supply current consumed by the LT8610. Therefore, the VIN(EN) resistors should be large to minimize their effect on efficiency at low loads. INTVCC Regulator An internal low dropout (LDO) regulator produces the 3.4V supply from VIN that powers the drivers and the internal bias circuitry. The INTVCC can supply enough current for the LT8610’s circuitry and must be bypassed to ground with a minimum of 1μF ceramic capacitor. Good bypassing is necessary to supply the high transient currents required by the power MOSFET gate drivers. To improve efficiency the internal LDO can also draw current from the BIAS pin when the BIAS pin is at 3.1V or higher. Typically the BIAS pin can be tied to the output of the LT8610, or can be tied to an external supply of 3.3V or above. If BIAS is connected to a supply other than VOUT, be sure to bypass with a local ceramic capacitor. If the BIAS pin is below 3.0V, the internal LDO will consume current from VIN. Applications with high input voltage and high switching frequency where the internal LDO pulls current from VIN will increase die temperature because of the higher power dissipation across the LDO. Do not connect an external load to the INTVCC pin. Output Voltage Tracking and Soft-Start The LT8610 allows the user to program its output voltage ramp rate by means of the TR/SS pin. An internal 2.2μA pulls up the TR/SS pin to INTVCC. Putting an external capacitor on TR/SS enables soft starting the output to prevent current surge on the input supply. During the soft-start ramp the output voltage will proportionally track the TR/SS pin voltage. For output tracking applications, TR/SS can be externally driven by another voltage source. From 0V to 0.97V, the TR/SS voltage will override the internal 0.97V reference input to the error amplifier, thus regulating the FB pin voltage to that of TR/SS pin. When TR/SS is above 0.97V, tracking is disabled and the feedback voltage will regulate to the internal reference voltage. The TR/SS pin may be left floating if the function is not needed. An active pull-down circuit is connected to the TR/SS pin which will discharge the external soft-start capacitor in the case of fault conditions and restart the ramp when the faults are cleared. Fault conditions that clear the soft-start capacitor are the EN/UV pin transitioning low, VIN voltage falling too low, or thermal shutdown. 8610fa For more information www.linear.com/LT8610 15 LT8610 APPLICATIONS INFORMATION Output Power Good When the LT8610’s output voltage is within the ±9% window of the regulation point, which is a VFB voltage in the range of 0.883V to 1.057V (typical), the output voltage is considered good and the open-drain PG pin goes high impedance and is typically pulled high with an external resistor. Otherwise, the internal pull-down device will pull the PG pin low. To prevent glitching both the upper and lower thresholds include 1.3% of hysteresis. The PG pin is also actively pulled low during several fault conditions: EN/UV pin is below 1V, INTVCC has fallen too low, VIN is too low, or thermal shutdown. Synchronization To select low ripple Burst Mode operation, tie the SYNC pin below 0.4V (this can be ground or a logic low output). To synchronize the LT8610 oscillator to an external frequency connect a square wave (with 20% to 80% duty cycle) to the SYNC pin. The square wave amplitude should have valleys that are below 0.4V and peaks above 2.4V (up to 6V). The LT8610 will not enter Burst Mode operation at low output loads while synchronized to an external clock, but instead will pulse skip to maintain regulation. The LT8610 may be synchronized over a 200kHz to 2.2MHz range. The RT resistor should be chosen to set the LT8610 switching