lt3680 Linear Technology Corporation, lt3680 Datasheet
lt3680
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lt3680 Summary of contents
Page 1
... RUN/SS pin provide a controlled output voltage ramp (soft-start). A power good fl ag signals when V 91% of the programmed output voltage. The LT3680 is available in 10-Pin MSOP and 3mm × 3mm DFN packages with exposed pads for low thermal resistance. ...
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... Quiescent Current from V IN Quiescent Current from (Note 1) Operating Junction Temperature Range (Note 2) LT3680E ............................................. –40°C to 125°C LT3680I ............................................. –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 LT3680E 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 LT3680I specifi ...
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... LT3680 W U TYPICAL PERFOR A CE CHARACTERISTICS Effi ciency 100 V = 12V 34V 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 3.5 RUN/SS PIN VOLTAGE (V) LT3680 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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... LT3680 W U TYPICAL PERFOR A CE 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 ...
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... PG remains low until the FB pin is within 9% of the fi nal regulation voltage. PG output is valid when V is above 3.6V and RUN/SS is high (Pin 8): The LT3680 regulates the FB pin to 0.790V. Connect the feedback resistor divider tap to this pin. V (Pin 9): The V C amplifi er. The voltage on this pin controls the peak switch current ...
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... The LT3680 contains a power good comparator which trips pin, IN when the FB pin is at 91% of its regulated value. The PG output is an open-collector transistor that is off when the output is in regulation, allowing an external resistor to pull the PG pin high. Power good is valid when the LT3680 is enabled and V is above 3.6V. IN 3680f ...
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... The reason input voltage range depends on the switching frequency is because the LT3680 switch has fi nite minimum on and off times. The switch can turn on for a minimum of ~150ns and turn off for a minimum of ~150ns. ...
Page 10
... L OUT(MAX) where I is the maximum output load current. To OUT(MAX) guarantee suffi cient output current, peak inductor current must be lower than the LT3680’s switch current limit (I The peak inductor current is ΔI /2 L(PEAK) OUT(MAX) L where I is the peak inductor current, I L(PEAK) the maximum output load current, and Δ ...
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... OUT IN LT3680 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 LT3680’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance ...
Page 12
... When in Burst Mode operation, the LT3680’s switching frequency depends on the load current, and at very light loads the LT3680 can excite the ceramic capaci- tor at audio frequencies, generating audible noise. Since the LT3680 operates at a lower current limit during Burst Mode operation, the noise is nearly silent to a casual ear ...
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... Figure 2 shows an equivalent circuit for the LT3680 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 LT3680 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 ...
Page 15
... Output Voltage, Load Current and Boost Circuit 3680 FO5 Soft-Start = 30V The RUN/SS pin can be used to soft-start the LT3680, 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 LT3680 will not enter Burst Mode at low output loads while synchronized to an external clock, but instead will skip pulses to maintain regulation. ...
Page 17
... Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation when the LT3680 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 ...
Page 18
... IN nominal input voltage, possibly exceeding the LT3680’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3680 into an energized supply, the input network should be designed to prevent this overshoot. Figure 10 shows the waveforms that result when an LT3680 circuit is connected to a 24V supply through six feet of 24-gauge twisted pair. The fi ...
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... BD IN RUN/SS BOOST ON OFF LT3680 RT 19k PG SYNC 63.4k FB GND f = 600kHz 2.5V Step-Down Converter RUN/SS BOOST ON OFF LT3680 RT 15.4k PG SYNC FB 63.4k GND f = 600kHz LT3680 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 47μF 100k 3680 TA04 3680f 19 ...
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... Step-Down Converter RUN/SS BOOST ON OFF LT3680 RT 15k PG SYNC FB 12.7k GND f = 2MHz 12V Step-Down Converter RUN/SS BOOST ON OFF LT3680 RT 17.4k PG SYNC FB 63.4k GND f = 600kHz V OUT 5V 2.5A L 0.47μF 2.2μH D 536k 22μF 100k 3680 TA05 V OUT 12V 3.5A L 0.47μF 8.2μH D 715k 47μ ...
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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 OFF RUN/SS BOOST LT3680 RT 16.9k PG SYNC FB 78.7k GND f = 500kHz LT3680 V OUT 1.8V 3.5A L 0.47μF 3.3μH D 127k 100k 47μF 3680 TA08 3680f 21 ...
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... LT3680 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 PIN 1 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 (2 SIDES) (4 SIDES) 0.75 ± ...
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... MAX DETAIL “A” SEATING PLANE 0.17 – 0.27 (.007 – .011) 0.50 TYP (.0197) BSC LT3680 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 ...
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... High Effi ciency 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 LT3680 RT 17k PG SYNC FB 78.7k GND f = 500kHz COMMENTS V : 5.5V to 60V TSSOP16/E Package 25V Package ...