LTC3868 Linear Technology, LTC3868 Datasheet
LTC3868
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LTC3868 Summary of contents
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... SENSE2 OUT2 8.5V V FB2 3.5A 193k I TH2 680pF 150µF SS2 20k 15k 0.1µF 3868 TA01 LTC3868 www.DataSheet4U.com Low I Q 2-Phase Synchronous Step-Down Controller 3868 is a high performance dual step-down and UltraFast are trademarks of Linear Technology SENSE Efficiency and Power Loss vs Load Current 100 90 80 EFFICIENCY 70 60 ...
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... Storage Temperature Range . .................. –65°C to 150°C orDer inForMaTion LEAD FREE FINISH TAPE AND REEL LTC3868EUH#PBF LTC3868EUH#TRPBF LTC3868IUH#PBF LTC3868IUH#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: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ elecTrical characTerisTics temperature range, otherwise specifications are at T ...
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... FB1,2 SENSE1 0.7V, V –, – = 3.3V, I FB1,2 SENSE1 2 (Note 3300pF LOAD C = 3300pF LOAD (Note 3300pF LOAD C = 3300pF LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD (Note 7) LTC3868 www.DataSheet4U.com = 5V, EXTV = 0V unless otherwise noted. CC MIN TYP MAX 2 1.3 2 170 300 3.6 3 FB1,2 540 98 99.4 0.7 1.0 1.21 1 ...
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... FB V Ramping Negative FB Hysteresis V with Respect to Set Regulated Voltage FB V Ramping Positive FB Hysteresis Note 4: The LTC3868 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. Note 7: The minimum on-time condition is specified for an inductor peak-to-peak ripple current ≥ 40 Considerations in the Applications Information section). and power A www.DataSheet4U.com = 0V unless otherwise noted. ...
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... OUT FIGURE 12 CIRCUIT Inductor Current at Light Load FORCED CONTINUOUS MODE Burst Mode OPERATION 2A/DIV PULSE- SKIPPING MODE V = 3.3V 2µs/DIV OUT I = 200µA LOAD FIGURE 12 CIRCUIT LTC3868 www.DataSheet4U.com Efficiency vs Output Current 100 12V 3.3V ...
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... LTC3868 Typical perForMance characTerisTics Total Input Supply Current vs Input Voltage 400 FIGURE 12 CIRCUIT V = 3.3V 350 OUT ONE CHANNEL ON 300 300µA LOAD 250 200 NO LOAD 150 100 INPUT VOLTAGE (V) 3868 G10 Maximum Current Sense Voltage vs I Voltage TH 80 PULSE-SKIPPING ...
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... INPUT VOLTAGE (V) 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 – 3868 G28 LTC3868 www.DataSheet4U.com Regulated Feedback Voltage vs Temperature 808 806 804 802 800 798 796 794 792 105 130 –45 – TEMPERATURE (°C) 3868 G20 Oscillator Frequency vs Temperature 800 700 600 ...
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... PLLIN/MODE (Pin 5): External Synchronization Input to Phase Detector and Forced Continuous Mode Input. When an external clock is applied to this pin, the phase-locked CC loop will force the rising TG1 signal to be synchronized with the rising edge of the external clock. When not syn- chronizing to an external clock, this input, which acts on both controllers, determines how the LTC3868 operates at light loads. Pulling this pin to ground selects Burst Mode operation. An internal 100k resistor to ground also invokes Burst Mode operation when the pin is floated. Tying this pin to INTV CC Tying this pin to a voltage greater than 1.2V and less than INTV – 1.3V selects pulse-skipping operation ...
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... The I pin voltage and controlled offsets between the TH – SENSE and SENSE . the current trip threshold. CC pins. Voltage swing + INTV ). IN CC LTC3868 www.DataSheet4U.com pin is not within ±10% of its set point. voltage to the smaller of 0.8V FB1,2 (Pin 31, Pin 11): Receives the remotely sensed + (Pin 32, Pin 10): The (+) Input to the + pins in conjunction with R – 0.5V CC set SENSE 3868fb ...
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... LTC3868 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 LIMIT EXTV CC 20 5.1V 5.1V LDO LDO 4.7V – 6 SGND 19 INTV CC 0 DUPLICATE FOR SECOND ...
