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| FEATURES n n n n n n n n n n n n n n n n n LTC3611 10A, 32V Monolithic Synchronous Step-Down DC/DC Converter DESCRIPTION The LTC(R)3611 is a high efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 10A output current from a 4.5V to 32V (36V maximum) input supply. It uses a constant on-time valley current mode control architecture to deliver very low duty cycle operation at high frequency with excellent transient response. The operating frequency is selected by an external resistor and is compensated for variations in VIN and VOUT. The LTC3611 can be configured for discontinuous or forced continuous operation at light load. Forced continuous operation reduces noise and RF interference while discontinuous mode provides high efficiency by reducing switching losses at light loads. Fault protection is provided by internal foldback current limiting, an output overvoltage comparator and an optional short-circuit shutdown timer. Soft-start capability for supply sequencing is accomplished using an external timing capacitor. The regulator current limit is user programmable. A power good output voltage monitor indicates when the output is in regulation. The LTC3611 is available in a compact 9mm x 9mm QFN package. 10A Output Current Wide VIN Range = 4.5V to 32V (36V Maximum) Internal N-Channel MOSFETs True Current Mode Control Optimized for High Step-Down Ratios t0N(MIN) 100ns Extremely Fast Transient Response Stable with Ceramic COUT 1% 0.6V Voltage Reference Power Good Output Voltage Monitor Adjustable On-Time/Switching Frequency (>1MHz) Adjustable Current Limit Programmable Soft-Start Output Overvoltage Protection Optional Short-Circuit Shutdown Timer Low Shutdown IQ: 15A Available in a 9mm x 9mm 64-Pin QFN Package APPLICATIONS n n Point of Load Regulation Distributed Power Systems L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 6100678, 6580258, 5847554, 6304066. TYPICAL APPLICATION High Efficiency Step-Down Converter 0.1F VOUT 182k VON RUN/SS 100pF LTC3611 1H SW 680pF 12.5k ITH SGND 39.2k INTVCC 11k VRNG PGOOD EXTVCC PGND VFB 3611 TA01a Efficiency and Power Loss vs Load Current 100 90 VIN 4.5V TO 32V EFFICIENCY (%) 80 70 60 50 40 30 20 POWER LOSS, VIN = 25V 1 0.1 1 LOAD CURRENT (A) 10 3611 TA01b VOUT = 2.5V VIN = 5V VIN = 25V 10000 ION VIN 10F x3 1000 POWER LOSS (mW) 0.22F BOOST INTVCC FCB 4.7F 100F x2 VOUT 2.5V 10A POWER LOSS, VIN = 5V 100 10 30.1k 10 0 0.01 9.5k 3611fb 1 LTC3611 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION TOP VIEW 54 INTVCC 53 INTVCC 64 PGND 63 PGND 62 PGND 61 PGND 60 PGND 59 PGND 58 PGND 57 PGND 56 PGND 50 SGND 49 SGND 52 SVIN 51 SVIN 55 SW Input Supply Voltage (VIN, ION) .................. 36V to -0.3V Boosted Topside Driver Supply Voltage (BOOST) ................................................ 42V to -0.3V SW Voltage ............................................... 36V to -5V INTVCC, EXTVCC, (BOOST - SW), RUN/SS, PGOOD Voltages ...................................... 7V to -0.3V FCB, VON, VRNG Voltages............ INTVCC + 0.3V to -0.3V ITH, VFB Voltages ....................................... 2.7V to -0.3V Operating Temperature Range (Note 4) ............................................. -40C to 125C Junction Temperature (Note 2) ............................. 125C Storage Temperature Range...................-55C to 125C PGND 1 PGND 2 PGND 3 SW 4 SW 5 SW 6 SW 7 SW 8 SW 9 SW 10 SW 11 PVIN 12 PVIN 13 PVIN 14 PVIN 15 PVIN 16 65 PGND 48 SGND 47 SGND 46 SGND 45 SGND 44 EXTVCC 43 VFB 66 SW 42 SGND 41 ION 40 SGND 39 FCB 68 SGND 38 ITH 37 VRNG 36 PGOOD 35 VON 34 SGND 33 SGND 67 PVIN SGND 28 BOOST 29 RUN/SS 30 SGND 31 WP PACKAGE 64-LEAD (9mm x 9mm) QFN MULTIPAD TJMAX = 125C, JA = 28C/W ORDER INFORMATION LEAD FREE FINISH LTC3611EWP#PBF LTC3611IWP#PBF LEAD BASED FINISH LTC3611EWP LTC3611IWP TAPE AND REEL LTC3611EWP#TRPBF LTC3611IWP#TRPBF TAPE AND REEL LTC3611EWP#TR LTC3611IWP#TR PART MARKING* LTC3611WP LTC3611WP PART MARKING* LTC3611WP LTC3611WP PACKAGE DESCRIPTION 64-Lead (9mm x 9mm) Plastic QFN 64-Lead (9mm x 9mm) Plastic QFN PACKAGE DESCRIPTION 64-Lead (9mm x 9mm) Plastic QFN 64-Lead (9mm x 9mm) Plastic QFN TEMPERATURE RANGE -40C to 125C -40C to 125C TEMPERATURE RANGE -40C to 125C -40C to 125C 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/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ SGND 32 PVIN 17 PVIN 18 PVIN 19 PVIN 20 PVIN 21 PVIN 22 PVIN 23 PVIN 24 PVIN 25 SW 26 NC 27 3611fb 2 LTC3611 ELECTRICAL CHARACTERISTICS SYMBOL Main Control Loop VIN IQ Operating Input Voltage Range Input DC Supply Current Normal Shutdown Supply Current Feedback Reference Voltage LTC3611E LTC3611I Feedback Voltage Line Regulation Feedback Voltage Load Regulation Feedback Input Current Error Amplifier Transconductance Forced Continuous Threshold Forced Continuous Pin Current On-Time Minimum On-Time Minimum Off-Time Maximum Valley Current Maximum Reverse Valley Current Output Overvoltage Fault Threshold RUN Pin Start Threshold RUN Pin Latchoff Enable Threshold RUN Pin Latchoff Threshold Soft-Start Charge Current Soft-Start Discharge Current Undervoltage Lockout Undervoltage Lockout Release Top Switch On-Resistance Bottom Switch On-Resistance RUN/SS Pin Rising RUN/SS Pin Falling VRUN/SS = 0V VRUN/SS = 4.5V, VFB = 0V VIN Falling VIN Rising l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 15V unless otherwise noted. PARAMETER CONDITIONS MIN 4.5 900 15 ITH = 1.2V (Note 3) -40C TJ 85C -40C TJ 125C VIN = 4V to 30V, ITH = 1.2V (Note 3) ITH = 0.5V to 1.9V (Note 3) VFB = 0.6V ITH = 1.2V (Note 3) VFCB = 0.6V ION = 60A, VON = 1.5V ION = 60A, VON = 0V ION = 180A, VON = 0V ION = 30A, VON = 1.5V VRNG = 0V, VFB = 0.56V, FCB = 0V VRNG = 1V, VFB = 0.56V, FCB = 0V VRNG = 0V, VFB = 0.64V, FCB = 0V VRNG = 1V, VFB = 0.64V, FCB = 0V l l l l TYP MAX 32 2000 30 0.606 0.610 -0.3 50 2 0.66 -2 310 100 500 UNITS V A A V V %/V % nA mS V A ns ns ns ns A A VFB l 0.594 0.590 0.600 0.600 0.002 -0.05 -5 VFB(LINEREG) VFB(LOADREG) IFB gm(EA) VFCB IFCB tON tON(MIN) tOFF(MIN) IVALLEY(MAX) IVALLEY(MIN) VFB(OV) VRUN/SS(ON) VRUN/SS(LE) VRUN/SS(LT) IRUN/SS(C) IRUN/SS(D) VIN(UVLO) VIN(UVLOR) RDS(ON) 1.4 0.54 190 1.7 0.6 -1 250 120 60 290 6 8 -4 -6 7 0.8 10 15 -6 -8 10 1.5 4 3.5 -8 -10 13 2 4.5 4.2 -3 3 3.9 4 22 14 A A % V V V A A V V m m -0.5 0.8 -1.2 1.8 3.4 3.5 15 9 3611fb 3 LTC3611 ELECTRICAL CHARACTERISTICS SYMBOL VINTVCC VLDO(LOADREG) VEXTVCC VEXTVCC VEXTVCC(HYS) PGOOD Output VFBH VFBL VFB(HYS) VPGL PGOOD Upper Threshold PGOOD Lower Threshold PGOOD Hysteresis PGOOD Low Voltage