LTC1778 Linear Technology, LTC1778 Datasheet
LTC1778
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LTC1778 Summary of contents
Page 1
... Optimized for High Step-Down Ratios t 100ns ON(MIN) Extremely Fast Transient Response Stable with Ceramic C OUT Dual N-Channel MOSFET Synchronous Drive Power Good Output Voltage Monitor (LTC1778) Adjustable On-Time (LTC1778-1) Wide V Range 36V IN 1% 0.8V Voltage Reference Adjustable Current Limit Adjustable Switching Frequency ...
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... 30V 1.2V (Note 0.5V to 1.9V (Note 0. 1.2V (Note 0.8V FCB (LTC1778- (LTC1778- 180 EXTV Peak Currents .................... EXTV RMS Currents .............. 50mA CC CC ORDER PART TOP VIEW NUMBER 16 BOOST 15 TG LTC1778EGN PGND ...
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... V Returning 5mA PGOOD Note 3: The LTC1778 is tested in a feedback loop that adjusts V a specified error amplifier output voltage (I and power Note 4: The LTC1778E is guaranteed to meet performance specifications from Specifications over the – operating temperature range are assured by design, characterization and correlation with statistical process controls ...
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... LTC1778/LTC1778 TYPICAL PERFOR A CE CHARACTERISTICS Transient Response V OUT 50mV/DIV I L 5A/DIV 20 s/DIV 1778 G01 LOAD STEP 0A TO 10A V = 15V 2.5V OUT FCB = 0V FIGURE 9 CIRCUIT Efficiency vs Load Current 100 DISCONTINUOUS 90 MODE 80 CONTINUOUS MODE 10V 2.5V OUT EXTV = 5V CC FIGURE 9 CIRCUIT 50 0 ...
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... Maximum Current Sense Threshold vs Temperature 150 RNG 140 130 120 110 100 50 125 –50 – 100 TEMPERATURE ( C) 1778 G11 LTC1778/LTC1778-1 On-Time vs V Voltage ON 1000 ION 800 600 400 200 VOLTAGE (V) ON 1778 G21 Maximum Current Sense ...
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... LTC1778/LTC1778 TYPICAL PERFOR A CE CHARACTERISTICS Error Amplifier g vs Temperature m 2.0 1.8 1.6 1.4 1.2 1.0 –50 – 100 125 TEMPERATURE ( C) 1778 G13 EXTV Switch Resistance CC vs Temperature –50 – 125 100 TEMPERATURE ( C) 1778 G14 RUN/SS Latchoff Thresholds vs Temperature 5.0 4.5 LATCHOFF ENABLE 4 ...
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... Tying this pin to the output voltage or an external resistive divider from the output makes the on-time proportional to V comparator input defaults to 0.7V when the pin is grounded or unavailable (LTC1778) and defaults to 2.4V when the pin is tied to INTV . Tie this pin to INTV CC applications to use a lower R value ...
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... ON I ION S Q 20k + + I I CMP – – 1.4V V RNG 3 0.7V 3 240k THB 0.8V – – 0.8V * LTC1778 ** LTC1778 FCB 9 EXTV CC 4.7V + – 0.8V – FCNT ON SWITCH REV LOGIC SHDN RUN SS SHDN – + 0.6V C RUN/ 0. ...
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... U OPERATIO Main Control Loop The LTC1778 is a current mode controller for DC/DC step-down converters. In normal operation, the top MOSFET is turned on for a fixed interval determined by a one-shot timer OST. When the top MOSFET is turned off, the bottom MOSFET is turned on until the current com- ...
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... The current mode control loop will RNG not allow the inductor current valleys to exceed (0.133 practice, one should allow some RNG SENSE margin for variations in the LTC1778 and external compo- nent values and a good guide for selecting the sense resistance is: V RNG R SENSE 10 • ...