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... FB current into the RUN pin does not exceed 100µA. The start-up of each controller’s output voltage, V controlled by the voltage on the SS pin for that channel. When the voltage on the SS pin is less than the 0.8V internal reference, the LTC3868 regulates the V pin voltage instead of the 0.8V reference. This allows the SS pin to be used to program a soft-start by connecting an external capacitor from the SS pin to SGND. An internal 1µA pull-up current charges this capacitor creating a volt- age ramp on the SS pin. As the SS voltage rises linearly from 0V to 0.8V (and beyond up to the absolute maximum pin ...
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... FB Light Load Current Operation (Burst Mode Operation, 1µA Pulse-Skipping or Forced Continuous Mode) (PLLIN/MODE Pin) The LTC3868 can be enabled to enter high efficiency Burst Mode operation, constant frequency pulse-skip- 3868 F01 ping mode, or forced continuous conduction mode at t LATCH low load currents. To select Burst Mode operation, tie the PLLIN/ MODE pin to ground. To select forced continuous ...
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... PolyPhase Applications (CLKOUT and PHASMD Pins) ® The LTC3868 features two pins (CLKOUT and PHASMD) that allow other controller ICs to be daisy-chained with the LTC3868 in PolyPhase applications. The clock output signal on the CLKOUT pin can be used to synchronize additional power stages in a multiphase power supply solution feeding a single, high current output or multiple separate outputs. The PHASMD pin is used to adjust the phase of the CLKOUT signal as well as the relative phases LTC3868 www ...
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... With 2-phase operation, the two channels of the dual switching regulator are operated 180 degrees out of phase. pin rises by more FB This effectively interleaves the current pulses drawn by the switches, greatly reducing the overlap time where they add together. The result is a significant reduction in total RMS input current, which in turn allows less expensive input capacitors to be used, reduces shielding requirements for EMI and improves real world operating efficiency. Figure 2 compares the input waveforms for a representa- tive single-phase dual switching regulator to the LTC3868 pin FB 2-phase dual switching regulator. An actual measurement of the RMS input current under these conditions shows that 2-phase operation dropped the input current from 2.53A pin voltage FB to 1.55A RMS remember that the power losses are proportional to I ...
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... It can readily be seen that the advantages of 2-phase op- eration are not just limited to a narrow operating range, for most applications is that 2-phase operation will reduce the input capacitor requirement to that for just one channel operating at maximum current and 50% duty cycle. 3.0 SINGLE PHASE DUAL CONTROLLER 2.5 2.0 1.5 2-PHASE DUAL CONTROLLER 1.0 0 5V/ 3.3V/ INPUT VOLTAGE (V) 3868 F03 Figure 3. RMS Input Current Comparison LTC3868 www.DataSheet4U.com /V ). Figure 3 shows how OUT IN 3868fb ...
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... LTC3868 applicaTions inForMaTion The Typical Application on the first page is a basic LTC3868 application circuit. LTC3868 can be configured to use either DCR (inductor resistance) sensing or low value resistor sensing. The choice between the two current sensing schemes is largely a design trade off between cost, power consumption and accuracy. DCR sensing ...
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... BOOST TG R SENSE SW V OUT LTC3868 BG SENSE SENSE SGND 3868 F05a *PLACE C1 NEAR SENSE PINS (5b) Using the Inductor DCR to Sense Current Figure 5. Current Sensing Methods LTC3868 www.DataSheet4U.com V SENSE(MAX) = ∆ MAX the Electrical Characteristics SENSE(MAX) is 100°C. L(MAX) ) value, use the divider ratio: D ...
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... Power MOSFET and Schottky Diode (Optional) Selection Two external power MOSFETs must be selected for each controller in the LTC3868: one N-channel MOSFET for the top (main) switch, and one N-channel MOSFET for the : IN bottom (synchronous) switch. The peak-to-peak drive levels are set by the INTV This voltage is typically 5.2V during start-up (see EXTV www.DataSheet4U.com ...
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... THMIN RMS capacitor current requirement. Increasing the out- put current drawn from the other controller will actually ) R decrease the input RMS ripple current from its maximum DS(ON) value. The out-of-phase technique typically reduces the input capacitor’s RMS ripple current by a factor of 30% and DS(ON) to 70% when compared to a single phase power supply solution. is the THMIN In continuous mode, the source current of the top MOSFET is a square wave of duty cycle (V LTC3868 www.DataSheet4U.com 2 R losses while the topside N-channel > 20V the transition losses rapidly IN DS(ON) actually provides higher efficiency. The MILLER vs Temperature curve, but DS(ON) Selection OUT is simplified by the 2-phase architec- IN )(I ) product needs to be used in the ...
