LTC1702 Linear Technology, LTC1702 Datasheet
LTC1702
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LTC1702 Summary of contents
Page 1
... FAULT mode protects the load if the output rises 15% above the intended voltage. Each channel can be enabled independently; with both channels disabled, the LTC1702 shuts down and supply current drops below 100 A. Dual Output High Power 3.3V/2.5V Logic Supply V ...
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... All Other Inputs ......................... – 0. Peak Output Current < ............................................................... 5A Operating Temperature Range LTC1702C ............................................... LTC1702I ........................................... – Storage Temperature Range ................. – 150 C Lead Temperature (Soldering, 10 sec).................. 300 C ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are ...
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... FB FAULT Note 5: Supply current in shutdown is dominated by external MOSFET leakage and may be significantly higher than the quiescent current drawn by the LTC1702, especially at elevated temperature. of GS(ON) Note 6: This parameter is guaranteed by correlation and is not tested directly. Note 7: Rise and fall times are measured using 10% and 90% levels. Delay and nonoverlap times are measured using 50% levels ...
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... LTC1702 W U TYPICAL PERFOR A CE CHARACTERISTICS Efficiency vs Load Current 100 3.3V OUT V = 2.5V OUT 1.6V OUT LOAD CURRENT (A) 1702 G01 Supply Current vs Temperature 2.6 TEST CIRCUIT 0pF 2 2 2.0 1.8 1.6 1.4 BOOST1, BOOST2 1.2 1.0 – 50 – 100 125 TEMPERATURE ( C) ...
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... Power Supply Input. All internal circuits CC except the output drivers are powered from this pin. V should be connected to a low noise power supply voltage between 3V and 7V and should be bypassed to SGND with at least capacitor in close proximity to the LTC1702. LTC1702 . To force CC to set the ...
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... If either regulated output voltage rises more than 15% above its programmed value for more than 25 s, the FAULT output will go high and the entire LTC1702 will be disabled. When FAULT is high, both BG pins will go high, turning on the bottom MOSFET switches and pulling down the high output voltage ...
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... OV fault has occurred automatically resume operation when the fault is removed. The LTC1702 takes a low input voltage and generates two lower output voltages at very high currents. Its strengths are small size, unmatched regulation and transient response and high efficiency ...
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... PCB area and simplified power trace routing. 2-step regulation can buy advantages in thermal manage- ment as well. Power dissipation in the LTC1702 portion of a 2-step circuit is lower than it would typical 1-step converter, even in cases where the 1-step converter has higher total efficiency than the 2-step system ...
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... Fast Transient Response The LTC1702 uses a fast 25MHz GBW op amp as an error amplifier. This allows the compensation network to be designed with several poles and zeros in a more flexible ...
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... IN LTC1702 Feedback Amplifier Each side of the LTC1702 senses the output voltage at V with an internal feedback op amp (see Block Dia- OUT gram). This is a real op amp with a low impedance output, 85dB open-loop gain and 25MHz gain-bandwidth product. ...
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... PGOOD pin will pull low until the output voltage is valid. If both sides are shut down at the same time, both PGOOD pins will go high. To avoid confusion, if either side of the LTC1702 is shut down, the host system should ignore the associated PGOOD pin. LTC1702 (Figure 3) ...
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... SHUTDOWN/SOFT-START Each half of the LTC1702 has a RUN/SS pin. The RUN/SS pins perform two functions: when pulled to ground, each shuts down its half of the LTC1702, and each acts as a conventional soft-start pin, enforcing a maximum duty cycle limit proportional to the voltage at RUN/SS. An internal 3.5 A current source pull-up is connected to each RUN/SS pin, allowing a soft-start ramp to be generated with a single external capacitor to ground ...
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... Continuous mode works efficiently when the load current is greater than half of the ripple current in the inductor buck converter like the LTC1702, the average current in the inductor (averaged over one switching cycle) is equal to the load current. The ripple current is the difference between the maximum and the minimum current during a switching cycle (see Figure 5a) ...
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... Burst Mode Operation Discontinuous mode removes the resistive loss drop term in QB, but the LTC1702 is still switching QT and QB on and off once a cycle. Each time an external MOSFET is turned on, the internal driver must charge its gate to V time it is turned off, that charge is lost to ground ...
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... In some circumstances desirable to control or disable discontinuous and Burst Mode operations. The FCB (Force Continuous Bar) pin allows the user to do this. When the FCB pin is high, the LTC1702 is allowed to enter discon- tinuous and Burst Mode operations at either side as required. If FCB is taken low, discontinuous and Burst Mode operations are disabled and both sides of the LTC1702 run in continuous mode regardless of load ...
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... A current source pull-up will not be able to pull FAULT high, and the LTC1702 will ignore the latch and continue normal operation. The MAX com- parator will act as usual, turning on QB until output is within range and then allowing the loop to resume normal operation ...
