ltc3858-2 Linear Technology Corporation, ltc3858-2 Datasheet

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... OPTI-LOOP compensa- tion allows the transient response to be optimized over a wide range of output capacitance and ESR values. The LTC3858-2 differs from the LTC3858 by having the overvolt- age protection crowbar and short-circuit latchoff disabled. A wide 4V to 38V input supply range encompasses a wide range of intermediate bus voltages and battery chemistries ...

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... LTC3858-2 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (V ) ......................... –0.3V to 40V IN Topside Driver Voltages BOOST1, BOOST2 ................................. –0.3V to 46V Switch Voltage (SW1, SW2) ......................... –5V to 40V (BOOST1-SW1), (BOOST2-SW2) ................ –0. RUN1, RUN2 ............................................... –0. Maximum Current Sourced into Pin from Source >8V ..............................................100μ – ...

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... FB1,2 SENSE1 2 LIM CC (Note 3300pF LOAD C = 3300pF LOAD (Note 3300pF LOAD C = 3300pF LOAD C = 3300pF Each Driver LOAD C = 3300pF Each Driver LOAD (Note 7) LTC3858-2 = 5V, EXTV = 0V unless RUN1,2 CC MIN TYP MAX UNITS l 0.01 0.1 l –0.01 –0.1 2 mmho 1.3 2 170 250 300 450 ...

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... Note 4: The LTC3858-2 is tested in a feedback loop that servos V a 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 ...

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... OUTPUT CURRENT (A) Load Step (Forced Continuous Mode) V OUT 100mV/DIV AC- COUPLED I L 2A/DIV 38582 G04 V = 3.3V 20μs/DIV OUT FIGURE 13 CIRCUIT Soft-Start 38582 G07 20ms/DIV FIGURE 13 CIRCUIT LTC3858-2 Efficiency vs Input Voltage 98 FIGURE 13 CIRCUIT V 96 OUT I OUT 3. ...

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... LTC3858-2 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) 38582 G10 Maximum Current Sense Voltage vs I Voltage TH 80 ...

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... INPUT VOLTAGE (V) Undervoltage Lockout Threshold vs Temperature 4.4 4.3 4.2 4.1 4.0 3.9 3.8 3.7 3.6 3.5 3.4 40 –45 – TEMPERATURE (°C) LTC3858-2 Regulated Feedback Voltage vs Temperature 808 806 804 802 800 798 796 794 792 –45 – 130 105 TEMPERATURE (°C) 38582 G20 Oscillator Frequency vs Temperature 800 700 ...

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... RUN1, RUN2 (Pin 7, Pin 8): Digital Run Control Inputs for Each Controller. Forcing either of these pins below 1.2V shuts down that controller. Forcing both of these pins below 0.7V shuts down the entire LTC3858-2, reducing quiescent current to approximately 8μA. I (Pin 28): Current Comparator Sense Voltage Range ...

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... SS1,2 pin. An internal 1μA pull- up current source is connected to this pin. A capacitor to ground at this pin sets the ramp time to final regulated output voltage. Alternatively, a resistor divider on another voltage supply connected to this pin allows the LTC3858-2 output to track the other supply during start-up ...

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... LTC3858-2 FUNCTIONAL DIAGRAM 10 38582f ...

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... After the top MOSFET is turned off each cycle, the bottom MOSFET is turned on until either the inductor current starts to reverse, as indicated by the current comparator IR, or the beginning of the next clock cycle. Table 1. Summary of the Differences Between LTC3858, LTC3858-1 and LTC3858-2 Short-Circuit Latchoff Feature? Overvoltage Protection Optional Tracking Start-Up? ...

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... LTC3858-2 draws only 170μA of quiescent current. If both channels are in sleep mode, the LTC3858-2 draws only 300μA of qui- escent current. In sleep mode, the load current is supplied by the output capacitor. As the output voltage decreases, the EA’ ...

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... The typical capture range of the phase-locked loop is from approximately 55kHz to 1MHz, with a guarantee over all manufacturing variations to be between 75kHz and 850kHz. In other words, the LTC3858-2’s PLL is guaranteed to lock to an external clock source whose frequency is between 75kHz and 850kHz. The typical input clock thresholds on the PLLIN/MODE pin are 1 ...

