LTC3858 Linear Technology, LTC3858 Datasheet
LTC3858
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LTC3858 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 3858 TA01 LTC3858 www.DataSheet4U.com Low I Q 2-Phase Synchronous Step-Down Controller 3858 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 LTC3858EUH#PBF LTC3858EUH#TRPBF LTC3858IUH#PBF LTC3858IUH#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 junction temperature range, otherwise specifications are at T ...
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... FB1,2 SENSE1 2 LIM V = 0.7V, V –, – = 3.3V INTV FB1,2 SENSE1 2 LIM CC (Note 3300pF LOAD C = 3300pF LOAD (Note 3300pF LOAD C = 3300pF LOAD LTC3858 www.DataSheet4U.com = 0V unless otherwise noted. CC MIN TYP MAX UNITS 0.01 0 –0.01 –0 mmho 1 170 250 µA ...
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... FB Hysteresis V with Respect to Set Regulated Voltage FB V Ramping Positive FB Hysteresis Note 4: The LTC3858 is tested in a feedback loop that servos V specified voltage and measures the resultant V 85°C is not tested in production. This specification is assured by design, characterization and correlation to production testing at 125°C. 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 and power peak-to-peak ripple current ≥ ...
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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 LTC3858 www.DataSheet4U.com Efficiency vs Output Current 100 12V 3.3V ...
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... LTC3858 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) 3858 G10 Maximum Current Sense Voltage vs I Voltage TH 80 ...
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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 – 3858 G28 LTC3858 www.DataSheet4U.com Regulated Feedback Voltage vs Temperature 808 806 804 802 800 798 796 794 792 105 130 –45 – TEMPERATURE (°C) 3858 G20 Oscillator Frequency vs Temperature 800 700 600 ...
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... CLKOUT (Pin 4): Output clock signal available to daisy- chain other controller ICs for additional MOSFET driver stages/phases. The output levels swing from INTV ground. 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 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 LTC3858 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. CC ...
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... R set the current trip threshold. SENSE . CC pins. Voltage swing + INTV ). IN CC LTC3858 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 pin voltage and controlled offsets TH – + and SENSE pins in conjunction with – 0.5V ...
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... LTC3858 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 allows the RUN pin to be connected through a resistor to a higher voltage (for example, V 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 LTC3858 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- pin. When CC age ramp on the SS pin. As the SS voltage rises linearly from ...
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... FB Light Load Current Operation (Burst Mode Operation, Pulse-Skipping or Forced Continuous) (PLLIN/MODE Pin) 3858 F01 t LATCH The LTC3858 can be enabled to enter high efficiency Burst Mode operation, constant frequency pulse-skip- ping mode, or forced continuous conduction mode at low load currents. To select Burst Mode operation, tie the PLLIN/ MODE pin to ground. To select forced continuous operation, tie the PLLIN/MODE pin to INTV pulse-skipping mode, tie the PLLIN/MODE pin voltage greater than 1.2V and less than INTV ...
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... PolyPhase Applications (CLKOUT and PHASMD Pins) ® The LTC3858 features two pins (CLKOUT and PHASMD) that allow other controller ICs to be daisy-chained with the LTC3858 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 LTC3858 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 LTC3858 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) 3858 F03 Figure 3. RMS Input Current Comparison LTC3858 www.DataSheet4U.com /V ). Figure 3 shows how OUT IN 3858fa ...
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... LTC3858 applicaTions inForMaTion The Typical Application on the first page is a basic LTC3858 application circuit. LTC3858 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 tradeoff between cost, power consumption and accuracy. DCR sensing is becoming popular because it saves expensive current sensing resistors and is more power efficient, especially in high current applications ...
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... BOOST TG R SENSE SW V OUT LTC3858 BG SENSE SENSE SGND 3858 F05a *PLACE C1 NEAR SENSE PINS (5b) Using the Inductor DCR to Sense Current Figure 5. Current Sensing Methods LTC3858 www.DataSheet4U.com ) in the Electrical Characteristics SENSE(MAX) is 100°C. L(MAX) ) value, use the divider ratio SENSE EQUIV ( ) at T MAX L MAX ( ) + pin’ ...
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... Power MOSFET and Schottky Diode (Optional) Selection Two external power MOSFETs must be selected for each : IN controller in the LTC3858: 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 typically 5.2V during start-up (see EXTV Pin Connection). Consequently, logic-level threshold MOSFETs must be used in most applications. The only www.DataSheet4U.com = 0 ...
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... R RMS capacitor current requirement. Increasing the out put current drawn from the other controller will actually decrease the input RMS ripple current from its maximum and DS(ON) value. The out-of-phase technique typically reduces the input capacitor’s RMS ripple current by a factor of 30% is the THMIN to 70% when compared to a single phase power supply solution. LTC3858 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 OUT OUT < ...
