LT3845 LINER [Linear Technology], LT3845 Datasheet
LT3845
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LT3845 Summary of contents
Page 1
... N-channel MOSFETs, a precision undervoltage lockout, 10μA shutdown current, short-circuit protection and a programmable soft-start. The LT3845 is available in a 16-lead thermally enhanced TSSOP package 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 Pin Currents ..................................................1mA Operating Junction Temperature Range (Note 2) LT3845E (Note 3) ............................... –40°C to 125°C LT3845I .............................................. –40°C to 125°C Storage Temperature .............................. –65°C to 150°C Lead Temperature (Soldering, 10 sec) .................. 300°C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL ...
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... V – V SENSE SENSE + – V – SENSE SENSE BURST_EN BURST_EN BURST_EN SENSE(CM SENSE(CM) V > 4V SENSE(CM) LT3845 = 49.9kΩ, SET MIN TYP MAX UNITS ● ● 7.5 V ● 3.6 3 670 mV 20 μA 20 μA ● μA ● ...
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... Specifi cations over the – 40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3845I is guaranteed over the full –40°C to 125°C operating junction temperature range. TYPICAL PERFORMANCE CHARACTERISTICS ...
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... CC Operating Frequency vs Temperature 308 306 304 302 300 298 296 294 292 290 –50 – TEMPERATURE (°C) LT3845 I Current Limit vs Temperature CC 225 200 175 150 125 100 75 50 –50 – TEMPERATURE (°C) 3845 G05 Error Amp Transconductance ...
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... LT3845 TYPICAL PERFORMANCE CHARACTERISTICS Maximum Current Sense Threshold vs Temperature 106 104 102 100 100 125 –50 – TEMPERATURE (°C) 3845 G13 TYPICAL APPLICATION V (Pin 1): The V pin is the main supply pin and should decoupled to SGND with a low ESR capacitor (at least 0.1μ ...
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... PCB layout of grounds. Exposed Pad (SGND) (Pin 17): The exposed leadframe is internally connected to the SGND pin. Solder the exposed pad to the PCB ground for electrical contact and optimal thermal performance. LT3845 pin from an external CC output of the regula- OUT Supply and High Cur- ...
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... LT3845 BLOCK DIAGRAM 8 3845fc ...
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... BOOST bootstrapped supply. Power Requirements The LT3845 is biased using an internal linear regulator to generate operational voltages from the V all of the circuitry in the LT3845 is biased via this internal linear regulator output (V ). This pin is decoupled with CC a low ESR, 1μF capacitor to PGND. ...
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... This overdrive condition is sensed internally and forces the voltage on the V voltage on V Si1555DL switching is disabled and the LT3845 shuts down most of its internal circuitry, reducing total quiescent current to 120μA. When the converter output begins to fall, the V pin voltage begins to climb. When the voltage on the ...
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... If the inductor current is allowed to go negative before the synchronous switch is disabled, the switch node could inductively kick positive with a high dv/dt. The LT3845 prevents this by incorporating a 10mV positive offset at the sense inputs. With the reverse-current inhibit feature enabled, an LT3845 converter will operate much like a nonsynchronous converter during light loads ...
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... Selection SENSE The current sense resistor, R current of the supply (See Typical Application on front page). Its value is chosen based on the maximum required output load current. The LT3845 current sense amplifi er regulator pin. When the regulator is enabled. CC pin, when the remainder of the supply to ground ...
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... LT3845 (see the Minimum On-time Considerations section). A fi nal consideration for operating frequency is that in noise-sensitive communications systems often desirable to keep the switching noise out of a sensitive frequency band. The LT3845 uses a constant frequency 200 180 160 140 ...
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... IN plications (V . OUT(MAX) losses: P TRAN(TOP) where constant inversely related to the gate driver current, approximated for LT3845 applications. The total maximum power dissipations of the MOSFET are: P TOP(TOTAL) P BOT(TOTAL) To achieve high supply effi ciency, keep the total power dis- sipation in each switch to less than 3% of the total output power ...
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... RC snubber. In some applications, parasitic FET capacitances couple the negative going switch node transient onto the bottom gate drive pin of the LT3845, causing a negative voltage in excess of the Absolute Maximum Rating to be imposed on that pin. Connection of a catch Schottky diode from this pin to ground will eliminate this effect current rating is typically suffi ...
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... Undervoltage , an additional OUT lockout keeps the LT3845 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. ...
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... Minimum On-Time Considerations (Buck Mode) Minimum on-time t that the LT3845 is capable of turning the top MOSFET on and off again determined by internal timing delays and the amount of gate charge required turning on the top MOSFET. Low duty cycle applications may approach ...
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... Locate the small-signal components away from high frequency switching nodes (BOOST, SW, TG, V oriented on the left side of the LT3845, while high current switching nodes are oriented on the right side of the IC to simplify layout. This also helps prevent corruption of the SGND reference ...
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... APPLICATIONS INFORMATION Locate the feedback resistors in close proximity to the LT3845 to minimize the length of the high impedance V node. FB – + The SENSE and SENSE traces should be routed together and kept as short as possible. Orientation of Components Isolates Power Path and PGND Currents, COMPONENTS The LT3845 packaging has been designed to effi ciently remove heat from the IC via the Exposed Pad on the backside of the package ...
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... C2 R6 6800pF 49. TDK C4532X7R2A225K MURATA GRM32ER60J107ME20 OUT D1: DIODES INC. B3100 L1: WURTH 7443551370 20 All Ceramic Capacitors and Soft-Start Enabled BOOST SHDN TG LT3845 BURST_EN D2A BAV99 PGND SYNC SENSE ...
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... Effi ciency and Power Loss 100 14V 16V IN 75 POWER LOSS V = 14V LOAD CURRENT (A) 3845 TA03b LT3845 SENSE Si7884DP 2.7μH 0.005Ω Si7884DP Si1555DL OUT 5V 10A C OUT 100μF 6.3V × ...
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... PGND SYNC SYNC SENSE C11 8 47pF – f SENSE SET R6 SGND 130k 17 C IN3 0.1μF 100V 1 V BOOST IN 2 SHDN TG C8 8200pF LT3845 BURST_EN PGND SYNC SYNC SENSE 47pF 4.99k – f SENSE SET ...
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... REF 0° – 8° 0.65 (.0256) BSC 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT (INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE LT3845 4.90 – 5.10* (.193 – .201) 3.58 (.141) 16 1514 6.40 2.94 (.252) (.116) ...
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... High Voltage Current Mode Controller with Programmable Operating Frequency trademark of Linear Technology Corporation. SENSE Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● BOOST SHDN TG LT3845 BURST_EN BAS521 ...