LTC8606

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Technical content

8606fbFor more information www.linear.com/LT8606

FEATURES

DESCRIPTION

42V, 350mA Synchronous Step-Down Regulator with 2.5µA Quiescent Current The LT®8606 is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7µA of non-switching quiescent current. The LT8606 can deliver 350mA of continuous 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 10mV P-P. Internal com- pensation 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 LT8606 reducing the input supply current to 1µA. The PG pin signals when V OUT is within ±8.5% of the programmed output voltage as well as fault conditions. The MSOP package includes a SYNC pin to synchronize to an external clock, or to select Burst Mode operation or pulse-skipping with or without spread-spectrum; the TR/SS pin programs soft-start or tracking.

APPLICATIONS

n Wide Input Voltage Range: 3.0V to 42V n Ultralow Quiescent Current Burst Mode® Operation: n <3µA IQ Regulating 12VIN to 3.3VOUT n Output Ripple <10mVP-P n High Efficiency 2MHz Synchronous Operation: n >92% Efficiency at 0.35A, 12VIN to 5VOUT n 350mA Maximum Continuous Output n Fast Minimum Switch-On Time: 35ns n Adjustable and Synchronizable: 200kHz to 2.2MHz n Spread Spectrum Frequency Modulation for Low EMI n Allows Use of Small Inductors n Low Dropout n Peak Current Mode Operation n Accurate 1V Enable Pin Threshold n Internal Compensation n Output Soft-Start and T racking n Small Thermally Enhanced 10-Lead MSOP Package or 8-Pin 2mm × 2mm DFN Package n General Purpose Step-Down Converter n Low EMI Step Down All registered trademarks and trademarks are the property of their respective owners. 5V, 2MHz Step-Down 12VIN to 5VOUT Efficiency VIN BST EN/UV C1 0.1µF 10pF 1µF V IN 5.5V TO 42V 10nF 1µF V OUT 350mA POWER GOOD 187k

8606 TA01a

10µH SYNC INTVCC TR/SS RT L T8606 GND SW PG FB 100k 18.2k L1 = XFL3010-103ME 10µF X7R 0805 f SW = 2MHz f SW = 2MHz L = 10µH I OUT (mA) 100 150 200 250 300 350 100 EFFICIENCY (%)

8606 TA01b

8606fb For more information www.linear.com/LT8606 PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS FB, TR/SS . SYNC Voltage . (Note 1) BST SW INTV CC RT SYNC EN/UV V IN PG TR/SS FB TOP VIEW GND MSE PACKAGE 10-LEAD PLASTIC MSOP θJA = 40°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB TOP VIEW BST SW INTVCC RT EN/UV VIN PG FB DC PACKAGE 8-LEAD (2mm × 2mm) PLASTIC DFN GND 3 6 θJA = 102°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8606EMSE#PBF LT8606EMSE#TRPBF L TGXT 10-Lead Plastic MSOP –40°C to 125°C LT8606IMSE#PBF LT8606IMSE#TRPBF L TGXT 10-Lead Plastic MSOP –40°C to 125°C LT8606HMSE#PBF LT8606HMSE#TRPBF L TGXT 10-Lead Plastic MSOP –40°C to 150°C LT8606EDC#PBF LT8606EDC#TRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C LT8606IDC#PBF LT8606IDC#TRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C LT8606HDC#PBF LT8606HDC#TRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 150°C Consult L TC 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/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. http://www.linear .com/product/LT8606#orderinfo

ELECTRICAL CHARACTERISTICS

Operating Junction Temperature Range (Note 2) LT 8606E LT 8606I LT 8606H to 150°C Storage Temperature Range PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage l 2.5 3.0 3.2 V VIN Quiescent Current VEN/UV = 0V VEN/UV = 2V, Not Switching, VSYNC = 0V or DFN, VIN ≤ 36V l 1.7 µA µA VIN Current in Regulation VIN = 6V, VOUT = 2.7V, Output Load = 100µA VIN = 6V, VOUT = 2.7V, Output Load = 1mA l l 500 700 µA µA

