LTC3857IUH#TRPBF Linear Technology, LTC3857IUH#TRPBF Datasheet

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... PGOOD output, without phase modulation or a clock output, see the LTC3857-1 data sheet. L, LT, LTC, LTM, Burst Mode, OPTI-LOOP , PolyPhase, μModule, Linear Technology and the Linear logo are registered trademarks and No R Technology Corporation. All other trademarks are the property of their respective owners. ...

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... LTC3857EUH#PBF LTC3857EUH#TRPBF LTC3857IUH#PBF LTC3857IUH#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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ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T SYMBOL PARAMETER V Output Voltage Load Regulation LOADREG g Transconductance Amplifier g m1 Input DC Supply Current Q Pulse-Skipping or Forced Continuous Mode (One Channel On) Pulse-Skipping or Forced ...

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LTC3857 ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T SYMBOL PARAMETER INTV Linear Regulator CC V Internal V Voltage INTVCCVIN CC V INTV Load Regulation LDOVIN CC V Internal V Voltage INTVCCEXT CC V INTV Load Regulation LDOEXT CC ...

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TYPICAL PERFORMANCE CHARACTERISTICS Efficiency and Power Loss vs Output Current 100 V = 12V 3.3V OUT FIGURE 13 CIRCUIT 0.00001 0.0001 0.001 0.01 0.1 1 OUTPUT CURRENT ...

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LTC3857 TYPICAL PERFORMANCE CHARACTERISTICS Total Input Supply Current vs Input Voltage 500 V = 3.3V OUT1 450 RUN2 = 0V FIGURE 13 CIRCUIT 400 350 300 250 500μA 200 300μA 150 100 NO LOAD ...

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TYPICAL PERFORMANCE CHARACTERISTICS TRACK/SS Pull-Up Current vs Temperature 1.10 1.05 1.00 0.95 0.90 –45 – 105 TEMPERATURE (°C) 3857 G19 – SENSE Pin Input Current vs Temperature < INTV – 0.5V –50 OUT ...

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LTC3857 PIN FUNCTIONS – – SENSE1 , SENSE2 (Pin 1, Pin 9): The (–) Input to the Differential Current Comparators. When greater than – INTV – 0.5V, the SENSE pin supplies current to the CC current comparator. FREQ (Pin 2): ...

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PIN FUNCTIONS TG1, TG2 (Pin 26, Pin 15): High Current Gate Drives for Top N-Channel MOSFETs. These are the outputs of float- ing drivers with a voltage swing equal to INTV superimposed on the switch node voltage SW. PGOOD1, PGOOD2 ...

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LTC3857 FUNCTIONAL DIAGRAM PHASMD PGOOD1 + 0.88V 27 3 – V FB1 + – 0.72V PGOOD2 + 0.88V 14 – V FB2 + – 0.72V 20μA FREQ 2 VCO C LP SYNC DET PLLIN/MODE 5 100k I LIM CURRENT 28 ...

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OPERATION (Refer to the Functional Diagram) Main Control Loop The LTC3857 uses a constant frequency, current mode step-down architecture with the two controller channels operating 180 degrees out of phase. During normal op- eration, each external top MOSFET is turned ...

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LTC3857 OPERATION (Refer to the Functional Diagram) Light Load Current Operation (Burst Mode Operation, Pulse-Skipping or Forced Continuous Mode) (PLLIN/MODE Pin) The LTC3857 can be enabled to enter high efficiency Burst Mode operation, constant frequency pulse-skipping mode, or forced continuous ...

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OPERATION (Refer to the Functional Diagram) selects 535kHz. Placing a resistor between FREQ and SGND allows the frequency to be programmed between 50kHz and 900kHz, as shown in Figure 10. A phase-locked loop (PLL) is available on the LTC3857 to ...

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LTC3857 OPERATION (Refer to the Functional Diagram) pulses increased the total RMS current flowing from the input capacitor, requiring the use of more expensive input capacitors and increasing both EMI and losses in the input capacitor and battery. With 2-phase ...

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APPLICATIONS INFORMATION The Typical Application on the first page is a basic LTC3857 application circuit. LTC3857 can be configured to use either DCR (inductor resistance) sensing or low value resistor sensing. The choice between the two current sensing schemes is ...

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LTC3857 APPLICATIONS INFORMATION placed close to the switching node, to prevent noise from coupling into sensitive small-signal nodes. Low Value Resistor Current Sensing A typical sensing circuit using a discrete resistor is shown in Figure 4a chosen based ...

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APPLICATIONS INFORMATION The equivalent resistance R1 scaled to the room temperature inductance and maximum DCR: L R1||R2 DCR at 20°C •C1 The sense resistor values are: R1||R2 R1•R D R1= ; R2= R 1– ...

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LTC3857 APPLICATIONS INFORMATION The peak-to-peak drive levels are set by the INTV voltage. This voltage is typically 5.1V during start-up (see EXTV Pin Connection). Consequently, logic-level CC threshold MOSFETs must be used in most applications. The only exception is if ...

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APPLICATIONS INFORMATION maximum RMS capacitor current requirement. Increas- ing the output current drawn from the other controller will actually decrease the input RMS ripple current from its maximum value. The out-of-phase technique typically reduces the input capacitor’s RMS ripple current ...

