LTC3853 Linear Technology, LTC3853 Datasheet
LTC3853
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LTC3853 Summary of contents
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... V FB1 RUN1,2,3 10k I TH1,2,3 TG3 V SW3 FB3 BG3 SGND + SENSE3 – SENSE3 TK/SS1,2,3 0.1μF LTC3853 Triple Output, Step-Down Controller ® 3853 is a high performance triple output step- ® operation, pulse-skipping 24V 22μF 50V 2.2μH 1μH 2.2k 1k 0.1μF 0.1μF V OUT2 3 ...
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... FB1 FB3 INTV Peak Output Current ................................150mA CC Operating Temperature Range (Note 2) LTC3853E ............................................. –40°C to 85°C LTC3853I............................................ –40°C to 125°C Junction Temperature (Note 3) ............................. 125°C Storage Temperature Range ................... –65°C to 125°C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL ...
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... LOAD C = 3300pF LOAD (Note 3300pF LOAD C = 3300pF LOAD (Note 3300pF Each Driver LOAD (Note 3300pF Each Driver LOAD (Note 7) LTC3853 = 5V, unless otherwise noted. MIN TYP MAX l 0.792 0.800 0.808 0.794 0.800 0.806 –10 –50 0.002 0.02 l 0.01 0.1 l –0.01 – ...
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... FB V Ramping Positive FB Note 4: The LTC3853 is tested in a feedback loop that servos V specifi ed 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. ...
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... LOAD CURRENT (mA) 3853 G01 100mV/DIV AC COUPLED 3853 G04 40μs/DIV CONTINUOUS Burst Mode OPERATION PULSE SKIPPING 3853 G06 40μs/DIV LTC3853 Effi ciency and Power Loss vs Input Voltage 100 95 90 EFFICIENCY 85 80 POWER LOSS 3.3V OUT ...
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... LTC3853 TYPICAL PERFORMANCE CHARACTERISTICS Prebiased Output at 2V www.datasheet4u.com V 1V/DIV V 500mV/DIV V 500mV/DIV 3853 G08 50ms/DIV Quiescent Current vs Input Voltage Without EXTV 6.0 5.5 5.0 4.5 4 INPUT VOLTAGE (V) Maximum Current Sense Threshold vs Common Mode Voltage INTV LIM FLOAT LIM GND LIM ...
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... Shutdown Current vs Temperature 12V –50 – TEMPERATURE (°C) 3853 G23 LTC3853 Regulated Feedback Voltage vs Temperature 806 804 802 800 798 796 794 100 125 –50 – TEMPERATURE (°C) 3853 G18 Oscillator Frequency vs Input Voltage ...
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... LTC3853 PIN FUNCTIONS + + + SENSE1 , SENSE2 , SENSE3 (Pins 3, 5, 7): Current Sense Comparator Inputs. The (+) inputs to the current compara- tors are normally connected to DCR sensing networks or www.datasheet4u.com current sensing resistors. SENSE3 to 13.5V, allowing higher V OUT – – – SENSE1 , SENSE2 , SENSE3 Sense Comparator Inputs. The (–) inputs to the current comparators are connected to the outputs ...
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... Exposed Pad (Pin 41): Power Ground. Connect these pins to enable pulse closely to the sources of the bottom N-channel MOSFETs, CC the (–) terminal of C LTC3853 to set the maximum current sense threshold to CC voltage of the master channel is reproduced and the (–) terminal of C VCC ...
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... LTC3853 FUNCTIONAL DIAGRAM FREQ/PLLFLTR MODE/PLLIN www.datasheet4u.com MODE/SYNC DETECT PLL-SYNC OSC CMP – I LIM COMPENSATION INTV CC 1 SLOPE RECOVERY ACTIVE CLAMP 51k I THB V SLEEP IN 0.8V REF EA – – + 0.55V 10 EXTV CC 4.7V – 0.8V 5V REG – BURSTEN S FCNT SWITCH LOGIC – AND ANTI- ...
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... IN Light Load Current Operation (Burst Mode Operation, Pulse Skipping or Continuous Conduction) The LTC3853 can be enabled to enter high effi ciency Burst Mode operation, constant-frequency pulse skipping mode, or forced continuous conduction mode. To select forced continuous operation, tie the MODE/PLLIN pin LTC3853 regulator ...