8606fbFor more information www.linear.com/LT8606 The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. 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. Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT8606E 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 LT8606I is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT8606H 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 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. PARAMETER CONDITIONS MIN TYP MAX UNITS Feedback Reference Voltage MSOP Package VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.774 0.762 0.778 0.778 0.782 0.798 V V V IN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.771 0.753 0.778 0.778 0.785 0.803 V V Feedback V oltage Line Regulation VIN = 4.0V to 40V l ±0.02 ±0.06 %/V Feedback Pin Input Current VFB = 1V ±20 nA Minimum On-Time ILOAD = 350mA ILOAD = 350mA, SYNC = 1.9V l l ns ns Minimum Off T ime ILOAD = 300mA l 93 130 ns Oscillator Frequency MSOP Package RT = 221k, ILOAD = 250mA RT = 60.4k, ILOAD = 250mA RT = 18.2k, ILOAD = 250mA l l l 155 640 1.90 200 700 2.00 245 760 2.10 kHz kHz MHz R T = 221k, ILOAD = 250mA RT = 60.4k, ILOAD = 250mA RT = 18.2k, ILOAD = 250mA l l l 140 610 1.85 200 700 2.00 260 790 2.15 kHz kHz MHz T op Power NMOS On-Resistance ILOAD = 250mA 375 mΩ Top Power NMOS Current Limit MSOP Package l 0.65 0.9 1.15 A Bottom Power NMOS On-Resistance 240 mΩ SW Leakage Current VIN = 36V 5 µA EN/UV Pin Threshold EN/UV Rising l 0.99 1.05 1.11 V EN/UV Pin Hysteresis 50 mV EN/UV Pin Current VEN/UV = 2V ±20 nA PG Upper Threshold Offset from VFB VFB Rising l 5.0 8.5 13.0 % PG Lower Threshold Offset from VFB VFB Falling l 5.0 8.5 13.0 % PG Hysteresis 0.5 % PG Leakage VPG = 42V ±200 nA PG Pull-Down Resistance VPG = 0.1V 550 1200 Ω Sync Low Input Voltage MSOP Only l 0.4 0.9 V Sync High Input Voltage INTVCC = 3.5V, MSOP Only l 2.7 3.2 V TR/SS Source Current MSOP Only l 1 2 3 µA TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V, MSOP Only 300 900 Ω Spread Spectrum Modulation Frequency V SYNC = 3.3V, MSOP Only 0.5 3 6 kHz

8606fb For more information www.linear.com/LT8606 FB Voltage Load Regulation Efficiency (3.3V Output, Burst Mode Operation) TYPICAL PERFORMANCE CHARACTERISTICS Efficiency (5V Output, Burst Mode Operation) Efficiency (5V Output, Burst Mode Operation) Efficiency (3.3V Output, Burst Mode Operation) I OUT (mA) 100 150 200 250 300 350 100 EFFICIENCY (%)

8606 G01

L = 10µH fSW = 2MHz VIN = 12V VIN = 24V I OUT (mA) 0.001 0.01 0.1 100 500 100 EFFICIENCY (%)

8606 G02

L = 10µH fSW = 2MHz VIN = 12V VIN = 24V I OUT (mA) 100 150 200 250 300 350 100 EFFICIENCY (%)

8606 G03

L = 6.8µH fSW = 2MHz VIN = 12V VIN = 24V I OUT (mA) 0.001 0.01 0.1 100 500 100 EFFICIENCY (%)

8606 G04

L = 6.8µH fSW = 2MHz VIN = 12V VIN = 24V TEMPERATURE (°C) –50 –10 110 150 775 776 777 778 779 780 FB REGULATION VOL TAGE (mV)

8606 G05

OUTPUT CURRENT (mA) 100 150 200 250 300 350 –0.20 –0.15 –0.10 –0.05 0.00 0.05 0.10 0.15 0.20 CHANGE IN V OUT (%)

8606 G06

TA = 25°C, unless otherwise noted.

