LTM4609 36VIN 34VOUT 141-LEAD LTM4609EV LTM4609V LTM4609IV LTM4609E LTM4609I - Datasheet Archive

 

36VIN, 34VOUT High Efficiency Buck-Boost DC/DC µModule FEATURES DESCRIPTION n The LTM®4609 is a high efficiency

 

LTM4609 LTM4609 36VIN 36VIN, 34VOUT 34VOUT High Efficiency Buck-Boost DC/DC µModule FEATURES DESCRIPTION n The LTM®4609 is a high efficiency switching mode buckboost power supply. Included in the package are the switching controller, power FETs and support components. Operating over an input voltage range of 4.5V to 36V, the LTM4609 LTM4609 supports an output voltage range of 0.8V to 34V, set by a resistor. This high efficiency design delivers up to 4A continuous current in boost mode (10A in buck mode). Only the inductor, sense resistor, bulk input and output capacitors are needed to finish the design. n n n n n n n n n n n Single Inductor Architecture Allows VIN Above, Below or Equal to VOUT Wide VIN Range: 4.5V to 36V Wide VOUT Range: 0.8V to 34V IOUT: 4A DC (10A DC in Buck Mode) Up to 98% Efficiency Current Mode Control Power Good Output Signal Phase-Lockable Fixed Frequency: 200kHz to 400kHz Ultrafast Transient Response Current Foldback Protection Output Overvoltage Protection Small, Low Profile Surface Mount LGA Package (15mm × 15mm × 2.8mm) The low profile package enables utilization of unused space on the bottom of PC boards for high density point of load regulation. The high switching frequency and current mode architecture enable a very fast transient response to line and load changes without sacrificing stability. The LTM4609 LTM4609 can be frequency synchronized with an external clock to reduce undesirable frequency harmonics. APPLICATIONS n n n Fault protection features include overvoltage and foldback current protection. The DC/DC Module® is offered in a small thermally enhanced 15mm × 15mm × 2.8mm LGA package. The LTM4609 LTM4609 is Pb-free and RoHS compliant. Telecom, Servers and Networking Equipment Industrial and Automotive Equipment High Power Battery-Operated Devices L, LT, LTC, LTM, Linear Technology, the Linear logo and Module are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Efficiency and Power Loss vs Input Voltage 30V/2A Buck-Boost DC/DC Module with 5V to 36V Input VIN PLLIN V OUT RUN LTM4609 LTM4609 5.6H SW1 SW2 RSENSE SENSE+ 0.1F SENSE­ SS SGND PGND + 330F 50V VOUT 30V 2A 98 R2 15m 2 VFB 4609 TA01a 4 96 95 3 94 2 93 92 91 2.74k 5 97 POWER LOSS (W) 10F 50V FCB ON/OFF 6 99 CLOCK SYNC 10F 50V EFFICIENCY (%) VIN 6.5V TO 36V EFFICIENCY POWER LOSS 8 12 16 24 20 VIN (V) 28 32 36 1 0 4609 TA01b 4609fa 1 LTM4609 LTM4609 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) (See Table 6 Pin Assignment) VIN . ­0.3V to 36V VOUT . 0.8V to 36V INTVCC, EXTVCC, RUN, SS, PGOOD . ­0.3V to 7V SW1, SW2 . ­5V to 36V VFB, COMP . ­0.3V to 2.4V FCB, STBYMD . ­0.3V to INTVCC PLLIN . ­0.3V to 5.5V PLLFLTR. ­0.3V to 2.7V Operating Temperature Range (Note 2).­40°C to 85°C Junction Temperature . 125°C Storage Temperature Range.­55°C to 125°C Solder Temperature (Note 3). 245°C TOP VIEW BANK 2 M L BANK 4 BANK 1 K J H BANK 3 G BANK 5 F E D C BANK 6 B A 1 2 3 4 5 6 7 8 LGA PACKAGE 141-LEAD 141-LEAD (15mm 15mm 9 10 11 12 2.8mm) TJMAX = 125°C, JP = 4°C/W, WEIGHT = 1.5g ORDER INFORMATION LEAD FREE FINISH PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTM4609EV LTM4609EV#PBF LTM4609V LTM4609V 141-Lead (15mm × 15mm × 2.8mm) LGA ­40°C to 85°C LTM4609IV LTM4609IV#PBF LTM4609V LTM4609V 141-Lead (15mm × 15mm × 2.8mm) LGA ­40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://www.linear.com/packaging/ ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the ­40°C to 85°C temperature range, otherwise specifications are at TA = 25°C, VIN = 12V. Per typical application (front page) configuration. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Input Specifications l VIN(DC) Input DC Voltage VIN(UVLO) Undervoltage Lockout Threshold VIN Falling IQ(VIN) Input Supply Bias Current Normal Standby Shutdown Supply Current VRUN = 0V, VSTBYMD > 2V VRUN = 0V, VSTBYMD = Open l 4.5 36 3.4 2.8 1.6 35 V 4 V 60 mA mA A 4609fa 2 LTM4609 LTM4609 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the ­40°C to 85°C temperature range, otherwise specifications are at TA = 25°C, VIN = 12V. Per typical application (front page) configuration. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Output Specifications IOUTDC Output Continuous Current Range VIN = 32V, VOUT = 12V (See Output Current Derating Curves VIN = 6V, VOUT = 12V for Different VIN, VOUT and TA) VFB/VFB(NOM) Reference Voltage Line Regulation Accuracy VIN = 4.5V to 36V, VCOMP = 1.2V (Note 4) VFB/VFB(LOAD) Load Regulation Accuracy VCOMP = 1.2V to 0.7V VCOMP = 1.2V to 1.8V (Note 4) M1 tr Turn-On Time (Note 5) Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 50 ns M1 tf Turn-Off Time Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 40 ns M3 tr Turn-On Time Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 25 ns M3 tf Turn-Off Time Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 20 ns M2, M4 tr Turn-On Time Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 20 ns M2, M4 tf Turn-Off Time Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 20 ns t1d M1 Off to M2 On Delay (Note 5) Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 50 ns t2d M2 Off to M1 On Delay Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 50 ns t3d M3 Off to M4 On Delay Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 50 ns t4d M4 Off to M3 On Delay Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 50 ns Mode Transition 1 M2 Off to M4 On Delay Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 220 ns Mode Transition 2 M4 Off to M2 On Delay Drain to Source Voltage VDS = 12V, Bias Current ISW = 10mA 220 ns M1 RDS(ON) Static Drain-to-Source On-Resistance Bias Current ISW = 3A 10 m M2 RDS(ON) Static Drain-to-Source On-Resistance Bias Current ISW = 3A 14 20 m M3 RDS(ON) Static Drain-to-Source On-Resistance Bias Current ISW = 3A 14 20 m M4 RDS(ON) Static Drain-to-Source On-Resistance Bias Current ISW = 3A 14 20 m 10 4 A A 0.002 %/V 0.15 ­0.15 l l 0.02 0.5 ­0.5 % % Switch Section Oscillator and Phase-Locked Loop fNOM Nominal Frequency VPLLFLTR = 1.2V 260 300 330 kHz fLOW Lowest Frequency VPLLFLTR = 0V 170 200 220 kHz fHIGH Highest Frequency VPLLFLTR = 2.4V 340 400 440 kHz RPLLIN PLLIN Input Resistance IPLLFLTR Phase Detector Output Current 50 fPLLIN < fOSC fPLLIN > fOSC k ­15 15 A A 4609fa 3 LTM4609 LTM4609 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the ­40°C to 85°C temperature range, otherwise specifications are at TA = 25°C, VIN = 12V. Per typical application (front page) configuration. SYMBOL PARAMETER CONDITIONS VFB Feedback Reference Voltage MIN VCOMP = 1.2V TYP MAX UNITS 0.792 0.8 0.808 V 2.2 Control Section l VRUN RUN Pin ON/OFF Threshold ISS Soft-Start Charging Current VRUN = 2.2V 1 VSTBYMD(START) Start-Up Threshold VSTBYMD Rising VSTBYMD(KA) Keep-Active Power On Threshold VSTBYMD Rising, VRUN = 0V VFCB Forced Continuous Pin Current VBURST Burst Inhibit (Constant Frequency) Threshold DF(BOOST, MAX) A 0.7 V 1.25 VFCB = 0.85V 1.7 0.4 Forced Continuous Threshold IFCB 1.6 1 V V 0.76 0.8 0.84 V ­0.3 ­0.2 ­0.1 A Measured at FCB Pin 5.3 5.5 V Maximum Duty Factor % Switch M4 On 99 % DF(BUCK, MAX) Maximum Duty Factor % Switch M1 On 99 % tON(MIN, BUCK) Minimum On-Time for Synchronous Switch M1 (Note 6) Switch in Buck Operation RFBHI Resistor Between VOUT and VFB