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... The PGOOD12 pin is also pulled low when either RUN1 pin, just as in nor RUN2 pin is below 1.2V or when the LTC3853 is in the soft-start or tracking phase. When the V is within the ±7.5% requirement, the MOSFET is turned off and the pin is allowed to be pulled external resistor to a source ...
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... In dual ( mode, phase 1 and phase 2 are 180 degrees apart (instead of 120 degrees) with phase 3 remaining at APPLICATIONS INFORMATION The Typical Application on the fi rst page is a basic LTC3853 application circuit. LTC3853 can be confi gured to use either DCR (inductor resistance) sensing or low value resistor sensing ...
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... F + SENSE – SENSE SGND FILTER COMPONENTS PLACED NEAR SENSE PINS (2a) Using a Resistor to Sense Current V IN INTV CC BOOST TG SW LTC3853 BG PGND R1 + SENSE C1* R2 – SENSE SGND • *PLACE C1 NEAR SENSE , DCR – SENSE PINS (2b) Using the Inductor DCR to Sense Current Figure 2 ...
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... Inductor DCR Sensing For applications requiring the highest possible effi ciency at high load currents, the LTC3853 is capable of sensing the voltage drop across the inductor DCR, as shown in Figure 2b. The DCR of the inductor represents the small amount of DC winding resistance of the copper, which can be less than 1mΩ ...
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... Normally, this results in a reduction of maximum inductor peak cur- rent for duty cycles >40%. However, the LTC3853 uses a patented scheme that counteracts this compensating ramp, which allows the maximum inductor peak current to remain unaffected throughout all duty cycles ...
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... Power MOSFET and Schottky Diode (Optional) Selection Two external power MOSFETs must be selected for each controller in the LTC3853: 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 DRV voltage ...
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... Larger diodes result in additional transition losses due to their larger junction capacitance. Soft-Start and Tracking The LTC3853 has the ability to either soft-start by itself with a capacitor or track the output of another channel or external supply. When one particular channel is confi gured to soft-start by itself, a capacitor should be connected to its TK/SS pin ...
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... For better output regulation, use the coincident tracking mode instead of ratiometric. INTV CC The LTC3853 features an NPN linear regulator that supplies power to INTV gate drivers and much of the LTC3853’s internal circuitry. The linear regualtor regulates the voltage at the INTV ...
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... CC remains on as long as the voltage applied to EXTV above 4.5V. Using the EXTV allows the MOSFET driver CC and control power to be derived from one of the LTC3853’s switching regulator outputs during normal operation and from the INTV when the output is out of regulation CC (e.g., start-up, short-circuit). If more current is required through the EXTV than is specifi ...
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... C is high enough. An extra if there is any question. The benefi the LTC3853 3-phase operation can be cal- culated by using the equation above for the higher power controller and then calculating the loss that would have resulted if all controller channels switched on at the same ...
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... The output ripple is highest at maximum input voltage since I increases with input voltage. RIPPLE Setting Output Voltage The LTC3853 output voltages are each set by an external feedback resistive divider carefully placed across the output, as shown in Figure 9. The regulated output volt- age is determined by: ⎛ ...
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... Minimum On-Time Considerations Minimum on-time t that the LTC3853 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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... L1, L2, etc. are the individual losses as a percent- age of input power. Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3853 circuits regulator current losses, 4) topside MOSFET transition losses. ...
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... APPLICATIONS INFORMATION minimum of 20μF to 40μF of capacitance having a maxi- mum of 20mΩ to 50mΩ of ESR. The LTC3853 3-phase architecture reduces this input capacitance requirement up www.datasheet4u.com to 66% over competing solutions. Other losses including Schottky conduction losses during dead time and induc- tor core losses generally account for less than 2% total additional loss ...
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... All of these nodes have very large and fast moving signals and therefore should be kept on the “output side” of the LTC3853 and occupy minimum PC trace area. If DCR sensing is used, place the top resistor (Figure 2b, R1) close to the switching node. 7. Use a modifi ...
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... C IN BOLD LINES INDICATE HIGH SWITCHING CURRENTS. KEEP LINES TO A MINIMUM LENGTH. SW1 L1 R SENSE1 C D1 OUT1 SW2 L2 R SENSE2 C D2 OUT2 SW3 L3 R SENSE3 C D3 OUT3 Figure 12. Branch Current Waveforms LTC3853 V OUT1 + OUT2 + OUT3 + R L3 3853 F12 27 3853f ...