8606fbFor more information www.linear.com/LT8606 TYPICAL PERFORMANCE CHARACTERISTICS Line Regulation No-Load Supply Current (3.3V Output Switching) No-Load Supply Current vs Temperature (Not Switching) Top FET Current Limit vs Duty Cycle Top FET Current Limit vs Temperature Switch Drop vs Temperature Switch Drop vs Switch Current INPUT VOL TAGE (V) –0.20 –0.15 –0.10 –0.05 0.00 0.05 0.10 0.15 0.20 CHANGE IN V OUT (%)

8606 G07

L = 10µH INPUT VOL TAGE (V) 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 I IN (µA)

8606 G08

TEMPERATURE (°C) –50 –10 110 150 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 INPUT CURRENT (µA)

8606 G09

DUTY CYCLE (%) 100 0.60 0.70 0.80 0.90 1.00 1.10 TOP FET CURRENT LIMIT (A)

8606 G10

DUTY CYCLE = 0 TEMPERATURE (°C) –50 –10 110 150 0.90 0.95 1.00 1.05 1.10 TOP FET CURRENT LIMIT (A)

8606 G11

SWITCH CURRENT = 350mA TEMPERATURE (°C) –50 –30 –10 110 130 150 100 150 200 250 SWITCH DROP (mV)

8606 G12

SWITCH CURRENT (mA) 100 150 200 250 300 350 100 125 150 175 200 SWITCH DROP (mV)

8606 G13

TA = 25°C, unless otherwise noted.

8606fb For more information www.linear.com/LT8606 TYPICAL PERFORMANCE CHARACTERISTICSTA = 25°C, unless otherwise noted. Minimum On-Time vs Temperature Minimum Off-Time vs Temperature Dropout Voltage vs Output Current Switching Frequency vs Temperature Burst Frequency vs Output Current Minimum Load to Full Frequency (SYNC Float to 1.9V) (MSOP Package) I OUT = 350mA TEMPERATURE (°C) –50 –30 –10 110 130 150 MINIMUM ON–TIME (ns)

8606 G14

I OUT = 300mA TEMPERATURE (°C) –50 –30 –10 110 130 150 100 105 110 MINIMUM OFF–TIME (ns)

8606 G15

L = XFL3010–682ME 0.05 0.10 0.15 0.20 0.25 0.30 0.35 100 150 200 250 DROPOUT VOL TAGE (mV)

8606 G16

OUTPUT CURRENT (A) R T = 18.2kΩ TEMPERATURE (°C) –50 –10 110 150 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 SWITCHING FREQUENCY (kHz)

8606 G17

OUTPUT CURRENT (mA) 100 125 250 500 750 1000 1250 1500 1750 2000 2250 2500 SWITCHING FREQUENCY (kHz)

8606 G18

L = 6.8µH VIN = 12V VOUT = 3.3V SYNC = 0V L = 10µH VIN = 12V VOUT = 5V RT = 18.2k/uni03A9 INPUT VOL TAGE (V) OUTPUT CURRENT (mA)

8606 G19

8606fbFor more information www.linear.com/LT8606 TYPICAL PERFORMANCE CHARACTERISTICSTA = 25°C, unless otherwise noted. Frequency Foldback Soft-Start T racking (MSOP Package) Soft-Start Current vs Temperature (MSOP Package) V IN UVLO Start-Up Dropout Start-Up Dropout FB VOL TAGE (V) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 250 500 750 1000 1250 1500 1750 2000 2250 2500 FREQUENCY (kHz)

8606 G20

SYNC = 0V RT = 18.2k/uni03A9 SS VOL TAGE (V) 0.1 0.2 0.4 0.5 0.6 0.7 0.8 1.0 1.1 1.2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 FB VOL TAGE (V)

8606 G21

TEMPERATURE (°C) –50 –30 –10 110 130 150 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 SOFT START CURRENT (µA)

8606 G22

TEMPERATURE (°C) –50 –30 –10 110 130 150 2.00 2.25 2.50 2.75 3.00 3.25 V IN UVLO (V)

8606 G23

R LOAD = 50Ω INPUT VOL TAGE (V) INPUT VOL TAGE (V) OUTPUT VOL TAGE (V)

8606 G24

R LOAD = 15Ω INPUT VOL TAGE (V) INPUT VOL TAGE (V) OUTPUT VOL TAGE (V)

