LT3481 LINER [Linear Technology], LT3481 Datasheet
LT3481
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LT3481 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 LT3481 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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... For more information on tape and reel specifi cations, go to: 2 (Note 1) Operating Temperature Range (Note 2) LT3481E ............................................... –40°C to 85°C LT3481I.............................................. –40°C to 125°C LT3481H ............................................ –40°C to 150°C Storage Temperature Range ................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) (MSE Only) ....................................................... 300° ...
Page 3
... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3481E 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. The LT3481I specifi ...
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... LT3481 TYPICAL PERFORMANCE 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) 3481 G01 No Load Supply Current 25° FRONT PAGE APPLICATION ...
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... FB PIN VOLTAGE (mV) RUN/SS Pin Current 3.5 RUN/SS PIN VOLTAGE (V) LT3481 Feedback Voltage 1.290 1.285 1.280 1.275 1.270 1.265 1.260 1.255 1.250 –50 – 3500 TEMPERATURE (°C) 3481 G11 Minimum Switch On-Time ...
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... LT3481 TYPICAL PERFORMANCE CHARACTERISTICS Error Amp Output Current 100 –20 –40 –60 –80 1.065 1.165 1?.265 1.365 1.465 FB PIN VOLTAGE (V) 3481 G19 V Voltages C 2.50 2.00 CURRENT LIMIT CLAMP 1.50 1.00 SWITCHING THRESHOLD 0.50 0 –50 – 100 125 150 TEMPERATURE (°C) 3481 G22 Switching Waveforms ...
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... LT3481’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 8): The LT3481 regulates the FB pin to 1.265V. Connect the feedback resistor divider tap to this pin. V (Pin 9): The V C amplifi ...
Page 8
... The LT3481 contains a power good comparator which trips 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 LT3481 is enabled and V is above 3.6V. IN ...
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... Input Voltage Range 14.3 12.1 The maximum input voltage for LT3481 applications de- 10.2 pends on switching frequency, the Absolute Maximum Rat- 8.66 ings the output is in start-up or short-circuit operating modes, then V IN following equation: ...
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 LT3481 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 LT3481 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 LT3481’ ...
Page 12
... Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT3481 due to their piezoelectric nature. When in Burst Mode operation, the LT3481’s switching frequency depends on the load current, and at very light loads the LT3481 can excite the ceramic capacitor at audio frequencies, generating audible noise ...
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... If the LT3481 circuit is plugged into a live supply, the input volt- age can ring to twice its nominal value, possibly exceeding the LT3481’s rating. This situation is easily avoided (see the Hot Plugging Safely section) ...
Page 14
... For proper startup, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3481 is turned on with its RUN/SS pin when the output is already in regulation, then the boost capacitor V OUT ...
Page 15
... The LT3481 should not be synchronized until its output is near regulation as indicated by the PG fl ag. This can be done with the system microcontroller/microprocessor or with a discrete circuit by using the PG output sync signal is applied while the PG is low, the LT3481 may exhibit erratic operation. See Typical Applications = 5.0V OUT = 25 ° ...
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... To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT3481 to additional ground planes within the circuit board and on the bottom side. pin is grounded while IN pin ...
Page 17
... Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation when the LT3481 is Connected to a Live Supply Hot Plugging Safely The small size, robustness and low impedance of ceramic capacitors make them an attractive option for the input bypass capacitor of LT3481 circuits ...
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... D: DIODES INC. DFLS240L L: TAIYO YUDEN NP06DZB6R8M 18 the LT3481 possible to dissipate enough heat to raise the junction temperature beyond the absolute maximum of 125°C (150°C for the H grade). When operating at high ambient temperatures, the maximum load current should be derated as the ambient temperature approaches 125°C (150° ...
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... FB GND f = 600kHz 5V, 2MHz Step-Down Converter RUN/SS BOOST ON OFF LT3481 RT 20k PG BIAS 16.9k FB GND 330pF f = 2MHz D: DIODES INC. DFLS240L L: SUMIDA CDRM4D22/HP-2R2 LT3481 V OUT 3. 0.47μF 4.7μH D 324k 22μF 200k 3481 TA03 V OUT 2. 1μF 4.7μH D1 196k 47μF 200k 3481 TA04 ...
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... RUN/SS BOOST ON OFF LT3481 RT 30k PG BIAS 60.4k FB GND f = 800kHz 5V Step-Down Converter with Sync Input RUN/SS ON OFF V C 8.2pF RT LT3481 PG 11.8k 100k 226k GND V OUT 1000pF f = 250kHz D: DIODES INC. DFLS240L L: NEC/TOKIN PLC-0755-8R2 V OUT 12V 2A L 0.47μF 10μH D 845k 22μF 100k 3481 TA06 V ...
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... OUT 1000pF f = 300kHz D: DIODES INC. DFLS240L L: NEC/TOKIN PLC-0755-150 Q1: ON SEMI MMBT3904 1.8V Step-Down Converter OFF RUN/SS BOOST LT3481 RT 15.4k PG BIAS 105k FB GND f = 500kHz LT3481 V OUT BOOST L 0.47μF 15μ BIAS 75pF 29.4k FB 10k 47μF 3481 TA08 V OUT 1. 0.47μF 3.3μ ...
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... LT3481 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 6) 0.200 REF 22 DD 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) 1.65 0.10 3.00 0.10 (4 SIDES) (2 SIDES) 0.75 0.05 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 LT3481 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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... Step-Down DC/DC Converter with Burst Mode Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● 1.265V Step-Down Converter OFF RUN/SS BOOST 0.47μ LT3481 BIAS 105k FB GND f = 500kHz COMMENTS V : 3.6V to 36V OUT(MIN 3.3V to 80V OUT(MIN ...