VFB Rising VFB Falling VFB Returning IPGOOD = 5mA 7 -7 10 -10 1 0.15 13 -13 2.5 0.4 % % % V PARAMETER Internal VCC Voltage Internal VCC Load Regulation EXTVCC Switchover Voltage EXTVCC Switch Drop Voltage EXTVCC Switchover Hysteresis Internal VCC Regulator 6V < VIN < 30V, VEXTVCC = 4V ICC = 0mA to 20mA, VEXTVCC = 4V ICC = 20mA, VEXTVCC Rising ICC = 20mA, VEXTVCC = 5V l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 15V unless otherwise noted. CONDITIONS MIN 4.7 4.5 TYP 5 -0.1 4.7 150 500 300 MAX 5.6 2 UNITS V % V m/V m/V 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: TJ is calculated from the ambient temperature TA and power dissipation PD as follows: TJ = TA + (PD * 28C/W) (JA is simulated per JESD51-7 high effective thermal conductivity test board) JC = 1C/W (JC is simulated when heatsink is applied at the bottom of the package) Note 3: The LTC3611 is tested in a feedback loop that adjusts VFB to achieve a specified error amplifier output voltage (ITH). The specification at 85C is not tested in production. This specification is assured by design, characterization, and correlation to testing at 125C. Note 4: The LTC3611E is guaranteed to meet performance specifications from 0C to 125C. Specifications over the -40C to 125C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3611I is guaranteed over the full -40C to 125C operating temperature range. TYPICAL PERFORMANCE CHARACTERISTICS Transient Response VOUT 200mV/DIV VOUT 200mV/DIV RUN/SS 2V/DIV IL 5A/DIV ILOAD 5A/DIV 40s/DIV LOAD STEP 0A TO 8A VIN = 25V VOUT = 2.5V FCB = 0 FIGURE 6 CIRCUIT 3611 G01 Transient Response (Discontinuous Mode) Start-Up IL 5A/DIV ILOAD 5A/DIV 40s/DIV LOAD = 1A TO 10A VIN = 25V VOUT = 2.5V FCB = INTVCC FIGURE 6 CIRCUIT 3611 G02 VOUT 1V/DIV IL 5A/DIV 40ms/DIV VIN = 25V VOUT = 2.5V RLOAD = 0.5 FIGURE 6 CIRCUIT 3611 G03 3611fb 4 LTC3611 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency vs Load Current 100 DISCONTINUOUS 90 95 FREQUENCY (kHz) EFFICIENCY (%) 80 CONTINUOUS 70 VIN = 12V VOUT = 2.5V EXTVCC = 5V FIGURE 6 CIRCUIT 0.1 1 LOAD CURRENT (A) 10 3611 G04 Efficiency vs Input Voltage 100 FCB = 5V FIGURE 6 CIRCUIT 640 Frequency vs Input Voltage ILOAD = 10A 600 EFFICIENCY (%) 560 520 480 440 400 5 FCB = 0V FIGURE 6 CIRCUIT 10 15 20 25 INPUT VOLTAGE (V) 30 35 3611 G06 90 ILOAD = 10A 85 ILOAD = 1A 80 5 10 20 25 15 INPUT VOLTAGE (V) 30 35 3611 G05 ILOAD = 0A 60 50 0.01 Frequency vs Load Current 650 600 550 500 450 400 350 300 250 200 150 100 50 0 0 2 0.80 CONTINUOUS MODE 0.60 Load Regulation FIGURE 6 CIRCUIT 2.5 ITH Voltage vs Load Current FIGURE 6 CIRCUIT 2.0 0.40 VOUT (%) 0.20 0 ITH VOLTAGE (V) FREQUENCY (kHz) DISCONTINUOUS MODE 1.5 CONTINUOUS MODE -0.20 -0.40 -0.60 -0.80 1.0 DISCONTINUOUS MODE 0.5 4 6 LOAD CURRENT (A) 8 10 3611 G07 0 2 4 6 LOAD CURRENT (A) 8 10 3611 G08 0 0 5 10 LOAD CURRENT (A) 15 3611 G09 Load Current vs ITH Voltage and VRNG 25 20 VRNG = 1V LOAD CURRENT (A) 15 ON-TIME (ns) 0.7V 10 5 0 0.5V 1000 10000 On-Time vs ION Current VVON = 0V 1000 On-Time vs VON Voltage ION = 30A 800 ON-TIME (ns) 600 400 100 200 -5 -10 0 0.5 1.5 2 1 ITH VOLTAGE (V) 2.5 3 3611 G10 10 1 10 ION CURRENT (A) 100 3611 G11 0 0 1 2 VON VOLTAGE (V) 3 3611 G12 3611fb 5 LTC3611 TYPICAL PERFORMANCE CHARACTERISTICS On-Time vs Temperature 300 250 200 150 100 50 0 -50 -25 20 MAXIMUM VALLEY CURRENT LIMIT (A) MAXIMUM VALLEY CURRENT LIMIT (A) IION = 30A VVON = 0V Maximum Valley Current Limit vs VRNG Voltage 18 15 12 9 6 3 Maximum Valley Current Limit vs RUN/SS Voltage FIGURE 6 CIRCUIT ON-TIME (ns) 15 10 0 50 25 75 TEMPERATURE (C) 100 125 5 0.5 0.6 0.8 0.7 VRNG VOLTAGE (V) 0.9 1 3611 G15 0 1.65 1.9 2.15 2.4 2.65 2.9 3.15 3.4 RUN/SS VOLTAGE (V) 3611 G16 3611 G13 Maximum Valley Current Limit vs Temperature 20 MAXIMUM VALLEY CURRENT LIMIT (A) VRNG = 1V MAXIMUM VALLEY CURRENT (A) 18 16 14 12 10 8 6 4 Input Voltage vs Maximum Valley Current 20 MAXIMUM VALLEY CURRENT LIMIT (A) Maximum Valley Current Limit in Foldback VRNG = 1V 15 15 10 10 5 5 0 -50 -25 25 50 75 0 TEMPERATURE (C) 100 125 0 4 8 12 16 20 24 28 INPUT VOLTAGE (V) 32 36 0 0.1 0.2 0.3 0.4 VFB (V) 0.5 0.6 3611 G14 3611 G17 3611 G27 Feedback Reference Voltage vs Temperature 0.62 FEEDBACK REFERENCE VOLTAGE (V) 2.0 Error Amplifier gm vs Temperature 0.61 gm (mS) -25 75 0 25 50 TEMPERATURE (C) 100 125 1.8 1.6 0.60 1.4 0.59 1.2 0.58 -50 1.0 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 3611 G18 3611 G19 3611fb 6 LTC3611 TYPICAL PERFORMANCE CHARACTERISTICS Input and Shutdown Currents vs Input Voltage 1400 1200 INPUT CURRENT (A) 1000 800 SHUTDOWN 600 15 400 200 0 0 5 10 20 15 INPUT VOLTAGE (V) 25 30 3611 G20 INTVCC Load Regulation 40 0.30 0.20 SHUTDOWN CURRENT (A) 0.10 INTVCC (%) 0 IEXTVCC (mA) 30 25 20 15 10 -0.20 -0.30 -0.40 5 35 30 25 20 IEXTVCC vs Frequency VIN = 24V VOUT = 2.5V EXTVCC OPEN -0.10 EXTVCC = 5V 10 5 0 0 40 10 20 30 INTVCC LOAD CURRENT (mA) 50 3611 G21 0 400 500 700 800 600 FREQUENCY (KHz) 900 1000 3611 G28 EXTVCC Switch Resistance vs Temperature 10 EXTVCC SWITCH RESISTANCE () 0 -0.25 -0.50 -0.75 -1.00 -1.25 FCB Pin Current vs Temperature 3 RUN/SS Pin Current vs Temperature RUN/SS PIN CURRENT (A) 8 FCB PIN CURRENT (A) 2 PULL-DOWN CURRENT 1 6 4 0 2 -1 PULL-UP CURRENT 0 -50 -25 0 50 75 25 TEMPERATURE (C) 100 125 -1.50 -50 -25 0 50 25 75 TEMPERATURE (C) 100 125 -2 -50 -25 0 50 75 25 TEMPERATURE (C) 100 125 3611 G24 3611 G23 3611 G22 RUN/SS Pin Current vs Temperature UNDERVOLTAGE LOCKOUT THRESHOLD (V) 100 125 5.0 4.0 Undervoltage Lockout Threshold vs Temperature RUN/SS PIN CURRENT (A) 4.5 LATCHOFF ENABLE 4.0 3.5 3.0 3.5 LATCHOFF THRESHOLD 2.5 3.0 -50 -25 75 0 25 50 TEMPERATURE (C) 2.0 -50 -25 3611 G25 75 0 25 50 TEMPERATURE (C) 100 125 3611 G26 3611fb 7 LTC3611 PIN FUNCTIONS PGND (Pins 1, 2, 3, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65): Power Ground. Connect this pin closely to the (-) terminal of CVCC and the (-) terminal of CIN. SW (Pins 4, 5, 6, 7, 8, 9, 10, 11, 26, 55, 66): Switch Node Connection to the Inductor. The (-) terminal of the bootstrap capacitor CB also connects here. This pin swings from a diode voltage drop below ground up to VIN. PVIN (Pins 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 67): Main Input Supply. Decouple this pin to power PGND with the input capacitance CIN. NC (Pin 27): No Connection. SGND (Pins 28, 31, 32, 33, 34, 40, 42, 45, 46, 47, 48, 49, 50, 68): Signal Ground. All small-signal components and compensation components should connect to this ground, which in turn connects to PGND at one point. BOOST (Pin 29): Boosted Floating Driver