8606 G25

8606fb For more information www.linear.com/LT8606 TYPICAL PERFORMANCE CHARACTERISTICS T ransient Response T ransient Response Switching Waveforms Switching Waveforms Switching Waveforms 200ns/DIV VSW 5V/DIV ILOAD 100mA/DIV

8606 G26

8606 G27

2µs/DIV SW 5V/DIV ILOAD 100mA/DIV VOUT 20mV/DIV

8606 G28

10µF COUT 200µs/DIV VOUT 100mV/DIV ILOAD 100mA/DIV

8606 G29

VIN =12V, VOUT = 5V 25mA TO 275mA COUT = 22µF fSW = 2MHz 200µs/DIV VOUT 100mV/DIV ILOAD 100mA/DIV

8606 G30

VIN =12V, VOUT = 5V 100mA TO 350mA C OUT = 22µF fSW = 2MHz TA = 25°C, unless otherwise noted. FREQUENCY (MHz) AMPLITUDE (dBµV) –10

8606 G31

0 500 900300 700 1000400 800200 600100 VERTICAL POLARIZATION PEAK DETECTOR CLASS 5 PEAK LIMIT SPREAD SPECTRUM MODE FIXED FREQUENCY DC2564A DEMO BOARD WITH EMI FIL TER INSTALLED 14V INPUT TO 5V OUTPUT AT 350mA, f SW = 2MHz Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits)

8606fbFor more information www.linear.com/LT8606 PIN FUNCTIONS BST: 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. Do not place a resistor in series with this pin. SW: The SW pin is the output of the internal power switches. Connect this pin to the inductor and boost capacitor . This node should be kept small on the PCB for good performance. INTV CC Internal 3.5V Regulator Bypass Pin. The internal power drivers and control circuits are powered from this voltage. INTV CC max output current is 20mA. Voltage on INTVCC will vary between 2.8V and 3.5V. Decouple this pin to power ground with at least a 1μF low ESR ceramic capacitor . Do not load the INTVCC pin with exter- nal circuitry. RT: A resistor is tied between RT and ground to set the switching frequency. When synchronizing, the RT resistor should be chosen to set the LT8606 switching frequency to equal or below the lowest synchronization input. SYNC (MSOP Only): External Clock Synchronization Input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a clock source for synchroni - zation to an external frequency. Leave floating for pulse- skipping mode with no spread spectrum modulation. T ie to INTVCC or tie to a voltage between 3.2V and 5.0V for pulse-skipping mode with spread spectrum modulation. When in pulse-skipping mode, the I Q regulating no load will increase to several mA. There is no SYNC pin on the LT8606 DFN and the node is internally tied to ground. FB: The LT8606 regulates the FB pin to 0.778V. Connect the feedback resistor divider tap to this pin. TR/SS (MSOP Only): Output T racking and Soft-Start Pin. This pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.778V forces the LT8606 to regulate the FB pin to equal the TR/SS pin volt- age. When TR/SS is above 0.778V, the tracking function is disabled and the internal reference resumes control of the error amplifier . An internal 2μA pull-up current from INTVCC on this pin allows a capacitor to program out - put voltage slew rate. This pin is pulled to ground with a 300Ω MOSFET during shutdown and fault conditions; use a series resistor if driving from a low impedance output. There is no TR/SS pin on the LT8606 DFN and the node is internally floated. PG: The PG pin is the open-drain output of an internal comparator . PG remains low until the FB pin is within ±8.5% of the final regulation voltage, and there are no fault conditions. PG is valid when V IN is above 3.2V and when EN/UV is high. PG is pulled low when VIN is above 3.2V and EN/UV is low. If VIN is near zero, PG will be high impedance. VIN: The VIN pin supplies current to the LT8606 internal circuitry and to the internal topside power switch. This pin must be locally bypassed. Be sure to place the positive terminal of the input capacitor as close as possible to the V IN pins, and the negative capacitor terminal as close as possible to the GND pins. EN/UV: The LT8606 is shut down when this pin is low and active when this pin is high. The hysteretic threshold volt- age is 1.05V going up and 1.00V going down. Tie to V IN if the shutdown feature is not used. An external resistor divider from V IN can be used to program a VIN threshold below which the LT8606 will shut down. GND: Exposed Pad Pin. The exposed pad must be con - nected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the thermal resistance.

