lt3681 Linear Technology Corporation, lt3681 Datasheet
lt3681
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lt3681 Summary of contents
Page 1
... Schottky diode and the necessary oscillator, control, and logic circuitry. An undedicated power Schottky diode is integrated into the LT3681 to minimize the solution size. Current mode topology is used for fast transient response and good loop stability. Low ripple Burst Mode operation maintains high effi ...
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... Voltage .......................................................5V C BIAS, PG, BD Voltage ................................................30V Maximum Junction Temperature .......................... 125°C DC above DA .............................................................40V Operating Temperature Range (Note 2) LT3681E ............................................... –40°C to 85°C Storage Temperature Range ................... –65°C to 150°C ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T noted. (Note 2) PARAMETER ...
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... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3681E is guaranteed to meet performance specifi cations from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. ● ...
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... LT3681 W U TYPICAL PERFOR A CE CHARACTERISTICS Effi ciency (V = 5.0V) OUT 100 12V 24V NEC PLC-0745-4R7 10 f: 800kHz 0 0.0001 0.001 0.01 0.1 1 LOAD CURRENT (A) 3681 G01 No Load Supply Current FRONT PAGE APPLICATION ...
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... FB PIN VOLTAGE (mV) RUN/SS Pin Current 3 RUN/SS PIN VOLTAGE (V) LT3681 T = 25°C unless otherwise noted. A Feedback Voltage 1.290 1.285 1.280 1.275 1.270 1.265 1.260 1.255 1.250 3500 –50 – TEMPERATURE (°C) ...
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... LT3681 W U TYPICAL PERFOR A CE CHARACTERISTICS Error Amp Output Current 100 –20 –40 –60 –80 1.065 1.165 1 .265 1.365 1.465 FB PIN VOLTAGE (V) 3681 G19 V Voltages C 2.50 2.00 CURRENT LIMIT CLAMP 1.50 1.00 SWITCHING THRESHOLD 0.50 0 –50 – 100 TEMPERATURE (°C) 3681 G22 Switching Waveforms ...
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... LT3681’s internal regulator. Tie this pin to the lowest available voltage source above 3V (typically V architecture increases effi ciency especially when the input voltage is much higher than the output. FB (Pin 3): The LT3681 regulates the FB pin to 1.265V. Connect the feedback resistor divider tap to this pin. V (Pin 5): The V ...
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... 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 LT3681 is enabled and V The LT3681 integrates a high quality, 36V, 2A power Schottky diode to reduce the overall solution size ...
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... The reason input voltage range depends on the switching frequency is because the LT3681 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. This means that the minimum ...
Page 10
... If the output is in regulation and no short-circuit or start-up events are expected, then input voltage transients 36V are acceptable regardless of the switching frequency. In this mode, the LT3681 may enter pulse skipping opera- tion where some switching pulses are skipped to maintain output regulation. In this mode the output voltage ripple and inductor current ripple will be higher than in normal operation ...
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... Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it fi lters the square wave generated by the LT3681 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 LT3681’ ...
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... If the LT3681 circuit is plugged into a live supply, the input volt- age can ring to twice its nominal value, possibly exceeding the LT3681’s rating. This situation is easily avoided (see the Hot Plugging Safely section) ...
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... In addition, V reduced to typically 20µA and 50µA respectively during the sleep time. As the load current decreases towards a no load condition, the percentage of time that the LT3681 operates in sleep mode increases and the average input current is greatly reduced resulting in higher effi ciency. ...
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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 LT3681 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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... PG output sync signal is applied while the PG is low, the LT3681 may exhibit erratic operation. When applying a sync signal, positive clock transitions reset LT3681’s internal clock and negative transitions initiate a switch cycle ...
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... V IN 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 LT3681 Runs Only When the Input is Present 16 a battery or some other supply is diode ORed with the LT3681’ ...
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... IN plane as much as possible, and add thermal vias under and near the LT3681 to additional ground planes within the circuit board and on the bottom side. Keep in mind that the thermal design must keep the junctions of the IC and power diode below the specifi ed absolute maximum temperature of 125° ...
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... LT3681 can ring IN to twice the nominal input voltage, possibly exceeding the LT3681’s rating and damaging the part. If the input supply is poorly controlled or the user will be plugging the LT3681 into an energized supply, the input network should be designed to prevent this overshoot. Figure 10 ...
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... INDUCTANCE ENERGIZED DUE TO 6 FEET 24V SUPPLY (2 METERS) OF TWISTED PAIR + 0 35V AI.EI. Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation when the LT3681 is Connected to a Live Supply 20V/DIV LT3681 4 10A/DIV (10a) 0.7 ...
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... Step-Down Converter OFF RUN/SS BOOST LT3681 20k PG BIAS 60.4k FB GND f = 800kHz 3.3V Step-Down Converter RUN/SS BOOST ON OFF LT3681 20k PG BIAS 60.4k FB GND f = 800kHz V OUT 0.47 F 6.8 H 590k 200k 22 F 3681 TA02 V OUT 3. 0.47 F 4.7 H 324k 200k 22 F ...
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... BOOST LT3681 22k PG BIAS 84.5k FB GND f = 600kHz 5V, 2MHz Step-Down Converter RUN/SS BOOST ON OFF LT3681 6.8k PG BIAS 16.9k FB GND f = 2MHz LT3681 V OUT 2. 4.7 H 196k 47 F 200k 3681 TA04 V OUT 0.47 F 2.2 H 590k 200k 10 F 3681 TA05 3681f 21 ...
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... Step-Down Converter RUN/SS BOOST ON OFF LT3681 24k PG BIAS 60.4k FB GND f = 800kHz 1.8V Step-Down Converter RUN/SS BOOST ON OFF LT3681 15k PG BIAS 105k FB GND f = 500kHz V OUT 12V 845k 100k 22 F 3681 TA06 V OUT 1. 0.47µF 3.3µH 84.5k 200k 47µ ...
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... LTC DWG # 05-08-1731 Rev 0) 0.70 ±0.05 1.65 ± 0.05 1.07 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 3.00 REF 4.00 ±0.10 (2 SIDES 0.05 TYP 3.00 ±0.10 1.65 ± 0.10 (2 SIDES) 0.40 ± 0.10 0.75 ±0.05 0.00 – 0.05 LT3681 R = 0.115 1.78 ±0.10 TYP 8 14 1.07 ±0.10 0.10 TYP 1.65 ± 0.10 0.51 TYP PIN 1 NOTCH 0.25 × 45° 0.25 ± 0.05 CHAMFER 0.50 BSC 3.00 REF (DE14MA) DFN 1106 REV Ø ...
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... Transient Protection to 60V 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 1.265V Step-Down Converter RUN/SS BOOST ON OFF LT3681 13k PG BIAS 105k FB GND 330pF f = 500kHz L: NEC PLC-0745-3R3 COMMENTS V IN TSSOP16E Package V ...