lt3972 Linear Technology Corporation, lt3972 Datasheet
lt3972
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lt3972 Summary of contents
Page 1
... Low ripple Burst Mode operation maintains high effi ciency at low output currents while keeping output ripple below 15mV in a typical application. In addition, the LT3972 can fur- ther enhance low output current effi ciency by drawing bias current from the output when V Shutdown reduces input supply current to less than 1μ ...
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... IN Quiescent Current from V IN Quiescent Current from BD 2 (Note 1) Operating Junction Temperature Range (Note 2) LT3972E .............................................– 40°C to 125°C LT3972I ..............................................– 40°C to 125°C Storage Temperature Range ...................–65°C to 150°C Lead Temperature (Soldering, 10 sec) (MSE Only) ....................................................... 300° ...
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... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3972E is guaranteed to meet performance specifi cations from 0°C to 125°C. Specifi cations over the –40°C to 125°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3972I specifi ...
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... LT3972 TYPICAL PERFORMANCE CHARACTERISTICS Effi ciency 100 V = 12V 30V 24V OUT L = 4.7μ 600kHz 50 0 0.5 1 1.5 2 2.5 3 OUTPUT CURRENT (A) 3680 G01 No Load Supply Current 130 V = 3.3V OUT 110 INPUT VOLTAGE (V) 3680 G04 Maximum Load Current 5 ...
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... FB PIN VOLTAGE (mV) RUN/SS Pin Current 3 RUN/SS PIN VOLTAGE (V) LT3972 T = 25°C unless otherwise noted. A Feedback Voltage 840 820 800 780 760 –50 – TEMPERATURE (°C) 3680 G11 Minimum Switch On-Time ...
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... LT3972 TYPICAL PERFORMANCE CHARACTERISTICS Error Amp Output Current –10 –20 –30 –40 –50 –200 –100 0 100 FB PIN ERROR VOLTAGE (mV) 3680 G19 V Voltages C 2.50 2.00 CURRENT LIMIT CLAMP 1.50 1.00 SWITCHING THRESHOLD 0.50 0 –50 – 100 125 TEMPERATURE (°C) 3680 G22 Switching Waveforms; Transition ...
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... PG (Pin 7): The PG pin is the open collector output of an internal comparator. PG remains low until the FB pin is within 9% of the fi nal regulation voltage. PG output is valid when (Pin 8): The LT3972 regulates the FB pin to 0.790V. Connect the feedback resistor divider tap to this pin. V (Pin 9): The V C amplifi ...
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... IN output is in regulation, allowing an external resistor to pull the PG pin high. Power good is valid when the LT3972 is enabled and V The LT3972 has an overvoltage protection feature which disables switching action when the V typical (33V minimum). When switching is disabled, the LT3972 can safely sustain input voltages up to 62V ...
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... V IN Value The LT3972 can operate from input voltages 33V, T and withstand voltages up to 62V. Note that while V above 35V typical (33V minimum and 37V maximum) the part will keep the switch off and the output will not be in regulation. ...
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... SW ΔI = 0.4(I L where I OUT(MAX) guarantee suffi cient output current, peak inductor current must be lower than the LT3972’s switch current limit (I The peak inductor current is: ), and T I L(PEAK) where I L(PEAK) the maximum output load current, and ΔI ripple current. The LT3972’ ...
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... OUT IN LT3972 to produce the DC output. In this role it determines the output ripple, and low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT3972’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance ...
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... LT3972 can excite the ceramic capaci- tor at audio frequencies, generating audible noise. Since the LT3972 operates at a lower current limit during Burst Mode operation, the noise is nearly silent to a casual ear. If this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output ...
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... Figure 2 shows an equivalent circuit for the LT3972 control loop. The error amplifi transconductance amplifi er with fi nite output impedance. The power section, consisting of the modulator, power switch and inductor, is modeled as a transconductance amplifi ...
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... For proper startup, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3972 is turned on with its RUN/SS pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is ...
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... Output Voltage, Load Current and Boost Circuit 3680 FO5 Soft-Start = 30V The RUN/SS pin can be used to soft-start the LT3972, reducing the maximum input current during start-up. The RUN/SS pin is driven through an external RC fi lter to IN create a voltage ramp at this pin. Figure 7 shows the start- up and shut-down waveforms with the soft-start circuit ...
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... SYNC pin. The square wave amplitude should have valleys that are below 0.3V and peaks that are above 0.8V (up to 6V). The LT3972 will not enter Burst Mode at low output loads while synchronized to an external clock, but instead will skip pulses to maintain regulation. ...
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... Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation when the LT3972 is Connected to a Live Supply traces will shield them from the SW and BOOST nodes. The Exposed Pad on the bottom of the package must be soldered to ground so that the pad acts as a heat sink. To ...
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... IN nominal input voltage, possibly exceeding the LT3972’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3972 into an energized supply, the input network should be designed to prevent this overshoot. Figure 10 shows the waveforms that result when an LT3972 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The fi ...
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... RUN/SS BOOST ON OFF LT3972 RT 19k PG SYNC 63.4k FB GND f = 600kHz 2.5V Step-Down Converter OFF RUN/SS BOOST LT3972 RT 15.4k PG SYNC FB 63.4k GND f = 600kHz LT3972 V OUT 3.3V 3.5A L 0.47μF 3.3μH D 316k 22μF 100k 3680 TA03 V OUT 2.5V 3. 1μF 3.3μH D1 215k 100k 47μF 3680 TA04 3972f 19 ...
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... Step-Down Converter OFF RUN/SS BOOST LT3972 RT 15k PG SYNC FB 12.7k GND f = 2MHz 12V Step-Down Converter OFF RUN/SS BOOST LT3972 RT 17.4k PG SYNC FB 63.4k GND f = 600kHz V OUT 5V 2.5A L 0.47μF 2.2μH D 536k 100k 22μF 3680 TA05 V OUT 12V 3.5A L 0.47μF 8.2μH D ...
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... TYPICAL APPLICATIONS V IN 3.5V TO 27V 4.7μF 680pF D: ON SEMI MBRA340 L: NEC MPLC0730L3R3 1.8V Step-Down Converter RUN/SS BOOST ON OFF LT3972 RT 16.9k PG SYNC FB 78.7k GND f = 500kHz LT3972 V OUT 1.8V 3.5A L 0.47μF 3.3μH D 127k 100k 47μF 3680 TA08 3972f 21 ...
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... LT3972 PACKAGE DESCRIPTION 3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) 0.25 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS TOP MARK (SEE NOTE Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 0.05 PACKAGE OUTLINE 0.50 BSC 2.38 0.05 (2 SIDES) 3.00 0.10 1.65 0.10 (4 SIDES) (2 SIDES) PIN 1 0.75 0.05 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). ...
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... TYP 0.53 0.152 1.10 (.021 .006) (.043) MAX DETAIL “A” SEATING PLANE 0.17 – 0.27 (.007 – .011) 0.50 TYP (.0197) BSC LT3972 2.06 0.102 (.081 .004) 1.83 0.102 (.072 .004) 0.497 0.076 (.0196 .003 REF 3.00 0.102 (.118 .004) (NOTE 4) 0.86 (.034) REF 0 ...
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... LT3693 36V, 3.5A, 2.4MHz, Step-Down DC/DC Converter Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● 1.2V Step-Down Converter RUN/SS BOOST ON OFF LT3972 RT 17k PG SYNC FB 78.7k GND f = 500kHz COMMENTS V : 3.6V to 36V ThinSOT V : 3.6V to 36V MS8E Package ...