8606fb For more information www.linear.com/LT8606 BLOCK DIAGRAM ++– SLOPE COMP INTERNAL 0.778V REF OSCILLATOR 200kHz TO 2.2MHz BURST DETECT 3.5V REG CBST COUT VOUT 8606 BD SW L BST SWITCH LOGIC AND ANTI- SHOOT THROUGH ERROR AMP SHDN ±8.5% VC SHDN TSD INTV CC UVLO VIN UVLO SHDN TSD V IN UVLO EN/UV 1V + – INTVCC GND PG FB RPG RT CSS VOUT CFF TR/SS (MSOP ONL Y) 2µA RT SYNC (MSOP ONL Y) VINVIN CIN CVCC OPT OPT

8606fbFor more information www.linear.com/LT8606 OPERATION The LT8606 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 V FB pin with an inter - nal 0.778V 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 volt- age 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 excess current 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 LT8606 is shut down and draws 1µA from the input. When the EN/UV pin is above 1.05V, the switching regulator becomes active. To optimize efficiency at light loads, the LT8606 enters Burst Mode operation during 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, 3.0μA 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 floated 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 oper- ates 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 mA. The SYNC pin may be tied high for spread spectrum modulation mode, and the LT8606 will operate similar to pulse-skipping mode but vary the clock fre - quency to reduce EMI. The LT8606 DFN has no SYNC pin and will always operate in Burst Mode operation. Comparators monitoring the FB pin voltage will pull the PG pin low if the output voltage varies more than ±8.5% (typi- cal) from the set point, or if a fault condition is present. The oscillator reduces the LT8606’s operating frequency when the voltage at the FB pin is low and the part is in Burst Mode operation. This frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up.

mode the LT8606 consumes 1.7μA. be minimized as it appears to the output as load current. capacitance will decrease the output ripple proportionally.

1. The output load at which the

voltage, and inductor choice. tion with pulse-skipping mode, the SYNC pin is tied high. Figure 2. Full Switching Frequency Minimum Load Figure 3. Burst Mode Operation Figure 1. SW Burst Mode Frequency vs Output Current

8606 F01

8606 F02

8606 F03

optimize the quiescent current at low loads. upwards of the frequency set by RT. Table 1. SW Frequency vs RT Value control of inductor current to assure safe operation. dropped to achieve higher duty cycle.

8606fb For more information www.linear.com/LT8606 APPLICATIONS INFORMATION Inductor Selection and Maximum Output Current The LT8606 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 LT8606 safely tolerates opera- tion with a saturated inductor through the use of a high speed peak-current mode architecture. A good first choice for the inductor value is: L = VOUT + VSW(BOT) fSW

• 4 where fSW is the switching frequency in MHz, V OUT is the output voltage, V SW(BOT) is the bottom switch drop (~0.06V) 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 applica - tion. 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: IL(PEAK) =ILOAD(MAX)+ 1 2 ΔL where ∆IL is the inductor ripple current as calculated sev- eral paragraphs below and I LOAD(MAX) is the maximum output load for a given application. As a quick example, an application requiring 0.25A output should use an inductor with an RMS rating of greater than 0.5A and an I SAT of greater than 0.7A. 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. The LT8606 limits the peak switch current in order to protect the switches and the system from overload faults. The top switch current limit (I LIM) is at least 0.65A at low duty cycles and decreases linearly to at least 0.5A at D = 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 (I LIM) and the ripple current: IOUT(MAX) =ILIM – ΔIL The peak-to-peak ripple current in the inductor can be calculated as follows: ΔIL = VOUT L • fSW 1– VOUT VIN(MAX) where fSW is the switching frequency of the LT8606, and L is the value of the inductor . Therefore, the maximum output current that the LT8606 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 requir- ing smaller load currents, the value of the inductor may be lower and the LT8606 may operate with higher ripple 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 Analog Devices 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 LT8606 circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor per - formance over temperature and applied voltage, and should not be used. A 4.7μF to 10μF ceramic capacitor is adequate to bypass the LT8606 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

