lt3844 Linear Technology Corporation, lt3844 Datasheet
lt3844
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lt3844 Summary of contents
Page 1
... N-channel MOSFETs; a precision undervoltage lockout function; 10μA shutdown current; short-circuit protection and a programmable soft-start function. The LT3844 is available in a 16-lead thermally enhanced TSSOP package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. ...
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... SHDN Voltages ..... 5V to –0. SHDN Pin Currents ................................................. 1mA Operating Junction Temperature Range (Note 2) LT3844E (Note 3) ..............................–40°C to 125°C LT3844I .............................................–40°C to 125°C Storage Temperature .............................–65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300° ORDER I FOR ATIO ...
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... Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 3: The LT3844E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3844I is guaranteed ● ...
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... LT3844 W U TYPICAL PERFOR A CE CHARACTERISTICS Shutdown Threshold (Rising) vs Temperature 1.38 1.37 1.36 1.35 1.34 1.33 1.32 –50 – 100 TEMPERATURE (°C) 3844 G01 CC(LOAD) 8. 25°C A 8.00 7.95 7.90 7. (mA) CC(LOAD) 3844 G04 V UVLO Threshold (Rising Temperature 6.5 6.4 6.3 6.2 6.1 6.0 –50 – 100 TEMPERATURE (° ...
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... Use the following formula to calculate C for a given output voltage slew rate 2μA The pin should be left unconnected when not using the soft-start function. supply IN LT3844 Error Amp Reference vs Temperature 1.234 1.233 1.232 1.231 1.230 1.229 1.228 1.227 –50 – ...
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... LT3844 CTIO S BURST_EN (Pin 4): The BURST_EN pin is used to enable or disable Burst Mode operation. Connect the BURST_EN pin to ground to enable the burst mode function. Connect the pin disable the burst mode function (Pin 5): The output voltage feedback pin, V ...
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... REFERENCE 1.231V NOL SWITCH LOGIC + – DRIVE CONTROL – + 0.5V Q – R CURRENT + SENSE COMPARATOR SOFT-START ~1V BURST DISABLE + – BURST MODE OPERATION – UVLO LT3844 BOOSTED SWITCH BOOST DRIVER 16 C BOOST TG M1 DRIVER VCC D3 (OPTIONAL) PGND 12 SYNC 7 OSCILLATOR ...
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... MOSFET Driver The LT3844 contains a high speed boosted driver to turn on and off an external N-channel MOSFET switch. The MOSFET driver derives its power from the boost capacitor which is referenced to the SW pin and the source of the MOSFET ...
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... When the voltage 150mV below the 15% load level, switching is disabled, and the LT3844 shuts down most of its internal circuitry, reducing total quiescent current to 120μA. When the converter output begins to fall, the V to climb. When the voltage on the V ...
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... As the slope com- pensation ramp is added to the sensed current, a similar ramp is added to the current limit threshold. The end result is that the current limit is not compromised so the LT3844 can provide full power regardless of required duty cycle. Shutdown The LT3844 includes a shutdown mode where all the internal IC functions are disabled and the V reduced to less than 10μ ...
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... For convert- ers with high step-down consideration is the minimum on-time of the LT3844 (see the Minimum On-time Considerations section). A final consideration for operating frequency is that in noise- 200 180 ...
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... SW Calculate the maximum transition losses: P TRAN where constant inversely related to the gate driver current, approximated for LT3844 applications. /2. The inductor L The total maximum power dissipation of the MOSFET is the sum of these two loss terms: P FET(TOTAL) To achieve high supply efficiency, keep the P ...
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... back driven from an external supply, the CC MOSFET drive current is not sourced from the internal regulator of the LT3844 and the Q G limited by the IC. However, note that the MOSFET drive current is supplied by the internal regulator when the external supply back driving V ...
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... Undervoltage lockout keeps the LT3844 in shutdown until the supply input voltage is above a certain voltage programmed by the user. The hysteresis voltage prevents noise from falsely tripping UVLO additional ...
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... MOSFET transition loss 4. Schottky diode conduction loss 1. The V IN currents of the LT3844 and the MOSFET drive currents. The quiescent currents are in the LT3844 Electrical Char- acteristics table. The MOSFET drive current is a result of charging the gate capacitance of the power MOSFET each cycle with a packet of charge, Q MOSFET data sheet ...
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... These items are illustrated graphically in the layout dia- gram of Figure 3. 1. Keep the signal and power grounds separate. The signal ground consists of the LT3844 SGND pin, the exposed pad on the backside of the LT3844 IC and the (–) terminal The signal ground is the quiet ground and does not OUT contain any high, fast currents. The power ground con- sists of the Schottky diode anode, the (– ...
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... U U APPLICATIO S I FOR ATIO SET Figure 4. LT3844 Layout Diagram (See PCB Layout Checklist BOOST BOOST LT3844 2 14 SHDN BURST_EN VCC PGND SENSE ...
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... ON(MIN) Boost Converter Design The LT3844 can be used to configure a boost converter to step-up voltages to as high as hundreds of volts. An example of a boost converter circuit schematic is shown in the Typical Applications section. The following sections are a guide to designing a boost converter: The maximum duty cycle of the main switch is: − ...
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... P TRAN − where constant inversely related to the gate driver current, approximated for LT3844 applications. The total maximum power dissipation of the MOSFET is the sum of these two loss terms FET(TOTAL) COND TRAN To achieve high supply efficiency, keep the P less than 3% of the total output power ...
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... In the case where the input voltage exceeds the voltage limits on the LT3844 Sense pins, the sense resistor can be moved to the source of the MOSFET. In both cases the resistor value is the calculated using the same formula. ...
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... BURST_EN LT3844 12 1μF V PGND FB 25V SENSE C 10 – SYNC SENSE 9 f SGND SET LT3844 = 250kHz SW C5 0.22μ SENSE D2 6.8μH 0.01Ω IN4148 D1 3844 TA02 L1 = VISHAY, IHLP5050FD- VISHAY, SI7852DP D1 = DIODES INC, PDS760 C = TDK, C4532X5R0J107K OUT C = TDK, C4532X7R2A225K IN C5 • ...
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... SYNC SENSE SGND SET R5 49.9k R13 BOOST IN 2 SHDN TG C11 3 2200pF R16 270k 4 BURST_EN V CC LT3844 5 V PGND SENSE C 7 – SYNC2 SYNC SENSE 8 f SGND SET R12 R11 R15 87.5k 10k 49.9k C5 0.22μF 16V SENSE 15μH 0.02Ω ...
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... REF 0° – 8° 0.65 (.0256) BSC 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT MILLIMETERS (INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE LT3844 4.90 – 5.10* (.193 – .201) 3.58 (.141) 16 1514 6.40 2.94 (.252) ( ...
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... FAX: (408) 434-0507 ● R SENSE 0.01Ω D1 BAV99 BOOST 4. SHDN BURST_EN CC C5 LT3844 12 5 2.2μF PGND V FB 25V SENSE – SYNC SENSE SGND SET R5 33.2k COMMENTS 60V, Drivers 10000pF Gate Capacitance Buck, Boost, SEPIC, 3.5V ≤ ...