LT4256-1CS8 Linear Technology, LT4256-1CS8 Datasheet
LT4256-1CS8
Specifications of LT4256-1CS8
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LT4256-1CS8 Summary of contents
Page 1
... N-channel MOSFET shuts off and the PWRGD output asserts low. The LT4256-2 automatically restarts after a time-out delay. The LT4256-1 latches off until the UV pin is cycled low. The PWRGD output indicates when the output voltage rises above a programmed level. An external resistor string from V protection ...
Page 2
... FB High-to-Low Transition FB Low-to-High Transition I = 1.6mA 5mA 80V 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 ...
Page 3
... 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 ...
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 10. –50 – 100 TEMPERATURE (°C) 4256 G10 TIMER Pin Currents ...
Page 5
... W U TYPICAL PERFOR A CE CHARACTERISTICS otherwise noted. 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. Under an output short-circuit condition, the LT4256-2 cycles on and off with a 3% duty cycle ...
Page 7
... REF GEN 3.99V 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. As the output at FB increases, the voltage across ...
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
... V IN 48V (SHORT PIN) OFF SIGNAL VN2222 FROM MPU Q2 GND Figure 11. How to Use a Logic Signal to Control LT4256 Turn-On/-Off V IN (SHORT PIN) 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’ ...
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
... GND Figure 14. Negative Output Voltage Protection Diode Application Notes on Using the LT4256 in LT1641 Applications Even though the LT4256 and LT1641 have the same pinout, several changes were made to improve overall system accuracy and increase noise immunity. These changes are spelled out in Table 1 and must be accounted for if using the LT4256 in an LT1641 application ...
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) NOTE 3 ...
Page 16
... IRF530 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 –15V, Active Current Limiting, Power Good Output Floating Supply from – ...