8606fbFor more information www.linear.com/LT8606 APPLICATIONS INFORMATION significant inductance due to long wires or cables, addi - tional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor . Step-down regulators draw current from the input sup - ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage rip - ple at the LT8606 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 LT8606 (see the PCB Layout section). A second precaution regarding the ceramic input capaci- tor concerns the maximum input voltage rating of the LT8606. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8606 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8606’s voltage rating. This situation is easily avoided (see Analog Devices 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 LT8606 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 sta- bilize the LT8606’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: COUT = 100 VOUT • fSW where f SW is in MHz, and C OUT is the recommended output capacitance in μF . Use X5R or X7R types. This choice will provide low output ripple and good tran - sient response. T ransient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between V OUT 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 per - formance 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 capaci - tance 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 LT8606 due to their piezoelectric nature. When in Burst Mode operation, the LT8606’s switching frequency depends on the load current, and at very light loads the LT8606 can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT8606 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. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LT8606. As pre- viously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8606 circuit is plugged into a live supply, the input voltage can ring to twice its nomi- nal value, possibly exceeding the LT8606’s rating. This situation is easily avoided (see Analog Devices Application Note 88). Enable Pin The LT8606 is in shutdown when the EN pin is low and active when the pin is high. The rising threshold of the EN comparator is 1.05V, with 50mV 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 V IN to EN programs the LT8606 to regulate the output only when V IN is above a desired voltage (see Block Diagram). Typically, this threshold, VIN(EN), is used in situations where the input

8606fb For more information www.linear.com/LT8606 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: VIN(EN) = R3 R4 +1⎛ ⎝⎜ ⎞ ⎠⎟•1V where the LT8606 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 in Burst Mode operation for light-load currents, the current through the VIN(EN) resistor network can eas- ily be greater than the supply current consumed by the LT8606 . 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 3.5V supply from V IN that powers the drivers and the internal bias circuitry. The INTVCC can supply enough cur- rent for the LT8606’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. Applications with high input voltage and high switching frequency 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 T racking and Soft-Start (MSOP ONL Y) The LT8606 allows the user to program its output voltage ramp rate by means of the TR/SS pin. An internal 2μA pulls up the TR/SS pin to INTV CC. 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 APPLICATIONS INFORMATION TR/SS pin voltage. For output tracking applications, TR/ SS can be externally driven by another voltage source. From 0V to 0.778V, the TR/SS voltage will override the internal 0.778V reference input to the error amplifier , thus regulating the FB pin voltage to that of TR/SS pin. When TR/SS is above 0.778V, tracking is disabled and the feed- back voltage will regulate to the internal reference voltage. 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. The LT8606 DFN does not have TR/SS pin or functionality. Output Power Good When the LT8606’s output voltage is within the ±8.5% window of the regulation point, which is a VFB voltage in the range of 0.716V to 0.849V (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 drain pull-down device will pull the PG pin low. To prevent glitching both the upper and lower thresholds include 0.5% 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 (MSOP ONL Y) To select low ripple Burst Mode operation, tie the SYNC pin below 0.4V (this can be ground or a logic low out - put). To synchronize the LT8606 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 0.9V and peaks above 2.7V (up to 5V). The LT8606 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 LT8606 may be synchronized over a 200kHz to 2.2MHz range. The RT resistor should be chosen to set the LT8606 switching

500kHz and higher , the RT should be selected for 500kHz. during short circuit conditions. switching if the inductor current exceeds safe levels. other supply is diode ORed with the LT8606 ’s output. grounded the SW pin current will drop to near 0.7µA. against a shorted or reversed input.

8606 F04

Figure 4. Reverse VIN Protection

planes within the circuit board and on the bottom side. placement with trace, ground plane and via locations. temperature approaches the maximum junction rating. a fault condition if safe junction temperature is exceeded. placing the capacitor adjacent to the V IN and GND pins. Figure 5. PCB Layout

8606 F05GND VIA V IN VIA V OUT VIA EN/UV VIA OTHER SIGNAL VIA

8606fbFor more information www.linear.com/LT8606 TYPICAL APPLICATIONS VIN BST EN/UV C1 0.1µF 10pF VIN 5.5V TO 42V 10nF 1µF V OUT 350mA POWER GOOD 187k

