LTC3868-1 Linear Technology, LTC3868-1 Datasheet
LTC3868-1
Related parts for LTC3868-1
LTC3868-1 Summary of contents
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... SENSE2 0.01Ω – V SENSE2 OUT2 8.5V V FB2 3.5A 193k I TH2 680pF 150µF SS2 20k 15k 0.1µF 38681 TA01 LTC3868-1 www.DataSheet4U.com Low I , Dual Q 2-Phase Synchronous Step-Down Controller and UltraFast are trademarks of Linear Technology SENSE Efficiency and Power Loss vs Load Current 100 EFFICIENCY 60 50 POWER LOSS 40 30 ...
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... LTC3868-1 absoluTe MaxiMuM raTings Input Supply Voltage (V ) ......................... –0.3V to 28V IN Topside Driver Voltages BOOST1, BOOST2 . ................................ –0.3V to 34V Switch Voltage (SW1, SW2) ........................ –5V to 28V (BOOST1-SW1), (BOOST2-SW2) . ............... –0. RUN1, RUN2 . .............................................. –0. Maximum Current Sourced into Pin from Source >8V ......................................................100µ – SENSE1 , SENSE2 , SENSE1 – SENSE2 Voltages . ..................................... –0.3V to 16V pin conFiguraTion TOP VIEW ...
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... In Dropout, FREQ = SS1 Rising RUN1 RUN2 Rising from 1V SS1 SS2 Rising from 2V SS1 SS2 Short-Circuit Condition V = 0.5V FB1 4.5V SS1 0.7V, V –, – = 3.3V FB1,2 SENSE1 2 LTC3868-1 www.DataSheet4U.com = 5V, EXTV = 0V unless otherwise noted. CC MIN TYP MAX 4 0.788 0.8 0.812 l ±5 0.002 0.01 l –0. 1.3 2 170 300 3.6 3.8 ...
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... V with Respect to Set Regulated Voltage FB V Ramping Positive FB Hysteresis where θ = 43°C for the QFN package and θ JA package. Note 4: The LTC3868-1 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 and power A peak-to-peak ripple current ≥ 40 Considerations in the Applications Information section). 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 LTC3868-1 www.DataSheet4U.com Efficiency vs Load Current 100 12V 3.3V ...
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... LTC3868-1 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) 38681 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 38681 G28 LTC3868-1 www.DataSheet4U.com Regulated Feedback Voltage vs Temperature 808 806 804 802 800 798 796 794 792 105 130 –45 – TEMPERATURE (°C) 38681 G20 Oscillator Frequency vs Temperature 800 700 600 ...
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... EXTV EXTV 160 180 200 38681 G26 LTC3868-1 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 continuous inductor current operation. Tying this pin to a voltage greater than 1.2V and less than INTV selects pulse-skipping operation. ...
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... FB1 FB2 remotely sensed feedback voltage for each controller from an external resistive divider across the output. + SENSE1 , SENSE2 input to the differential current comparators are normally connected to DCR sensing networks or current sensing resistors. The the SENSE CC set the current trip threshold. LTC3868-1 www.DataSheet4U.com FB1,2 (Pin 27, Pin 1/Pin 11, Pin 13): Error Amplifier (Pin 28, Pin 2/Pin 10, Pin 12): Receives the + (Pin 1, Pin 3/Pin 9, Pin 11): The (+) pin voltage and controlled offsets between TH – + and SENSE pins in conjunction with R FB1 voltage ...
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... LTC3868-1 FuncTional DiagraM PGOOD1 0.88V + – V FB1 + 0.72V – 20µA FREQ VCO SYNC DET PLLIN/MODE 100k V IN EXTV CC 5.1V 5.1V LDO LDO 4.7V – SGND INTV CC 0 DUPLICATE FOR SECOND CONTROLLER CHANNEL DROP OUT DET TOP SHDN CLK2 0.425V + CLK1 SLEEP – ...
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... 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 LTC3868-1 regulates the V age to the SS 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 ca- pacitor creating a voltage ramp on the SS pin. As the SS pin ...
