ltc1702a Linear Technology Corporation, ltc1702a Datasheet
ltc1702a
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ltc1702a 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 LTC1702A shuts down and supply current drops below 100µA. Dual Output High Power 3.3V/2.5V Logic Supply = 5V ± ...
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... All Other Inputs ......................... – 0. Peak Output Current < 10µ ............................................................... 5A Operating Temperature Range LTC1702AC ............................................. 0°C to 70°C LTC1702AI ........................................ – 40°C to 85°C Storage Temperature Range ................. – 65°C to 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 25° ...
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... Note 5: Supply current in shutdown is dominated by external MOSFET of leakage and may be significantly higher than the quiescent current drawn GS(ON) by the LTC1702A, especially at elevated temperature. 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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... LTC1702A 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) 1702A 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 (Pin 9): Controller 1 Run/Soft-start. Pulling RUN/SS1 to SGND will disable controller 1 and turn off both of its external MOSFET switches. Pulling both RUN/SS pins down will shut down the entire LTC1702A, dropping the quiescent supply current below 100µA. 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. An internal 3.5µ ...
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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 a 1µF capacitor in close proximity to the LTC1702A. FB2 (Pin 14): Controller 2 Feedback Input. See FB1. COMP2 (Pin 15): Controller 2 Loop Compensation. See COMP1 ...
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... OV fault has occurred automatically resume operation when the fault is removed. The LTC1702A takes a low input voltage and generates two lower output voltages at very high currents. Its strengths are small size, unmatched regulation and tran- sient response and high efficiency ...
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... U regulation system happens in the 5V supply, which is usually located away from the CPU. The power lost to heat in the LTC1702A section of the system is relatively low, minimizing the added heat near the CPU. See the Optimizing Performance section for a detailed explanation of how to calculate system efficiency. ...
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... Fast Transient Response The LTC1702A 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 configuration than with a typical g ...
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... QT requires V and the IN minimum R LTC1702A— it needs to generate a gate drive signal at TG higher than its highest supply voltage. To get around this, the TG driver runs from floating supplies, with its negative supply attached to SW and its power supply at BOOST. This allows it to slew up and down with the source of QT. ...
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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 LTC1702A is shut down, the host system should ignore the associated PGOOD pin. + ...
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... SHUTDOWN/SOFT-START Each half of the LTC1702A has a RUN/SS pin. The RUN/SS pins perform two functions: when pulled to ground, each shuts down its half of the LTC1702A, and each acts as a conventional soft-start pin, enforcing a maximum duty cycle limit proportional to the voltage at RUN/SS. An internal 3.5µA 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. The 3.5µ ...
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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 LTC1702A, 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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... LTC1702A to operate in continuous mode at all loads by tying the FCB (Force Continuous Bar) pin to ground. Discontinuous Mode To minimize the efficiency loss due to reverse current flow at light loads, the LTC1702A switches to a second mode of I RIPPLE TIME Figure 5a. Continuous Mode ...
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... INFORMATION Burst Mode Operation Discontinuous mode removes the resistive loss drop term in QB, but the LTC1702A 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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... MOSFETs without heat sinks. Gate Charge Gate charge is amount of charge (essentially, the number of electrons) that the LTC1702A 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 ...
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... MOSFETs. Gate charge loss is also the primary cause of power dissipation in the LTC1702A itself. TG Charge Pump There’s another nuance of MOSFET drive that the LTC1702A needs to get around. The LTC1702A is designed to use N- channel MOSFETs for both QT and QB, primarily because N-channel MOSFETs generally cost less and have lower R than similar P-channel MOSFETs ...
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... These requirements can be met with multiple low ESR tantalum or electrolytic capacitors in parallel, or with a large monolithic ceramic capacitor. The two sides of the LTC1702A 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 0.01Ω ...
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... Generic tantalum capacitors have a destruc- current, we can add tive failure mechanism when they are subjected to large RMS currents (like those seen at the input of a LTC1702A). 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 “ ...
