lt3742 Linear Technology Corporation, lt3742 Datasheet
lt3742
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lt3742 Summary of contents
Page 1
... An internal boost regulator generates a bias rail provide gate drive for the N-channel MOSFETs allowing low dropout and 100% duty cycle operation. The LT3742 can be used for applications where both controllers need to operate independently, or where both controllers are used to provide a single higher current output. ...
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... ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL LT3742EUF#PBF LT3742EUF#TRPBF Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: For more information on tape and reel specifi ...
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... V = 12V SWB Note 2: The LT3742E is guaranteed to meet performance specifi cations from 0°C to 125°C operating junction temperature range. Specifi cations over the – 40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls ...
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... LT3742 TYPICAL PERFORMANCE CHARACTERISTICS I -SHDN vs Temperature –50 – 100 125 TEMPERATURE (°C) 3742 G01 V Minimum vs Temperature –50 – 100 125 TEMPERATURE (°C) 3742 G04 RUN/SS Current vs Temperature 1.8 1.2 0.6 0 –50 – TEMPERATURE (°C) ...
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... TEMPERATURE (°C) PG Threshold vs Temperature 1.0 0.9 0.8 POWER GOOD 0.7 0.6 125 –50 – TEMPERATURE (°C) 1.0 0.7 0.4 0 100 125 –25 3742 G12 LT3742 V – Temperature BIAS 100 125 –50 – TEMPERATURE (°C) 3742 G10 RUN/SS Threshold vs Temperature 100 125 TEMPERATURE (° ...
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... V is tied to this pin to program the minimum IN input voltage at which the LT3742 will operate. When this pin is less than 1.25V, the controllers are disabled (the RUN/SS pins are still used to turn on each switching regulator). Once this pin drops below 1.25V, a 3μA current sink draws current into the pin to provide programmable hysteresis for UVLO ...
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... BLOCK DIAGRAM GND 1.25V UVLO – 3 3μA UVLO LT3742 CONTROLLER 1 AND 2 TO ENABLE COMPARATOR 1μA RUN/SS SHDN PG PGOOD GATE DRIVE BIAS BOOST REGULATOR UNDERVOLTAGE LOCKOUT THERMAL SHUTDOWN 1.25V 0.86V V REF 0.80V 0.74V INTERNAL SUPPLY ENABLE COMPARATOR – ...
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... Control of the inductor current is strictly maintained until the output voltage is reached. The LT3742 is ideal for applications where both DC/DC controllers need to operate separately. A pulse from the 500kHz oscillator sets the RS fl ip-fl op and turns on the external N-channel MOSFET ...
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... To disable either controller, pull its RUN/SS pin to ground with an open-drain or open-collector device. If both RUN/SS pins are pulled to ground, the LT3742 is placed in shutdown mode, and quiescent current is re- duced to ~20μA. Internal 1μA current sources pull up on each RUN/SS pin, and when either pin reaches ~0 ...
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... Tie the PG pin to any supply less than 30V with a pull-up resistor that will supply less than 200μA. This pin will be open when the LT3742 is placed in shutdown mode regardless of the voltage at the FB pin. The power good indication is valid only when the LT3742 is enabled (RUN/SS is high) and greater ...
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... The minimum input voltage is determined by either the LT3742’s minimum operating voltage of 4V, UVLO or by the output voltages of a given application. The LT3742 can operate at 100% duty cycle the input voltage drops close to or equal to one of the output voltages, the control- ler will go into low dropout operation (100% duty cycle) ...
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... SW2 ( Figure 4. Example Waveforms for a Single Phase Dual Controller vs the 2-Phase LT3742 12 The Benefi 2-Phase Operation Traditionally, dual controllers operate with a single phase. = 15%. MIN This means that both power MOSFETs are turned on at the same time, causing current pulses twice the – ...
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... Pick a standard value inductor close to the 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) 3742 F05 Figure 5. RMS Input Current Comparison LT3742 . Lower OUT(MAX) and V IN(TYP) IN(MAX OUT OUT • • V 500 kHz ( ) when 3742f ...