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... C OUT is the output OUT is the ripple current in the inductor. L increases with input voltage. R may be used. Great care should be taken to FF line away from noise sources, such as the FB V OUT R C 1/2 LTC3868 3868 F06 Figure 6. Setting Output Voltage is controlled by the voltage on OUT 3868fb ...
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... SGND 3868 F07 Figure 7. Using the TRACK/SS Pin to Program Soft-Start INTV Regulators CC The LTC3868 features two separate internal P-channel low dropout linear regulators (LDO) that supply power at the INTV pin from either the V CC EXTV pin depending on the connection of the EXTV CC pin. INTV powers the gate drivers and much of the CC LTC3868’ ...
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... Connected to an Output-Derived Boost Network. CC For 3.3V and other low voltage regulators, efficiency gains can still be realized by connecting EXTV output-derived voltage that has been boosted to greater than 4.7V. This can be done with the capacitive charge pump shown in Figure 8. Ensure that EXTV C IN BAT85 V IN MTOP TG1 1/2 LTC3868 L EXTV SW CC MBOT BG1 D PGND Figure 8. Capacitive Charge Pump for EXTV Topside MOSFET Driver Supply (C External bootstrap capacitors connected to the BOOST B pins supply the gate drive voltages for the topside MOSFETs. ...
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... A shorted top MOSFET will result in a high current condition which will open the system fuse. The switching regulator will regulate properly with a leaky top MOSFET by altering the duty cycle to accommodate the leakage. Phase-Locked Loop and Frequency Synchronization The LTC3868 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 locked to the rising edge of an external clock signal applied to the PLLIN/MODE pin. The turn-on of controller 2’s top MOSFET is thus 180 degrees out of phase with the external clock ...
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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. Percent efficiency can be expressed as: %Efficiency = 100% – ( ...) where 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 LTC3868 circuits regulator current losses, 4) topside MOSFET transition losses The the Electrical Characteristics table, which excludes MOSFET driver and control currents. V cally results in a small (< ...
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... TH A second, more severe transient is caused by switching in loads with large (>1µF) supply bypass capacitors. 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 sudden step change in output voltage if the load switch resistance is low and it is driven quickly. If the ratio of LTC3868 www.DataSheet4U.com external components shown in Figure 12 -C filter sets the dominant pole-zero C C pin waveforms that will TH pin signal which increased by the same factor that C C ...
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... LTC3868 applicaTions inForMaTion greater than 1:50, the switch rise time LOAD OUT should be controlled so that the load rise time is limited to approximately 25 • Thus a 10µF capacitor would LOAD require a 250µs rise time, limiting the charging current to about 200mA. Design Example As a design example for one channel, assume V 12V(nominal 22V (max OUT V = 75mV and f = 350kHz. SENSE(MAX) The inductance value is chosen first based on a 30% ripple current assumption ...
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... INTVCC minals. The path formed by the top N-channel MOSFET, Schottky diode and the C capacitor should have short IN leads and PC trace lengths. The output capacitor (–) terminals should be connected as close as possible to the (–) terminals of the input capacitor by placing the capacitors next to each other and away from the Schottky loop described above the LTC3868 V pins’ resistive dividers connect to FB the (+) terminals The resistive divider must be OUT connected between the (+) terminal of C ground. The feedback resistor connections should not be along the high current input feeds from the input capacitor(s). ...
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... SENSE1 FREQ PHASMD CLKOUT f IN PLLIN/MODE RUN1 RUN2 SGND SENSE2 SENSE2 V FB2 I TH2 SS2 Figure 10. Recommended Printed Circuit Layout Diagram SS1 R PU2 V PULL-UP LTC3868 (<6V) PGOOD2 PGOOD2 PGOOD1 + TG1 – SW1 C B1 BOOST1 BG1 PGND EXTV V CC OUT1 C INTVCC – INTV ...
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... BOLD LINES INDICATE HIGH SWITCHING CURRENT. KEEP LINES TO A MINIMUM LENGTH. SW1 L1 R SENSE1 D1 C OUT1 SW2 L2 R SENSE2 D2 C OUT2 Figure 11. Branch Current Waveforms LTC3868 www.DataSheet4U.com V OUT1 OUT2 R L2 3868 F11 3868fb ...