8606 TA02

10µH SYNC INTVCC TR/SS RT L T8606 GND SW PG FB 100k 18.2k L1 = XFL3010-103ME 10µF X7R 0805 f SW = 2MHz 1µF X7R 0805 VIN BST EN/UV C1 0.1µF 10pF V IN 3.8V TO 42V 10nF 1µF V OUT 3.3V 350mA POWER GOOD 309k

8606 TA03

6.8µH SYNC INTVCC TR/SS RT L T8606 GND SW PG FB 100k 18.2k L1 = XFL3010-682ME 10µF X7R 0805 f SW = 2MHz 1µF X7R 0805 VIN BST EN/UV C1 0.1µF 100pF V IN 12.7V TO 42V 10nF 1µF V OUT 12V 350mA POWER GOOD 69.8k

8606 TA04

47µH SYNC INTVCC TR/SS RT L T8606 GND SW PG FB 100k 40.2k L1 = MSS6132-473MLB 22µF X7R 1210 f SW = 1MHz 4.7µF X7R 1206 5V 2MHz Step Down 3.3V 2MHz Step Down 12V 1MHz Step Down

8606fb For more information www.linear.com/LT8606 VIN BST EN/UV C1 0.1µF 10pF VIN 3.2V TO 20V (42V TRANSIENT) 10nF 1µF V OUT 1.8V 350mA POWER GOOD 768k

8606 TA05

3.3µH SYNC INTVCC TR/SS RT L T8606 GND SW PG FB 100k 18.2k L1 = XFL3010-332ME 22µF X7R 1206 f SW = 2MHz 4.7µF VIN BST EN/UV C1 0.1µF 47pF V IN

5.8 TO 40V

1µF V OUT 350mA POWER GOOD 187k

8606 TA06

27µH 4.7µH BEAD SYNC INTVCC TR/SS RT L T8606 (MSOP) GND SW PG FB 100k 60.4k 22µF X7R 1206 f SW = 700kHz 4.7µF 33µF 4.7µF 4.7µF C8, C7, C2: X7R 1206 C9: 63SXV33M L1: MSS5121-273 L2: MPZ2012S221AT000 L3: XAL4030-472 Ultralow EMI 5V 1.5A Step Down 1.8V 2MHz Step Down TYPICAL APPLICATIONS

8606fbFor more information www.linear.com/LT8606 PACKAGE DESCRIPTION Please refer to http://www.linear .com/product/LT8606#packaging for the most recent package drawings. MSOP (MSE) 0213 REV I 0.53 ±0.152 (.021 ±.006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 –/uni00A00.27 (.007 – .011) TYP 0.86 (.034) REF 0.50 (.0197) BSC 1 2 3 4 5 4.90 ±0.152 (.193 ±.006) 0.497 ±0.076 (.0196 ±.003) REF8 9 10 7 6 3.00 ±0.102 (.118 ±.004) (NOTE 3) 3.00 ±0.102 (.118 ±.004) (NOTE 4) 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. 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 0.889 ±0.127 (.035 ±.005) RECOMMENDED SOLDER PAD LAYOUT 1.68 ±0.102 (.066 ±.004) 1.88 ±0.102 (.074 ±.004) 0.50 (.0197) BSC 0.305 ± 0.038 (.0120 ±.0015) TYP BOTTOM VIEW OF EXPOSED PAD OPTION 1.68 (.066) 1.88 (.074) 0.1016 ±0.0508 (.004 ±.002) DETAIL “B” DETAIL “B” CORNER TAIL IS PART OF THE LEADFRAME FEATURE. FOR REFERENCE ONL Y NO MEASUREMENT PURPOSE

0.05 REF

0.29 REF 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I)

8606fb For more information www.linear.com/LT8606 PACKAGE DESCRIPTION Please refer to http://www.linear .com/product/LT8606#packaging for the most recent package drawings. 2.00 ±0.05 (4 SIDES) 2.00 SQ ±0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.55 ±0.05 BOTTOM VIEW—EXPOSED PAD 0.23 REF0.335 REF

0.335 REF

0.75 ±0.05 PIN 1 BAR TOP MARK (SEE NOTE 6)