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... Functional Diagram) PolyPhase ® Applications (CLKOUT and PHASMD Pins) The LTC3858-2 features two pins (CLKOUT and PHASMD) that allow other controller ICs to be daisy-chained with the LTC3858-2 in PolyPhase applications. The clock output signal on the CLKOUT pin can be used to synchronize ...

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... OPERATION (Refer to the Functional Diagram) Figure 1 compares the input waveforms for a representative single-phase dual switching regulator to the LTC3858-2 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 to 1 ...

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... The SENSE and SENSE pins are the inputs to the current comparators. The common mode voltage range on these pins 28V (Abs Max), enabling the LTC3858-2 to regulate output voltages nominal 24V (allowing plenty of margin for tolerances and transients). + The SENSE pin is high impedance over the full common mode range, drawing at most ± ...

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... SENSE SW V OUT LTC3858-2 BG SENSE SENSE SGND 38582 F04a *PLACE C1 NEAR SENSE PINS (4b) Using the Inductor DCR to Sense Current Figure 4. Current Sensing Methods LTC3858-2 V SENSE(MAX) = Δ MAX the Electrical Characteristics SENSE(MAX) is 100°C. L(MAX) ) value, use the divider ratio: ...

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... LTC3858-2 APPLICATIONS INFORMATION C1 is usually selected the range of 0.1μF to 0.47μF . This forces R1||R2 to around 2k, reducing error that might + have been caused by the SENSE pin’s ±1μA current. The equivalent resistance R1||R2 is scaled to the room temperature inductance and maximum DCR DCR at 20° ...

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... Power MOSFET and Schottky Diode (Optional) Selection Two external power MOSFETs must be selected for each controller in the LTC3858-2: 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 ...

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... C )/( prevent ing the sources and C IN and current resonances small (0.1μF to 1μF) bypass capacitor between the chip V pin and ground, placed close to the LTC3858-2, is also IN suggested. A small (1Ω to 10Ω) resistor placed between 1/ 2 ⎤ ⎦ ...

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... Soft-start is enabled by simply connecting a capacitor from the SS pin to ground, as shown in Figure 6. An internal 1μA current source charges the capacitor, providing a linear ramping voltage at the SS pin. The LTC3858-2 will regulate the V voltage on the SS pin, allowing its final regulated value. The total soft-start time will ...

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... For coincident tracking ( TRACKA the SS B TRACKB X TRACKB B V X(MASTER) V OUT(SLAVE OUT R 1/2 LTC3858 TRACKB SS R 38582 F08 TRACKA Figure 8. Using the SS Pin for Tracking = V during start-up): OUT X V X(MASTER) V OUT(SLAVE) 38582 F07b TIME (7b) Ratiometric Tracking ...

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... MOSFET gate drivers and to prevent interaction between the channels. High input voltage applications in which large MOSFETs are being driven at high frequencies may cause the maxi- mum junction temperature rating for the LTC3858 exceeded. The INTV current, which is dominated by the CC ...

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... Under short-circuit condi- 24 tions with very low duty cycles, the LTC3858-2 will begin cycle skipping in order to limit the short-circuit current. In this situation the bottom MOSFET will be dissipating BAT85 most of the power but less than in normal operation ...

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... Any of the Above Minimum On-Time Considerations Minimum on-time, t 38582 F10 tion that the LTC3858-2 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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... ...) 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 LTC3858-2 circuits regulator current losses, 4) topside MOSFET CC transition losses ...

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... If the ratio LOAD should be controlled so that the load rise time is limited to approximately 25 • C require a 250μs rise time, limiting the charging current to about 200mA. LTC3858-2 pin signal which increased by the same factor that causing a rapid drop in V ...

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... LTC3858-2 APPLICATIONS INFORMATION 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. The highest value of ripple current occurs at the maximum input voltage. Tie the FREQ pin to GND, generating 350kHz operation ...

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... OUT back pins. All of these nodes have very large and fast moving signals and therefore should be kept on the “output side” of the LTC3858-2 and occupy minimum PC trace area. 7. Use a modified “star ground” technique: a low imped- ance, large copper area central grounding point on ...

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... LTC3858-2 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 pin) to synchronize the oscilloscope to the internal oscillator and probe the actual output voltage as well ...

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... PGOOD2 PGOOD2 PGOOD1 + TG1 – SW1 C B1 BOOST1 BG1 V IN PGND EXTV V CC OUT1 C INTVCC – INTV CC + BG2 BOOST2 C B2 SW2 TG2 LTC3858-2 R PU1 V PULL-UP (<6V) PGOOD1 L1 R SENSE OUT1 1μ VIN CERAMIC OUT2 1μF CERAMIC M4 M3 ...

