lt3980 Linear Technology Corporation, lt3980 Datasheet
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lt3980
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lt3980 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 LT3980 can further enhance low output current effi ciency by drawing bias current from the output when V above 3V. Shutdown reduces input supply current to less than 1μ ...
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... Quiescent Current from (Note 1) Operating Junction Temperature Range (Note 2) LT3980E .............................................– 40°C to 125°C LT3980I ..............................................– 40°C to 125°C LT3980H ............................................– 40°C to 150°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 LT3980E 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 LT3980I specifi ...
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... LT3980 TYPICAL PERFORMANCE CHARACTERISTICS Effi ciency 3.3V OUT 12V 24V 48V 400kHz D = DIODES, INC. SBR3U100LP 50 0 0.5 1 1.5 I (A) LOAD 3980 G01 No-Load Supply Current 130 V = 3.3V OUT 110 INPUT VOLTAGE (V) 3980 G04 ...
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... FB PIN VOLTAGE (mV) Soft-Start 0.5 1 1.5 2 2.5 RUN/SS PIN VOLTAGE (V) LT3980 T = 25°C unless otherwise noted. A Feedback Voltage 840 820 800 780 760 3 –50 – TEMPERATURE (°C) 3980 G11 R vs Frequency T 3500 ...
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... LT3980 TYPICAL PERFORMANCE CHARACTERISTICS Boost Diode 1.4 1.2 1.0 0.8 0.6 0.4 0 0.5 1.0 1.5 BOOST DIODE CURRENT (A) Minimum Input Voltage OUT 400kHz TO START RUN 100 1000 2000 I (mA) LOAD Switching Waveforms: Burst Mode Operation V SW 5V/DIV I L 0.2A/DIV V OUT 10mV/DIV V = 12V 5μs/DIV ...
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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 4/Pin 4): The LT3980 regulates the FB pin to 0.790V. Connect the feedback resistor divider tap to this pin. V (Pin 5/Pin 6): The V pin is the output of the internal ...
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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 LT3980 is enabled and V The LT3980 has an overvoltage protection feature which disables switching action when the V typical (58V minimum) ...
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... V IN Value T The LT3980 can operate from input voltages 58V, and withstand voltages up to 80V. Note that while V above 61V typical (58V minimum and 64V maximum) the part will keep the switch off and the output will not be in regulation. ...
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 LT3980’s switch current limit (I The peak inductor current is ΔI /2 L(PEAK) OUT(MAX and ...
Page 11
... OUT IN LT3980 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 LT3980’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance ...
Page 12
... The LT3980 uses current mode control to regulate the EEF Series output. This simplifi es loop compensation. In particular, the LT3980 does not require the ESR of the output capacitor POSCAP for stability, so you are free to use ceramic capacitors to achieve low output ripple and small circuit size. Frequency ...
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... Figure 2 shows an equivalent circuit for the LT3980 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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... LT3980 APPLICATIONS INFORMATION If low quiescent current is not required the LT3980 can operate in pulse-skipping mode. The benefi this mode is that the LT3980 will enter full frequency standard PWM operation at a lower output load current than when in Burst Mode operation. The front page application circuit will switch at full frequency at output loads higher than about 60mA ...
Page 15
... For proper startup, the minimum input voltage is also limited by the boost circuit. If the input voltage is ramped slowly, or the LT3980 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 16
... If an inductor is chosen that will not saturate excessively, an LT3980 buck regulator will tolerate a shorted output. There is another situation to consider in systems where the output will be held high when the input to the LT3980 is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ORed with the LT3980’ ...
Page 17
... GND 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 LT3980 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 ...
Page 18
... Figure 10. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures Reliable Operation When the LT3980 Is Connected to a Live Supply High Temperature Considerations The PCB must provide heat sinking to keep the LT3980 cool. The Exposed Pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias ...
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... PG DA 97.6k SYNC FB GND 1nF f = 400kHz 3.3V Step-Down Converter RUN/SS BOOST ON OFF LT3980 RT 4.75k PG DA 97.6k SYNC FB GND 2.2nF f = 400kHz LT3980 V OUT 0.47μF 8.2μH 22pF D 536k 100k 47μF 3980 TA02 V OUT 3. 0.47μF 6.8μH 22pF D 316k 100k 47μF 3980 TA03 19 3980f ...
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... IN RUN/SS BOOST ON OFF LT3980 RT 8.45k PG DA 137k SYNC FB GND 2.2nF f = 300kHz 5V, 1.2MHz Step-Down Converter OFF RUN/SS BOOST LT3980 RT 4.75k PG DA 24.9k SYNC FB GND 1nF f = 1.2MHz V OUT 2. 1μF 4.7μH 22pF D1 215k 47μF 100k 3980 TA04 V OUT 0.47μ ...
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... SYNC FB GND 1nF f = 600kHz 1.8V Step-Down Converter RUN/SS BOOST ON OFF LT3980 RT 2.49k PG DA 97.6k SYNC FB GND 680pF f = 400kHz LT3980 V OUT 12V 2A L 0.47μF 15μH D 715k 50k 22μF 3980 TA06 V OUT 1. 0.47μF 3.3μH 22pF D 127k 100μF 100k 3980 TA08 3980f ...
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... LT3980 PACKAGE DESCRIPTION 3.30 ±0.05 3.60 ±0.05 2.20 ±0.05 1.70 ± 0.05 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 ±0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC PACKAGE OUTLINE MO-229 2 ...
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... DETAIL “A” 1.10 (.043) MAX SEATING PLANE 0.17 – 0.27 (.007 – .011) 0.50 TYP (.0197) BSC LT3980 8 0.35 REF 1.651 0.102 0.12 REF (.065 .004) DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY 9 NO MEASUREMENT PURPOSE 0 ...
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... High Effi ciency Step-Down DC/DC Converter OUT Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● 1.2V Step-Down Converter RUN/ BOOST ON OFF LT3980 97.6k SYNC GND FB 1nF f = 400kHz COMMENTS 3mm V 3mm ), 2.4MHz, High Effi ciency ...