Supply. The (+) terminal of the bootstrap capacitor CB connects here. This pin swings from a diode voltage drop below INTVCC up to VIN + INTVCC. RUN/SS (Pin 30): Run Control and Soft-Start Input. A capacitor to ground at this pin sets the ramp time to full output current (approximately 3s/F) and the time delay for overcurrent latchoff (see Applications Information). Forcing this pin below 0.8V shuts down the device. VON (Pin 35): On-Time Voltage Input. Voltage trip point for the on-time comparator. Tying this pin to the output volt-age or an external resistive divider from the output makes the on-time proportional to VOUT. The comparator input defaults to 0.7V when the pin is grounded and defaults to 2.4V when the pin is tied to INTVCC. Tie this pin to INTVCC in high VOUT applications to use a lower RON value. PGOOD (Pin 36): Power Good Output. Open drain logic output that is pulled to ground when the output voltage is not within 10% of the regulation point. VRNG (Pin 37): Current Limit Range Input. The voltage at this pin adjusts maximum valley current and can be set from 0.7V to 1V by a resistive divider from INTVCC. It defaults to 0.7V if the VRNG pin is tied to ground which results in a typical 10A current limit. ITH (Pin 38): Current Control Threshold and Error Amplifier Compensation Point. The current comparator threshold increases with this control voltage. The voltage ranges from 0V to 2.4V with 0.8V corresponding to zero sense voltage (zero current). FCB (Pin 39): Forced Continuous Input. Tie this pin to ground to force continuous synchronous operation at low load, to INTVCC to enable discontinuous mode operation at low load or to a resistive divider from a secondary output when using a secondary winding. ION (Pin 41): On-Time Current Input. Tie a resistor from VIN to this pin to set the one-shot timer current and thereby set the switching frequency. VFB (Pin 43): Error Amplifier Feedback Input. This pin connects the error amplifier input to an external resistive divider from VOUT. EXTVCC (Pin 44): External VCC Input. When EXTVCC exceeds 4.7V, an internal switch connects this pin to INTVCC and shuts down the internal regulator so that controller and gate drive power is drawn from EXTVCC. Do not exceed 7V at this pin and ensure that EXTVCC < VIN. SVIN (Pins 51, 52): Supply pin for internal PWM controller. INTVCC (Pins 53, 54): Internal 5V Regulator Output. The driver and control circuits are powered from this voltage. Decouple this pin to power ground with a minimum of 4.7F low ESR tantalum or ceramic capacitor. 3611fb 8 LTC3611 FUNCTIONAL DIAGRAM RON VON 35 ION 41 FCB 39 4.7V 0.7V 2.4V 1A EXTVCC 44 51, 52 PVIN SVIN + 0.6V - 0.6V REF 5V REG 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 67 CIN - F VVON tON = (10pF) IION + 29 INTVCC 53, 54 BOOST R S Q FCNT ON M1 CB + ICMP 20k + IREV SWITCH LOGIC SW 4, 5, 6, 7, 8, 9, 10, 11, 26, 55, 66 DB L1 VOUT - 1.4V - SHDN + COUT M2 PGND 1, 2, 3, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65 36 PGOOD CVCC OV VRNG 37 x (0.5 TO 2) 0.7V 1 240k Q2 Q4 ITHB Q6 1V UV + - R2 0.54V 43 Q3 Q1 OV VFB R1 + - SS RUN SHDN 1.2A 27 6V 0.6V 38 ITH NC 0.66V SGND 28, 31, 32, 33, 34, 40, 42, 45, 46, 47, 48, 49, 50, 68 + - 0.8V x3.3 EA + - + - - + 0.4V 30 RUN/SS CSS 3611 FD 3611fb 9 LTC3611 OPERATION Main Control Loop The LTC3611 is a high efficiency monolithic synchronous, step-down DC/DC converter utilizing a constant on-time, current mode architecture. It operates from an input voltage range of 4.5V to 32V and provides a regulated output voltage at up to 10A of output current. The internal synchronous power switch increases efficiency and eliminates the need for an external Schottky diode. In normal operation, the top MOSFET is turned on for a fixed interval determined by a one-shot timer OST. When the top MOSFET is turned off, the bottom MOSFET is turned on until the current comparator ICMP trips, restarting the one-shot timer and initiating the next cycle. Inductor current is determined by sensing the voltage between the PGND and SW pins using the bottom MOSFET on-resistance. The voltage on the ITH pin sets the comparator threshold corresponding to inductor valley current. The error amplifier EA adjusts this voltage by comparing the feedback signal VFB from the output voltage with an internal 0.6V reference. If the load current increases, it causes a drop in the feedback voltage relative to the reference. The ITH voltage then rises until the average inductor current again matches the load current. At light load, the inductor current can drop to zero and become negative. This is detected by current reversal comparator IREV which then shuts off M2 (see Functional Diagram), resulting in discontinuous operation. Both switches will remain off with the output capacitor supplying the load current until the ITH voltage rises above the zero current level (0.8V) to initiate another cycle. Discontinuous mode operation is disabled by comparator F when the FCB pin is brought below 0.6V, forcing continuous synchronous operation. The operating frequency is determined implicitly by the top MOSFET on-time and the duty cycle required to maintain regulation. The one-shot timer generates an on-time that is proportional to the ideal duty cycle, thus holding frequency approximately constant with changes in VIN. The nominal frequency can be adjusted with an external resistor RON. Overvoltage and undervoltage comparators OV and UV pull the PGOOD output low if the output feedback voltage exits a 10% window around the regulation point. Furthermore, in an overvoltage condition, M1 is turned off and M2 is turned on and held on until the overvoltage condition clears. Foldback current limiting is provided if the output is shorted to ground. As VFB drops, the buffered current threshold voltage ITHB is pulled down by clamp Q3 to a 1V level set by Q4 and Q6. This reduces the inductor valley current level to one sixth of its maximum value as VFB approaches 0V. Pulling the RUN/SS pin low forces the controller into its shutdown state, turning off both M1 and M2. Releasing the pin allows an internal 1.2A current source to charge up an external soft-start capacitor CSS. When this voltage reaches 1.5V, the controller turns on and begins switching, but with the ITH voltage clamped at approximately 0.6V below the RUN/SS voltage. As CSS continues to charge, the soft-start current limit is removed. INTVCC/EXTVCC Power Power for the top and bottom MOSFET drivers and most of the internal controller circuitry is derived from