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... LTC3868 applicaTions inForMaTion Reduce V from its nominal level to verify operation IN of the regulator in dropout. Check the operation of the undervoltage lockout circuit by further lowering V monitoring the outputs to verify operation. Investigate whether any problems exist only at higher out- put currents or only at higher input voltages. If problems coincide with high input voltages and low output currents, look for capacitive coupling between the BOOST, SW, TG, and possibly BG connections and the sensitive voltage and current pins. The capacitor placed across the current sensing pins needs to be placed immediately adjacent to the pins of the IC. This capacitor helps to minimize the effects of differential noise injection due to high frequency capacitive coupling ...
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... SGND EXTV TG2 CC RUN1 C B2 BOOST2 RUN2 0.47µF FREQ SW2 SS2 I BG2 TH2 V FB2 – SENSE2 + SENSE2 Start-Up 3868 F12c 20ms/DIV 10 LTC3868 www.DataSheet4U.com L1 MBOT1 3.3µH V OUT1 3. SENSE1 OUT1 6m 150µF MTOP1 24V C IN 22µF MTOP2 L2 R SENSE2 7.2µH ...
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... R A2 68. 1nF F2 15pF R B2 215k OUT1 OUT2 L1: SUMIDA CDEP105-2R5 L2: SUMIDA CDEP105-3R2M MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP High Efficiency Dual 2.5V/3.3V Step-Down Converter INTV CC LTC3868 100k + SENSE1 PGOOD2 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 I TH1 D1 V ...
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... FREQ SW2 SS2 I BG2 TH2 V FB2 C : KEMET T525D476M016E035 OUT1 – SENSE2 C : SANYO 10TPD150M OUT2 L1: SUMIDA CDR7D43MN L2: SUMIDA CDEP105-4R3M + SENSE2 MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP LTC3868 www.DataSheet4U.com L1 MBOT1 8.8µH V OUT1 12V SENSE1 OUT1 9m 47µF MTOP1 V IN 12.5V TO 24V C IN 22µF ...
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... SENSE2 56pF R B2 57.6k High Efficiency Dual 1V/1.2V Step-Down Converter INTV CC 100k + PGOOD2 100k – PGOOD1 BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 TH1 D1 LTC3868 V IN INTV CC LIM C INT 4.7µF PGND D2 TG2 BOOST2 0.47µF SW2 BG2 TH2 FB2 SANYO 2R5TPE220M OUT1 OUT2 – ...
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... SS2 I BG2 TH2 V FB2 – SENSE2 SANYO 2R5TPE220M OUT1 OUT2 L1, L2: VISHAY IHL P2525CZERR47M06 MTOP1, MTOP2: RENESAS RJK0305 + SENSE2 MBOT1, MBOT2: RENESAS RJK0328 R 1.18k S2 LTC3868 www.DataSheet4U.com L1 MBOT1 0.47µH V OUT1 OUT1 220µF ×2 MTOP1 V IN 12V C IN 22µF MTOP2 L2 0.47µ ...
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... LTC3868 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. DRAWING PROPOSED JEDEC PACKAGE OUTLINE M0-220 VARIATION WHHD-(X) (TO BE APPROVED) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4 ...
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... Change to Pin Functions Text Changes to Operation Section Text Changes to Applications Information Section Change to Table 2 Change to Figure 10 Changes to Related Parts 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. LTC3868 www.DataSheet4U.com PAGE NUMBER 11, 12, 13 21, 22, 23, 26 ...
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... LTC3868 relaTeD parTs PART NUMBER DESCRIPTION LTC3857/LTC3857-1 Low I , Dual Output 2-Phase Synchronous Step-Down Q DC/DC Controllers with 99% Duty Cycle LTC3858/LTC3858-1 Low I , Dual Output 2-Phase Synchronous Step-Down Q DC/DC Controllers with 99% Duty Cycle LTC3834/LTC3834-1 Low I , Synchronous Step-Down DC/DC Controllers Q LTC3835/LTC3835-1 Low I , Synchronous Step-Down DC/DC Controllers Q LT3845 Low I , High Voltage Synchronous Step-Down Q DC/DC Controller LT3800 Low I , High Voltage Synchronous Step-Down Q DC/DC Controller LTC3824 Low I , High Voltage DC/DC Controller, 100% Duty Cycle Q LTC3850/LTC3850-1 Dual 2-Phase, High Efficiency Synchronous Step-Down ...