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... Figure 2. For a maximum junction temperature of 100 C, using a value = 1.3 is reasonable. T The power dissipated by the top and bottom MOSFETs strongly depends upon their respective duty cycles and the load current. When the LTC1778 is operating in continuous mode, the duty cycles for the MOSFETs are: V OUT D TOP ...
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... Minimum Off-time and Dropout Operation The minimum off-time t is the smallest amount of OFF(MIN) time that the LTC1778 is capable of turning on the bottom MOSFET, tripping the current comparator and turning the MOSFET back off. This time is generally about 250ns. The minimum off-time limit imposes a maximum duty cycle of ...
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... To dampen input voltage transients, add a small aluminum electrolytic capacitor with an ESR in the range of 0 High performance through-hole capacitors may also be used, Kool registered trademark of Magnetics, Inc. LTC1778/LTC1778 This simple worst-case condition is is primarily determined by the ESR ...
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... Fault Conditions: Current Limit and Foldback The maximum inductor current is inherently limited in a current mode controller by the maximum sense voltage. In the LTC1778, the maximum sense voltage is controlled by the voltage on the V the maximum sense voltage and the sense resistance determine the maximum allowed inductor valley current. ...
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... GATECHG g(TOP) TG Soft-Start and Latchoff with the RUN/SS Pin The RUN/SS pin provides a means to shut down the LTC1778 as well as a timer for soft-start and overcurrent CC latchoff. Pulling the RUN/SS pin below 0.8V puts the LTC1778 into a low quiescent current shutdown (I CC until 30 A) ...
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... It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Although all dissipative elements in the circuit produce losses, four main sources account for most of the losses in LTC1778 circuits losses. These arise from the resistances of the ...
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... P TOP (0.7W)(40 C/ The junction temperatures will be significantly less at V nominal current, but this analysis shows that careful attention to heat sinking will be necessary in this circuit. LTC1778/LTC1778 – 250 kHz ...
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... Place C compact area. It may help to have some components on the bottom side of the board. • Place LTC1778 chip with pins facing the power components. Keep the components connected to pins close to LTC1778 (noise sensitive components). • Use an immediate via to connect the components to ground plane including SGND and PGND of LTC1778 ...
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... SW RNG 13 PGND VCC 11 INTV EXTV FB CC Figure 10. LTC1778 Layout Diagram LTC1778/LTC1778-1 close to the power IN decoupling capacitor C CC and PGND pins. CC closely to the B pin decoupling capacitor C IN and PGND pins – – ...
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... BOOST IRF7811A PGND IRF7811A VCC 4 INTV EXTV CC 1.2V/6A at 300kHz D B CMDSH-3 LTC1778 16 RUN/SS BOOST PGOOD RNG 13 FCB PGND VCC 4 SGND INTV ...
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... SGND INTV 0 EXTV FB CC (619) 661-6835 (847) 956-0667 (408) 822-2126 (805) 446-4800 LTC1778/LTC1778 OUT 18V 6A 12V 18V 50V IR 12CWQ03FN 2 V OUT 12V C + OUT 100 F M3 20V ...
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... LTC1778/LTC1778-1 U TYPICAL APPLICATIO 0.1 F LTC1778-1 1 RUN/ RNG 4 FCB 4700pF C 10k 100pF 6 SGND 10k 698k 52. TAIYO YUDEN TMK432BJ106MM IN1 C : SANYO 35CV10GX IN2 C : PANASONIC EEFUD0J101R OUT L1: PANASONIC ETQPAF2R7H 22 Positive-to-Negative Converter, –5V/5A at 300kHz ...
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... TYP 0.008 – 0.012 (0.203 – 0.305) LTC1778/LTC1778-1 0.189 – 0.196* (4.801 – 4.978) 0.009 (0.229 REF 0.150 – 0.157** (3.810 – 3.988 ...
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... Low Synchronous Step-Down Controller OUT SENSE Burst Mode is a registered trademark of Linear Technology Corporation. Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 Typical Application 2.5V/3A at 1.4MHz D B CMDSH-3 LTC1778 1 16 RUN/SS BOOST PGOOD ...