Pins 200 250 ns 99.5 100 100.5 k 5.7 6 6.3 V 0.3 2 % Internal VCC Regulator INTVCC Internal VCC Voltage VIN > 7V, VEXTVCC = 5V VLDO/VLDO Internal VCC Load Regulation ICC = 0mA to 20mA, VEXTVCC = 5V VEXTVCC EXTVCC Switchover Voltage ICC = 20mA, VEXTVCC Rising VEXTVCC(HYS) EXTVCC Switchover Hysteresis VEXTVCC EXTVCC Switch Drop Voltage l l 5.4 5.6 V 300 ICC = 20mA, VEXTVCC = 6V mV 60 150 mV 160 ­130 190 ­150 mV mV Current Sensing Section VSENSE(MAX) Maximum Current Sense Threshold l l Boost Mode Buck Mode ­95 Minimum Current Sense Threshold Discontinuous Mode Sense Pins Total Source Current VSENSE­ = VSENSE+ = 0V VFBH PGOOD Upper Threshold VFB Rising 5.5 7.5 10 % VFBL PGOOD Lower Threshold VFB Falling ­5.5 ­7.5 ­10 % VFB(HYS) PGOOD Hysteresis VFB Returning 2.5 VPGL PGOOD Low Voltage IPGOOD = 2mA 0.2 IPGOOD PGOOD Leakage Current VPGOOD = 5V VSENSE(MIN, BUCK) ISENSE ­6 mV ­380 A PGOOD 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 LTM4609E LTM4609E is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the ­40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LTM4609I LTM4609I is guaranteed over the full ­40°C to 85°C temperature range. % 0.3 V 1 A Note 3: See Application Note 100. Note 4: The LTM4609 LTM4609 is tested in a feedback loop that servos VCOMP to a specified voltage and measures the resultant VFB. Note 5: Turn-on and turn-off time are measured using 10% and 90% levels. Transition delay time is measured using 50% levels. Note 6: 100% test at wafer level only. 4609fa 4 LTM4609 LTM4609 TYPICAL PERFORMANCE CHARACTERISTICS 100 Efficiency vs Load Current 6VIN to 12VOUT 12VOUT 100 (Refer to Figure 18) Efficiency vs Load Current 12VIN 12VIN to 12VOUT 12VOUT Efficiency vs Load Current 32VIN 32VIN to 12VOUT 12VOUT 100 80 80 70 70 70 60 50 40 30 20 0 0.01 0.1 1 LOAD CURRENT (A) 60 50 40 30 0 0.01 0.1 1 LOAD CURRENT (A) 4609 G01 0 0.01 10 100 99 98 1 2 3 4 5 6 7 LOAD CURRENT (A) 8 9 96 95 94 93 28VIN 28VIN to 20VOUT 20VOUT 32VIN 32VIN to 20VOUT 20VOUT 36VIN 36VIN to 20VOUT 20VOUT 91 10 90 0 1 2 4 5 3 6 LOAD CURRENT (A) 96 7 8 93 0 1 3 2 4 LOAD CURRENT (A) 100 6 5 4609 G06 Transient Response from 12VIN 12VIN to 12VOUT 12VOUT Transient Response from 6VIN to 12VOUT 12VOUT Efficiency vs Load Current IOUT 2A/DIV IOUT 2A/DIV VOUT 200mV/DIV 95 30VIN 30VIN to 30VOUT 30VOUT 32VIN 32VIN to 30VOUT 30VOUT 36VIN 36VIN to 30VOUT 30VOUT 94 4609 G05 4609 G04 EFFICIENCY (%) 97 95 92 12VIN 12VIN TO 5VOUT 24VIN 24VIN TO 5VOUT 32VIN 32VIN TO 5VOUT 0 98 97 EFFICIENCY (%) EFFICIENCY (%) EFFICIENCY (%) 95 80 100 Efficiency vs Load Current 8H Inductor 99 85 0.1 1 10 LOAD CURRENT (A) 4609 G03 100 90 SKIP CYCLE DCM CCM 10 Efficiency vs Load Current 5.6H Inductor 100 70 40 4609 G02 Efficiency vs Load Current 3.3H Inductor 75 50 20 BURST DCM CCM 10 10 60 30 20 BURST DCM CCM 10 EFFICIENCY (%) 90 EFFICIENCY (%) 90 80 EFFICIENCY (%) 90 VOUT 200mV/DIV 90 85 80 200s/DIV 70 LOAD STEP: 0A TO 3A AT CCM OUTPUT CAPS: 4x 22F CERAMIC CAPS AND 2x 180F ELECTROLYTIC CAPS 2x 15m SENSING RESISTORS 5VIN to 16VOUT 16VOUT 5VIN to 24VOUT 24VOUT 5VIN to 30VOUT 30VOUT 75 0 0.5 1.5 1 2 LOAD CURRENT (A) 2.5 4609 G08 200s/DIV 4609 G09 LOAD STEP: 0A TO 3A AT CCM OUTPUT CAPS: 4x 22F CERAMIC CAPS AND 2x 180F ELECTROLYTIC CAPS 2x 15m SENSING RESISTORS 3 4609 G07 4609fa 5 LTM4609 LTM4609 TYPICAL PERFORMANCE CHARACTERISTICS Transient Response from 32VIN 32VIN to 12VOUT 12VOUT Start-Up with 6VIN to 12VOUT 12VOUT at IOUT = 4A Start-Up with 32VIN 32VIN to 12VOUT 12VOUT at IOUT = 5A IL 5A/DIV 200s/DIV IIN 2A/DIV VOUT 10V/DIV VOUT 100mV/DIV IL 5A/DIV IIN 5A/DIV IOUT 2A/DIV VOUT 10V/DIV 4609 G10 50ms/DIV 4609 G11 10ms/DIV 4609 G12 LOAD STEP: 0A TO 5A AT CCM OUTPUT CAPS: 4x 22F CERAMIC CAPS AND 2x 180F ELECTROLYTIC CAPS 2x 