the INTVCC pin. The top MOSFET driver is powered from a floating bootstrap capacitor CB. This capacitor is recharged from INTVCC through an external Schottky diode DB when the top MOSFET is turned off. When the EXTVCC pin is grounded, an internal 5V low dropout regulator supplies the INTVCC power from VIN. If EXTVCC rises above 4.7V, the internal regulator is turned off, and an internal switch connects EXTVCC to INTVCC. This allows a high efficiency source connected to EXTVCC, such as an external 5V supply or a secondary output from the converter, to provide the INTVCC power. Voltages up to 7V can be applied to EXTVCC for additional gate drive. If the input voltage is low and INTVCC drops below 3.5V, undervoltage lockout circuitry prevents the power switches from turning on. 3611fb 10 LTC3611 APPLICATIONS INFORMATION The basic LTC3611 application circuit is shown on the front page of this data sheet. External component selection is primarily determined by the maximum load current. The LTC3611 uses the on-resistance of the synchronous power MOSFET for determining the inductor current. The desired amount of ripple current and operating frequency also determines the inductor value. Finally, CIN is selected for its ability to handle the large RMS current into the converter and COUT is chosen with low enough ESR to meet the output voltage ripple and transient specification. VON and PGOOD The LTC3611 has an open-drain PGOOD output that indicates when the output voltage is within 10% of the regulation point. The LTC3611 also has a VON pin that allows the on-time to be adjusted. Tying the VON pin high results in lower values for RON which is useful in high VOUT applications. The VON pin also provides a means to adjust the on-time to maintain constant frequency operation in applications where VOUT changes and to correct minor frequency shifts with changes in load current. VRNG Pin and ILIMIT Adjust The VRNG pin is used to adjust the maximum inductor valley current, which in turn determines the maximum average output current that the LTC3611 can deliver. The maximum output current is given by: IOUT(MAX) = IVALLEY(MAX) + 1/2 IL, The IVALLEY(MAX) is shown in the figure "Maximum Valley Current Limit vs VRNG Voltage" in the Typical Performance Characteristics. An external resistor divider from INTVCC can be used to set the voltage on the VRNG pin from 1V to 1.4V, or it can be simply tied to ground force a default value equivalent to 0.7V. Do not float the VRNG pin. Operating Frequency The choice of operating frequency is a tradeoff between efficiency and component size. Low frequency operation improves efficiency by reducing MOSFET switching losses but requires larger inductance and/or capacitance in order to maintain low output ripple voltage. The operating frequency of LTC3611 applications is determined implicitly by the one-shot timer that controls the on-time tON of the top MOSFET switch. The on-time is set by the current into the ION pin and the voltage at the VON pin according to: tON = VVON (10pF) IION Tying a resistor RON from VIN to the ION pin yields an on-time inversely proportional to VIN. The current out of the ION pin is: IION = VIN RON For a step-down converter, this results in approximately constant frequency operation as the input supply varies: f= VVON VOUT [Hz] RON (10pF) To hold frequency constant during output voltage changes, tie the VON pin to VOUT or to a resistive divider from VOUT when VOUT > 2.4V. The VON pin has internal clamps that limit its input to the one-shot timer. If the pin is tied below 0.7V, the input to the one-shot is clamped at 0.7V. Similarly, if the pin is tied above 2.4V, the input is clamped at 2.4V. In high VOUT applications, tying VON to INTVCC so that the comparator input is 2.4V results in a lower value for RON. Figures 1a and 1b show how RON relates to switching frequency for several common output voltages. 3611fb 11 LTC3611 APPLICATIONS INFORMATION 1000 VOUT = 3.3V VOUT = 1.5V VOUT = 2.5V 100 100 1000 RON (k) 10000 3611 F01a as current increases, constant frequency operation can be maintained. This is accomplished with a resistive divider from the ITH pin to the VON pin and VOUT. The values required will depend on the parasitic resistances in the specific application. A good starting point is to feed about 25% of the voltage change at the ITH pin to the VON pin as shown in Figure 2a. Place capacitance on the VON pin to filter out the ITH variations at the switching frequency. The resistor load on ITH reduces the DC gain of the error amp and degrades load regulation, which can be avoided by using the PNP emitter follower of Figure 2b. Minimum Off-time and Dropout Operation The minimum off-time tOFF(MIN) is the smallest amount of time that the LTC3611 is capable of turning on the bottom MOSFET, tripping the current comparator and turning the MOSFET back off. This time is generally about 250ns. The minimum off-time limit imposes a maximum duty cycle of tON/(tON + tOFF(MIN)). If the maximum duty cycle is reached, due to a dropping input voltage for example, then the output will drop out of regulation. The minimum input voltage to avoid dropout is: Figure 1a. Switching Frequency vs RON (VON = 0V) 1000 SWITCHING FREQUENCY (kHz) SWITCHING FREQUENCY (kHz) VOUT = 12V VOUT = 5V VOUT = 3.3V 100 100 1000 RON (k) 10000 3611 F01b VIN(MIN) = VOUT tON + tOFF(MIN) tON Figure 1b. Switching Frequency vs RON (VON = INTVCC) Because the voltage at the ION pin is about 0.7V, the current into this pin is not exactly inversely proportional to VIN, especially in applications with lower input voltages. To correct for this error, an additional resistor RON2 connected from the ION pin to the 5V INTVCC supply will further stabilize the frequency. RON2 = 5V R 0.7V ON A plot of maximum duty cycle vs frequency is shown in Figure 3. Setting the Output Voltage The LTC3611 develops a 0.6V reference voltage between the feedback pin, VFB, and the signal ground as shown in Figure 6. The output voltage is set by a resistive divider according to the following formula: VOUT = 0.6V 1+ R2 R1 Changes in the load current magnitude will also cause frequency shift. Parasitic resistance in the MOSFET switches and inductor reduce the effective voltage across the inductance, resulting in increased duty cycle as the load current increases. By lengthening the on-time slightly To improve the frequency response, a feedforward capacitor C1 may also be used. Great care should be taken to route the VFB line away from noise sources, such as