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... LTC3853 APPLICATIONS INFORMATION PC Board Layout Debugging Start with one controller at a time helpful to use a www.datasheet4u.com DC-50MHz current probe to monitor the current in the inductor while testing the circuit. Monitor the output switching node (SW pin) to synchronize the oscilloscope to the internal oscillator and probe the actual output voltage as well ...
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... For each channel, 0.1μF is selected for C1 Δ NOM ( ) ) + ≅ Ω Δ ⎞ MAX ( ) ⎠ ⎟ 2 LTC3853 M2 M3 3.3μH 4.75k 0.1μF 1430Ω V OUT2 3.3V 63.4k 5A 10pF 1% + 20k 330μ 3853 F13 is the same for channels 1, 2 SENSE Ω SENSE EQUIV ...
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... LTC3853 APPLICATIONS INFORMATION For channel 1, the DCR fi lter/divider values are: SENSE Ω 1100 = = ≅ www.datasheet4u.com • • − − The power loss the maximum input voltage is: − ...
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... V TG3 FB3 SW3 BG3 SGND + SENSE3 – EXTV SENSE3 CC TK/SS1,2,3 C SS1,2,3 0.1μF = 220pF *THESE FILTER COMPONENTS NEED TO BE CLOSE TO THE IC = 220pF = 220pF LTC3853 33μF 35V M2 M3 1.5μH 2.2μH 0.008Ω 10Ω* 5% 10Ω* 10Ω* 1000pF* V OUT2 1.8V 10Ω* 5A 24. 63.4k 20k 220μ ...
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... FILTER COMPONENTS NEED TO BE CLOSE TO THE IC = 220pF = 330pF D B1,2,3 V DRV INTV IN CC CC12 TG1 TG2 C 0.1μF B1,2,3 PGOOD12 PGOOD3 BOOST1,2,3 SW1,2,3 SW1 SW2 LTC3853 BG1 BG2 MODE/PLLIN PGND 10k ILIM FREQ/PLLFLTR INTV SENSE1 SENSE2 1000pF* – SENSE2 – SENSE1 V FB2 V FB1 ...
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... BG3 SGND + SENSE3 – SENSE3 TK/SS1 TK/SS3 C C SS1 SS3 0.22μF 0.1μF = 220pF *THESE FILTER COMPONENTS NEED TO BE CLOSE TO THE IC = 330pF LTC3853 SENSE 180μF 16V 0.47μH 0.78μH 0.002Ω 100Ω* 5% 100Ω* 1000pF* 100Ω* 100Ω* V OUT1 200k 43.2k ...
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... ITH1 ITH1 P1 SHORT TK/SS1, TK/SS2 AND TK/SS3 TOGETHER 34 4.7μF D B1,2,3 V DRV INTV IN CC12 CC TG1 TG2 C 0.1μF B1,2,3 PGOOD12 PGOOD3 BOOST1,2,3 SW1,2,3 SW1 SW2 LTC3853 BG1 BG2 MODE/PLLIN PGND 10k ILIM FREQ/PLLFLTR INTV SENSE1 SENSE2 1000pF* EXTV CC – SENSE2 – SENSE1 V RUN1 FB1 V ...
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... Plastic QFN (6mm × 6mm) (Reference LTC DWG # 05-08-1728 Rev Ø) 0.70 0.05 6.50 0.05 5.10 0.05 4.50 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 0.75 0. 0.10 TYP 4.50 REF (4-SIDES) 0.200 REF 0.00 – 0.05 LTC3853 R = 0.115 TYP 39 40 0.40 0. PIN 1 NOTCH R = 0.45 OR 0.35 45 CHAMFER 4.42 0.10 4.42 0.10 (UJ40) QFN REV Ø 0406 0.25 0.05 0.50 BSC BOTTOM VIEW—EXPOSED PAD ...
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... V Differential Remote Sense Amplifi er, R 30μ Six Phases, 0.8V ≤ V 30μA I 1.23V ≤ V 2-Phase Version of LTC3853 in a 28-Lead 4mm × 4mm QFN, 4mm × 5mm QFN or 28-Lead SSOP Narrow 4V ≤ trademark of Linear Technology Corporation. SENSE www.linear.com ● ...