LTC1704 Linear Technology, LTC1704 Datasheet
LTC1704
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LTC1704 Summary of contents
Page 1
... The LTC1704 features automatic transition to power saving Burst Mode operation at light loads. The LTC1704B does not shift into Burst Mode operation at light loads, eliminat- ing low frequency output ripple at the expense of light load efficiency ...
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... Test Circuit (Notes 5, 6) RUN/SS V RUN/ RUN/ 3.3V to 5.5V CC (Note 100kHz (Note IMAX ORDER PART NUMBER 16 BOOST LTC1704EGN LTC1704BEGN PGND 12 PGOOD PART MARKING 10 REGILM 9 REGFB 1704 1704B = 130 C MIN TYP MAX UNITS 3.15 5 5.5 3. ...
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... PGOOD Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC1704E is guaranteed to meet performance specifications from Specifications over the – operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: All currents into device pins are positive ...
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... LTC1704/LTC1704B W U TYPICAL PERFOR A CE CHARACTERISTICS V vs Temperature FB 0.812 0.808 0.804 0.800 0.796 0.792 0.788 –50 – TEMPERATURE ( C) V Load Regulation OUTSW 0.6 0 –0.6 –1.2 –1.8 –2.4 –3.0 –3 LOAD V 0.5A to 5.5A Load Step OUTSW (Burst Mode Operation) 100 s/DIV ...
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... V vs Temperature REGFB 0.820 V = 3.3V REGDR 0.815 0.810 0.805 0.800 0.795 0.790 0.785 0.780 – 50 – 100 125 TEMPERATURE ( C) LTXXX • TPCXX LTC1704/LTC1704B IMAX CC –8 –9.0 –9.5 –10.0 –10.5 –11.0 –11.5 3 3.5 4 4.5 5 125 V (V) CC Maximum TG Duty Cycle ...
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... LTC1704/LTC1704B W U TYPICAL PERFOR A CE CHARACTERISTICS V Load Regulation OUTREG 0.5 0 –0.5 –1.0 –1.5 –2 1.5V OUTREG –2 REGILM QEXT = D44H11 –3.0 0 0.4 0.8 1.2 1.6 I (A) OUTREG 1704 G18 Minimum OUTREG 5 REGILM OUTREG V = –1% OUTREG 5.0 QEXT = D44H11 4.5 4 – 3 ...
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... An internal 3 A current source pull-up at RUN/SS sets the turn-on time at approximately 300ms both RUN/SS and REGILM are pulled low, the LTC1704 enters shutdown mode. COMP (Pin 5): Switcher Controller Loop Compensation. The COMP pin is connected directly to the output of the switcher controller’ ...
Page 8
... Refer to the Linear Regulator Current Limit Programming sec- tion for more information on choosing R Pulling REGILM to GND turns off the linear regulator. If both RUN/SS and REGILM are pulled low, the LTC1704 enters shutdown mode. V (Pin 11): Power Supply Input. All internal circuits ...
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... W BLOCK DIAGRA LTC1704/LTC1704B 1704bfa 9 ...
Page 10
... LTC1704, are tiny, allowing an entire power convertor to be constructed in 1.5in Fast Transient Response The LTC1704 switcher supply uses a fast 20MHz GBW op amp as an error amplifier. This allows the compensation network to be designed with several poles and zeros in a more flexible configuration than with a typical g amplifier ...
Page 11
... QT is on, its source (the SW pin also the power supply for the LTC1704. However, QT requires V The LTC1704, needs to generate a gate drive signal at TG higher than its highest supply voltage. To accomplish this, the TG driver runs from floating supplies, with its negative supply attached to SW and its power supply at BOOST ...
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... LTC1704/LTC1704B U U APPLICATIO S I FOR ATIO In combination with a simple external charge pump (Fig- ure 2), this allows the LTC1704 to completely enhance the gate of QT without requiring an additional, higher supply voltage. Switcher Supply Feedback Amplifier The LTC1704 senses the switcher output voltage at V with an internal feedback op amp (see Block Diagram). ...
Page 13
... RUN/SS is released. The RUN/SS pin shuts down the switcher drivers when it falls below 0.5V (Figure 4). Between 0.5V and about 1V, the LTC1704 wakes up and the duty cycle is kept to minimum. As the potential at RUN/SS goes higher, the duty cycle increases linearly between 1V and 2V, reaching its final value of 90% when RUN/SS is above 2V. Some- ...