the inductor or the SW line. 3611fb 12 LTC3611 APPLICATIONS INFORMATION RVON1 30k VOUT RVON2 100k CVON 0.01F RC ITH CC VON LTC3611 ripple. Highest efficiency operation is obtained at low frequency with small ripple current. However, achieving this requires a large inductor. There is a tradeoff between component size, efficiency and operating frequency. A reasonable starting point is to choose a ripple current that is about 40% of IOUT(MAX). The largest ripple current occurs at the highest VIN. To guarantee that ripple current does not exceed a specified maximum, the inductance should be chosen according to: L= VOUT f IL(MAX) 1 VOUT VIN(MAX) (2a) RVON1 3k VOUT INTVCC 10k Q1 2N5087 RVON2 10k CVON 0.01F RC ITH CC 3611 F02 VON LTC3611 (2b) Figure 2. Correcting Frequency Shift with Load Current Changes 2.0 Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores. A variety of inductors designed for high current, low voltage applications are available from manufacturers such as Sumida, Panasonic, Coiltronics, Coilcraft and Toko. CIN and COUT Selection SWITCHING FREQUENCY (MHz) 1.5 DROPOUT REGION 1.0 The input capacitance CIN is required to filter the square wave current at the drain of the top MOSFET. Use a low ESR capacitor sized to handle the maximum RMS current. IRMS IOUT(MAX) VOUT VIN VIN -1 VOUT 0.5 0 0 0.25 0.50 0.75 DUTY CYCLE (VOUT/VIN) 1.0 3611 F03 Figure 3. Maximum Switching Frequency vs Duty Cycle Inductor Selection Given the desired input and output voltages, the inductor value and operating frequency determine the ripple current: IL = VOUT fL 1 VOUT VIN This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT(MAX)/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to derate the capacitor. The selection of COUT is primarily determined by the ESR required to minimize voltage ripple and load step transients. The output ripple VOUT is approximately bounded by: VOUT IL ESR + 1 8fCOUT Lower ripple current reduces core losses in the inductor, ESR losses in the output capacitors and output voltage 3611fb 13 LTC3611 APPLICATIONS INFORMATION Since IL increases with input voltage, the output ripple is highest at maximum input voltage. Typically, once the ESR requirement is satisfied, the capacitance is adequate for filtering and has the necessary RMS current rating. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR but have lower capacitance density than other types. Tantalum capacitors have the highest capacitance density but it is important to only use types that have been surge tested for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR, but can be used in cost-sensitive applications providing that consideration is given to ripple current ratings and long term reliability. Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing. When used as input capacitors, care must be taken to ensure that ringing from inrush currents and switching does not pose an overvoltage hazard to the power switches and controller. To dampen input voltage transients, add a small 5F to 50F aluminum electrolytic capacitor with an ESR in the range of 0.5 to 2. High performance through-hole capacitors may also be used, but an additional ceramic capacitor in parallel is recommended to reduce the effect of their lead inductance. Top MOSFET Driver Supply (CB, DB) An external bootstrap capacitor CB connected to the BOOST pin supplies the gate drive voltage for the topside MOSFET. This capacitor is charged through diode DB from INTVCC when the switch node is low. When the top MOSFET turns on, the switch node rises to VIN and the BOOST pin rises to approximately VIN + INTVCC. The boost capacitor needs to store about 100 times the gate charge required by the top MOSFET. In most applications an 0.1F to 0.47F, X5R or X7R dielectric capacitor is adequate. Discontinuous Mode Operation and FCB Pin The FCB pin determines whether the bottom MOSFET remains on when current reverses in the inductor. Tying this pin above its 0.6V threshold enables discontinuous operation where the bottom MOSFET turns off when inductor current reverses. The load current at which current reverses and discontinuous operation begins depends on the amplitude of the inductor ripple current and will vary with changes in VIN. Tying the FCB pin below the 0.6V threshold forces continuous synchronous operation, allowing current to reverse at light loads and maintaining high frequency operation. In addition to providing a logic input to force continuous operation, the FCB pin provides a means to maintain a flyback winding output when the primary is operating in discontinuous mode. The secondary output VOUT2 is normally set as shown in Figure 4 by the turns ratio N of the transformer. However, if the controller goes into discontinuous mode and halts switching due to a light primary load current, then VOUT2 will droop. An external resistor divider from VOUT2 to the FCB pin sets a minimum voltage VOUT2(MIN) below which continuous operation is forced until VOUT2 has risen above its minimum: VOUT2(MIN) = 0.6V 1+ R4 R3 Fault Conditions: Current Limit and Foldback The LTC3611 has a current mode controller which inherently limits the cycle-by-cycle inductor current not only in steady state operation but also in transient. To further limit current in the event of a short circuit to ground, the LTC3611 includes foldback current limiting. If the output falls by more than 25%, then the maximum sense voltage is progressively lowered to about one sixth of its full value. INTVCC Regulator and EXTVCC Connection An internal P-channel low dropout regulator produces the 5V supply that powers the drivers and internal circuitry within the LTC3611. The INTVCC pin can supply up to 50mA 3611fb 14 LTC3611 APPLICATIONS INFORMATION PGND SW 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 SVIN INTVCC INTVCC PGND PGND PGND PGND PGND PGND PGND PGND PGND SVIN SW SGND IN4148 VOUT2 CSEC 1F VOUT1 COUT SGND SGND 1 2 3 PGND PGND PGND SW SW SW SW SW SW SW SW PVIN PVIN PVIN PVIN RUN/SS BOOST PVIN SGND PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SW NC SGND LTC3611 SGND SGND SGND SGND EXTVCC VFB SGND ION SGND FCB ITH VRNG PGOOD VON SGND SGND SGND 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 R3 OPTIONAL EXTVCC CONNECTION 5V < VOUT2 < 7V R4 + * * T1 1:N 4 5 6 7 8 9 10 11 VIN 12 13 14 15 16 + + CIN 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 3611 F04 SW SGND Figure 4. Secondary Output Loop and EXTVCC Connection RMS and must be bypassed to ground with a minimum of 4.7F tantalum or ceramic capacitor. Good bypassing is necessary to supply the high transient currents required by the MOSFET gate drivers. The EXTVCC pin can be used to provide MOSFET gate drive and control power from the output or another external source during normal operation. Whenever the EXTVCC pin is above 4.7V the internal 5V regulator is shut off and an internal 50mA P-channel switch connects the EXTVCC pin to INTVCC. INTVCC power is supplied from EXTVCC until this pin drops below 4.5V. Do not apply more than 7V to the EXTVCC pin and ensure that EXTVCC VIN. The following list summarizes the possible connections for EXTVCC: 1. EXTVCC grounded. INTVCC is always powered from the internal 5V regulator. 