frequency equal to or below the lowest synchronization input. For example, if the synchronization signal will be 500kHz and higher, the RT should be selected for 500kHz. The slope compensation is set by the RT value, while the minimum slope compensation required to avoid subharmonic oscillations is established by the inductor size, input voltage, and output voltage. Since the synchronization frequency will not change the slopes of the inductor current waveform, if the inductor is large enough to avoid subharmonic oscillations at the frequency set by RT, then the slope compensation will be sufficient for all synchronization frequencies. For some applications it is desirable for the LT8610 to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. Second is that full switching frequency is reached at lower output load than in Burst Mode operation. These 16 two differences come at the expense of increased quiescent current. To enable pulse-skipping mode, the SYNC pin is tied high either to a logic output or to the INTVCC pin. The LT8610 does not operate in forced continuous mode regardless of SYNC signal. Never leave the SYNC pin floating. Shorted and Reversed Input Protection The LT8610 will tolerate a shorted output. Several features are used for protection during output short-circuit and brownout conditions. The first is the switching frequency will be folded back while the output is lower than the set point to maintain inductor current control. Second, the bottom switch current is monitored such that if inductor current is beyond safe levels switching of the top switch will be delayed until such time as the inductor current falls to safe levels. Frequency foldback behavior depends on the state of the SYNC pin: If the SYNC pin is low the switching frequency will slow while the output voltage is lower than the programmed level. If the SYNC pin is connected to a clock source or tied high, the LT8610 will stay at the programmed frequency without foldback and only slow switching if the inductor current exceeds safe levels. There is another situation to consider in systems where the output will be held high when the input to the LT8610 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 LT8610’s output. If the VIN pin is allowed to float and the EN pin is held high (either by a logic signal or because it is tied to VIN), then the LT8610’s internal circuitry will pull its quiescent current through its SW pin. This is acceptable if the system can tolerate several μA in this state. If the EN pin is grounded the SW pin current will drop to near 1µA. However, if the VIN pin is grounded while the output is held high, regardless of EN, parasitic body diodes inside the LT8610 can pull current from the output through the SW pin and the VIN pin. Figure 3 shows a connection of the VIN and EN/UV pins that will allow the LT8610 to run only when the input voltage is present and that protects against a shorted or reversed input. For more information www.linear.com/LT8610 8610fa LT8610 APPLICATIONS INFORMATION D1 VIN VIN LT8610 GND EN/UV GND 8610 F03 1 16 TR/SS 2 15 RT 3 14 BIAS 4 13 INTVCC 5 12 6 11 7 10 8 9 SYNC Figure 3. Reverse VIN Protection PCB Layout EN/UV For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 4 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT8610’s VIN pins, PGND pins, and the input capacitor (C1). The loop formed by the input capacitor should be as small as possible by placing the capacitor adjacent to the VIN and PGND pins. When using a physically large input capacitor the resulting loop may become too large in which case using a small case/value capacitor placed close to the VIN and PGND pins plus a larger capacitor further away is