12m SENSING RESISTORS 0.1F SOFT-START CAP OUTPUT CAPS: 4x 22F CERAMIC CAPS AND 2x 180F ELECTROLYTIC CAPS 2x 12m SENSING RESISTORS 0.1F SOFT-START CAP OUTPUT CAPS: 4x 22F CERAMIC CAPS AND 2x 180F ELECTROLYTIC CAPS 2x 12m SENSING RESISTORS Short Circuit with 6VIN to 12VOUT 12VOUT at IOUT = 4A Short Circuit with 32VIN 32VIN to 12VOUT 12VOUT at IOUT = 5A Short Circuit with 12VIN 12VIN to 34VOUT 34VOUT at IOUT = 2A VOUT 10V/DIV VOUT 5V/DIV IIN 2A/DIV VOUT 5V/DIV IIN 5A/DIV 50s/DIV 4609 G13 OUTPUT CAPS: 4x 22F CERAMIC CAPS AND 2x 180F ELECTROLYTIC CAPS 2x 12m SENSING RESISTORS IIN 5A/DIV 50s/DIV 4609 G14 OUTPUT CAPS: 4x 22F CERAMIC CAPS AND 2x 180F ELECTROLYTIC CAPS 2x 12m SENSING RESISTORS 20s/DIV 4607 G15 OUTPUT CAPS: 2x 10F 50V CERAMIC CAPS AND 2x 47F 50V ELECTROLYTIC CAPS 2x 15m SENSING RESISTORS 4609fa 6 LTM4609 LTM4609 PIN FUNCTIONS VIN (Bank 1): Power Input Pins. Apply input voltage between these pins and PGND pins. Recommend placing input decoupling capacitance directly between VIN pins and PGND pins. VOUT (Bank 5): Power Output Pins. Apply output load between these pins and PGND pins. Recommend placing output decoupling capacitance directly between these pins and PGND pins. PGND (Bank 6): Power Ground Pins for Both Input and Output Returns. SW1, SW2 (Bank 4, Bank 2): Switch Nodes. The power inductor is connected between SW1 and SW2. RSENSE (Bank 3): Sensing Resistor Pin. The sensing resistor is connected from this pin to PGND. SENSE+ (Pin A4): Positive Input to the Current Sense and Reverse Current Detect Comparators. SENSE­ (Pin A5): Negative Input to the Current Sense and Reverse Current Detect Comparators. EXTVCC (Pin F6): External VCC Input. When EXTVCC exceeds 5.7V, an internal switch connects this pin to INTVCC and shuts down the internal regulator so that the controller and gate drive power is drawn from EXTVCC. Do not exceed 7V at this pin and ensure that EXTVCC < VIN INTVCC (Pin F5): Internal 6V Regulator Output. This pin is for additional decoupling of the 6V internal regulator. PLLIN (Pin B9): External Clock Synchronization Input to the Phase Detector. This pin is internally terminated to SGND with a 50k resistor. The phase-locked loop will force the rising bottom gate signal of the controller to be synchronized with the rising edge of PLLIN signal. PLLFLTR (Pin B8): The lowpass filter of the phase-locked loop is tied to this pin. This pin can also be used to set the frequency of the internal oscillator with an AC or DC voltage. See the Applications Information section for details. STBYMD (Pin A10): LDO Control Pin. Determines whether the internal LDO remains active when the controller is shut down. See Operations section for details. If the STBYMD pin is pulled to ground, the SS pin is internally pulled to ground to disable start-up and thereby providing a single control pin for turning off the controller. An internal decoupling capacitor is tied to this pin. VFB (Pin B6): The Negative Input of the Error Amplifier. Internally, this pin is connected to VOUT with a 100k precision resistor. Different output voltages can be programmed with an additional resistor between VFB and SGND pins. See the Applications Information section. FCB (Pin A9): Forced Continuous Control Input. The voltage applied to this pin sets the operating mode of the module. When the applied voltage is less than 0.8V, the forced continuous current mode is active in boost operation and the skip cycle mode is active in buck operation. When the pin is tied to INTVCC, the constant frequency discontinuous current mode is active in buck or boost operation. See the Applications Information section. SGND (Pin A7): Signal Ground Pin. This pin connects to PGND at output capacitor point. COMP (Pin B7): 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. PGOOD (Pin B5): Output Voltage Power Good Indicator. Open drain logic output that is pulled to ground when the output voltage is not within ±7.5% of the regulation point. RUN (Pin A8): Run Control Pin. A voltage below 1.6V will turn off the module. There is a 100k resistor between the RUN pin and SGND in the module. Do not apply more than 6V to this pin. See the Applications Information section. SS (Pin A6): Soft-Start Pin. Soft-start reduces the input surge current from the power source by gradually increasing the controller's current limit. 4609fa 7 LTM4609 LTM4609 SIMPLIFIED BLOCK DIAGRAM VIN 4.5V TO 36V EXTVCC C1 CIN M1 SW2 INTVCC M2 PGOOD L SW1 RUN ON/OFF VOUT 100k 12V 4A STBYMD CO1 M3 COUT 0.1F 100k COMP VFB M4 INT COMP CONTROLLER RFB 7.15k RSENSE SENSE+ SS SS 0.1F PLLIN INT FILTER RSENSE SENSE­ PLLFLTR PGND INT FILTER FCB SGND 1000pF TO PGND PLANE AS SHOWN IN FIGURE 15 4609 BD Figure 1. Simplified LTM4609 LTM4609 Block Diagram DECOUPLING REQUIREMENTS TA = 25°C. Use Figure 1 configuration. SYMBOL PARAMETER CONDITIONS MIN CIN External Input Capacitor Requirement (VIN = 4.5V to 36V, VOUT = 12V) IOUT = 4A 10 COUT External Output Capacitor Requirement (VIN = 4.5V to 36V, VOUT = 12V) IOUT = 4A 200 TYP MAX UNITS F 300 F 4609fa 8 LTM4609 LTM4609 OPERATION Power Module Description The LTM4609 LTM4609 is a non-isolated buck-boost DC/DC power supply. It can deliver a wide range output voltage from 0.8V to 34V over a wide input range from 4.5V to 36V, by only adding the sensing resistor, inductor and some external input and output capacitors. It provides precisely regulated output voltage programmable via one external resistor. The typical application schematic is shown in Figure 18. The LTM4609 LTM4609 has an integrated current mode buck-boost control, ultralow RDS(ON) FETs with fast switching speed and integrated Schottky diodes. With current mode control and internal feedback loop compensation, the LTM4609 LTM4609 module has sufficient stability margins and good transient performance under a wide range of operating conditions and with a wide range of output capacitors. The frequency of LTM4609 LTM4609 can be operated from 200kHz to 400kHz by setting the voltage on the PLLFLTR pin. Alternatively, its frequency can be synchronized by the input clock signal from the PLLIN pin. The typical switching frequency is 400kHz. The Burst Mode® and skip-cycle mode operations can be enabled at light loads in the LTM4609 LTM4609 to improve its efficiency, while the forced continuous mode and discontinuous mode operations are used for constant frequency applications. Foldback current limiting is activated in an overcurrent condition as VFB drops. Internal overvoltage and undervoltage comparators pull the open-drain PGOOD output low if the output feedback voltage exits the ±7.5% window around the regulation point. Pulling the RUN pin below 1.6V forces the controller into its shutdown state. If an external bias supply is applied on the EXTVCC pin, then an efficiency improvement will occur due to the reduced power loss in the internal linear regulator. This is especially true at the higher input voltage range. Burst Mode is a registered trademark of Linear Technology Corporation. APPLICATIONS INFORMATION The typical LTM4609 LTM4609 application circuit is shown in Figure 18. External component selection is primarily determined by the maximum load current and output voltage. Refer to Table 3 for specific external capacitor requirements for a particular application. Output Voltage Programming The PWM controller has an internal 0.8V±1% reference voltage. As shown in the Block Diagram, a 100k 0.5% internal feedback resistor