LTC3854 LINER [Linear Technology], LTC3854 Datasheet
LTC3854
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LTC3854 Summary of contents
Page 1
... Current foldback OUT functions are disabled during soft-start. The LTC3854 has a minimum on-time at 75ns, making it well suited for high step-down ratios. The strong onboard MOSFET drivers allow the use of high power external MOSFETs to produce output currents up to 20A. ...
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... LTC3854EDDB#PBF LTC3854EDDB#TRPBF LTC3854IDDB#PBF LTC3854IDDB#TRPBF LTC3854EMSE#PBF LTC3854EMSE#TRPBF LTC3854IMSE#PBF LTC3854IMSE#TRPBF Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: ...
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... C = 3300pF LOAD C = 3300pF LOAD (Note 3300pF LOAD C = 3300pF LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD (Note 7) 6V < V < 38V 20mA CC LTC3854 MIN TYP MAX UNITS 4.5 38 0.792 0.8 0.808 l ±5 ±50 0.002 0.02 %/V 0.1 0.5 l –0.1 –0.5 l 2.0 mmho 3 MHz 2 ...
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... LOAD STEP 50µs/DIV 3854 G03 Note 4: The LTC3854 is tested in a feedback loop that servos V specified voltage and measures the resultant V Note 5: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. See Applications Information. Note 6: Rise and fall times are measured using 10% and 90% levels. Delay times are measured using 50% levels ...
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... TEMPERATURE (°C) Maximum Current Sense Threshold vs Duty Cycle 100 DUTY CYCLE (%) LTC3854 2µs/DIV 3854 G07 INTV vs Input Voltage CC 5.05 5.00 4.95 4.90 4.85 4. (V) IN 3854 G09 Maximum Current Sense Voltage vs Feedback Voltage ...
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... LTC3854 Typical perForMance characTerisTics Oscillator Frequency vs Temperature 440 430 420 410 400 390 380 –40 – 100 TEMPERATURE (°C) 3854 G15 Current Sense Threshold vs I Voltage –10 0 0.5 1 1.5 2 2.5 V (V) ITH 3854 G18 INTV Load Regulation CC 5 ...
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... Comparator. The ITH pin voltage and controlled offsets between the SENSE R (or R SENSE SGND (Exposed Pad Pin 13): The exposed pad must be soldered to PCB ground for electrical contact and rated thermal performance LTC3854 . CC – + and SENSE pins in conjunction with ) set the peak current trip threshold. DCR 3854fa ...
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... LTC3854 FuncTional DiagraM OSCILLATOR SLOPE COMP GENERATOR – SENSE CONVERTER V ICS + SENSE SENSE 1.2V 0.88V 0.80V INTV CC UVLO DRIVE CONTROL AND ANTI-SHOOT THROUGH ON CLK TG_OFF CURRENT SENSE COMPARATOR + RUN I CMP – SS – ERROR ITH + AMP + – V ITH V IN BANDGAP/ ...
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... MOSFET off for 1/10 of the clock period every fourth cycle to allow C to recharge. B Shutdown and Start-Up (RUN/SS) The LTC3854 is shut down using the RUN/SS pin. Pulling this pin below 1.2V disables the controller and most of the internal circuitry, including the INTV , CMP However, for RUN/SS> ...
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... When the SENSE pins ramp down from 5.5V to 1.1V, the small bias currents flow into the SENSE pins. The high impedance inputs to the current comparator allow accurate DCR sensing. Figure 1. Using a Resistor to Sense Current with the LTC3854 0 Using a Sense Resistor for Current Sensing A typical sensing circuit using a discrete resistor is shown in Figure 1 ...
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... It is accomplished internally by adding a compensating ramp to the inductor current signal. Normally, this results in a reduction of maximum inductor peak current for high duty cycles. However, the LTC3854 uses a novel scheme that allows the maximum inductor peak current to remain unaffected throughout all duty cycles. V ...
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... Power MOSFET and Schottky Diode (Optional) Selection Two external power MOSFETs must be selected for the LTC3854 controller: one N-channel MOSFET for the top (main) switch, and one N-channel MOSFET for the bottom (synchronous) switch. The peak-to-peak drive levels are set by the INTV This voltage is 5V during start-up ...
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... Soft-Start When the LTC3854 is configured to soft-start by itself, a capacitor must be connected to the RUN/SS pin. The LTC3854 is in the shutdown state if the RUN/SS pin volt- age is below 1.2V. The RUN/SS pin has an internal 1.25µA pull-up current and should be externally pulled low (<0.4V) to keep IC in shutdown mode. ...
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... If there is no change in input current, then there is no change in efficiency. Undervoltage Lockout The LTC3854 has two functions that help protect the controller in case of undervoltage conditions. A precision UVLO comparator constantly monitors the INTV to ensure that an adequate gate-drive voltage is present. ...
