lt3845a Linear Technology Corporation, lt3845a Datasheet
lt3845a
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lt3845a Summary of contents
Page 1
... N-channel MOSFETs, a precision undervoltage lockout, 10µA shutdown current, short-circuit protection and a programmable soft-start. The LT3845A is available in a 16-lead thermally enhanced TSSOP package. L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.. ...
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... SHDN Voltages .................... SHDN Pin Currents ..................................................1mA Operating Junction Temperature Range (Note 2) LT3845AE (Note 3) ............................ –40°C to 125°C LT3845AI .......................................... –40°C to 125°C LT3845AMP ....................................... –55°C to 125°C Storage Temperature.............................. –65°C to 150°C Lead Temperature (Soldering, 10 sec) ................... 300°C ORDER INFORMATION ...
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... FB + – V – V SENSE SENSE + – V – SENSE SENSE BURST_EN BURST_EN BURST_EN SENSE(CM SENSE(CM) V > 4V SENSE(CM) LT3845A = 49.9kΩ, SET MIN TYP MAX UNITS 7 3.6 3 670 mV 20 µA 20 µ µ ...
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... The LT3845AI is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT3845AMP is 100% tested and guaranteed over the –55°C to 125°C temperature range. ...
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... V ( (SHDN = 0V 25° (V) CC LT3845A V vs Temperature CC 8 20mA CC 8.1 8.0 7.9 7.8 7.7 7.6 7.5 100 125 –50 – TEMPERATURE (°C) 3845A G02 I Current Limit vs Temperature CC 225 200 175 150 125 ...
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... LT3845A TYPICAL PERFORMANCE CHARACTERISTICS + – (SENSE + SENSE ) SENSE(CM) 800 T = 25°C A 600 400 200 0 –200 –400 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 V (V) SENSE(CM) 3845A G10 Maximum Current Sense Threshold vs Temperature 106 104 102 100 –50 – TEMPERATURE (°C) Current Sense Threshold vs Duty Cycle ...
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... If unused the Sync pin is connected to SGND. For more information see “Oscillator Sync” in the Application Information section of this data sheet. Sync pin not available in PDIP package. LT3845A CC decoupling capacitor. See the Application – pin is the negative input for the ...
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... LT3845A PIN FUNCTIONS TG: The TG pin is the bootstrapped gate drive for the top N-Channel MOSFET. Since very fast high currents are driven from this pin, connect it to the gate of the power MOSFET with a short and wide, typically 0.02” width, PCB trace to minimize inductance. ...
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... BLOCK DIAGRAM LT3845A 3845afa 9 ...
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... BOOST bootstrapped supply. Power Requirements The LT3845A is biased using an internal linear regulator to generate operational voltages from the V of the circuitry in the LT3845A 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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... APPLICATIONS INFORMATION Because the LT3845A uses a linear regulator to generate V , power dissipation can become a concern with high CC V voltages. Gate drive currents are typically in the range IN of 5mA to 15mA per MOSFET, so gate drive currents can create substantial power dissipation advisable to derive V ...
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... Reverse-current inhibit reduces resistive losses associated with inductor ripple currents, which improves operating efficiencies during light-load conditions. An LT3845A DC/DC converter that is operating in reverse- current inhibit mode has a minimum load requirement of 1mA (BURST_EN = V output-generated power for the LT3845A, this requirement ...
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... FB “turn on” command to their associated switch driver until the other switch gate is fully discharged. Shutdown The LT3845A SHDN pin uses a bandgap generated reference threshold of 1.35V. This precision threshold allows use of pin voltage so that SS the SHDN pin for both logic-level controlled applications ...
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... A final 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 LT3845A uses a constant frequency architecture that can be programmed over a 100kHz to 500kHz range with a single resistor from the f 14 ground, as shown in Figure 2 ...
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... SW condition very low duty cycle. Calculate the maximum conduction losses of the MOSFETs /2. The inductor L P COND(TOP) P COND(BOT) LT3845A OUT(MAX) ), maximum drain RSS ), total gate charge (Q ) and maximum DSS G and C DS(ON) minimizes conduction losses while low selecting the top MOSFET ...
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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 LT3845A, causing a negative voltage 16 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 ...
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... Bias and the C current error at the output can be estimated as: L OUT DV OUT(BIAS) ) OUT LT3845A OUT (DV )(L)(f ) OUT SW V OUT V • ...
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... The SHDN pin has a precision voltage threshold with hysteresis which can be used as an undervoltage lockout threshold (UVLO) for the power supply. Undervoltage lockout keeps the LT3845A 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 t is the smallest amount of time that ON(MIN) the LT3845A 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 this minimum ...
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... DC/DC converter layouts. Orient power path components such that current paths in the ground plane do not cross through signal ground areas. Signal ground refers to the Exposed Pad on the backside of the LT3845A IC in the TSSOP package. SGND is referenced to the (–) terminal of the V decoupling capacitor and is used as the converter OUT voltage feedback reference ...
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... Efficiency and Power Loss 14V 16V POWER LOSS V = 14V LOAD CURRENT (A) 3845A TA02b LT3845A C5 1µF 16V SENSE Si7370DP 3.3µH 0.006 D1 M2 Si7370DP D2B BAV99 3845A TA02 OUT 3 ...
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... 154k 100pF 10k C2 R6 5600pF 23. TDK C4532X7R1H685K MURATA GRM32ER60J107ME20 OUT D1: DIODES INC. B170 L1: WURTH 744318270LF 22 C5 1µF 16V V BOOST IN SHDN TG LT3845A BURST_EN BAS19 PGND C + SYNC SENSE C4 – f SENSE 2.2µF SET 16V SGND D3B BAV99 C6 D3A 1µ ...
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... BURST_EN PGND R1 C 10k SYNC SYNC SENSE C6 R9 47pF 4.99k f SENSE SET C7 R10 SGND 5600pF 130k : MURATA GRM32ER60J107ME20 LT3845A C5 1µF 16V M1 L1 Si7850DP 4.7µH D2 BAS19 D1 B160 M2 Si7850DP + C4 – 2.2µF 16V C10 1µF 16V M3 L2 Si7850DP 4.7µH D4 BAS19 D3 ...
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... LT3845A PACKAGE DESCRIPTION 3.58 (.141) 6.60 ± 0.10 4.50 ± 0.10 SEE NOTE 4 RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 0.50 – 0.75 (.0035 – .0079) (.020 – .030) NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS 2. DIMENSIONS ARE IN 3. DRAWING NOT TO SCALE 24 FE Package 16-Lead Plastic TSSOP (4.4mm) ...
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... Added Military grade to Note 3 in the Electrical Characteristics 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. LT3845A PAGE NUMBER 2 4 ...
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... Dual Output 2-Phase Synchronous Step-Down Q LTC3858/LTC3858-1 DC/DC Controllers with 99% Duty Cycle LTC3859 Low I , Triple Output Buck/Buck/Boost Synchronous Q DC/DC Controller 26 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● V BOOST IN SHDN TG LT3845A BURST_EN BAS521 PGND C + SYNC SENSE C4 – f SENSE 2.2µ ...