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... LTC3858-2 APPLICATIONS INFORMATION BOLD LINES INDICATE HIGH SWITCHING CURRENT. KEEP LINES TO A MINIMUM LENGTH. 32 SW1 L1 R SENSE1 D1 C OUT1 SW2 L2 R SENSE2 D2 C OUT2 Figure 12. Branch Current Waveforms V OUT1 OUT2 R L2 38582 F12 38582f ...

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... RUN1 C RUN2 B2 BOOST2 0.47μF FREQ SW2 SS2 I TH2 BG2 V FB2 – SENSE2 + SENSE2 , C : SANYO 10TPD150M OUT2 Start-Up 38582 F13c 20ms/DIV 10 LTC3858-2 L1 MBOT1 3.3μ SENSE1 OUT1 7mΩ 150μF MTOP1 38V C IN 22μF C INT 4.7μF MTOP2 L2 R SENSE2 7.2μH 10mΩ ...

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... C 1nF F2 15pF R B2 215k SANYO 10TPD150M OUT1 OUT2 L1: SUMIDA CDEP105-2R5 L2: SUMIDA CDEP105-3R2M MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP 34 High Efficiency Dual 2.5V/3.3V Step-Down Converter INTV CC LTC3858-2 100k + SENSE1 PGOOD2 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47μF TG1 I TH1 ...

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... TG2 BOOST2 0.47μF SW2 TH2 BG2 FB2 C : KEMET T525D476M016E035 OUT1 – SANYO 10TPD150M OUT2 L1: SUMIDA CDEP105-8R8M + L2: SUMIDA CDEP105-4R3M MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP LTC3858-2 L1 MBOT1 8.8μH V OUT1 12V SENSE1 OUT1 10mΩ 47μF MTOP1 V IN 12.5V TO 38V C IN 22μF ...

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... R B2 392k 36 High Efficiency Dual 24V/5V Step-Down Converter INTV CC 100k + PGOOD2 100k – PGOOD1 BG1 FB1 SW1 C B1 BOOST1 0.47μF TG1 TH1 D1 LTC3858 INTV LIM CC C INT 4.7μF PGND D2 TG2 BOOST2 0.47μF SW2 TH2 BG2 FB2 – SANYO 10TPD150M ...

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... FREQ SW2 SS2 I TH2 BG2 V FB2 SANYO 2R5TPE220M OUT1 OUT2 – SENSE2 L1: SUMIDA CDEP105-0R4 L2: SUMIDA CDEP105-0R4 MTOP1, MTOP2: RENESAS RJK0305 + SENSE2 MBOT1, MBOT2: RENESAS RJK0328 LTC3858-2 L1 MBOT1 0.47μH V OUT1 OUT1 SENSE1 220μF 4mΩ 2 MTOP1 V IN 12V C IN 22μ ...

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... B2 57. 1.18k S1 100k + PGOOD2 SENSE1 INTV CC 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47μF TG1 I TH1 D1 LTC3858 SS1 INTV I CC LIM C INT PHASMD 4.7μF CLKOUT PGND PLLIN/MODE D2 SGND EXTV CC TG2 RUN1 RUN2 C B2 BOOST2 0.47μF FREQ SW2 SS2 ...

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... UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693 Rev D) 0.70 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC R = 0.05 0.75 0.05 TYP 0.00 – 0.05 3.50 REF (4-SIDES) 0.200 REF LTC3858-2 BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.30 TYP R = 0.115 OR 0.35 45 CHAMFER TYP 31 32 0.40 0. 3.45 0.10 3.45 0.10 (UH32) QFN 0406 REV D 0.25 0.05 ...

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... FAX: (408) 434-0507 ● 100k + SENSE1 INTV PGOOD2 CC 100k – SENSE1 PGOOD1 MBOT1 V BG1 FB1 SW1 C B1 BOOST1 0.47μF TG1 MTOP1 I TH1 D1 LTC3858 SS1 I INTV CC LIM C INT PHASMD 4.7μF CLKOUT PGND PLLIN/MODE D2 SGND EXTV TG2 MTOP2 CC RUN1 C B2 BOOST2 RUN2 0.47μ ...