LTC3708 LINER [Linear Technology], LTC3708 Datasheet
LTC3708
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LTC3708 Summary of contents
Page 1
... Power supply sequencing is accomplished using an external soft-start timing capacitor. The LTC3708 uses a constant on-time, valley current mode control architecture to deliver very low duty factors without requiring a sense resistor. Operating frequency is selected by an external resistor and is compensated for variations in input supply voltage ...
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... LTC3708EUH#TRPBF LEAD BASED FINISH TAPE AND REEL LTC3708EUH LTC3708EUH#TR Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi ...
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... PGOOD PGOOD V Falling FB Measured with a DC Voltage at FCB Pin Measured with a AC Pulse at FCB Pin f < FCB SW1 EXTLPF f > 2.4 FCB SW1 EXTLPF LTC3708 MIN TYP MAX UNITS –0.05 –0.2 % 1.2 1.45 1 116 138 ns 186 233 280 ...
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... T J dissipation P as follows • 34°C/ Note 3: The LTC3708 is tested in a feedback loop that adjusts V achieve a specifi ed error amplifi er output voltage (I TYPICAL PERFORMANCE CHARACTERISTICS Load Transient on Channel 1 I OUT1 10A/DIV V OUT1 100mV/DIV V OUT2 100mV/DIV 20μ ...
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... ON 250 200 150 I = 60μA ON 100 50 0 –50 – 100 125 150 TEMPERATURE (°C) 3708 G11 LTC3708 V = 2.5V OUT V = 1.8V OUT INPUT VOLTAGE (V) 3708 G06 Frequency vs Load Current 250 200 150 100 FORCED CONTINUOUS MODE 50 EXTERNAL SYNCHRONIZATION DISCONTINUOUS MODE ...
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... LTC3708 TYPICAL PERFORMANCE CHARACTERISTICS Maximum Current Sense Threshold vs V Voltage RNG 350 300 250 200 150 100 50 0 1.5 0.5 0.75 1 1.25 1.75 V VOLTAGE (V) RNG 3708 G13 Error Amplifi Temperature 1.6 1.5 1.4 1.3 1.2 1.1 1.0 –50 – 100 125 TEMPERATURE (°C) 3708 G16 Feedback Voltage vs RUN/SS ...
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... G23 Load Transient Response with External Synchronization I OUT1 10A/DIV f = 240kHz S SW1 10V/DIV V OUT1 50mV/DIV 3708 G25 Power Good Mask V FB 0.2V/DIV PGOOD 2V/DIV 3708 G027 LTC3708 2-Phase Operation I IN 2A/DIV V IN 200mV/DIV V SW1 10V/DIV V SW2 10V/DIV V = 15V 1μs/DIV OUT1 ...
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... The Exposed Pad of the LTC3708EUH must be soldered to the PCB. EXTLPF (Pin 9): Filter Connection for the External PLL. This PLL is used to synchronize the LTC3708 to an external clock. If external clock is not used, leave this pin fl oating. INTLPF (Pin 10): Filter Connection for the Internal PLL. ...
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... FCNT ON Q SWITCH LOGIC + I REV – SHDN OV – 1.3V – RUN SHDN + – RUN/SS 1.3V NOTE: THE RUN/SS PIN ONLY CLAMPS V FOR PHASE 1 NOT PHASE 2. REF LTC3708 0.6V IN REF C VCC BOOST SENSE B DRV CC C DRVCC BG M2 PGND – ...
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... V frequency can be adjusted with an external resistor R 10 When the LTC3708 is synchronized to an external clock, the operating frequency will then be solely determined by the external clock. Output Overvoltage Protection An overvoltage comparator OV guards against transient overshoots (> ...
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... DRV CC Schottky diode when the top MOSFET is turned off. B 2-Phase Operation For the LTC3708 to operate optimally as a 2-phase controller, the resistors connected to the I pins must be selected ON such that the free-running frequency of each channel is close to that of the other. An internal phase-locked loop (PLL) will then ensure that channel 2 operates at the same frequency as channel 1, but phase shifted by 180° ...
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... LTC3708 OPERATION (Refer to Functional Diagram) While this is an impressive reduction in itself, remember that the power losses are proportional to I that the actual power wasted is reduced by a factor of 2.66. The reduced input ripple current also means that less power is lost in the input power path, which could include batteries, switches, trace/connector resistances and protection circuitry ...
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... APPLICATIONS INFORMATION The basic LTC3708 application circuit is shown on the fi rst page of this data sheet. External component selection is primarily determined by the maximum load current and begins with the selection of the power MOSFET switches and/or sense resistor. For the LTC3708, the inductor cur- ...
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... JUNCTION TEMPERATURE (°C) Figure Temperature DS(ON) The power dissipated by the top and bottom MOSFETs strongly depends upon their respective duty cycles and the load current. When the LTC3708 is operating in continuous mode, the duty cycles for the MOSFETs are: V OUT = D TOP V ...
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... APPLICATIONS INFORMATION PLL and Frequency Synchronization In the LTC3708, there are two onboard phase-locked loops (PLL). One PLL is used to achieve frequency locking and 180° phase shift between the two channels while the sec- ond PLL locks onto the rising edge of an external clock. ...