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... big deal since the source attached to PGND; the LTC1702 just switches the BG pin between PGND and V . Driving QT is another matter. The source connected to SW which rises to V on. To keep QT on, the LTC1702 must get TG one MOSFET V above does this by utilizing a floating driver GS(ON) CC ...
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... ESR tantalum or electrolytic capacitors in parallel, or with a large mono- lithic ceramic capacitor. The two sides of the LTC1702 run off a single master clock and are wired 180 out of phase with each other to significantly reduce the total capacitance/ESR needed at the input ...
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... DC current. Sum the results and take the square root. The result is the approximate RMS current as seen by the input capacitor with both sides of the LTC1702 at full load. Actual RMS current will differ due to inductor ripple cur- rent and resistive losses, but this approximate value is adequate for input capacitor calculation purposes ...
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... The output bypass capacitor has quite different require- ments from the input capacitor. The ripple current at the output of a buck regulator like the LTC1702 is much lower than at the input, due to the fact that the inductor current is constantly flowing at the output whenever the LTC1702 is operating in continuous mode ...
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... LC combinations where low capacitor ESR keeps the phase shift near 180 –90 for an extended frequency range. LTC1702 circuits using conventional switching grade electrolytic output capaci- –180 –6dB/OCT tors can often get acceptable phase margin with type 2 compensation ...
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... To measure the modulator gain and phase directly, wire up a breadboard with an LTC1702 and the actual MOSFETs, inductor, and input and output capacitors that the final design will use. This breadboard ...
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... Type 3 Loop: K Tan LTC1702 (this converts GAIN absolute BOOST GKR – REF – V OUT REF BOOST – ...
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... DS(ON) to 150% of the LIM The FCB pin can be used in conjunction with a secondary winding on one side of the LTC1702 to generate a third regulated voltage output. This output can be directly regulated at the FCB pin. In theory, a fourth output could be added, either unregulated or with additional external circuitry at the FCB pin. ...
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... If the LTC1702 is in discontinuous or Burst Mode operation and the auxiliary output voltage drops, the FCB pin will trip and the LTC1702 will resume continuous operation regardless of the load on the main output. The FCB pin removes the requirement that power must be drawn from the inductor primary in order to extract power from the auxiliary windings ...
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... QT cost efficiency, eliminating any advantage the 1-step conver- sion might have had. Note that power dissipation in the LTC1702 portion of a 2-step circuit is lower than it would typical 1-step converter, even in cases where the 1-step converter has higher total efficiency than the 2-step system ...
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... Total system efficiency = 51.35W/(51.35W + 4.4W) = 92. Maximizing High Load Current Efficiency Efficiency at high load currents (when the LTC1702 is operating in continuous mode) is primarily controlled by the resistance of the components in the power path (QT, QB MOSFET gate charge. Maximizing efficiency in this region of operation is as simple as minimizing these terms ...
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... Minimize ringing at the SW node so that the discontinuous comparator leaves as little residual current in the inductor as possible when QB turns off. It helps to connect the SW pin of the LTC1702 as close to the drain possible snubber network can also be added from SW to PGND. REGULATION OVER COMPONENT TOLERANCE/ ...
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... I) is known, an optimum inductor value can be chosen OUT V ESR V CAP V OUT TRANSIENT HITS V OUT TURNS AROUND Figure 16b. Transient Recovery Curves LTC1702 ESR – V • • C OUT OUT V ESR V CAP V OUT V OUT(NOMINAL) I > I TIME ...
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... W U Optimizing Loop Compensation Loop compensation has a fundamental impact on tran- sient recovery time, the time it takes the LTC1702 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. The Feedback Component Selec- tion section describes in detail how to design an optimized feedback loop, appropriate for most LTC1702 systems ...
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... LTC1702 circuits. Solder the MOSFET and the resistor(s) as close to the output of the LTC1702 circuit as possible and set up the signal generator to pulse at a 100Hz rate with a 5% duty cycle. This pulses the LTC1702 with 500 s transients ...
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... If this condition persists for more than 10 s, the overvoltage fault circuitry will fire and latch off the LTC1702. The simplest solution is to disable the fault circuit by grounding the FAULT pin. Systems that must keep the ...
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... U TYPICAL APPLICATIONS LTC1702 33 ...
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... LTC1702 U TYPICAL APPLICATIONS 34 ...
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... Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 24 0.229 – 0.244 (5.817 – 6.198) 0.015 0.004 45 0.053 – 0.068 (0.38 0.10) (1.351 – 1.727) 0 – 8 TYP 0.008 – 0.012 (0.203 – 0.305) LTC1702 0.337 – 0.344* (8.560 – 8.738) 0.033 (0.838 ...
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