2. EXTVCC connected to an external supply. A high efficiency supply compatible with the MOSFET gate drive requirements (typically 5V) can improve overall efficiency. 3. EXTVCC connected to an output derived boost network. The low voltage output can be boosted using a charge pump or flyback winding to greater than 4.7V. The system will start-up using the internal linear regulator until the boosted output supply is available. Soft-Start and Latchoff with the RUN/SS Pin The RUN/SS pin provides a means to shut down the LTC3611 as well as a timer for soft-start and overcurrent latchoff. Pulling the RUN/SS pin below 0.8V puts the LTC3611 into a low quiescent current shutdown (IQ < 30A). Releasing the pin allows an internal 1.2A current source to charge up the external timing capacitor CSS. If RUN/SS has been pulled all the way to ground, there is a delay before starting of about: tDELAY = 1.5V C = (1.3s/F ) CSS 1.2A SS When the voltage on RUN/SS reaches 1.5V, the LTC3611 begins operating with a clamp on ITH of approximately 3611fb 15 LTC3611 APPLICATIONS INFORMATION 0.9V. As the RUN/SS voltage rises to 3V, the clamp on ITH is raised until its full 2.4V range is available. This takes an additional 1.3s/F, during which the load current is folded back until the output reaches 75% of its final value. After the controller has been started and given adequate time to charge up the output capacitor, CSS is used as a short-circuit timer. After the RUN/SS pin charges above 4V, if the output voltage falls below 75% of its regulated value, then a short-circuit fault is assumed. A 1.8A current then begins discharging CSS. If the fault condition persists until the RUN/SS pin drops to 3.5V, then the controller turns off both power MOSFETs, shutting down the converter permanently. The RUN/SS pin must be actively pulled down to ground in order to restart operation. The overcurrent protection timer requires that the soft-start timing capacitor CSS be made large enough to guarantee that the output is in regulation by the time CSS has reached the 4V threshold. In general, this will depend upon the size of the output capacitance, output voltage and load current characteristic. A minimum soft-start capacitor can be estimated from: CSS > COUT VOUT RSENSE (10 -4 [F/V s]) Generally 0.1F is more than sufficient. Overcurrent latchoff operation is not always needed or desired. Load current is already limited during a short-circuit by the current foldback circuitry and latchoff operation can prove annoying during troubleshooting. The feature can be overridden by adding a pull-up current greater than 5A to the RUN/SS pin. The additional current prevents the discharge of CSS during a fault and also shortens the soft-start period. Using a resistor to VIN as shown in Figure 5a is simple, but slightly increases shutdown current. Connecting a resistor to INTVCC as shown in Figure 5b eliminates the additional shutdown current, but requires a diode to isolate CSS. Any pull-up network must be able to pull RUN/SS above the 4.2V maximum threshold of the latchoff circuit and overcome the 4A maximum discharge current. INTVCC RSS* RUN/SS RSS* D2* RUN/SS VIN 3.3V OR 5V D1 2N7002 CSS CSS 3611 F05 *OPTIONAL TO OVERRIDE OVERCURRENT LATCHOFF (5a) (5b) Figure 5. RUN/SS Pin Interfacing with Latchoff Defeated Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Although all dissipative elements in the circuit produce losses, four main sources account for most of the losses in LTC3611 circuits: 1. DC I2R losses. These arise from the resistance of the internal resistance of the MOSFETs, inductor and PC board traces and cause the efficiency to drop at high output currents. In continuous mode the average output current flows through L, but is chopped between the top and bottom MOSFETs. If the two MOSFETs have approximately the same RDS(ON), then the DC I2R loss for one MOSFET can simply be determined by [RDS(ON) + RL] * IO. 2. Transition loss. This loss arises from the brief amount of time the top MOSFET spends in the saturated region during switch node transitions. It depends upon the input voltage, load current, driver strength and MOSFET capacitance, among other factors. The loss is significant at input voltages above 20V and can be estimated from: Transition Loss (1.7A-1) VIN2 IOUT CRSS f 3. INTVCC current. This is the sum of the MOSFET driver and control currents. This loss can be reduced by supplying INTVCC current through the EXTVCC pin from a high efficiency source, such as an output derived boost network or alternate supply if available. 3611fb 16 LTC3611 APPLICATIONS INFORMATION 4. CIN loss. The input capacitor has the difficult job of filtering the large RMS input current to the regulator. It must have a very low ESR to minimize the AC I2R loss and sufficient capacitance to prevent the RMS current from causing additional upstream losses in fuses or batteries. Other losses, including COUT ESR loss, Schottky diode D1 conduction loss during dead time and inductor core loss generally account for less than 2% additional loss. When making adjustments to improve efficiency, the input current is the best indicator of changes in efficiency. If you make a change and the input current decreases, then the efficiency has increased. If there is no change in input current, then there is no change in efficiency. Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ILOAD (ESR), where ESR is the effective series resistance of COUT. ILOAD also begins to charge or discharge COUT generating a feedback error signal used by the regulator to return VOUT to its steady-state value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem. The ITH pin external components shown in Figure 6 will provide adequate compensation for most applications. For a detailed explanation of switching control loop theory see Application Note 76. Design Example As a design example, take a supply with the following specifications: VIN = 5V to 36V (12V nominal), VOUT = 2.5V 5%, IOUT(MAX) = 10A, f = 550kHz. First, calculate the timing resistor with VON = VOUT: RON = 2.5V =187k (2.4) (550kHz ) (10pF ) Selecting a standard value of 1H results in a maximum ripple current of: IL = 2.5V 2.5V 1- = 3.6A (550kHz )(1H) 12V Next, set up VRNG voltage and check the ILIMIT. Tying VRNG to 1V will set the typical current limit to 15A, and tying VRNG to GND will result in a typical current around 10A. CIN is chosen for an RMS current rating of about 5A at 85C. The output capacitors are chosen for a low ESR of 0.013 to minimize output voltage changes due to inductor ripple current and load steps. The ripple voltage will be only: VOUT(RIPPLE) = IL(MAX) (ESR) = (3.6A) (0.013) = 47mV However, a 0A to 10A load step will cause an output change of up to: VOUT(STEP) = ILOAD (ESR) = (10A) (0.013) =130mV An optional 22F ceramic output capacitor is included to minimize the effect of ESL in the output ripple. The complete circuit is shown in Figure 6. PC Board Layout Checklist When laying out a PC board follow one of the two suggested approaches. The simple PC board layout requires a dedicated ground plane layer. Also, for higher currents, a multilayer board is recommended to help with heat sinking of power components. * The ground plane layer should not have any traces and it should be as close as possible to the layer with the LTC3611. * Place CIN and COUT all in one compact area, close to the LTC3611. It may help to have some components on the bottom side of the board. * Keep small-signal components close to the LTC3611. * Ground connections (including LTC3611 SGND and PGND) should be made through immediate vias to the ground plane. Use several larger vias for power components. 3611fb and choose the inductor for about 40% ripple current at the maximum VIN: L= 2.5V 2.5V 1 = 1H (550kHz )(0.4)(10A ) 36V 17 LTC3611 APPLICATIONS INFORMATION INTVCC CF 0.1F 50V VIN CVCC 4.7F 6.3V PGND SW SGND 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 SVIN INTVCC INTVCC PGND PGND PGND PGND PGND PGND PGND PGND PGND SVIN SW SGND SGND 1 2 3 VOUT 2.5V AT 10A 4 C5 22F 6.3V COUT1 100F x2 L1 1H 5 6 7 8 9 10 11 VIN 5V TO 32V CIN 4.7F 50V x2 C6 + 100F 50V (OPTIONAL) VIN GND 12 13 14 15 16 PGND PGND PGND SW SW SW SW SW SW SW SW PVIN PVIN PVIN PVIN RUN/SS BOOST PVIN SGND PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SW NC SGND LTC3611 SGND SGND SGND SGND EXTVCC VFB SGND ION SGND FCB ITH VRNG PGOOD VON SGND SGND 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 EXTVCC C4 0.01F R1 9.5k 1% RON 182k 1% C1 (OPTIONAL) R2 30.1k 1% (OPTIONAL) C2 VOUT (OPTIONAL) GND VIN CON 0.01F (OPTIONAL) R5 12.5k CC1 680pF R3 11k 39.2k RPG1 100k CC2 100pF INTVCC RVON 0 VOUT SGND 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 SW CIN = MURATA GRM32ER71H475K COUT = MURATA GRM43SR60J107M L1 = COOPER HCP0703-IRO C5: MURATA GRM31CR60J226KE19 KEEP POWER AND SIGNAL GROUNDS SEPARATE. CONNECT TO ONE POINT. 2 INTVCC DB CMDSH-3 SW CB1 0.22F CSS 0.1F RSS1 510k VIN (OPTIONAL) 0.01F 3611 F06 Figure 6. Design Example: 5V to 32V Input to 2.5V/10A at 550kHz * Use a compact plane for the switch node (SW) to improve cooling of the MOSFETs and to keep EMI down. * Use planes for VIN and VOUT to maintain good voltage filtering and to keep power losses low. * Flood all unused areas on all layers with copper. Flooding with copper reduces the temperature rise of power components. Connect these copper areas to any DC net (VIN, VOUT, GND or to any other DC rail in your system). When laying out a printed circuit board without a ground plane, use the following checklist to ensure proper operation of the controller. These items are also illustrated in Figure 7. * Segregate the signal and power grounds. All small signal components should return to the SGND pin at one point, which is then tied to the PGND pin. * Connect the input capacitor(s) CIN close to the IC. This capacitor carries the MOSFET AC current. * Keep the high dV/dT SW, BOOST and TG nodes away from sensitive small-signal nodes. * Connect the INTVCC decoupling capacitor CVCC closely to the INTVCC and PGND pins. * Connect the top driver boost capacitor CB closely to the BOOST and SW pins. * Connect the VIN pin decoupling capacitor CF closely to the VIN and PGND pins. 3611fb 18 LTC3611 APPLICATIONS INFORMATION CVCC SW 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 PGND PGND PGND PGND PGND PGND PGND PGND PGND SGND INTVCC INTVCC SGND SW SVIN SVIN 1 2 3 4 COUT 5 6 7 8 VOUT 9 10 11 12 13 CIN 14 15 16 PGND PGND PGND SW SW SW SW SW SW SW SW PVIN PVIN PVIN PVIN RUN/SS BOOST PVIN SGND PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SW NC SGND LTC3611 SGND SGND SGND SGND EXTVCC VFB SGND ION SGND FCB ITH VRNG PGOOD VON SGND SGND 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 CC2 RC CC1 RON R2 R1 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 DB CB RF CSS 3611 F07 Figure 7. LTC3611 Layout Diagram 3611fb 19 LTC3611 TYPICAL APPLICATIONS 3.3V Input to 1.5V/10A at 750kHz INTVCC CF 0.1F 50V SGND CVCC 4.7F 6.3V PGND SW 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 SW SVIN INTVCC INTVCC PGND PGND PGND PGND PGND PGND PGND PGND PGND SVIN SGND SGND 1 2 3 VOUT 1.5V AT 10A 4 C5 22F 6.3V COUT1 100F x2 L1 0.47H 5 6 7 8 9 10 11 VIN 3.3V CIN 4.7F 50V x2 C6 100F 50V VIN GND 12 13 14 15 16 PGND PGND PGND SW SW SW SW SW SW SW SW PVIN PVIN PVIN PVIN RUN/SS BOOST PVIN SGND PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SW NC SGND LTC3611 SGND SGND SGND SGND EXTVCC VFB SGND ION SGND FCB ITH VRNG PGOOD VON SGND SGND 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 VIN2 = 5V C4 0.01F R1 20.43k 1% RON 113k 1% C1 (OPTIONAL) R2 30.1k 1% (OPTIONAL) C2 VOUT (OPTIONAL) GND VIN CON 0.01F (OPTIONAL) R5 12.5k CC1 1500pF 39.2k 11k RPG1 100k INTVCC CC2 100pF + (OPTIONAL) 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 RSS1 510k 2 CSS 0.1F (OPTIONAL) VIN CVON VOUT SGND (OPTIONAL) 3611 TA02 C5: TAIYO YUDEN JMK316BJ226ML-T CIN: MURATA GRM31CR71H475K INTVCC COUT1: MURATA GRM435R60J107M L1: TOKO FDV0630-R47M KEEP POWER AND SIGNAL GROUNDS SEPARATE. CONNECT TO ONE POINT. CB1 0.22F 3611fb 20 LTC3611 TYPICAL APPLICATIONS 5V to 24V Input to 1.2V/10A at 550kHz INTVCC CF 0.1F 50V VIN CVCC 4.7F 6.3V PGND SW SGND 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 INTVCC INTVCC SW SVIN PGND PGND PGND PGND PGND PGND PGND PGND PGND SVIN SGND SGND 1 2 3 VOUT 1.2V AT 10A 4 C5 22F 6.3V COUT1 100F x2 L1 