lt3971 Linear Technology Corporation, lt3971 Datasheet
lt3971
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lt3971 Summary of contents
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... A power good fl ag signals when V OUT age. The LT3971 is available in small 10-pin MSOP and 3mm × 3mm DFN packages with exposed pads for low thermal resistance. L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation ...
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... For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: 2 Operating Junction Temperature Range (Note 2) LT3971E ............................................. –40°C to 125°C LT3971I .............................................. –40°C to 125°C Storage Temperature Range .............. –65°C to 150°C Lead Temperature (Soldering, 10 sec) (MSE Only) ....................................................... 300°C 10 ...
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... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3971E is guaranteed to meet performance specifi cations from 0°C to 125°C junction temperature. Specifi cations over the –40°C to 125°C operating junction temperature range are assured by design, ...
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... LT3971 TYPICAL PERFORMANCE CHARACTERISTICS Effi ciency OUT 100 V = 12V 36V 24V FRONT PAGE APPLICATION OUT 309k 20 0 0.2 0.4 0.6 0.8 1 LOAD CURRENT (A) 3971 G01 Effi ciency 3.3V OUT 90 FRONT PAGE APPLICATION 12V 24V ...
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... MIN T 1A LOAD OFF 250 200 MIN T 0.5A LOAD OFF 150 100 MIN 1.2 –55 – TEMPERATURE (°C) LT3971 T = 25°C, unless otherwise noted. A Switch Current Limit 3.0 2.5 2.0 1.5 1.0 0 125 155 DUTY CYCLE (%) 3971 G11 Boost Pin Current 30 25 ...
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... LT3971 TYPICAL PERFORMANCE CHARACTERISTICS Minimum Input Voltage 5.0 FRONT PAGE APPLICATION 4 3.3V OUT 4.6 4.4 4.2 TO START 4.0 3.8 TO RUN 3.6 3.4 3.2 3.0 0 200 400 600 800 1000 LOAD CURRENT (mA) 3971 G19 Boost Diode Forward Voltage 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0 250 500 750 1000 1250 BOOST DIODE CURRENT (mA) 3971 G22 Transient Load Response, Load Current Stepped from ...
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... EN to place the part in shutdown. Tie shutdown feature is not used (Pin 6): The LT3971 regulates the FB pin to 1.19V. Connect the feedback resistor divider tap to this pin. Also, connect a phase lead capacitor between FB and V Typically this capacitor is 10pF . ...
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... LT3971 BLOCK DIAGRAM INTERNAL 1.19V REF + 1V – SHDN SYNC PG ERROR AMP + + 1.09V – – GND – + SWITCH SLOPE COMP LATCH R OSCILLATOR Q 200kHz TO 2MHz S Burst Mode DETECT V CLAMP SHDN BD BOOST OUT 1μA ...
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... SS pin; soft-start is implemented by generating a voltage ramp at the SS pin using an external capacitor. If the EN pin is low, the LT3971 is shut down and draws 700nA from the input. When the EN pin exceeds 1V, the switching regulator will become active. The switch driver operates from either V BOOST pin ...
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... To ensure proper Burst Mode operation, the SYNC pin must be grounded. When synchronized with an external clock, the LT3971 will pulse skip at light loads. The qui- escent current will signifi cantly increase to 1.5mA in light load situations when synchronized with an external clock. ...
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... Input Voltage Range section, lower frequency allows a lower dropout voltage. The input voltage range depends on the switching frequency because the LT3971 switch has fi nite minimum on and off times. The minimum switch on and off times are strong functions of temperature. Use the typical minimum on and off curves to design for an application’ ...
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... I – OUT MAX ( ) LIM 2 The LT3971 limits its peak switch current in order to protect itself and the system from overload faults. The LT3971’s switch current limit ( least 2.4A at low duty cycles LIM and decreases linearly to 1.75A 0. the LT3971 will enter Table 2 ...