0.200 REF

0.00 – 0.05 (DC8MA) DFN 0113 REV Ø 0.23 ±0.05

0.45 BSC

0.25 ±0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 0.90 REF 0.23 REF 0.85 ±0.05

1.8 REF

2.60 ±0.05 PACKAGE OUTLINE R = 0.15 8-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1939 Rev Ø) Exposed Pad Variation AA

8606fbFor more information www.linear.com/LT8606 Information furnished by Analog Devices is believed to be accurate and reliable. However , no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER A 06/17 Added DFN package option Clarified electrical parameters for DFN package option Clarified graphs for MSOP package option Clarified Pin Functions for DFN package option Clarified Operation section to include DFN option Clarified Applications last paragraph and Figure 2 to include DFN option Clarified Applications section to include DFN operation Added DFN Package Description 1,2 2,3 6,7 16,17 B 11/17 Added H-grade option Clarified Oscillator Frequency R T conditions Clarified efficiency graphs Clarified Frequency Foldback graph Clarified Switching Waveform graph Clarified Block Diagram Added Figure 5 Clarified Typical Applications for MSOP package option 2, 3 20, 24

8606fb  ANALOG DEVICES, INC. 2017 LT 1117 • PRINTED IN USA www.linear.com/LT8606 RELATED PARTS TYPICAL APPLICATION PART NUMBER DESCRIPTION COMMENTS LT8607 42V, 750mA, 92% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 3µA VIN = 3V to 42V, VOUT(MIN) = 0.778V, IQ = 3µA, ISD < 1µA, MSOP-10E Package LT8608 42V, 1.5A, 92% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3V to 42V, VOUT(MIN) = 0.778V, IQ = 2.5µA, ISD < 1µA, MSOP-10E Package LT8609/LT8609A/ LT8609B 42V, 2A/3A Peak, 93% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3V to 42V, VOUT(MIN) = 0.782V, IQ = 2.5µA, ISD < 1µA, MSOP-10E Package LT8609S 42V, 2A/3A Peak, 93% Efficiency, 2.2MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3V to 42V, VOUT(MIN) = 0.774V, IQ = 2.5µA, ISD < 1µA, 3mm × 3mm LQFN-16 Package LT8610A/ LT8610AB/LT8610AC 42V , 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, MSOP-16E Package LT8616 42V, Dual 2.5A + 1.5A, 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.8V, IQ = 5µA, ISD < 1µA, TSSOP-28E, 3mm × 6mm QFN-28 Packages LT8620 65V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 65V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, MSOP-16E, 3mm × 5mm QFN-24 Packages LT8614 42V, 4A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 3mm × 4mm QFN-18 Package LT8612 42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 3.0µA, ISD < 1µA, 3mm × 6mm QFN-28 Package LT8640 42V, 5A, 96% Efficiency, 3MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 3mm × 4mm QFN-18 Package LT8640S 42V, 6A, 96% Efficiency, 3MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 4mm × 4mm LQFN-24 Package LT8645S 65V, 8A, 96% Efficiency, 3MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 65V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 4mm × 6mm LQFN-32 Package Synchronous MicroPower Step-Down DC/DC Converter with I Q = 25µA VIN = 3V to 42V, VOUT(MIN)= 0.8V, IQ = 25µA, ISD < 1µA, 6mm × 6mm QFN-40 Package 5V and 3.3V with Ratio T racking VIN BST EN/UV C1 0.1µF C11, 10pF R6, 1M R2, 1M R10 22k 80.6k C12 1µF V OUT 3.3V 350mA POWER GOOD 309k

8606 TA07

6.8µH SYNC INTVCC TR/SS RT L T8606 (MSOP) GND SW PG FB 100k 18.2k C2, C4, C8, C10: X7R 0805 L1: XFL3010-103ME L2: XFL3010-682ME C10 10µF f SW = 2MHz 1µF V IN BST EN/UV C1 0.1µF C5, 10pF V IN 5.6V TO 42V 10nF 1µF V OUT 350mA POWER GOOD 187k 10µH SYNC INTV CC TR/SS RT L T8606 (MSOP) GND SW PG FB 100k 18.2k 10µF f SW = 2MHz 1µF