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... Any inductance present in the circuit board traces negates their usefulness. Setting Output Voltage The LTC3854 output voltage is set by an external feed- back resistive divider carefully placed across the output, as shown in Figure 3. The regulated output voltage is determined by: ...
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... Minimum and Maximum On-Time Considerations Minimum on-time t is the smallest time duration ON(MIN) that the LTC3854 is capable of turning on the top MOSFET determined by internal timing delays and the gate charge required to turn on the top MOSFET. Low duty cycle applications may approach this minimum on-time ...
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... The discharged bypass capacitors are effectively put in parallel with C , causing a rapid drop in V OUT alter its delivery of current quickly enough to prevent this LTC3854 -C filter sets the dominant pole-zero C C and the bandwidth of the loop C ...
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... Are the signal and power grounds segregated? The LTC3854 GND pin should tie to the ground plane close to the output capacitor(s). The low current or signal ground trace should make a single point connection directly to the GND pin. The synchronous MOSFET source pins should connect to the input capacitor(s) ground ...
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... All of these nodes have very large and fast moving signals and therefore should be kept on the “output side” (Pins 4,5,6 and 8) of the LTC3854 GND and occupy minimum PC trace area. SENSE+ SENSE– Figure 5. Kelvin Sensing R ...
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... LTC3854 applicaTions inForMaTion Design Example Consider the design of a 1.2V, 15A buck regulator with a V range of 4.5V to 28V using a DCR sensing scheme. IN Inductor Selection Assuming an inductor ripple of 40 calculated for the worst case • V 1− MIN OUT ∆ ...
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... INTVCC R = 2.6Ω DR,PULLUP R DR,PULLDOWN the total losses in the main FET will be: 1. MAIN 20V • 13mΩ + 20V • 0.55W MAIN . B LTC3854 Capacitors OUT(MAX test 10V results 1.5nC/10V DS MILLER = 4. 15A, estimated T = 100°C for the OUT J = 1.5Ω • (15A) • 1+ 0.005 • 100°C – 25°C ...
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... The resulting controller temperature at 60°C and a 20V input will be 60°C + 20V • 14mA • 76°C/W = 81°C J which is well under the maximum junction temperature of 125° LTC3854 RUN/SS 0.1µF L 0.56µH ITH BOOST 1.8m DCR SW 100pF 3.09k D1 INTV CC 4.7µ ...
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... LTC3854 RUN/SS 0.1µF ITH BOOST L SW 100pF 0.56µH D1 INTV CC 4.7µF FB – M2 SENSE BG 1nF + SENSE GND 47 47 Figure 7. 1.5V/15A R Application SENSE LTC3854 V IN 4.5V TO 14V 180µF 47µF 25V 25V 2 R SENSE V 2m OUT 1.5V 15A + C OUT1 330µ OUT2 47µF 2 3854 TA02 ...
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... RUN/SS BOOST 1.8m DCR ITH SW 100pF D1 1.21k INTV CC 4.7µ – SENSE + SENSE GND Figure 8. 1.0V/20A DCR Sense Application LTC3854 RUN/SS 0.1µF ITH BOOST L SW 100pF 3.6µH D1 INTV CC 4.7µF FB – M2 SENSE BG 4.7nF + SENSE GND 16 16 Figure 9. 5.0V/10A R Application ...
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... LTC DWG # 05-08-1723 Rev Ø) 0.70 ±0.05 PACKAGE OUTLINE 0.45 BSC 2.39 ±0.05 (2 SIDES 0.115 3.00 ±0.10 TYP R = 0.05 (2 SIDES) 7 TYP 2.00 ±0.10 (2 SIDES) 0.64 ± 0.10 (2 SIDES) 6 0.23 ± 0.05 0.75 ±0.05 0 – 0.05 BOTTOM VIEW—EXPOSED PAD LTC3854 0.40 ± 0.10 12 PIN 0.20 OR 0.25 × 45° CHAMFER 1 (DDB12) DFN 0106 REV Ø 0.45 BSC 2.39 ±0.10 (2 SIDES) 3854fa ...
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... LTC3854 package DescripTion 2.845 0.102 (.112 .004) 5.23 (.206) MIN 0.42 0.038 (.0165 .0015) TYP RECOMMENDED SOLDER PAD LAYOUT DETAIL “A” 0.254 (.010) GAUGE PLANE DETAIL “A” 0.18 (.007) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. ...
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... Updated Related Parts Table Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. LTC3854 PAGE NUMBER 1 1 ...
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... LTC3854 relaTeD parTs PART NUMBER DESCRIPTION LTC3851A ™ Wide V Range Synchronous Step-Down SENSE IN LTC3851A-1 DC/DC Controller LTC3878 No R Constant On-Time Synchronous Step-Down SENSE DC/DC Controller LTC3879 No R Constant On-Time Synchronous Step-Down SENSE DC/DC Controller LTC3850/ Dual 2-Phase, High Efficiency Synchronous Step-Down LTC3850-1/ DC/DC Controllers, R ...