connects VOUT and VFB pins together. Adding a resistor RFB from the VFB pin to the SGND pin programs the output voltage: VOUT = 0.8V · 100k + RFB RFB Operation Frequency Selection The LTM4609 LTM4609 uses current mode control architecture at constant switching frequency, which is determined by the internal oscillator's capacitor. This internal capacitor is charged by a fixed current plus an additional current that is proportional to the voltage applied to the PLLFLTR pin. The PLLFLTR pin can be grounded to lower the frequency to 200kHz or tied to 2.4V to yield approximately 400kHz. When PLLIN is left open, the PLLFLTR pin goes low, forcing the oscillator to its minimum frequency. A graph for the voltage applied to the PLLFLTR pin vs frequency is given in Figure 2. As the operating frequency increases, the gate charge losses will be higher, thus the efficiency is low. The maximum switching frequency is approximately 400kHz. Table 1. RFB Resistor (0.5%) vs Output Voltage VOUT 0.8V 1.5V 2.5V 3.3V 5V 6V 8V 9V RFB Open 115k 47.5k 32.4k 19.1k 15.4k 11k 9.76k VOUT 10V 12V 15V 16V 20V 24V 30V 34V 5.23k 4.12k 3.4k 2.74k 2.37k RFB 8.66k 7.15k 5.62k FREQUENCY SYNCHRONIZATION The LTM4609 LTM4609 can also be synchronized to an external source via the PLLIN pin instead of adjusting the voltage on the PLLFLTR pin directly. The power module has a phase4609fa 9 LTM4609 LTM4609 APPLICATIONS INFORMATION locked loop comprised of an internal voltage controlled oscillator and a phase detector. This allows turning on the internal top MOSFET for locking to the rising edge of the external clock. A pulse detection circuit is used to detect a clock on the PLLIN pin to turn on the phase-lock loop. The input pulse width of the clock has to be at least 400ns, and 2V in amplitude. The synchronized frequency ranges from 200kHz to 400kHz, corresponding to a DC voltage input from 0V to 2.4V at PLLFLTR. During the start-up of the regulator, the phase-lock loop function is disabled. 450 OPERATING FREQUENCY (kHz) 400 350 300 250 200 150 100 50 0 0 1.0 1.5 2.0 0.5 PLLFLTR PIN VOLTAGE (V) lower than the preset minimum output current level. The MOSFETs will turn on for several cycles, followed by a variable "sleep" interval depending upon the load current. During buck operation, skip-cycle mode sets a minimum positive inductor current level. In this mode, some cycles will be skipped when the output load current drops below 1% of the maximum designed load in order to maintain the output voltage. When the FCB pin voltage is tied to the INTVCC pin, the controller enters constant frequency discontinuous current mode (DCM). For boost operation, if the output voltage is high enough, the controller can enter the continuous current buck mode for one cycle to discharge inductor current. In the following cycle, the controller will resume DCM boost operation. for buck operation, constant frequency discontinuous current mode is turned on if the preset minimum negative inductor current level is reached. At very light loads, this constant frequency operation is not as efficient as Burst Mode operation or skip-cycle, but does provide low noise, constant frequency operation. 