lt4351 Linear Technology Corporation, lt4351 Datasheet
lt4351
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lt4351 Summary of contents
Page 1
... The IC monitors the input supply with respect to the load and turns on the MOSFET(s) when the input supply is higher. If the MOSFET’s R LT4351 will regulate the voltage across the MOSFET(s) to 15mV. A STATUS pin indicates the MOSFET on state. An internal boost regulator generates the MOSFET gate drive voltage. Low operating voltage allows for OR’ ...
Page 2
... FAULT, STATUS Current ........................................ 8mA UV, OV Voltages ........................................ – 0. Voltage .............................................. – 0.3V to 32V Operating Temperature Range LT4351C .................................................. LT4351I .............................................. – Junction Temperature (Note 2) ............................ 125 C Storage Temperature Range ................ – 150 C Lead Temperature (Soldering, 10 sec).................. 300 C ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T unless otherwise specified ...
Page 3
... Overvoltage Threshold vs Temperature 305 12V 303 20V IN 301 299 297 295 293 50 125 –50 – 100 TEMPERATURE ( C) 4351 G02 LT4351 = 0.4V 0.2V, GATE Open MIN TYP MAX UNITS 30 V 3.0 4.0 mA 3.6 5 185 210 230 mV 0.13 0. and power ...
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... LT4351 W U TYPICAL PERFOR A CE CHARACTERISTICS Specifications are unless otherwise specified. A Overvoltage Threshold 310 308 306 304 302 300 298 296 294 292 290 (V) IN 4351 G04 I vs Temperature VIN 2 1. ...
Page 5
... GND (Pin 5): Device Ground Pin. This pin is ground for the boost switch, gate driver as well as the control circuitry. Tie the close to this pin to minimize the effects of switching currents on part performance. LT4351 SW Pin Waveform at Maximum Boost Regulator Output s/DIV IN 3451 G13 4 ...
Page 6
... LT4351 CTIO S OV (Pin 6): Overvoltage Shutdown Pin. This pin is used for input overvoltage detection connected to a resistive divider from V . When the voltage exceeds the IN OV threshold (0.3V), GATE is pulled to GND disabling power transfer. In addition, the FAULT pin pulls low indicating a fault ...
Page 7
... – 0. – 10.7V REG – + 600ns ONE SHOT OVF – + 0.33V GND 5 LT4351 TO COMMON SUPPLY GATE IN + ENABLE DRIVER – + 15mV – OUT 10 OPEN OUT MOSFET DETECT STATUS + 9 ST – FAULT 8 4351 BD sn4351 4351fs V OUT 7 ...
Page 8
... MOSFET, thereby matching the function and performance of an ideal diode. The LT4351 drives either a single MOSFET or dual back- to-back MOSFETs. Dual MOSFETs are chosen to eliminate current flow from the input supply to the output supply when the V voltage is greater than OUT ...
Page 9
... 300mV R A 4351 F02 Figure 2 LT4351 capacitor still too low approximately 10. When V is above this level, the SW transistor DD falls below this level by the DD is the part undervoltage trip point (0.3V the undervoltage hysteresis current (10 A) ...
Page 10
... H for V IN greater than 10V. Several inductors that work well with the provided IN LT4351 are listed in Table 1. Many different sizes and shapes are available. Consult each manufacturer for more . IN detailed information and for their entire selection of related parts ...
Page 11
... V Capacitors Two types of input capacitors are generally needed for the LT4351. The first is a large bulk capacitor that takes care of ringing associated with inductance of the input supply lines and provides charge for the load when switching the MOSFET ...
Page 12
... ESR (less than 10m for the 10 F and 40m for the 0.1 F). These capacitors help to eliminate problems associated with noise produced by the boost regulator. They are decoupled from the small 1 resistor as shown in Figure 8. The LT4351 will perform better with a small ceramic capacitor ( OUT to GND. V ...
Page 13
... LTC4350 may be a more suitable part. Redundant Supplies The LT4351 is an improved solution for ORing redundant supplies because of its lower forward drop versus conven- tional diodes. The lower forward drop significantly im- proves overall efficiency, improves the voltage tolerance ...
Page 14
... OUT, the GATE pin actively sinks low. Power Dissipation The internal power dissipation of the LT4351 is comprised of the following four major components: DC power dissi- pation from power dissipation from V IN ...
Page 15
... MOSFETs so a decision must be made whether to use multiple MOSFETs or to live with an unregulated offset. Since low m using a single FET would still be acceptable. For R 4m the drop is 2 • 5A • 4m schematic is shown in Figure 15 LT4351 0. 0.5mA GATE CURRENT 0.14 0. 4.7 H ...
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... PCB traces. Keep the traces to the MOSFETs wide and short and close to the part. The PCB traces associated with the power path through the MOSFETs should have low resistance. Si4838DY OUT GATE OUT LT4351 STATUS 8 FAULT GND 5 4351 F15 IN R ...
Page 17
... Lead Acid Battery Backup Si4408DY 12.7k V GATE 0 365 LT4351 MBR0530 1.5k 1% LT4351 14V POWER SUPPLY OUT 10 F LOAD 1 10 OUT 10k 10k 9 STATUS 8 FAULT GND UV = 10.8V FAULT OV = 15V 5 FAULT 4351TA02 sn4351 4351fs 17 ...
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... Redundant Supply with External V Si4838DY 24.9k V GATE 0 25.5k 1.69k LT4351 1.47k GND 1ST SOURCE 2ND LT4351 CIRCUIT OUT STATUS 8 FAULT 4351 F15 COMMON LOAD 4351 TA03 sn4351 4351fs ...
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... BSC 4.90 0.152 DETAIL “A” (.193 .006) 0.254 0 – 6 TYP 0.53 0.152 (.021 .006) DETAIL “A” SEATING PLANE 0.17 – 0.27 (.007 – .011) TYP LT4351 0.497 0.076 (.0196 .003 REF 3.00 0.102 (.118 .004) (NOTE 0.86 1.10 (.034) (.043) ...
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... V DD GND Si4408DY 120k 0 GATE 300k 1N914 LT4351 STATUS MBR0530 GND COMMENTS Switches and Isolates Sources Up to 30V Output Voltage 1.2V to 12V, Equal Load Sharing TM P-Channel MOSFET 28V Range www.linear.com OUT ...