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... ESR of the output bypass capacitor until the feedback loop in the LTC1702A can change the inductor current to match the new load current value. This ESR step at the output is often the single largest budget item in the load regulation calculation example, our hypothetical 1.6V, 10A switcher with a 0.01Ω ...
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... 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 LTC1702A 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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... To measure the modulator gain and phase directly, wire up a breadboard with an LTC1702A and the actual MOSFETs, inductor, and input and output capacitors that the final design will use. This breadboard ...
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... U U APPLICATIONS INFORMATION 10Ω MBR0530T + 10µ BOOST2 TG 1/2 LTC1702A V COMP TO COMP SW ANALYZER 0.1µ RUN/SS FCB R 10k B FAULT AC SOURCE SGND PGND FROM ANALYZER Figure 12. Modulator Gain/Phase Measurement Set-Up If breadboard measurement is not practical, a SPICE simulation can be used to generate approximate gain/ phase curves. Plug the expected capacitor, inductor and ...
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... MOSFET that is running quite a bit higher than its R FCB OPERATION/SECONDARY WINDINGS The FCB pin can be used in conjunction with a secondary DS(ON) winding on one side of the LTC1702A to generate a third to 150% of the LIM regulated voltage output. This output can be directly regulated at the FCB pin. In theory, a fourth output could PROG pin using the internal 10µ ...
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... LTC1702A to resume normal operation, but will not reset the latch. If the pull-down is later removed, the LTC1702A will latch off again unless the latch is reset by cycling the power or RUN/SS pins. Note that both the PGOOD pins and the FAULT pin monitor the output voltages by watching the FB pins ...
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... QT cost efficiency, eliminating any advantage the 1-step conver- sion might have had. Note that power dissipation in the LTC1702A 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 + 5.74W Maximizing High Load Current Efficiency Efficiency at high load currents (when the LTC1702A is operating in continuous mode) is primarily controlled by the resistance of the components in the power path (QT, QB and power lost in the gate drive circuits due to EXT MOSFET gate charge ...
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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 LTC1702A as close to the drain possible snubber network can also be added from SW to PGND. REGULATION OVER COMPONENT TOLERANCE/ ...
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... OUT V ESR V CAP V OUT TRANSIENT HITS V OUT TURNS AROUND Figure 16b. Transient Recovery Curves LTC1702A ) ESR – V • • C OUT ∆ OUT V ESR V CAP V OUT V OUT(NOMINAL) I > I ...
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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 LTC1702A 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 LTC1702A systems ...
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... LTC1702A circuits. Solder the MOSFET and the resistor(s) as close to the output of the LTC1702A circuit as possible and set up the signal generator to pulse at a 100Hz rate with a 5% duty cycle. This pulses the LTC1702A with 500µs transients ...
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... If this condition persists for more than 10µs, the overvoltage fault circuitry will fire and latch off the LTC1702A. 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 LTC1702A 1702afa 33 ...
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... LTC1702A U TYPICAL APPLICATIONS 34 1702afa ...
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... BSC .015 ± .004 × 45° .0532 – .0688 (0.38 ± 0.10) (1.35 – 1.75) 0° – 8° TYP .008 – .012 (0.203 – 0.305) TYP LTC1702A .337 – .344* (8.560 – 8.738) .033 (0.838 ...
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... CC CC FB2 BOOST2 56pF QT2 TG2 COMP2 SW2 RUN/SS2 QB2 BG2 36.5k RUN/SS1 I MAX2 0.1µF FAULT LTC1702A BOOST1 QT1B FB1 TG1 39pF COMP1 SW1 BG1 FCB QB1B 15k I MAX1 SGND PGND QSS1, QSS2: MOTOROLA MMBT3904LT1 QT1A, QT1B, QB1A, QB1B: FAIRCHILD FDS6670A QT2, QB2: 1/2 SILICONIX Si4966 COMMENTS SO-8 with Current Limit ...