LT4256-2 Linear Technology Corporation, LT4256-2 Datasheet
LT4256-2
Available stocks
Related parts for LT4256-2
LT4256-2 Summary of contents
Page 1
... The LT4256 can be used as an upgrade to LT1641 designs. See Table 1 on page 14 for upgraded specifications. The LT4256-1 and LT4256-2 are available in an 8-pin SO package that is pin compatible with the LT1641. , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. ...
Page 2
... PWRGD FB = 4.5V TIMER = 3V, During Fault TIMER = 10nF TIMER U W ORDER PART NUMBER LT4256-1CS8 LT4256-1IS8 TOP VIEW LT4256-2CS8 LT4256-2IS8 7 SENSE S8 PART MARKING 6 GATE TIMER 5 42561 42561I S8 PACKAGE 8-LEAD PLASTIC SO 42562 = 125°C, θ = 110°C/W JA 42562I http://www.linear.com/leadfree/ MIN TYP MAX ● ...
Page 3
... –50 – 100 TEMPERATURE (°C) 4256 G02 PWRGD Thresholds vs Temperature 4.5 L-H THRESHOLD 4.4 4.3 4.2 4.1 H-L THRESHOLD 4.0 3.9 –50 – 100 TEMPERATURE (°C) 4256 G05 LT4256-1/LT4256-2 MIN TYP MAX UNITS 1 0 25°C unless 3.5 3.0 2.5 2.0 1.5 1.0 0 ...
Page 4
... LT4256-1/LT4256 TYPICAL PERFOR A CE CHARACTERISTICS otherwise noted. GATE Pin Pull-Up Current vs Temperature 0 –5 –10 –15 –20 –25 –30 –35 –40 –50 – 100 TEMPERATURE (°C) 4256 G07 V – V Voltage GATE CC vs Temperature 18V 12V ...
Page 5
... FB Pin Current vs FB Pin Voltage 0.2 0.1 0 –0.1 –0.2 –0.3 –0 Gate Pull-Down Capability vs V Below Minimum Operating Voltage (V) FB 4256 G15 LT4256-1/LT4256-2 Specifications are 25°C unless (V) CC 4256 G16 425612fa 5 ...
Page 6
... When TIMER falls below 0.65V (typ), GATE turns on again for the LT4256-2. UV must be cycled low after TIMER has discharged below 0.65V (typ) to reset the LT4256- not cycled low (LT4256-1), GATE remains latched off and TIMER is discharged to near GND ...
Page 7
... UV 1 – INTERNAL + 9.8V + 0.65V TIMER LOW – + TIMER HIGH – 4.65V SENSE 7 – CURRENT 14mV ~ 55mV LIMIT + + FOLDBACK – UV – 4V LOGIC UV + LT4256-1/LT4256-2 CHARGE PUMP AND 6 GATE GATE DRIVER + 3 PWRGD 3.99V – 108µA 5 TIMER 3µA 4 4256 BD GND 425612fa 7 ...
Page 8
... The transient currents can permanently damage the con- nector pins and glitch the system supply, causing other boards in the system to reset. The LT4256-1/LT4256-2 are 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 ...
Page 9
... When the FB voltage goes above the low-to-high V threshold, PWRGD goes high. Undervoltage Detection The LT4256-1/LT4256-2 uses UV to monitor the V voltage to determine when it is safe to turn on the load and allow the user the greatest flexibility for setting the thresh- old. Any time that UV goes below 3.6V, GATE will be pulled low until UV goes above 4V again ...
Page 10
... FB. If the LT4256-1/LT4256-2 go into current limit when the voltage 0V, the current limit circuit drives the GATE pin to force a constant 14mV drop across the sense resistor ...
Page 11
... When the voltage at the TIMER pin reaches 4.65V (typ), the GATE pin is pulled low. When the voltage at the TIMER pin ramps back down to 0.65V (typ), the LT4256-2 turns on again. If the short-circuit condition at the output still exists, the cycle will repeat itself indefinitely. The duty cycle under short-circuit conditions is 3% which prevents Q1 from overheating ...
Page 12
... C3 0.1µF GND Power Good Detection The LT4256-1/LT4256-2 includes a comparator for moni- toring the output voltage. The output voltage is sensed through the FB pin via an external resistor string. The comparator’s output (PWRGD open collector ca- pable of operating from a pull-up as high as 80V. ...
Page 13
... V and GND. CC placed from ground to V LT4256-2 can help reduce the amount of ringing on V but it may not be enough for some applications. During a fault condition, the LT4256-1/LT4256-2 pulls down on GATE with a switch capable of sinking about 60mA. Once GATE drops below the output voltage by a diode forward voltage, the external Zener will forward bias ...
Page 14
... SMAT70A SENSE CC R6 64.9k 10Ω GATE R7 LT4256-1/ 100Ω R2 LT4256-2 8.06k C1 10nF TIMER PWRGD C2 GND UV = 36V 33nF 4 PWRGD = 40V circuit) is recommended. 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. Note that 1oz copper exhibits a sheet resistance of about 530µ ...
Page 15
... TYP .016 – .050 .014 – .019 (0.406 – 1.270) (0.355 – 0.483) TYP INCHES (MILLIMETERS) LT4256-1/LT4256-2 .189 – .197 (4.801 – 5.004) NOTE .150 – .157 (3.810 – 3.988) ...
Page 16
... D2 SMAT70A SENSE 64.9k 10Ω GATE R7 LT4256-1/ 100Ω R2 LT4256-2 8.06k C1 10nF TIMER PWRGD C2 GND UV = 36V 33nF 4 PWRGD = 40V COMMENTS 9V to 80V Operation, Active Current Limit, Autoretry/Latchoff Floating Supply from –15V, Active Current Limiting, Fast Circuit Breaker Floating Supply from – ...