2.5 Input Capacitors 4609 F02 Figure 2. Frequency vs PLLFLTR Pin Voltage Low Current Operation To improve the efficiency at low current operation, LTM4609 LTM4609 provides three modes for both buck and boost operations by accepting a logic input on the FCB pin. Table 2 shows the different operation modes. Table 2. Different Operating Modes FCB PIN BUCK BOOST 0V to 0.75V Force Continuous Mode Force Continuous Mode 0.85V to 5V Skip-Cycle Mode Burst Mode Operation >5.3V DCM with Constant Freq DCM with Constant Freq When the FCB pin voltage is lower than 0.8V, the controller behaves as a continuous, PWM current mode synchronous switching regulator. When the FCB pin voltage is below VINTVCC ­ 1V, but greater than 0.8V, the controller enters Burst Mode operation in boost operation or enters skipcycle mode in buck operation. During boost operation, Burst Mode operation is activated if the load current is In boost mode, since the input current is continuous, only minimum input capacitors are required. However, the input current is discontinuous in buck mode. So the selection of input capacitor CIN is driven by the need of filtering the input square wave current. For a buck converter, the switching duty-cycle can be estimated as: D= VOUT VIN Without considering the inductor current ripple, the RMS current of the input capacitor can be estimated as: ICIN(RMS) = IOUT(MAX) · D · (1- D) In the above equation, is the estimated efficiency of the power module. CIN can be a switcher-rated electrolytic aluminum capacitor, OS-CON capacitor or high volume ceramic capacitors. Note the capacitor ripple current rat4609fa 10 LTM4609 LTM4609 APPLICATIONS INFORMATION ings are often based on temperature and hours of life. This makes it advisable to properly derate the input capacitor, or choose a capacitor rated at a higher temperature than required. Always contact the capacitor manufacturer for derating requirements. ripple IL is typically set to 20% to 40% of the maximum inductor current. In the inductor design, the worst cases in continuous mode are considered as follows: LBOOST Output Capacitors In boost mode, the discontinuous current shifts from the input to the output, so the output capacitor COUT must be capable of reducing the output voltage ripple. For boost and buck modes, the steady ripple due to charging and discharging the bulk capacitance is given by: VRIPPLE,BOOST = VRIPPLE,BUCK = ( IOUT(MAX) · VOUT - VIN(MIN) COUT · VOUT · ( VOUT · VIN(MAX) - VOUT ) LBUCK ( V 2IN · VOUT(MAX) - VIN V 2 OUT(MAX) ) · ·IOUT(MAX) · Ripple% ( VOUT · VIN(MAX) - VOUT ) VIN(MAX) · ·IOUT(MAX) · Ripple% where: is operating frequency, Hz Ripple% is allowable inductor current ripple, % VOUT(MAX) is maximum output voltage, V ) 8 · L · COUT · VIN(MAX) · 2 The steady ripple due to the voltage drop across the ESR (effective series resistance) is given by: VESR,BUCK = IL(MAX) · ESR VESR,BOOST =IL(MAX) · ESR The LTM4609 LTM4609 is designed for low output voltage ripple. The bulk output capacitors defined as COUT are chosen with low enough ESR to meet the output voltage ripple and transient requirements. COUT can be the low ESR tantalum capacitor, the low ESR polymer capacitor or the ceramic capacitor. Multiple capacitors can be placed in parallel to meet the ESR and RMS current handling requirements. The typical capacitance is 300F Additional output filtering may . be required by the system designer, if further reduction of output ripple or dynamic transient spike is required. Table 3 shows a matrix of different output voltages and output capacitors to minimize the voltage droop and overshoot at a current transient. Inductor Selection The inductor is chiefly decided by the required ripple current and the operating frequency. The inductor current VIN(MAX) is maximum input voltage, V VOUT is output voltage, V IOUT(MAX) is maximum output load current, A The inductor should have low DC resistance to reduce the I2R losses, and must be able to handle the peak inductor current without saturation. To minimize radiated noise, use a toroid, pot core or shielded bobbin inductor. Please refer to Table 3 for the recommended inductors for different cases. RSENSE Selection and Maximum Output Current RSENSE is chosen based on the required inductor current. Since the maximum inductor valley current at buck mode is much lower than the inductor peak current at boost mode, different sensing resistors are suggested to use in buck and boost modes. The current comparator threshold sets the peak of the inductor current in boost mode and the maximum inductor valley current in buck mode. In boost mode, the allowed maximum average load current is: 160mV IL VIN IOUT(MAX,BOOST) = - · 2 VOUT RSENSE where IL is peak-to-peak inductor ripple current. 