0.47H 5 6 7 8 9 10 11 VIN 5V TO 24V CIN 4.7F 50V x2 C6 100F 50V VIN GND 12 13 14 15 16 PGND PGND PGND SW SW SW SW SW SW SW SW PVIN PVIN PVIN PVIN RUN/SS BOOST PVIN SGND PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SW NC SGND LTC3611 SGND SGND SGND SGND EXTVCC VFB SGND ION SGND FCB ITH VRNG PGOOD VON SGND SGND 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 EXTVCC C4 0.01F R1 30k 1% RON 182k 1% C1 (OPTIONAL) R2 30.1k 1% (OPTIONAL) C2 VOUT (OPTIONAL) GND VIN CON 0.01F (OPTIONAL) R5 4.75k CC1 1500pF + 11k 39.2k RPG1 100k INTVCC CC2 100pF (OPTIONAL) 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 CB1 0.22F C5: TAIYO YUDEN JMK316BJ226ML-T INTVCC CIN: MURATA GRM32ER71H475K COUT1: MURATA GRM435R60J167M L1: TOKO HCPO703-OR47 KEEP POWER AND SIGNAL GROUNDS SEPARATE. CONNECT TO ONE POINT. DB CMDSH-3 2 CSS 0.1F VOUT SGND RSS1 510k VIN (OPTIONAL) (OPTIONAL) CVON 3611 TA03 SGND 3611fb 21 LTC3611 TYPICAL APPLICATIONS 5V to 28V Input to 1.8V/10A All Ceramic 1MHz INTVCC CF 0.1F 50V VIN CVCC 4.7F 6.3V PGND SW SGND 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 SVIN INTVCC INTVCC PGND PGND PGND PGND PGND PGND PGND PGND PGND SVIN SW SGND SGND 1 2 3 VOUT 1.8V AT 10A 4 C5 22F 6.3V COUT 100F x2 L1 0.68H 5 6 7 8 9 10 11 VIN 5V TO 28V CIN 4.7F 50V x2 VIN 12 13 14 15 16 PGND PGND PGND SW SW SW SW SW SW SW SW PVIN PVIN PVIN PVIN RUN/SS BOOST PVIN SGND PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SW NC SGND LTC3611 SGND SGND SGND SGND EXTVCC VFB SGND ION SGND FCB ITH VRNG PGOOD VON SGND SGND 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 EXTVCC C4 0.01F R1 10k 1% RON 102k 1% C1 47pF R2 20k 1% (OPTIONAL) C2 VOUT (OPTIONAL) GND VIN CON 0.01F (OPTIONAL) R5 12.7k CC1 680pF 9.31k RPG1 100k 39.2k CC2 100pF INTVCC 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 CB1 0.22F COUT: MURATA GRM32ER60J107ME20L INTVCC CIN: MURATA GRM32ER71H475K L1: VISHAY IHLP2525CZERR68M01 KEEP POWER AND SIGNAL GROUNDS SEPARATE. CONNECT TO ONE POINT. DB CMDSH-3 2 CSS 0.1F RSS1 510k VIN (OPTIONAL) CVON VOUT SGND (OPTIONAL) 3611 TA04 3611fb 22 LTC3611 PACKAGE DESCRIPTION WP Package 64-Lead QFN Multipad (9mm x 9mm) (Reference LTC DWG # 05-08-1812 Rev A) SEATING PLANE 9.00 BSC A B PAD 1 CORNER 3.06 0.30 (2x) 0.95 2.98 4.53 3.60 1.92 2.01 48 0.53 (2x) 1.17 3.50 0.87 1.39 0.00 - 0.05 0.20 REF 1.19 49 50 51 52 53 54 3.30 0.50 64 0.30 - 0.50 1 5 9.00 BSC bbb M C A B 1.30 4.10 3.30 1.81 NX b aaa C 2x 3.99 33 32 17 1.42 3.85 2.04 16 WP64 QFN REV A 0707 aaa C 2x TOP VIEW // ccc C 0.90 0.10 0.20 - 0.30 NX 0.08 C 6 3.30 0.50 0.30 - 0.50 PIN 1 0.87 3.50 0.53 (2x) 1.17 0.30 (2x) 0.95 3.60 4.53 1.92 2.01 3.06 1.39 1.19 BOTTOM VIEW (BOTTOM METALLIZATION DETAILS) 2.98 NOTE: 1. DIMENSIONING AND TOLERANCING CONFORM TO ASME Y14.5M-1994 2. ALL DIMENSIONS ARE IN MILLIMETERS, ANGLES ARE IN DEGREES () 3. N IS THE TOTAL NUMBER OF TERMINALS 4. THE LOCATION OF THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION CONFORMS TO JEDEC PUBLICATION 95 SPP-002 5 6 DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15mm AND 0.30mm FROM THE TERMINAL TIP. COPLANARITY APPLIES TO THE TERMINALS AND ALL OTHER SURFACE METALLIZATION SYMBOL TOLERANCE 0.15 aaa 0.10 bbb 0.10 ccc 1.81 1.30 2.30 3.30 4.10 2.04 3.99 3.85 1.42 0.20 - 0.30 RECOMMENDED SOLDER PAD LAYOUT TOP VIEW 3611fb 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. 23 LTC3611 TYPICAL APPLICATION 14V to 32V Input to 12V/5A at 500kHz CVCC 4.7F 6.3V INTVCC CF 0.1F 50V VIN PGND SW 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 SVIN INTVCC INTVCC PGND PGND PGND PGND PGND PGND PGND PGND PGND SVIN SW SGND SGND SGND 1 2 3 VOUT 12V AT 5A 4 C5 22F 25V COUT 180F 16V L1 4.7H PGND PGND PGND SW SW SW SW SW SW SW SW PVIN PVIN PVIN PVIN RUN/SS BOOST PVIN SGND PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN PVIN SW NC SGND LTC3611 SGND SGND SGND SGND EXTVCC VFB SGND ION SGND FCB ITH VRNG PGOOD VON SGND SGND 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 EXTVCC C4 0.01F R1 1.58k 1% RON 1M 1% C1 (OPTIONAL) R2 30.1k 1% (OPTIONAL) C2 VOUT + 5 6 7 8 9 10 11 (OPTIONAL) GND VIN CON 0.01F (OPTIONAL) R5 20k CC1 560pF VIN 14V TO 32V CIN 4.7F 50V x2 C6 100F 50V VIN GND 12 13 14 15 16 + RPG1 100k INTVCC CC2 100pF (OPTIONAL) 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 CB1 0.22F INTVCC CIN: GRM31CR71H475K COUT: SANYO 16SVP180MX L1: HCP0703-4R7-R KEEP POWER AND SIGNAL GROUNDS SEPARATE. CONNECT TO ONE POINT. DB CMDSH-3 CSS 0.1F RSS1 510k VIN (OPTIONAL) RUN/SS CVON INTVCC SGND (OPTIONAL) 3611 TA05 RELATED PARTS PART NUMBER DESCRIPTION LTC1778 LTC3411 LTC3412 LTC3414 LTC3418 LTC3610 LTC3770 LTC3778 LT3800 LTM4600HV LTM4601HV LTM4602HV LTM4603HV No RSENSE Current Mode Synchronous Step-Down Controller COMMENTS Up to 97% Efficiency, VIN: 4V to 36V, 0.8V VOUT (0.9)(VIN), IOUT Up to 20A 1.25A (IOUT ), 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT: 0.8V, IQ: 60A, ISD: <1A, MS Package 2.5A (IOUT ) 4MHz Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.8V, IQ: 60mA, ISD: <1mA, TSSOP16E 95% Efficiency, VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, IQ = 64A, 4A (IOUT ), 4MHz, Synchronous Step-Down DC/DC Converter ISD: <1A, TSSOP20E Package 95% Efficiency, VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, Thermally 8A (IOUT ), 4MHz, Synchronous Step-Down DC/DC Converter Enhanced 38-Lead QFN Package 12A Current Mode Monolithic Synchronous Step-Down Converter Up to 24V Input (28V Maximum), Current Mode Extremely Fast Transient Response 0.67% 0.6V Reference Voltage; Programmable Margining; Fast, No RSENSE Step-Down Synchronous Controller with Margining, Tracking, PLL True Current Mode; 4V VIN 32V 0.6V VOUT (0.9) VIN, 4V VIN 36V, IOUT Up to 20A Low VOUT, No RSENSE Synchronous Step-Down Controller 60V Synchronous Step-Down Controller 10A Complete Switch Mode Power Supply 12A Complete Switch Mode Power Supply 6A Complete Switch Mode Power Supply 6A Complete Switch Mode Power Supply Current Mode, Output Slew Rate Control 92% Efficiency, VIN: 4.5V to 28V, VOUT: 0.6V, True Current Mode Control, Ultrafast Transient Response 92% Efficiency, VIN: 4.5V to 28V, VOUT: 0.6V, True Current Mode Control, Ultrafast Transient Response 92% Efficiency, VIN: 4.5V to 28V, VOUT: 0.6V, True Current Mode Control, Ultrafast Transient Response 93% Efficiency, VIN: 4.5V to 28V, with PLL, Output Tracking and Margining 3611fb 24 Linear Technology Corporation (408) 432-1900 FAX: (408) 434-0507 LT 0808 REV B * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2008 |
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