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... A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank cir- cuit. If the LT3971 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3971’s voltage rating. This situation is easily avoided (see the Hot Plugging Safely section) ...
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... If the LT3971 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3971’s rating. This situation is easily avoided (see the Hot Plugging Safely section). ...
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... V IN(MAX) OUT Figure 3. Three Circuits for Generating the Boost Voltage The minimum operating voltage of an LT3971 application is limited by the minimum input voltage (4.3V) and by the maximum duty cycle as outlined in the Input Voltage Range section. For proper start-up, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, the boost capacitor may not be fully charged ...
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... LT3971, requiring a higher input voltage to maintain regulation. Enable Pin The LT3971 is in shutdown when the EN pin is low and active when the pin is high. The rising threshold of the EN comparator is 1.01V, with 30mV of hysteresis. The EN pin can be tied the shutdown feature is not used ...
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... APPLICATIONS INFORMATION Soft-Start The SS pin can be used to soft-start the LT3971 by throttling the maximum input current during start-up. An internal 1μA current source charges an external capacitor generating a voltage ramp on the SS pin. The SS pin clamps the internal V node, which slowly ramps up the current limit. Maximum C current limit is reached when the SS pin is about 1 ...
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... FB Figure 8. Diode D4 Prevents a Shorted Input from Discharging a Backup Battery Tied to the Output. It Also Protects the Circuit from a Reversed Input. The LT3971 Runs Only When the Input is Present PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure 9 shows the recommended component placement with trace, ground plane and via locations ...
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... APPLICATIONS INFORMATION loss. The die temperature is calculated by multiplying the LT3971 power dissipation by the thermal resistance from junction to ambient. Also keep in mind that the leakage current of the power Schottky diode goes up exponentially with junction tem- perature. When the power switch is closed, the power Schottky diode is in parallel with the power converter’ ...
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... LT3971 100k 1nF 49.9k FB SYNC GND f = 800kHz 1.8V Step-Down Converter BOOST 0.47μF PG 4.7μ LT3971 RT 10pF 118k 511k FB SYNC GND 1M 100μ 400kHz 0.47μF 10μH 10pF 1M V OUT 12V 1.2A 110k 10μF 3971 TA06 0.47μF 4.7μH 150k PGOOD 10pF ...
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... OUT(MAX) 4R WHERE V IS VOLTAGE OF SOURCE INTERNAL SOURCE IMPEDANCE, AND OUT 1M LT3971 EFFICIENCY. MAXIMUM OUTPUT 4V CURRENT OF 1.2A CAN BE SUPPLIED FOR A 1.2A* SHORT TIME BASED ON THE ENERGY 100μF WHICH CAN BE SOURCED BY THE BULK INPUT CAPACITANCE. 3971 TA09a Start-Up from High Impedance Input Source ...
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... LT3971 PACKAGE DESCRIPTION 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3 ...
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... MAX DETAIL “A” SEATING PLANE 0.17 – 0.27 (.007 – .011) 0.50 TYP (.0197) BSC LT3971 2.06 0.102 (.081 .004) 0.29 1.83 0.102 REF (.072 .004) 0.05 REF DETAIL “B” CORNER TAIL IS PART OF THE LEADFRAME FEATURE. DETAIL “B” FOR REFERENCE ONLY NO MEASUREMENT PURPOSE ...
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... LT3971 RELATED PARTS PART DESCRIPTION LT3980 58V, 80V Transient Protection, 2A, 2.4MHz High Effi ciency Micropower Step-Down DC/DC Converter LT3970 40V, 350mA High Effi ciency Micropower Step-Down DC/DC Converter with I = 2.5μA Q LT3695 36V, 60V Transient Protection, 1A, 2.2MHz High Effi ciency Micropower Step-Down DC/DC Converter with 1A Fault Tolerance LT3689 36V, 60V Transient Protection, 800mA, 2.2MHz High Effi ...