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... MOSFET is turned on, the internal driver must charge its gate to PV charge is lost to ground. At the high switching frequency that the LTC1704 operates, the charge lost to the gates can add up to tens of milliamps from PV continues to drop, this quickly becomes the dominant power loss term, reducing efficiency once again. ...
Page 15
... PCB layout to ensure that proper kelvin sensing for the SW pin is provided. Connect the SW pin of the LTC1704 as close to the drain possible through a thick trace. The same applies to the PGND pin of the LTC1704, which is the negative input of the burst comparator and it should be connected close to the source of QB through a thick trace ...
Page 16
... Burst Mode operation as cleanly as possible. Minimize ringing at the SW node so that the Burst comparator leaves as little residual current in the inductor as possible when QB turns off. It helps to connect the SW pin of the LTC1704 as close to the drain possible snubber network can also be added from SW to PGND. 16 ...
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... APPLICATIO S I FOR ATIO Gate Charge Gate charge is amount of charge (essentially, the number of electrons) that the LTC1704 needs to put into the gate of an external MOSFET to turn it on. The easiest way to visualize gate charge is to think capacitance from the gate pin of the MOSFET to SW (for QT PGND (for QB) ...
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... LTC1704 applications, but they deserve a special caution here. Generic tantalum capacitors have a destruc- tive failure mechanism when they are subjected to large RMS currents (like those seen at the input of an LTC1704). At some random time after they are turned on, they can blow up for no apparent reason. The capacitor manufac- turers are aware of this and sell special “ ...
Page 19
... So far, the AC response of the loop is pretty well out of the user’s control. The modulator is a fundamental piece of the LTC1704 design, and the external L and C are usually chosen based on the regulation and load current require- ments without considering the AC loop response. The feedback amplifier, on the other hand, gives us a handle with which to adjust the AC response ...
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... U rate results, but simulation can often get close enough to give a working system. To measure the modulator gain and phase directly, wire up a breadboard with an LTC1704 and the actual MOSFETs, inductor, and input and output capaci- –6dB/OCT tors that the final design will use. This breadboard should ...
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... SWITCHING SUPPLY CURRENT LIMIT PROGRAMMING Programming the current limit on the LTC1704 switcher supply is straightforward. The I limit by setting the maximum allowable voltage drop across QB (the bottom MOSFET) before the current limit circuit engages. The voltage across QB is set by its on- resistance and the current flowing in the inductor, which ...
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... R can cause large I changes when the switch node ring- LIMIT ing makes up a large percentage of the total set too low, the LTC1704 may fail to start up. PROG Accuracy Trade-Offs The V sensing scheme used in the LTC1704 is not DS ...
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... Optimizing Loop Compensation ESR Loop compensation has a fundamental impact on tran- sient recovery time, the time it takes the LTC1704 to recover after the output voltage has dropped due to output capacitor ESR. Optimizing loop compensation entails maintaining the highest possible loop bandwidth while ensuring loop stability ...
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... LTC1704 circuits. Solder the MOSFET and the resistor(s) as close to the output of the LTC1704 circuit as possible and set up the signal generator to pulse at a 100Hz rate with a 5% duty cycle. This pulses the LTC1704 with 500 s transients ...
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... W U The MJD44H11 from ON Semiconductor and SGS- Thomson can be used in the LTC1704 linear regulator supply with current ratings up to 2A. The MJD44H11 from ON Semiconductor can supply 8A of output current and of BE the minimum DC Current Gain h DROPOUT power dissipation rating is 1 ...
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... REGON power down the linear regulator. When both the REGILM and RUN/SS pins are forced low, LTC1704 enters shut- down mode and the quiescent current is reduced Linear Regulator Turn-On Delay The external capacitor C ...
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... TYP .015 .004 45 .053 – .068 (0.38 0.10) (1.351 – 1.727) 0 – 8 TYP .008 – .012 (0.203 – 0.305) LTC1704/LTC1704B .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988) ...
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... FAX: (408) 434-0507 VID Controlled Power Supply D CP MBR0520LT1 BOOST PV QTA QTB QBB QBA BG R MAX LTC1704 13. MAX PGND 1. 11k 1800pF 330pF 5 COMP C : KEMET T510X337K010AS PANASONIC EEFUE0G181R OUTSW ...