LT4256-3 Linear Technology Corporation, LT4256-3 Datasheet
LT4256-3
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LT4256-3 Summary of contents
Page 1
... An external resistor string from V overvoltage protection. The LT4256-3 is available in a 16-lead SSOP package. , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. ...
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... RETRY ........................................................ – 0.3 to 15V TIMER Voltage ......................................... – 0.3V to 4.3V Maximum Input Current (TIMER) ....................... 100µA Operating Temperature LT4256-3C ............................................. 0°C to 70°C LT4256-3I ......................................... – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T ...
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... Note 2: An internal clamp limits the GATE pin to a minimum of 10V above V . Driving this pin to a voltage beyond the clamp voltage may damage CC the part 3.5 3.0 2.5 2.0 1.5 1.0 0 (V) CC 42563 G02 LT4256-3 MIN TYP MAX UNITS ● 3.95 3.99 4.03 V ● 4.20 4.45 4.65 V 0.3 0.45 0.60 V 0.25 0.4 V 0.60 1.0 V µA 0.1 1 µA – ...
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... LT4256 TYPICAL PERFOR A CE CHARACTERISTICS Specifications are 25°C unless otherwise noted. A GATE Pull-Up Current vs Temperature 0 –5 –10 –15 –20 –25 32µA @ 25°C –30 –35 –40 – 100 –25 TEMPERATURE (°C) 42563 G04 V – V Voltage GATE OUT vs Temperature ...
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... V – SENSE 3.0 2.5 2.0 1.5 1.0 0 –50 – TEMPERATURE (°C) 0.2 L-H THRESHOLD 0.1 0 –0.1 –0.2 –0.3 –0 100 42563 G16 LT4256-3 OV Thresholds vs Temperature 4.1 L-H THRESHOLD 4.0 3.9 3.8 3.7 H-L THRESHOLD 3.6 3.5 20 –50 – TEMPERATURE (°C) 42563 G19 PWRGD Output Voltage vs I PWRGD ...
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... If RETRY is floating or connected to a voltage above its 1.2V threshold, the LT4256-3 automatically restarts after a current fault. Under an output short-circuit condition, the LT4256-3 cycles on and off with a 3% on-time duty cycle. FB (Pin 10): Power Good Comparator Input. FB monitors the output voltage through an external resistive divider. ...
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... To defeat current limit, connect SENSE (Pin 16): Input Supply Voltage. The positive supply CC input ranges from 10.8V to 80V for normal operation typically 1.8mA. An internal circuit disables the LT4256-3 for inputs less than 9.8V (typ). LT4256-3 . When OUT by 2V, the 62mA is reduced to 130µA ...
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... LT4256-3 W BLOCK DIAGRA GEN REF GEN 3.99V 7V 100k 7 RETRY – INTERNAL + 9.8V + 0.65V TIMER LOW – + TIMER HIGH – 4.65V 8 SENSE 15 + OPEN 3mV CIRCUIT – – CURRENT 14mV TO 55mV LIMIT + + FOLDBACK – UV – 4V LOGIC ...
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... PLHUV GATE V +2V OUT Figure GATE Timing 4.45V FB t PLHFB 1V Figure PWRGD Timing OUT – SENSE 55mV t PHLSENSE V CC GATE Figure 4. SENSE to GATE Timing LT4256-3 + – 100pF 3.6V t PHLUV V +2V OUT 4256 F02 3.99V t PHLFB 1V 4256 F03 4256 F04 42563fa 9 ...
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... The transient currents can permanently damage the con- nector pins and glitch the system supply, causing other boards in the system to reset. The LT4256-3 is designed to turn on a board’s supply voltage in a controlled manner, allowing the board to be safely inserted or removed from a live backplane. The ...
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... V CC 48V OFF SIGNAL Q2 FROM MPU VN2222 0.01µF GND Figure 7. How to Use a Logic Signal to Control the LT4256-3 Turn On/Off W U noise spikes and capacitively coupled glitches from shut- ting down the LT4256-3 output erroneously. To calculate UV and OV thresholds, use the following equations ...
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... FB. If the LT4256-3 goes into current limit when the voltage 0V, the current limit circuit drives GATE to force a constant 14mV drop across the sense resistor. As the ...
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... Latch Off Operation If RETRY is grounded, the LT4256-3 will latch off after a current fault. After the part latches off, it may be com- manded to start back up. This is accomplished by cycling UV to ground and then back high (this command can only be accepted after TIMER discharges below the 0 ...
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... OPEN to be externally pulled high. OPEN is always active when V (the internal UVLO threshold), OPEN is pulled low. Open-circuit MOSFETs are detected with the LT4256-3 by monitoring the voltage across R5 with OPEN while moni- toring the output voltage with PWRGD. An open FET condition is signalled when OPEN is high and PWRGD is low (after the part has completed its start-up cycle) ...
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... PULL-DOWN Figure 13. Delay Circuit for OPEN FET Detection W U Supply Transient Protection The LT4256-3 is 100% tested and guaranteed to be safe from damage with supply voltages up to 80V. However, , given STARTUP voltage transients above 100V may cause permanent damage. During a short-circuit condition, the large change ...
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... In some applications it may be possible for V below ground (due to the parasitic trace inductance). Higher current applications, especially where the output load is physically far away from the LT4256-3 will be more susceptible to these transients. This is normal and the LT4256-3 has been designed to allow for some ringing below ground ...
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... U U APPLICATIO S I FOR ATIO In order to use this feature as designed, a bidirectional Zener diode is needed for D1. When the LT4256-3 com- mands the MOSFET off (and a bidirectional Zener is used), the output discharges very slowly (t 130µA). Several variations can be implemented to dis- charge the output faster. The recommeded method is shown in Figure 17 and uses an external PNP transistor, diode and resistor to discharge the output quickly ...
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... V traces. The minimum trace width for 1oz copper foil is 0.02" per amp to make sure the trace stays at a reasonable temperature. 0.03" per amp or wider is recommended. Figure 18 shows a layout that meets these requirements LT4256 Figure 18. Recommended Component Placement ...
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... TYP .008 – .012 (0.203 – 0.305) TYP LT4256-3 .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988) ...
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... OPEN PWRGD TIMER RETRY GND 33nF R5 0.020Ω 48V D2 SMAT70A (SHORT PIN SENSE CC 64.9k 10Ω UV GATE LT4256 OUT 0.01µF 4.02k 4.02k OPEN PWRGD TIMER RETRY C2 GND GND 33nF RELATED PARTS PART NUMBER DESCRIPTION LT1641-1/LT1641-2 Positive 48V Hot Swap Controller in SO-8 LTC4211 Single Hot Swap Controller with Multifunction Current Control 2 ...