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... Several capacitors may also be paralleled to meet size or height requirements in the design. Always consult the manufacturer if there is any question. The benefi the LTC3708 2-phase operation can be calculated by using the equation above for the higher power channel and then calculating the loss that would ...
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... Fault Conditions: Current Limit The maximum inductor current is inherently limited in a current mode controller by the maximum sense voltage. In the LTC3708, the maximum sense voltage is controlled by the voltage on the V the maximum sense voltage and the sense resistance determine the maximum allowed inductor valley current. ...
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... The minimum off time t is the smallest amount of OFF(MIN) time that the LTC3708 is capable of turning on the bottom MOSFET, tripping the current comparator and turning the MOSFET back off. This time is generally about 270ns. The minimum off time limit imposes a maximum duty ...
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... Figure 7. RUN/SS Pin Interfacing with Latchoff Defeated Output Voltage Tracking TIME 3708 F06 The LTC3708 allows the user to program how the second channel output ramps up and down by means of the TRACK2 pin. Through this pin, the second channel output can be set up to either coincidently or ratiometrically track the ...
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... FB2 TRACK1 pin. TRACK1 clamps channel 1’s reference in the same manner TRACK2 clamps channel 2. To eliminate the slightly lower than possibility of multiple LTC3708s coming on at different FB2 times, only the master LTC3708’s RUN/SS pin should be V OUT1 V OUT2 3708 F08 ...
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... APPLICATIONS INFORMATION connected to a soft-start capacitor. All other LTC3708s should have their RUN/SS pins pulled resistor between 50k and 300k. Figure 12 shows the circuit with four outputs. Three of them are programmed in the coincident mode while the fourth one tracks ratiometrically. ...
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... ESR to minimize the AC I suffi cient capacitance to prevent the RMS current from causing additional upstream losses in fuses or batteries. The LTC3708 2-phase architecture typically halves this C loss over the single phase solutions. Other losses, including C ESR loss, Schottky conduc- ...
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... However 10A load step will cause an output ( ) Ω change of up to: ΔV OUT(STEP) An optional 22μF ceramic output capacitor is included to minimize the effect of ESL in the output ripple. The = 0.0165Ω (max), complete circuit is shown in Figure 13. LTC3708 = 1V, θ = 42°C/W. Checking its GS(TH) JA 130° Ω ...
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... Cover the board area under the LTC3708 with a SGND plane. For the LTC3708EUH, solder the back of the IC to this plane. Separate SGND from the power ground and connect all signal components (I EXTLPF , INTLPF , V SGND plane before it joins PGND. Connect SGND to the gound plane at a single point. • ...
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... SENSE2 BOOST2 C OUT2 C B2 SW2 TG2 R ON2 Figure 14. LTC3708 Layout Diagram and C • Flood all unused areas on all layers with copper. DR1 DR2 and Flooding will reduce the temperature rise of the power B1 components. You can connect the copper area to any DC net (V ...
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... LTC3708 APPLICATIONS INFORMATION BOLD LINES INDICATE HIGH, SWITCHING CURRENT LINES. KEEP LINES TO A MINIMUM LENGTH SENSE SENSE (16a) Sensing the Bottom MOSFET 26 SW1 L1 D1 CERAMIC SW2 L2 D2 CERAMIC Figure 15. Branch Current Waveforms MOSFET – ...
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... TH2 INTLPF EXTLPF RUN/SS TRACK1 3.32k 470pF SGND V V RNG1 RNG2 130k C SS 24.9k 0.1μF DB1, DB2: CMDSH-3 M1, M2: RENESAS HAT2168H L1: PANASONIC ETQP3H1R4BF M3, M4: RENESAS HAT2165H L2: PANASONIC ETQP2H1R2BF LTC3708 24V C IN 10μF 25V 1.22μH 0.1μF + B340LA M4 12.1k 1% ...
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... LTC3708 TYPICAL APPLICATIONS 28 3708fb ...
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... SENSE2 SENSE1 PGND1 PGND2 V RNG1 274k I ON1 V FB1 TRACK2 PWRGD EXTLPF INTLPF I TH1 RUN/SS SGND 0.01μF 1000pF 100k V CC 22.1k 220pF LTC3708 1μF PGND1 1μF PGND2 BOOST2 CC TG2 M2 L2 0.19μH 0.22μF SW2 + C OUT4 470μF B340A BG2 M4 2.5V 2 100pF – RNG2 ...
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... Application 5V BAT54A 10Ω BOOST1 BOOST2 1μF V TRACK1 FCB DRV CC CC TG1 TG2 0Ω BOOST1 BOOST2 0.1μF LTC3708EUH SW1 SW2 + + SENSE1 SENSE2 0Ω 100pF BG1 BG2 0Ω – – SENSE1 SENSE2 PGND1 PGND2 V V RNG1 RNG2 5 ...
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... 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 LTC3708 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 ± ...
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... Area = 650mm , Height = 3mm 5V BAT54A 2.2μF 5V 6.3V 10Ω BOOST1 BOOST2 1μ 1μF V TRACK1 FCB DRV CC CC TG1 TG2 BOOST1 BOOST2 0.1μF LTC3708EUH SW1 SW2 + + SENSE1 SENSE2 BG1 BG2 – – SENSE1 SENSE2 PGND1 PGND2 V V RNG1 RNG2 ON1 ...