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... Inductor, Catch Diode and MOSFET Current Rating Once the inductor and R 1 current ratings of the inductor, catch diode and MOSFET can then be determined. The LT3742 current comparator kHz has a guaranteed maximum threshold of 70mV, and there is a small amount of current overshoot resulting from the response time of the current sense comparator ...
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... Power loss is calculated for both devices over a wide input voltage range (4V ≤ percentage of the 10W total power). Note that while the will actually low R RSS DS(ON) 0.7 0.6 0.5 0.4 0.3 0.2 0 3742 F06a Figure 6b. Power Loss Example for M2 (50mΩ, 45pF) LT3742 ( ) ( ) + ohmic loss transition loss ⎛ ⎞ ρ ...
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... The input capacitor is required to reduce the resulting voltage ripple at the LT3742 and to force this very high frequency switching current into a tight local loop, minimiz- ing EMI. The input capacitor must have low impedance at the switching frequency to do this effectively, and it must have an adequate ripple current rating ...
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... APPLICATIONS INFORMATION LT3742’s control loop. Output ripple can be estimated with the following equation: ⎛ Δ ⎜ RIPPLE L ⎝ 8 • f • OUT where ΔI is the inductor ripple current and f L switching frequency (500kHz). The ESR is so low for ce- ramic capacitors that it can be left out of the above calcula- tion ...
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... LT3742 APPLICATIONS INFORMATION Bias Supply Considerations The LT3742 uses an internal boost regulator to provide a bias rail for enhancement of the external MOSFETs. This bias rail is regulated and must be in regula- IN tion before either controller is allowed to start switching. As this is a high speed switching regulator, standard procedures must be followed regarding placement of the external components ...
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... APPLICATIONS INFORMATION VIAS TO LOCAL GROUND PLANE OUTLINE OF LOCAL GROUND PLANE Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation V OUT1 SYSTEM GROUND V OUT2 3742 F08 LT3742 RUN1 SHDN RUN2 SHDN 3742f 19 ...
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... GND 51k 680pF 25 8V and 5V Dual Step-Down Converter L3 C6 22μH 2.2μ SWB BIAS 45. UVLO 1μF R1 20k LT3742 6.5μH 0.01Ω SW1 SW2 SENSE1 SENSE2 20 11 SENSE1 – – SENSE2 19 12 FB1 ...
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... RUN/SS1 RUN/SS2 51k 51k GND 68pF Effi ciency vs Load Current 90 5V OUT 3.3V OUT LOAD CURRENT (A) 3742 TA01b LT3742 V IN 10μF L2 4.7μH 10mΩ V OUT2 5V 4A 1.05k 150μF D2 200Ω 1nF 680pF 3742 TA01 4 3742f 21 ...
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... OUTD D1, D2: DIODES INC. PDS1040 L1, L2: NEC/TOKIN PLC12458R2 M1, M2: ROHM RSS065N03 22 High Current, Low Ripple 12V Step-Down Converter L3 10μH R7 124k V SWB BIAS IN C5 UVLO 1μF R8 20.0k LT3742 8.2μH 0.010Ω SW1 SW2 + SENSE1 SENSE2 – SENSE1 SENSE2 FB2 ...
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... Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC 0.75 ± 0. 0.115 2.45 ± 0.10 (4-SIDES) 0.200 REF 0.00 – 0.05 LT3742 BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.35 × 45° CHAMFER TYP 23 24 0.40 ± 0. (UF24) QFN 0105 0.25 ± 0.05 ...
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... LT3742 RELATED PARTS PART NUMBER DESCRIPTION TM LTC1625/LTC1775 No R Current Mode Synchronous Step-Down SENSE Controllers LTC1735 High Effi ciency Synchronous Step-Down Switching Regulator LTC1778 No R Wide Input Range Synchronous Step-Down SENSE Contr oller LT3430/LT3431 Monolithic 3A, 200kHz/500kHz Step-Down Regulators LTC3703/LTC3703-5 100V Synchronous Switching Regulator Controllers ...