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... CC the internal sleep signal goes high (enabling sleep mode) and both external MOSFETs are turned off. In sleep mode, much of the internal circuitry is turned off, reducing the quiescent current. If one channel is shut down and the other channel is in sleep mode, the LTC3868-1 draws only 170µA of quiescent current. If both channels are in sleep mode, the LTC3868-1 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’s output begins to rise. When the output voltage drops enough, the I of the EA, the sleep signal goes low, and the controller resumes normal operation by turning on the top external MOSFET on the next cycle of the internal oscillator. ...
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... Burst Mode operation. However, continuous operation has the advantages of lower output voltage ripple and less interference to audio circuitry. In forced continuous mode, the output ripple is independent of load current. When the PLLIN/MODE pin is connected for pulse-skipping mode, the LTC3868-1 operates in PWM pulse-skipping mode at light loads. In this mode, constant frequency operation is maintained down to approximately 1% of designed maximum output current. At very light loads, the current comparator, ICMP , may remain tripped for several cycles and force the external top MOSFET to stay off for the same number of cycles (i ...
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... 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 representative single phase dual switching regulator to the LTC3868-1 2-phase dual switching regulator. An actual measure- ment of the RMS input current under these conditions shows that 2-phase operation dropped the input current from 2.53A reduction in itself, remember that the power losses are 5V SWITCH 20V/DIV 3.3V SWITCH 20V/DIV ...
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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) 38681 F03 Figure 3. RMS Input Current Comparison LTC3868-1 www.DataSheet4U.com /V ). Figure 3 shows how OUT IN 38681fb ...
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... Figure 4. Sense Lines Placement with Inductor or Sense Resistor V IN INTV CC BOOST TG SW LTC3868-1 BG SENSE SENSE SGND (5a) Using a Resistor to Sense Current V IN INTV CC – is less than BOOST ...
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... DCR 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 The equivalent resistance R1||R2 is scaled to the room temperature inductance and maximum DCR The sense resistor values are LTC3868-1 www.DataSheet4U.com V SENSE(MAX) = ∆ MAX the Electrical Characteristics SENSE(MAX) is 100°C. L(MAX) ) value, use the divider ratio SENSE EQUIV ( ) at T MAX ...
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... Power MOSFET and Schottky Diode (Optional) Selection Two external power MOSFETs must be selected for each controller in the LTC3868-1: 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 5.1V during start-up (see EXTV Pin Connection). Consequently, logic-level threshold MOSFETs must be used in most applications. The only ) ...
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... 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 large voltage transients, a low ESR capacitor sized for the maximum RMS current of one channel must be used. The < 20V IN maximum RMS capacitor current is given by: C Required I device DS(ON) IN LTC3868-1 www.DataSheet4U.com 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 )/( prevent OUT IN I MAX ...
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... IN current resonances small (0.1µF to 1µF) bypass capacitor between the chip V pin and ground, placed close to the LTC3868- also suggested. A 10Ω resistor placed between C and the V pin provides further isolation between the IN two channels. The selection driven by the effective series OUT resistance (ESR) ...
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... Power dissipation for the IC in this case is highest and is equal to V • The gate charge current is depen- IN INTVCC dent on operating frequency as discussed in the Efficiency Considerations section. The junction temperature can be estimated by using the equations given in Note 2 of the Electrical Characteristics. For example, the LTC3868-1 INTV current is limited to less than 22mA from a 28V CC supply when not using the EXTV supply at 70°C ambient CC temperature in the SSOP package 70°C + (22mA)(28V)(90°C/W) = 125°C ...
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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 LTC3868-1 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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... Note that the LTC3868-1 can only be synchronized to an external clock whose frequency is within range of the LTC3868-1’s internal VCO, which is nominally 55kHz , to 1MHz. This is guaranteed to be between 75kHz and OSC 850kHz. Table 2 summarizes the different states in which the FREQ pin can be used. ...
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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 LTC3868-1 circuits INTV regulator current losses, 4) topside MOSFET CC transition losses ...
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... C has adequate charge storage and very low ESR at IN the switching frequency. A 25W supply will typically require a minimum of 20µF to 40µF of capacitance having a maximum of 20mΩ to 50mΩ of ESR. The LTC3868-1 2-phase architecture typically halves this input capacitance requirement over competing solu- tions. Other losses including Schottky conduction losses during dead-time and inductor core losses generally account for less than 2% total additional loss. Checking Transient Response The regulator loop response can be checked by looking at the load current transient response ...