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... OUT is the output OUT is the ripple current in the inductor. L 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 LTC3858 3858 F06 Figure 6. Setting Output Voltage is controlled by the voltage on OUT 3858fa ...
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... OUT the SS pin, allowing V to rise smoothly from 0V to OUT its final regulated value. The total soft-start time will be approximately • µA 1/2 LTC3858 SGND 3858 F07 Figure 7. Using the TRACK/SS Pin to Program Soft-Start INTV Regulators CC The LTC3858 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 of the EXTV powers the gate drivers and much of the internal circuitry ...
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... 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 BAT85 V IN MTOP TG1 1/2 LTC3858 L EXTV SW CC MBOT D BG1 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. Capacitor C ...
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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 LTC3858 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 LTC3858 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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... C is decreased, the zero frequency will be kept the same, thereby keeping the phase shift the same in the most critical frequency range of the feedback loop. The output voltage settling behavior is related to the stability of the closed-loop system and will demonstrate the actual overall pin TH supply performance. LTC3858 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 ...
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... LTC3858 applicaTions inForMaTion 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 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 250µ ...
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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 LTC3858 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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... Figure 10. Recommended Printed Circuit Layout Diagram 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, SS1 R PU2 V PULL-UP LTC3858 (<6V) PGOOD2 PGOOD2 PGOOD1 + TG1 – SW1 C B1 BOOST1 BG1 PGND ...
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... OUT1 SW2 L2 R SENSE2 D2 C OUT2 Figure 11. Branch Current Waveforms The output voltage under this improper hookup will still be maintained but the advantages of current mode control will not be realized. Compensation of the voltage loop will be much more sensitive to component selection. This behavior can be investigated by temporarily shorting out the current sensing resistor—don’t worry, the regulator will still maintain control of the output voltage. LTC3858 www.DataSheet4U.com V OUT1 OUT2 R L2 3858 F11 3858fa ...
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... OUT 12V IN Burst Mode OPERATION 0 0.00001 0.0001 0.001 0.01 0.1 1 OUTPUT CURRENT (A) 3858 F12b Figure 12. High Efficiency Dual 8.5V/3.3V Step-Down Converter 0 INTV CC LTC3858 100k + SENSE1 PGOOD2 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 I TH1 SS1 ...
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... CLKOUT PGND PLLIN/MODE D2 SGND EXTV TG2 CC RUN1 C B2 BOOST2 RUN2 0.47µF FREQ SS2 SW2 I BG2 TH2 V FB2 – SENSE2 + SENSE2 LTC3858 www.DataSheet4U.com L1 MBOT1 2.4µH V OUT1 2. SENSE1 OUT1 7m 150µF MTOP1 38V C IN 22µF MTOP2 L2 R SENSE2 3.2µH ...
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... High Efficiency Dual 12V/5V Step-Down Converter 100k INTV CC + SENSE1 PGOOD2 100k – SENSE1 PGOOD1 BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 TH1 D1 LTC3858 V IN INTV LIM CC C INT 4.7µF PGND D2 EXTV TG2 CC RUN1 C B2 BOOST2 RUN2 0.47µF FREQ SW2 SS2 ...
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... C INT 4.7µF PGND D2 TG2 BOOST2 0.47µF SW2 BG2 FB2 – SANYO 10TPD150M OUT2 L1: SUMIDA CDRH105R-220M L2: SUMIDA CDEP105-4R3M + MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP LTC3858 www.DataSheet4U.com L1 MBOT1 22µH V OUT1 24V SENSE1 OUT1 25m 22µF 2 MTOP1 CERAMIC V IN 28V TO 38V C IN 22µ ...
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... B2 57.6k High Efficiency Dual 1V/1.2V Step-Down Converter 100k INTV CC + SENSE1 PGOOD2 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 I TH1 D1 LTC3858 V IN SS1 I INTV LIM CC C INT PHSMD 4.7µF CLKOUT PGND PLLIN/MODE D2 SGND EXTV TG2 CC RUN1 C B2 BOOST2 RUN2 0.47µF ...
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... SW2 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 LTC3858 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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... LTC3858 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. LTC3858 www.DataSheet4U.com PAGE NUMBER 11, 12, 13 21, 22, 23, 24, 26 ...
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... LTC3858 relaTeD parTs PART NUMBER DESCRIPTION LTC3857/LTC3857-1 Low I , Dual Output 2-Phase Synchronous Step-Down Q DC/DC Controller with 99% Duty Cycle LTC3868/LTC3868-1 Low I , Dual Output 2-Phase Synchronous Step-Down Q DC/DC Controller with 99% Duty Cycle LTC3834/LTC3834-1 Low I , Synchronous Step-Down DC/DC Controller Q LTC3835/LTC3835-1 Low I , Synchronous Step-Down DC/DC Controller 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 Selectable Fixed 200kHz to 600kHz Operating Frequency, Q LTC3850/LTC3850-1 ...