LTC1703 LINER [Linear Technology], LTC1703 Datasheet

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... Mode operation as the output load decreases, ensuring maximum efficiency over a wide range of load currents. The LTC1703 features an onboard reference trimmed to 1% and delivers better than 1.5% regulation at the converter outputs. An optional latching FAULT mode protects the load if the output rises 15% above the intended voltage. Each channel can be enabled independently ...

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... Test Circuit 1 (Note 4) RUN/SS1 = RUN/SS2 = 0V (Note 5) Test Circuit 1 (Note 4) RUN/SS1 = RUN/SS2 = 0V Test Circuit FB2 Only (Note 8) (Note 6) RUN/ ORDER PART NUMBER 28 I MAX2 27 BOOST2 LTC1703CG 26 BG2 25 TG2 24 SW2 23 PGND 22 FAULT 21 RUN/SS2 20 COMP2 19 FB2 VID4 ...

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... Note 5: Supply current in shutdown is dominated by external MOSFET leakage and may be significantly higher than the quiescent current drawn by the LTC1703, especially at elevated temperature. of GS(ON) Note 6: This parameter is guaranteed by correlation and is not tested directly. Note 7: Each built-in pull-up resistor attached to the VID inputs also has a ...

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... LTC1703 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) 1703 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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... RUN/SS1 to SGND will disable controller 1 and turn off IN both of its external MOSFET switches. Pulling both RUN/SS pins down will shut down the entire LTC1703, dropping the quiescent supply current below 100 A. A capacitor from RUN/SS1 to SGND will control the turn-on time and rate of rise of the controller 1 output voltage at power-up ...

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... 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 LTC1703. FB2 (Pin 19): Controller 2 Feedback Input. FB2 should be connected through a resistor divider network to V set the ouput voltage ...

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... U U APPLICATIO S I FOR ATIO OVERVIEW The LTC1703 is a dual, step-down (buck), voltage mode feedback switching regulator controller designed to be used in a synchronous switching architecture with two external N-channel MOSFETs per channel intended to operate from a low voltage input supply (7V maximum) and provide a high power, high efficiency, precisely regu- lated output voltage ...

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... GND Float Float Float * 01111 and 11111 are defined by Intel to signify “no CPU.” The LTC1703 will generate the output voltages shown when these codes are selected. regulated output voltages as low as 800mV without exter- nal level shifting amplifiers. The LTC1703’s synchronous switching logic transitions automatically into Burst Mode operation, maximizing effi- ciency with light loads ...

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... Fast Transient Response The LTC1703 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 the following discussions, when a pin is referred to without mentioning which side is involved, that discus- sion applies equally to both sides. Switching Architecture Each half of the LTC1703 is designed to operate as a current synchronous buck converter (Figure 1). Each channel DS includes two high power MOSFET gate drivers to control external N-channel MOSFETs QT and QB ...

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... RMS current seen by the capaci- tor and reducing the value required (see the 2-Phase section). Feedback Amplifier Each side of the LTC1703 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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... SHUTDOWN/SOFT-START Each half of the LTC1703 has a RUN/SS pin. The RUN/SS pins perform two functions: when pulled to ground, each shuts down its half of the LTC1703, 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 LTC1703, 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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... Continuous Bar) pin to ground. Discontinuous Mode To minimize the efficiency loss due to reverse current flow at light loads, the LTC1703 switches to a second mode of operation: discontinuous mode (Figure 5b). In discontinu- ous mode, the LTC1703 detects when the inductor current approaches zero and turns off QB for the remainder of the switch cycle ...

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... APPLICATIO S I FOR ATIO Burst Mode Operation Discontinuous mode removes a loss term due to resistive drop in QB, but the LTC1703 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 Each time it is turned off, that charge is lost to ground. At ...

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... U VID Considerations Some applications change the VID codes at channel 1 on the fly. This is possible with the LTC1703, but care must be taken to avoid tripping the overvoltage fault circuit. Step- ping the voltage upwards abruptly is safe, but stepping down quickly by more than 15% can leave the system in a ...

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... big deal since the source attached to PGND; the LTC1703 just switches the BG pin between becomes a trade-off PGND and connected to SW which rises to V on. To keep QT on, the LTC1703 must get TG one MOSFET V above V GS(ON) with the negative lead of the driver attached to SW (the source of QT) and the V separately at BOOST ...