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LTC3857 APPLICATIONS INFORMATION Tracking and Soft-Start (TRACK/SS Pins) The start-up of each V is controlled by the voltage on OUT the respective TRACK/SS pin. When the voltage on the TRACK/SS pin is less than the internal 0.8V reference, the LTC3857 ...

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APPLICATIONS INFORMATION INTV Regulators CC The LTC3857 features two separate internal P-channel low dropout linear regulators (LDO) that supply power at the INTV pin from either the V supply pin or the EXTV CC IN pin depending on the connection ...

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LTC3857 APPLICATIONS INFORMATION C IN BAT85 V IN MTOP VN2222LL TG1 1/2 LTC3857 L EXTV SW CC MBOT BG1 PGND Figure 9. Capacitive Charge Pump for EXTV 4. EXTV Connected to an Output-Derived Boost Network. CC For 3.3V and other ...

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APPLICATIONS INFORMATION Phase-Locked Loop and Frequency Synchronization The LTC3857 has an internal phase-locked loop (PLL) comprised of a phase frequency detector, a lowpass filter, and a voltage-controlled oscillator (VCO). This allows the turn-on of the top MOSFET of controller 1 ...

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LTC3857 APPLICATIONS INFORMATION If the duty cycle falls below what can be accommodated by the minimum on-time, the controller will begin to skip cycles. The output voltage will continue to be regulated, but the ripple voltage and current will increase. ...

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APPLICATIONS INFORMATION Other hidden losses such as copper trace and internal battery resistances can account for an additional 5% to 10% efficiency degradation in portable systems very important to include these system level losses during the design phase. ...

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LTC3857 APPLICATIONS INFORMATION Design Example As a design example for one channel, assume V (nominal 22V (max OUT V = 75mV and f = 350kHz. SENSE(MAX) The inductance value is chosen first based on a 30% ...

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APPLICATIONS INFORMATION PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the IC. These items are also illustrated graphically in the layout diagram of Figure 11. Figure ...

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LTC3857 APPLICATIONS INFORMATION BOLD LINES INDICATE HIGH SWITCHING CURRENT. KEEP LINES TO A MINIMUM LENGTH. – Are the SENSE and SENSE leads routed together with minimum PC trace spacing? The filter capacitor ...

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APPLICATIONS INFORMATION PC Board Layout Debugging Start with one controller time helpful to use a DC-50MHz current probe to monitor the current in the inductor while testing the circuit. Monitor the output switching node (SW ...

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LTC3857 APPLICATIONS INFORMATION R B1 215k 15pF 1nF R A1 68.1k C 150pF ITH1A R 15k ITH1 C 820pF ITH1 C 0.1μF SS1 C 0.1μF SS2 C 680pF ITH2 R 27k ITH2 C 100pF ITH2A R A2 ...

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TYPICAL APPLICATIONS R B1 143k 22pF 1nF R A1 68.1k C 100pF ITH1A R 22k ITH1 C 820pF ITH1 C 0.01μF SS1 C 0.01μF SS2 C 820pF ITH2 R 15k ITH2 C 150pF ITH2A R A2 68.1k ...

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LTC3857 TYPICAL APPLICATIONS R B1 475k 33pF 1nF R A1 34k C 100pF ITH1A R 10k ITH1 C 0.01μF C 680pF SS1 ITH1 R FREQ 60k C 0.01μF SS2 C 680pF ITH2 R 17k ITH2 C 100pF ...

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TYPICAL APPLICATIONS R B1 487k 18pF 1nF R A1 16.9k C 100pF ITH1A R 46k ITH1 C 0.01μF SS1 C 680pF ITH1 R FREQ 60k C 0.01μF SS2 C 680pF ITH2 R 17k ITH2 C 100pF ITH2A ...

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LTC3857 TYPICAL APPLICATIONS R B1 28. 56pF 1nF R A1 115k C 200pF ITH1A R 3.93k ITH1 C 1000pF ITH1 C 0.01μF SS1 R FREQ 60k C 0.01μF SS2 C 1000pF ITH2 R 3.93k ITH2 C 200pF ...

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TYPICAL APPLICATIONS High Efficiency Dual 1V/1.2V Step-Down Converter with Inductor DCR Current Sensing R B1 28. 56pF 0.1μ 115k C 200pF ITH1A R 3.93k ITH1 C 1000pF ITH1 C 0.01μF SS1 R FREQ 65k C ...

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LTC3857 PACKAGE DESCRIPTION 5.50 0.05 4.10 0.05 3.45 0.05 3.50 REF (4 SIDES) 3.45 0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) NOTE: 1. ...

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... Change to Figure 13 Change to Typical Applications drawings 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. LTC3857 ...

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... I = 170μA, OUT Q ≤ 24V 50μA, OUT Q ≤ 10V 30μA, OUT Q ≤ 10V 80μA, OUT Q ≤ 36V 120μA, TSSOP-16 OUT Q ≤ 40μA, MSOP-10E OUT 1110 REV C • PRINTED IN USA © LINEAR TECHNOLOGY CORPORA TION 2009 ≤ 38V, IN 3857fc ...