lt3991 Linear Technology Corporation, lt3991 Datasheet
lt3991
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lt3991 Summary of contents
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... A power good fl ag signals when V OUT age. The LT3991 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) LT3991E ............................................. –40°C to 125°C LT3991I .............................................. –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 LT3991E 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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... LT3991 TYPICAL PERFORMANCE CHARACTERISTICS Effi ciency OUT 100 V = 12V 24V 36V 48V IN 50 FRONT PAGE APPLICATION OUT 309k 30 0 0.2 0.4 0.6 0.8 1 LOAD CURRENT (A) 3991 G01 Effi ciency 3.3V OUT 90 FRONT PAGE APPLICATION 12V 24V IN 60 ...
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... LOAD OFF(MIN) 300 250 t 0.5A LOAD OFF(MIN) 200 150 t ON(MIN) 100 50 0 –55 – 1.2 TEMPERATURE (°C) LT3991 T = 25°C, unless otherwise noted. A Switch Current Limit 3.0 2.5 2.0 1.5 1.0 0.5 0 125 155 DUTY CYCLE (%) 3991 G11 Boost Pin Current ...
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... LT3991 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) 3991 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) 3991 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 LT3991 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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... LT3991 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 and resistor. If the EN pin is low, the LT3991 is shut down and draws 700nA from the input. When the EN pin exceeds 1.01V, the switching regulator will become active. ...
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... To ensure proper Burst Mode operation, the SYNC pin must be grounded. When synchronized with an external 10 clock, the LT3991 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. Holding the SYNC pin high yields no advantages in terms of output ripple or minimum load to full frequency not recommended ...
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... Input Voltage Range The minimum input voltage is determined by either the LT3991’s minimum operating voltage of 4. its maximum duty cycle (see equation in Operating Frequency Tradeoffs section). The minimum input voltage due to duty cycle is: ...
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... Shielded Shielded tors, and choose one to meet cost or space goals. Then Shielded use the equations above to check that the LT3991 will be Open able to deliver the required output current. Note again Shielded Shielded ...
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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 LT3991 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3991’s voltage rating. This situation is easily avoided (see the Hot Plugging Safely section) ...
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... If the LT3991 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT3991’s rating. This situation is easily avoided (see the Hot Plugging Safely section). ...
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... Figure 3a is more effi cient because the BOOST pin current comes from a lower voltage source. You must also be sure that the maximum voltage ratings of the BOOST and BD pins are not exceeded. The minimum operating voltage of an LT3991 application is limited by the minimum input voltage (4.3V) and ...
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... LT3991, requiring a higher input voltage to maintain regulation. Enable Pin The LT3991 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 LT3991 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 LT3991 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 LT3991 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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... Step-Down Converter BOOST OFF 10μF SS LT3991 RT BD 49.9k FB SYNC GND f = 800kHz 5M V BOOST LT3991 100k 1nF 118k FB SYNC GND f = 400kHz 0.47μF 6.8μH 10pF 511k V OUT 1.8V 1.2A 1M 100μF 3991 TA05 0.47μF 10μH 10pF V 1M ...
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... FB SYNC GND 412k f = 400kHz V IN 2V/DIV V OUT 2V/DIV I 1A/DIV 3991 TA07b LT3991 * AVERAGE OUTPUT POWER CANNOT 10μH EXCEED THAT WHICH CAN BE PROVIDED BY HIGH IMPEDANCE SOURCE. NAMELY • OUT(MAX) 4R WHERE V IS VOLTAGE OF SOURCE INTERNAL SOURCE IMPEDANCE, AND V OUT 1M LT3971 EFFICIENCY ...
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... LT3991 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 LT3991 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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... LT3991 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 ...