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... LTC3868-1 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 = 50mV and f = 350kHz. SENSE(MAX) The inductance value is chosen first based on a 30% ripple current assumption ...
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... PC trace area. 7. Use a modified star ground technique: a low impedance, large copper area central grounding point on the same side of the PC board as the input and output capacitors with tie-ins for the bottom of the INTV capacitor, the bottom of the voltage feedback resistive divider and the SGND pin of the IC ...
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... An embarrassing problem, which can be missed in an otherwise properly working switching regulator, results when the current sensing leads are hooked up backwards. 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. SS1 LTC3868-1 R PU1 V PULL-UP (<6V) PGOOD1 PGOOD1 + TG1 – SW1 ...
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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 LTC3868-1 www.DataSheet4U.com V OUT1 OUT2 R L2 38681 F11 38681fb ...
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... OUT OUT 12V IN Burst Mode OPERATION 0 0.00001 0.0001 0.001 0.01 0.1 1 OUTPUT CURRENT (A) 38681 F12b Figure 12. High Efficiency Dual 8.5V/3.3V Step-Down Converter 0 LTC3868-1 + SENSE1 INTV CC 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 I TH1 SS1 INTV ...
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... INT 4.7µF PGND PLLIN/MODE D2 SGND EXTV TG2 CC RUN1 C B2 RUN2 BOOST2 0.47µF FREQ SW2 SS2 I BG2 TH2 V FB2 – SENSE2 + SENSE2 LTC3868-1 www.DataSheet4U.com L1 MBOT1 2.4µH V OUT1 2. SENSE1 OUT1 7m 150µF MTOP1 24V C IN 22µF MTOP2 L2 R SENSE2 3.2µH ...
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... R B2 393k High Efficiency Dual 12V/5V Step-Down Converter + SENSE1 INTV CC 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 I TH1 D1 LTC3868-1 V SS1 IN INTV CC C INT 4.7µF PGND PLLIN/MODE D2 SGND EXTV TG2 CC RUN1 C B2 BOOST2 RUN2 0.47µF FREQ SW2 SS2 ...
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... FREQ SW2 SS2 I BG2 TH2 V FB2 SANYO 2RSTPE220M OUT1 OUT2 – SENSE2 L1: SUMIDA CDEP105-3R2M L2: SUMIDA CDEP105-7R2M MTOP1, MTOP2: RENESAS RJK0305 + SENSE2 MBOT1, MBOT2: RENESAS RJK0328 LTC3868-1 www.DataSheet4U.com L1 MBOT1 0.47µH V OUT1 OUT1 SENSE1 220µF 4m ×2 MTOP1 V IN 12V C IN 22µ ...
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... F2 56pF R B2 57. 1.18k S1 + SENSE1 INTV CC 100k – SENSE1 PGOOD1 V BG1 FB1 SW1 C B1 BOOST1 0.47µF TG1 I TH1 D1 LTC3868 SS1 INTV CC C INT 4.7µF PGND PLLIN/MODE D2 SGND EXTV TG2 CC RUN1 C B2 RUN2 BOOST2 0.47µF FREQ SS2 SW2 I BG2 TH2 V FB2 – ...
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... ON THE TOP AND BOTTOM OF PACKAGE UFD Package 28-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1712 Rev B) 0.70 0.05 3.65 0.05 PACKAGE OUTLINE 3.50 REF 4.10 0.05 5.50 0.05 0.75 0.05 4.00 0.10 (2 SIDES) 3.50 REF 0.200 REF 0.00 – 0.05 LTC3868-1 www.DataSheet4U.com PIN 1 NOTCH 2.50 REF R = 0. 0.115 45 CHAMFER TYP TYP 27 28 0.40 0. 3.65 0.10 2.65 0.10 (UFD28) QFN 0506 REV B ...
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... LTC3868-1 package DescripTion .254 MIN .0165 .0015 RECOMMENDED SOLDER PAD LAYOUT .0075 – .0098 (0.19 – 0.25) .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" ...
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... Change to Typical Performance Characteristics Change to Pin Functions Text Changes to Operation Section Text Changes to Applications Information Section 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. LTC3868-1 www.DataSheet4U.com PAGE NUMBER 11, 12, 13 21, 22, 23, 24, 26 ...
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... LTC3868-1 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 ...