preferred. These components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane under the application circuit on the layer closest to the surface layer. The SW and BOOST nodes should be as small as possible. Finally, keep the FB and RT nodes small so that the ground traces will shield them from the SW and BOOST nodes. The exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT8610 to additional ground planes within the circuit board and on the bottom side. High Temperature Considerations For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the LT8610. The exposed pad on the bottom of the package VIN VOUT FB PG BST SW GND VOUT VOUT LINE TO BIAS VIAS TO GROUND PLANE 8610 F04 OUTLINE OF LOCAL GROUND PLANE Figure 4. Recommended PCB Layout for the LT8610 must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread heat dissipated by the LT8610. Placing additional vias can reduce thermal resistance further. The maximum load current should be derated as the ambient temperature approaches the maximum junction rating. Power dissipation within the LT8610 can be estimated by calculating the total power loss from an efficiency measurement and subtracting the inductor loss. The die temperature is calculated by multiplying the LT8610 power dissipation by the thermal resistance from junction to ambient. The LT8610 will stop switching and indicate a fault condition if safe junction temperature is exceeded. 8610fa For more information www.linear.com/LT8610 17 LT8610 TYPICAL APPLICATIONS 5V Step-Down Converter VIN 5.5V TO 42V VIN 4.7µF BST EN/UV LT8610 0.1µF 2.5µH SW SYNC BIAS TR/SS PG 10nF 3.3V Step-Down Converter VOUT 5V 47µF 2.5A VIN 3.8V TO 27V (42V TRANSIENT) INTVCC RT PGND GND FB 1M POWER GOOD INTVCC RT PGND GND 4.7µF BST EN/UV LT8610 SYNC 0.1µF 10µH SW BIAS 10nF TR/SS PG INTVCC RT PGND GND 110k fSW = 400kHz FB 1M 8610 TA04 3.3V Step-Down Converter VIN 3.8V TO 42V 4.7µF VOUT 5V 2.5A 68µF VIN BST EN/UV PG SYNC LT8610 0.1µF 8.2µH SW BIAS VOUT 3.3V 2.5A 68µF 10nF 100k 1µF 4.7pF 412k fSW = 2MHz 8610 TA02 VIN VOUT 3.3V 2.5A 47µF 1M FB 18.2k 5V Step-Down Converter VIN 5.5V TO 42V BIAS TR/SS 1µF 243k fSW = 2MHz SW LT8610 SYNC 0.1µF 1.8µH 10nF 10pF 18.2k BST EN/UV PG 100k 1µF VIN 4.7µF POWER GOOD 1µF TR/SS INTVCC RT PGND GND 10pF 110k 243k fSW = 400kHz 8610 TA03 FB 1M 4.7pF 412k 8610 TA05 8610fa 18 For more information www.linear.com/LT8610 LT8610 TYPICAL APPLICATIONS 12V Step-Down Converter VIN 12.5V TO 42V 4.7µF VIN BST EN/UV LT8610 SYNC 1.8V Step-Down Converter VIN 3.4V TO 42V 0.1µF 10µH VOUT 12V 47µF 2.5A SW BIAS 10nF 4.7µF TR/SS PG INTVCC RT PGND GND FB 41.2k 1M LT8610 0.1µF 4.7µH SW BIAS SYNC VOUT 1.8V 120µF 2.5A 10nF POWER GOOD 1µF TR/SS INTVCC RT PGND GND 10pF FB 110k 88.7k fSW = 1MHz BST EN/UV PG 100k 1µF VIN 4.7pF 1M fSW = 400kHz 8610 TA09 866k 8610 TA07 1.8V 2MHz Step-Down Converter VIN 3.4V TO 15V (42V TRANSIENT) VIN 4.7µF BST 0.1µF 1µH EN/UV PG LT8610 VOUT 1.8V 68µF 2.5A SW BIAS SYNC 10nF TR/SS 1µF INTVCC RT PGND GND 866k FB 4.7pF 18.2k 1M fSW = 2MHz 8610 TA06 Ultralow EMI 5V 2.5A Step-Down Converter VIN 5.5V TO 42V FB1 BEAD 4.7µF 4.7µH 4.7µF 4.7µF VIN PG SYNC 10nF 1µF BST EN/UV LT8610 0.1µF 4.7µH SW BIAS TR/SS FB VOUT 5V 47µF 2.5A 1M 10pF INTVCC RT PGND GND 52.3k 243k FB1: TDK MPZ2012S221A fSW = 800kHz 8610 TA11 8610fa For more information www.linear.com/LT8610 19 LT8610 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev E) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ± 0.102 (.112 ± .004) 5.23 (.206) MIN 2.845 ± 0.102 (.112 ± .004) 0.889 ± 0.127 (.035 ± .005) 8 1 1.651 ± 0.102 (.065 ± .004) 1.651 ± 0.102 3.20 – 3.45 (.065 ± .004) (.126 – .136) 0.305 ± 0.038 (.0120 ± .0015) TYP 16 0.50 (.0197) BSC 4.039 ± 0.102 (.159 ± .004) (NOTE 3) RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) 0.35 REF 0.12 REF DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY 9 NO MEASUREMENT PURPOSE 0.280 ± 0.076 (.011 ± .003) REF 16151413121110 9 DETAIL “A” 0° – 6° TYP 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) GAUGE PLANE 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 1.10 (.043) MAX 0.18 (.007) SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP 1234567 8 0.50 (.0197) BSC NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 0.86 (.034) REF 0.1016 ± 0.0508 (.004 ± .002) MSOP (MSE16) 0911 REV E 8610fa 20 For more information www.linear.com/LT8610 LT8610 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 10/13 Added H-grade version ABS Max table, Order Information 2 Clarified Feedback Voltage specification to 150°C 2 Clarified 3.3V and 5V Efficiency graphs 4 Clarified RT Programmed Switching Frequency graph 7 8610fa 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 its circuits as described herein will not infringe on existing patent rights. For of more information www.linear.com/LT8610 21 LT8610 TYPICAL APPLICATION 3.3V and 1.8V with Ratio Tracking VIN 3.8V TO 42V 4.7µF VIN BST EN/UV PG LT8610 Ultralow IQ 2.5V, 3.3V Step-Down with LDO VIN 3.8V TO 27V 0.1µF 5.6µH SW SYNC 10nF VIN 4.7µF VOUT1 3.3V 47µF 2.5A BST EN/UV PG LT8610 SYNC 0.1µF 1.8µH VOUT1 3.3V 47µF 2.5A SW BIAS 10nF 1µF BIAS TR/SS INTVCC RT PGND GND FB 232k TR/SS 1µF 4.7pF 88.7k INTVCC RT PGND GND 97.6k 18.2k fSW = 500kHz fSW = 2MHz FB 1M 4.7pF IN 412k OUT LT3008-2.5 VOUT2 2.5V 2.2µF 20mA SHDN SENSE 8610 TA10 4.7µF VIN BST EN/UV PG LT8610 0.1µF 3.3µH VOUT2 1.8V 2.5A 68µF SW SYNC 24.3k TR/SS 10k 1µF BIAS INTVCC RT PGND GND 88.7k fSW = 500kHz FB 80.6k 4.7pF 93.1k 8610 TA08 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT8611 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous Micropower Step-Down DC/DC Converter with IQ = 2.5µA and Input/Output Current Limit/Monitor VIN: 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 3mm × 5mm QFN-24 Package LT3690 36V with 60V Transient Protection, 4A, 92% Efficiency, 1.5MHz Synchronous Micropower Step-Down DC/DC Converter with IQ = 70µA VIN: 3.9V to 36V, VOUT(MIN) = 0.985V, IQ = 70µA, ISD < 1µA, 4mm × 6mm QFN-26 Package LT3971 38V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC Converter with IQ = 2.8µA VIN: 4.2V to 38V, VOUT(MIN) = 1.21V, IQ = 2.8µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages LT3991 55V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC Converter with IQ = 2.8µA VIN: 4.2V to 55V, VOUT(MIN) = 1.21V, IQ = 2.8µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages LT3970 40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC Converter with IQ = 2.5µA VIN: 4.2V to 40V, VOUT(MIN) = 1.21V, IQ = 2.5µA, ISD < 1µA, 3mm × 2mm DFN-10 and MSOP-10 Packages LT3990 62V, 350mA, 2.2MHz High Efficiency MicroPower Step-Down DC/DC Converter with IQ = 2.5µA VIN: 4.2V to 62V, VOUT(MIN) = 1.21V, IQ = 2.5µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-6E Packages LT3480 36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High Efficiency Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.6V to 36V, Transient to 60V, VOUT(MIN) = 0.78V, IQ = 70µA, ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages LT3980 58V with Transient Protection to 80V, 2A (IOUT), 2.4MHz, High Efficiency Step-Down DC/DC Converter with Burst Mode Operation VIN: 3.6V to 58V, Transient to 80V, VOUT(MIN) = 0.78V, IQ = 85µA, ISD < 1µA, 3mm × 4mm DFN-16 and MSOP-16E Packages 8610fa 22 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LT8610 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT8610 LT 1013 REV A • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2012