4609fa 11 LTM4609 LTM4609 APPLICATIONS INFORMATION In buck mode, the allowed maximum average load current is: IOUT(MAX,BUCK) = 130mV IL + RSENSE 2 The maximum current sensing RSENSE value for the boost mode is: RSENSE(MAX,BOOST) = 2 · 160mV · VIN 2 ·IOUT(MAX,BOOST) · VOUT + IL · VIN The maximum current sensing RSENSE value for the buck mode is: RSENSE(MAX,BUCK) = 2 · 130mV 2 ·IOUT(MAX,BUCK) ­ IL A 20% to 30% margin on the calculated sensing resistor is usually recommended. Please refer to Table 3 for the recommended sensing resistors for different applications. Soft-Start The SS pin provides a means to soft-start the regulator. A capacitor on this pin will program the ramp rate of the output voltage. A 1.7A current source will charge up the external soft-start capacitor. This will control the ramp of the internal reference and the output voltage. The total soft-start time can be calculated as: t SOFTSTART = 2.4V · CSS 1.7µA When the RUN pin falls below 1.6V, then soft-start pin is reset to allow for proper soft-start control when the regulator is enabled again. Current foldback and force continuous mode are disabled during the soft-start process. The softstart function can also be used to control the output ramp up time, so that another regulator can be easily tracked. Do not apply more than 6V to the SS pin. Run Enable The RUN pin is used to enable the power module. The pin can be driven with a logic input, and not exceed 6V. The RUN pin can also be used as an undervoltage lockout (UVLO) function by connecting a resistor from the input supply to the RUN pin. The equation: V _UVLO = R1+ R2 · 1.6V R2 Power Good The PGOOD pin is an open drain pin that can be used to monitor valid output voltage regulation. This pin monitors a ±7.5% window around the regulation point, and tracks with margining. COMP Pin This pin is the external compensation pin. The module has already been internally compensated for most output voltages. A spice model will be provided for other control loop optimization. Fault Conditions: Current Limit and Overcurrent Foldback LTM4609 LTM4609 has a current mode controller, which inherently limits the cycle-by-cycle inductor current not only in steady state operation, but also in transient. Refer to Table 3. To further limit current in the event of an overload condition, the LTM4609 LTM4609 provides foldback current limiting. If the output voltage falls by more than 70%, then the maximum output current is progressively lowered to about 30% of its full current limit value for boost mode and about 40% for buck mode. Standby Mode (STBYMD) The standby mode (STBYMD) pin provides several choices for start-up and standby operational modes. If the pin is pulled to ground, the SS pin is internally pulled to ground, preventing start-up and thereby providing a single control pin for turning off the controller. If the pin is left open or decoupled with a capacitor to ground, the SS pin is internally provided with a starting current, permitting external control for turning on the controller. If the pin is connected to a voltage greater than 1.25V, the internal regulator (INTVCC) will be on even when the controller is shut down (RUN 4609fa 12 LTM4609 LTM4609 APPLICATIONS INFORMATION pin voltage