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... W U The two sides of the LTC1703 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. Assuming 100mV of ripple and 10A output current, we needed an ESR of 0.01 current capability for one side ...

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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 LTC1703 is much lower than at the input, due to the fact that the inductor current is constantly flowing at the output whenever the LTC1703 is operating in continuous mode ...

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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 LTC1703 at full load. Actual RMS current will differ due to inductor ripple 50% 16% 16% 18% 7 ...

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... APPLICATIO S I FOR ATIO FEEDBACK LOOP/COMPENSATION Feedback Loop Types In a typical LTC1703 circuit, the feedback loop consists of the modulator, the external inductor and output capacitor, and the feedback amplifier and its compensation network. All of these components affect loop behavior and need to be accounted for in the loop compensation ...

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... ESR causes the LC section to approach 180 phase shift well above the initial LC roll-off. As with a type 2 circuit, the loop should cross through 0dB in the middle of the phase bump to maximize phase margin. Many LTC1703 circuits using low ESR tantalum or OS-CON output capacitors 22 W ...

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... To measure the modulator gain and phase directly, wire up a breadboard with an LTC1703 and the actual MOSFETs, inductor, and input and output capacitors that the final design will use. This breadboard ...

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... A MAX /10 A PROG should be checked in an actual ILIM circuit kicks in as expected. LIM specs are like horsepower ratings in DS(ON) (< 20k) should IMAX changes when the 100mV correction LIM is set too low, the LTC1703 may fail to PROG DS(ON) is DROP can IMAX PROG ...

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... Burst Mode operation and the auxiliary output voltage W U drops, the FCB pin will trip and the LTC1703 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 LTC1703 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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... QB turns off. This current gets dissipated across the body diode of either QT or QB. Some LTC1703 systems lose as much to body diode conduction as they save in MOSFET conduction. The real efficiency benefit of ...

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... With a 5V supply, the errors contributed by the LTC1703 itself add more than 1.5% DC error at the output. At side 2, the output voltage setting resistors (R1 and R in Figure 3) are the other major contributor to DC error typical 1 ...

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... To minimize this drop, reduce the ESR as much as possible by choosing low ESR OUT V ESR V CAP V OUT TRANSIENT HITS V OUT TURNS AROUND Figure 16b. Transient Recovery Curves LTC1703 ESR – V • • OUT OUT V ESR V CAP V OUT ...

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... Optimizing Loop Compensation Loop compensation has a fundamental impact on tran- sient recovery time, the time it takes the LTC1703 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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... Changing the Output Voltage on the Fly The voltage at side 1 of the LTC1703 can be changed on the fly by changing the VID code while the output is enabled, but care must be taken to avoid tripping the overvoltage fault circuit ...

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... LTC1703 U TYPICAL APPLICATIO S 32 ...

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... U TYPICAL APPLICATIO S LTC1703 33 ...

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... Single Output, 2-Phase, 25A VID Converter ( 0.9V to 2.0V) IN OUT 10 MBR0530T 470 F* MBR0530T PV CC BOOST1 1 F TG1 SW1 BG1 LTC1703 BOOST2 TG2 SW2 BG2 FAULT FAULT VID4:0 VID4:0 PGND 0.003 0.003 0.5W 0.5W + 470 F* + 470 F* MBR 0530T MBR Q3 + 330T ...

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... DWG # 05-08-1640 – 8 0.65 (0.0256) BSC 0.25 – 0.38 (0.010 – 0.015) LTC1703 10.07 – 10.33* (0.397 – 0.407 7.65 – 7.90 (0.301 – 0.311 1.73 – 1.99 (0.068 – 0.078) 0.05 – 0.21 (0.002 – 0.008) ...

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... LTC1703 RELATED PARTS PART NUMBER DESCRIPTION LTC1530 High Power Synchronous Step-Down Controller TM LTC1625 No R Current Mode Synchronous Step-Down Controller SENSE LTC1628 Dual High Efficiency 2-Phase Synchronous Step-Down Controller LTC1702 Dual 550kHz Synchronous 2-Phase Switching Regulator Controller 550kHz, 25MHz GBW LTC1706-81 ...